Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE Transactions on Vehicular Technology  

Osamu Muta, Keisuke Takata, Kazuki Noguchi, Tomoki Murakami, and Shinya Ohtsuki, "Device-free WLAN Based Indoor Localization Scheme with Spatially Concatenated CSI and Distributed Antennas," IEEE Transactions on Vehicular Technology, Vol. 72, Issue 1, pp. 852-865, Jan. 2023.

DOI： 10.1109/TVT.2022.3205767

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Other Link： https://ieeexplore.ieee.org/document/9887900

Repository Public URL： https://hdl.handle.net/2324/7174367

Language：English   Publishing type：Research paper (scientific journal)  

Mohamed S. Abdalzaher, Osamu Muta, ``A Game-Theoretic Approach for Enhancing Security and Data Trustworthiness in IoT Applications,'' IEEE Internet-of-Things Journal, Volume 7, Issue 11, pp. 11250-11261, Nov. 2020

DOI： 10.1109/JIOT.2020.2996671

Language：English   Publishing type：Research paper (scientific journal)  

Tomoya Kageyama, Osamu Muta, Haris Gacanin, ``Enhanced Peak Cancellation with Simplified In-Band Distortion Compensation for Massive MIMO-OFDM'', IEEE Access, Vol.8, pp.73420-73431, July 2020.

Language：English   Publishing type：Research paper (scientific journal)  

Tomoya Kageyama, Osamu Muta, Haris Gacanin, ``Performance Analysis of OFDM with Peak Cancellation Under EVM and ACLR Restrictions'', IEEE Transactions on Vehicular Technology, Vol. 69, No. 6, pp.6230-6241, June 2020.

Language：English   Publishing type：Research paper (scientific journal)  

This paper presents two approaches for reducing the peak power in precoded multi-input multi-output (MIMO) systems with space division multiplexing (SDM). First, we present a peak power aware linear precoding scheme for MIMOSDM single carrier systems, where the precoder is designed to restrict per-antenna transmit power below a permissible level while mitigating the performance degradation caused by per-antenna power restriction. Second, we present an analytical method to represent bit error rate (BER) performance of maximum ratio combining (MRC) precoded massive MIMO OFDM systems with adaptive peak cancellation, where peak amplitude is canceled below a given threshold to reduce peak-to-average power ratio (PAPR). With this method, we clarify the impact of adaptive peak cancellation on approximated BER of MRCprecoded massive MIMO OFDM with an arbitrary number of the transmit antennas and users. Numerical results prove that our proposed approaches are effective in restricting the peak power at each antenna while mitigating performance degradation in BER performance of the precoded MIMO-SDM systems.

DOI： 10.3169/mta.8.2

Language：English   Publishing type：Research paper (scientific journal)  

In this paper, a novel interference mitigation and power allocation (PA) scheme is investigated for downlink non-orthogonal multiple access (NOMA) with multiple input multiple output (MIMO) technology in heterogeneous networks (HetNets). The proposed scheme, named PA based interference alignment and coordinated beamforming (PA-IA-CB), consists of two stages. The first stage applies two steps of IA-CB; one step for canceling the inter-cluster and the co-tier interference among small cells, whereas the other step deals with the inter-cluster interference within the macro cell. In the second stage, the cross-tier interference is proposed to be managed by properly handling the allocated power to the macro base station (MBS) and the small base stations (SBSs). The PA problem is modeled as a non-cooperative game between the MBS and the SBS with the aim of increasing the system sum rate. Simulation results verify the efficiency of the proposed technique in terms of total system sum rate and outage probability compared to the conventional schemes.

DOI： 10.1109/TVT.2019.2918336

Language：English   Publishing type：Research paper (scientific journal)  

In this paper, we investigate the bandwidth and power allocation problem in remote radio head cluster (RRHC)-based millimeter wave (mm-wave) massive MIMO heterogeneous cloud radio access networks with limited fronthaul capacity. The coordinated multipoint transmission is applied in each RRHC for cancelling the intra-cluster interference. To avoid the inter-tier interference, distinct bandwidths are allocated to macro base station and RRHs. Following this, we formulate a bandwidth and power allocation optimization problem to maximize the downlink weighted sum rate of the system subject to per-RRHC power and fronthaul capacity constraints, which is a non-convex optimization problem and is difficult to directly solve. Next, we fix the bandwidth allocation and the original problem can be divided into two independent optimization problems, i.e., the weighted sum rate maximization problems of MUs and RRH users, respectively. For the former, the convex optimization technique can be used to solve it. As for the latter, a two-loop iterative algorithm is proposed to deal with it. Specifically, we propose the price-based outer iteration to control the fronthaul capacity and the weighted minimum mean square error-based inner iteration to obtain the power allocation. To this end, a 1-D search method is adopted to find the optimal bandwidth allocation. Finally, numerical results are conducted to verify the effectiveness of the proposed algorithms under different parameters.

DOI： 10.1109/TWC.2018.2869749

Language：English   Publishing type：Research paper (scientific journal)  

In this paper, we investigate the dynamic small cell (SC) clustering strategy and their precoding design problem for interference coordination in two-Tier heterogeneous networks (HetNets) with massive MIMO (mMIMO). To reduce interference among different SCs, an interference graph-based dynamic SC clustering scheme is proposed. Based on this, we formulate an optimization problem as design precoding weights at macro base station (MBS) and clustered SCs for maximizing the downlink sum rate of SC users (SUs) subject to the power constraint of each SC BS (SBS), while mitigating inter-cluster, eliminating inter-Tier, intra-cluster and multi-macro user (MU) interference. To eliminate the inter-Tier and multi-MU interference simultaneously, we propose a clustered SC block diagonalization precoding scheme for the MBS. Next, each SU's precoding vector at clustered SCs is designed as the product of the following two parts. The first part is designed with singular value decomposition to remove the intra-cluster interference. The second part is designed to coordinate the inter-cluster interference for maximizing the downlink sum rate of SUs, which is a non-convex optimization problem and difficult to solve directly. A non-cooperative game-based distributed algorithm is proposed to obtain a suboptimal solution. Meanwhile, we prove the existence and uniqueness of Nash equilibrium for the formed game. Finally, simulation results verify the effectiveness of our proposed schemes.

DOI： 10.1109/TCOMM.2017.2756934

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1109/ACCESS.2024.3485733

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE/ACM Transactions on Networking  

This paper proposes a heterogeneous carrier-sense multiple access (CSMA) protocol named LoHEC as the first research attempt to improve energy fairness when applying CSMA to long-range wide area network (LoRaWAN). LoHEC is enabled by Channel Activity Detection (CAD), a recently introduced carrier-sensing technique to detect LoRaWAN signals even below the noise floor. The design of LoHEC is inspired by the fact that existing CAD-based CSMA proposals are in a homogeneous manner. In other words, they require LoRaWAN end devices to perform identical CAD regardless of the differences of their used network parameter &#x2013; spreading factor (SF). This causes energy consumption imbalance among end devices since the consumed energy during CAD is significantly affected by SF. By considering the heterogeneity of LoRaWAN in terms of SF, LoHEC requires end devices to perform different numbers of CAD operations with different CAD intervals during channel access. Particularly, the number of needed CADs and CAD interval are determined based on the CAD energy consumption under different SFs. We conduct extensive experiments regarding LoHEC with a practical LoRaWAN testbed including 60 commercial off-the-shelf end devices. Experimental results show that in comparison with the existing solutions, LoHEC can achieve up to 0.85<inline-formula> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> improvement of the energy fairness on average.

DOI： 10.1109/TNET.2024.3418913

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE Consumer Electronics Magazine  

Chenglong Shao, Osamu Muta, Qinghe Du, Kapil R. Dandekar, Xianpeng Wang, "Multiple Access in Large-Scale LoRaWAN: Challenges, Solutions, and Future Perspectives," IEEE Consumer Electronics Magazine, Early Access, June 2022.

DOI： 10.1109/MCE.2022.3182518

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Other Link： https://ieeexplore.ieee.org/document/9795666

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1109/ACCESS.2024.3454810

DOI： 10.1109/ACCESS.2024.3454810

Other Link： https://ieeexplore.ieee.org/document/10666695

Language：English   Publishing type：Research paper (scientific journal)  

Kazumitsu Sakamoto, and Osamu Muta, "Experimental evaluation of quasi-ZF-based fast beamforming method for short-range MIMO transmission," IEICE Transactions on Communications (JB), Vol.J107-B, No.7, pp.-, July 2024

DOI： 10.14923/transcomj.2023BLL0005

DOI： 10.14923/transcomj.2023BLL0005

Other Link： https://search.ieice.org/bin/summary.php?id=j107-b_7_371

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE  

DOI： 10.1109/ACCESS.2024.3417320

Other Link： https://ieeexplore.ieee.org/document/10565893

Language：English   Publishing type：Research paper (scientific journal)  

Ahmad Gendia, Osamu Muta, Sherief Hashima, and Kohei Hatano, "Energy-Efficient Trajectory Planning with Joint Device Selection and Power Splitting for mmWaves-Enabled UAV-NOMA Networks, " IEEE Transactions on Machine Learning in Communications and Networking, Vol.2, pp.617-632, May 2024.

DOI： 10.1109/TMLCN.2024.3396438

Other Link： https://ieeexplore.ieee.org/document/10517756

Repository Public URL： https://hdl.handle.net/2324/7238753

Language：English   Publishing type：Research paper (scientific journal)  

Chenglong Shao, and Osamu Muta, "TONARI: Reactive Detection of Close Physical Contact using Unlicensed LPWAN Signals," ACM Transactions on Internet of Things, accepted in Feb. 2024.

DOI： 10.1145/3648572

Language：English   Publishing type：Research paper (international conference proceedings)  

Simon Kaboyo, Ahmed Hassan Abd El-Malek, Osamu Muta, Mohammed Abo-Zahhad, Maha Elsabrouty, "Age of Information Analysis for Full Duplex Cooperative SWIPT NOMA System," IEEE Wireless Communications and Networking Conference (WCNC2024), April 2024.

Language：English   Publishing type：Research paper (scientific journal)  

Kazumitsu Sakamoto, and Osamu Muta, "Antenna Position Estimation Based on Weighted Centroid Localization for Short-range MIMO Transmission," IEICE Communications Express, Vol.13, No.2, 14–17, Feb. 2024.

Language：English   Publishing type：Research paper (scientific journal)  

Publisher：IEEE Access  

Unmanned aerial vehicles (UAVs) are expected to be integrated into future wireless networks to offer services, especially in unreachable or congested areas. To improve the spectral efficiency, non-orthogonal multiple access (NOMA) scheme can be utilised within the UAV communication to allow more users to be covered and associated. The performance of the NOMA-UAVs network is governed by several factors including power allocation, user association and pairing methods. This paper presents an approach that uses multi-armed bandit (MAB) and two-sided matching frameworks to maximize the throughput of multi-UAV-assisted NOMA networks in a decentralized manner. The approach enables the UAVs to propose to the ground users (GUs) without explicit cooperation among the UAVs while the GUs can accept or reject the proposals. To this end, we propose a modified Thompson sampling algorithm that we named decaying epsilon Thompson sampling (text {D}epsilon text {TS} ) MAB algorithm that is designed to improve the exploration-exploitation tradeoff in the MAB. The performance of the proposed text {D}epsilon text {TS} MAB algorithm is evaluated against other existing MAB techniques. Simulation results show that the text {D}epsilon text {TS} algorithm attains faster convergence and improved performance in terms of smaller regret and increased achievable system throughput. The text {D}epsilon text {TS} MAB algorithm particularly excels in regards of the convergence rate when the number of available action spaces increases.

DOI： 10.1109/ACCESS.2024.3417320

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Language：English   Publishing type：Research paper (international conference proceedings)  

Tanemasa Asano, Hideaki Iwahori, Ahmed Allam, Osamu Muta, Haruichi Kanaya and Adel B. Abdel-Rahman, "Experimental Study on Microwave Heating of Soil for Nematode Control," International Japan-Africa Conference on Electronics, Communications and Computations (JAC-ECC) 2023, Dec. 2023.

Language：English   Publishing type：Research paper (international conference proceedings)  

Zhuoran Li, Osamu Muta and Yutaka Jitsumatsu, "Performance Evaluation of Cooperative Positioning with User-Terminal Collaboration," International Japan-Africa Conference on Electronics, Communications and Computations (JAC-ECC) 2023, Dec. 2023.

Language：English   Publishing type：Research paper (international conference proceedings)  

Shunsuke Shimizu, Osamu Muta, Kazuki Noguchi, Tomoki Murakami, and Shinya Otsuki, "Performance of WLAN-based Object Detection with Distributed Antenna and Spatially Concatenated CSI," IEEE VTC2023-Fall Workshop (Workshop on Integrated Sensing, Communication, and Computation towards 6G held at VTC2023-Fall), Oct. 2023.

Language：English   Publishing type：Research paper (international conference proceedings)  

Boniface Uwizeyimana, Ahmed H. Abd El-Malek, Osamu Muta, Mohammed Abo-Zahhad, Maha Elsabrouty, "A Multi-agent Multi-armed Bandit Approach for User Pairing in UAV-assisted NOMA-Networks," Proc. the 10th International Symposium on Networks, Computers and Communications (ISNCC'23), Oct. 2023.

Language：English   Publishing type：Research paper (international conference proceedings)  

Takuto Suzuki, Salah Berra, Kazuki Maruta, and Osamu Muta, "Multiuser Scheduling to Improve Iterative Interference Replica Subtraction with Partial Zeroization for Massive MIMO Systems," 2023 International Conference On Advanced Technologies For Communications (ATC2023), Oct. 2023.

Language：English   Publishing type：Research paper (international conference proceedings)  

Shunsuke Shimizu, Osamu Muta, Kazuki Noguchi, Junsuke Izumi, Tomoki Murakami, and Shinya Otsuki, "Experimental Evaluation of MIMO-WLAN-based Object Detection with Reflectors," Proc. IEEE Vehicular Technology Conference 2023 Fall (VTC2023-Fall), Oct. 2023.

Language：English   Publishing type：Research paper (international conference proceedings)  

Takuto Suzuki, Salah Berra, Kazuki Maruta, and Osamu Muta, "Improving Iterative Interference Replica Subtraction based Precoding for Massive MIMO Systems by Partial Zeroization," 2023 IEEE 20th Consumer Communications & Networking Conference (CCNC).

Language：English   Publishing type：Research paper (international conference proceedings)  

Tanemasa Asano, Ahmed Allam, Osamu Muta, Haruichi Kanaya, Adel B. Abdel-Rahman, "Investigation on Microwave Heating Characteristic of Watery Object Buried in Soil," International Japan-Africa Conference on Electronics, Communications and Computations 2022, Dec. 2022.

Language：English   Publishing type：Research paper (international conference proceedings)  

Boniface Uwizeyimana, Ahmed Abd El-Malek, Osamu Muta, Mohammed Abo-Zahhad and Maha Elsabrouty,
Multi-Armed Bandit and Repeated Auction Approaches for User Admission and Channel Allocation in 5G HetNets ,"
International Japan-Africa Conference on Electronics, Communications and Computations 2022, Dec. 2022.

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Gendia Ahmad, Muta Osamu, Hashima Sherief, Hatano Kohei, "UAV Positioning with Joint NOMA Power Allocation and Receiver Node Activation," IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC) 2022, Sept. 2022.

Language：English   Publishing type：Research paper (international conference proceedings)  

Riku NOJIMA, Osamu MUTA, Tomofumi MAKITA, Kazuki MARUTA, "Joint Peak Cancellation and In-band Distortion Compensation Scheme for Precoded Massive MIMO-OFDM with Uniform Planar Array," IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC) 2022, Sept. 2022.

Language：English   Publishing type：Research paper (international conference proceedings)  

Kyosuke Nakano, Osamu Muta, Takahiro Inoue, Takuto Watanabe, Naohiro Ikeda, "Experimental Evaluation of Floor Height Estimation Using Unlicensed-Band LPWA Signals Toward Three-Dimensional NLOS Indoor Positioning," IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC) 2022, Sept. 2022.

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE Communications Letters  

Chenglong Shao, Osamu Muta, "LiCo: Toward Lightweight Resolution of Signal Collisions in LoRaWAN", IEEE Communications Letters, Vol. 26, Issue: 8, pp. 1957 - 1961, August 2022.

DOI： 10.1109/LCOMM.2022.3178208

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Language：English   Publishing type：Research paper (scientific journal)  

Tomofumi Makita, Osamu Muta,
"Compressed Sensing based Power Allocation and User Selection with Adaptive Resource Block Selection for Downlink NOMA Systems,"
IEICE Transactions on Communications, Vol.E105-B,No.8,pp.959-968, Aug. 2022.

DOI： https://doi.org/10.1587/transcom.2021EBP3173

Language：English   Publishing type：Research paper (international conference proceedings)  

Mostafa Samy, Mohammed Abo-Zahhad, Osamu Muta, Adel Bedair, Maha Elsabrouty, "Intelligent Reflecting Surface Joint Uplink-Downlink Optimization for NOMA Network," IEEE Vehicular Technology Conference Spring 2022, June. 2022.

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEJ Transactions on Electrical and Electronic Engineering  

``Cache-Enabled Reinforcement Learning Scheme for Power Allocation and User Selection
in Opportunistic Downlink NOMA Transmissions,'' IEEJ Transactions on Electrical and Electronic Engineering, Vol. 17, Issue 5, pp. 722-731, May 2022

DOI： 10.1002/tee.23560

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Language：English   Publishing type：Research paper (scientific journal)  

Chenglong Shao, Osamu Muta, Wenjie Wang, and Wonjun Lee,
``Toward Ubiquitous Connectivity via LoRaWAN: An Overview of Signal Collision Resolving Solutions,''
IEEE Internet of Things Magazine, Volume 4 Issue 4, pp.114 - 119, Dec. 2021.

DOI： 10.1109/IOTM.001.2100114

Language：English   Publishing type：Research paper (international conference proceedings)  

Chenglong SHAO and Osamu MUTA
VirCh: Virtual Mobile Charger-based Wireless Power Transfer for Large-Scale Internet-of-Things Systems
2021 International Conference on Emerging Technologies for Communications (ICETC 2021), Dec. 2021.

Language：English   Publishing type：Research paper (international conference proceedings)  

Hiroki HASE, and Osamu MUTA,
Adaptive In-band Distortion Compensation for Spatially Precoded Massive MU-MIMO Systems with Deep Peak Cancellation
2021 International Conference on Emerging Technologies for Communications (ICETC 2021), Dec. 2021.

Language：English   Publishing type：Research paper (international conference proceedings)  

Mostafa Samy, Mohammed Abo-Zahhad, Osamu Muta, Adel Bedair, Maha Elsabrouty,
'Performance Analysis of Intelligent Reflecting Surface Selection for Orthogonal and Non-Orthogonal Multiple Access'
International Conference on Wireless and Mobile Computing, Networking and Communications (WiMob)
October 11 to 13, 2021.

Language：English   Publishing type：Research paper (scientific journal)  

Ahmed Nasser, Osamu Muta, Maha Elsabrouty, and Haris Gacanin, "Non-Cooperative Game Based Power Allocation for Energy and Spectrum Efficient Downlink NOMA HetNets ", IEEE Access, Vol. 9, pp. 136334-136345, Sept. 2021.

DOI： 10.1109/ACCESS.2021.3116706

Language：English   Publishing type：Research paper (international conference proceedings)  

Kazuki Noguchi, Osamu Muta, Tomoki Murakami, and Shinya Otsuki
A CSI-based Object Detection Scheme using Interleaved Subcarrier Selection in Wireless LAN Systems with Distributed Antennas
Vehicular Technology Conference Fall 2021, Sept. 2021.

Language：English   Publishing type：Research paper (international conference proceedings)  

Tomofumi Makita and Osamu Muta, "QoS-aware Low-complexity User Pairing Based on Compressed Sensing in Downlink NOMA,' IEEE Vehicular Technology Conference Fall 2021, Sept. 2021.

Language：English   Publishing type：Research paper (international conference proceedings)  

Chenglong Shao and Osamu Muta,
``Dude, Are You Approaching Me? Detecting Close Physical Contact via Unlicensed LPWAN Signals,''
IEEE ICC 2021 Workshop - IoMT, June 2021.

Language：English   Publishing type：Research paper (scientific journal)  

Tomoya Kageyama, Osamu Muta, ``Partial Scrambling Overlapped Selected Mapping PAPR Reduction for OFDM/OQAM Systems,''
IEICE Transactions on Communications, Vol.E104-B, No.3, pp.338-347, Mar. 2021.

DOI： 10.1587/transcom.2020EBP3042

Language：English   Publishing type：Research paper (scientific journal)  

Ahmed Nasser, Osamu Muta, Maha Elsabrouty, Haris Gacanin,
``Joint User Pairing and Power Allocation with Compressive Sensing in NOMA Systems,''
IEEE Wireless Communications Letters, Vol. 10, No. 1, Jan. 2021.

DOI： 10.1109/LWC.2020.3023619

Language：English   Publishing type：Research paper (scientific journal)  

Hiroki Senji, Osamu Muta, Tomoki Murakami, Shinya Otsuki, ``An Interleaved Channel State Information Clustering Scheme for Wireless LAN-based Object Detection Systems,'' IEICE Communications Express, Vol.10, No.1, pp. 42–49, 2021.

Language：English   Publishing type：Research paper (international conference proceedings)  

Kazuki MUKAI, Kazuki MARUTA, Osamu MUTA, and Chang-Jun AHN, ``Improving Low Complexity Inter-User Interference Cancellation for Massive MIMO Systems,'' International Conference on Emerging Technologies for Communications (ICETC 2020), Dec. 2020.

Language：English   Publishing type：Research paper (international conference proceedings)  

Keisuke Takata, Osamu Muta, Tomoki Murakami, Shinya Otsuki, ``Performance Evaluation of Object Detection Utilizing Channel State Information in Wireless LAN Systems with Distributed Antennas,'' 23rd International Symposium on Wireless Personal Multimedia Communications (WPMC2020), Oct. 2020.

Language：English   Publishing type：Research paper (scientific journal)  

Tomoya Kageyama, Daisuke Kanemoto, Oruto Endo, Makoto Ohki, Osamu Muta, ``Effect of Hysteresis-based Simple Negative Feedback A/D Conversion on Channel Estimation for Single Carrier,'' IEICE Communications Express, Vol.9, No.7, 274-281, July 2020.

Language：English   Publishing type：Research paper (scientific journal)  

Shunsuke Kamiwatari, Osamu Muta, ``Cross-tier Interference Mitigation Considering Pilot Overhead for TDD MIMO Heterogeneous Networks'', IEICE Communications Express, Vol.9, No.6, pp.1-8, June 2020.

Language：English   Publishing type：Research paper (scientific journal)  

In this paper, we propose a femto base station cluster (FBSC)-based fog radio access network (F-RAN) structure, where multiple femto base stations (FBSs) coordinately serve users in each FBSC with the millimeter wave band. In addition, the FBS head (FBSH) in each FBSC receives data from the central processor (CP) via fronthaul link with the microwave band. Based on this, we formulate a transmission delay minimization problem by optimizing coordinated hybrid analog/digital precoding under transmit power constraints of each FBS in the FBSCs and the base station (BS) in the CP. Then, we propose a coordinated analog precoding scheme for multiple FBSs within the same FBSC. Meanwhile, we equivalently divide the original problem into two independent optimization problems, and propose an effective iterative algorithm to solve them. Simulation results show the effectiveness of our proposed algorithms.

DOI： 10.1109/JSYST.2019.2921557

Language：English   Publishing type：Research paper (scientific journal)  

A. M. Benaya, Osamu Muta, Maha Elsabrouty, ``Performance Analysis of Weighted Rank Constrained Rank Minimization Interference Alignment for Three-Tier Downlink Heterogeneous Networks,'' IEICE Transactions on Communications, Vol.E103-B, No.3, pp.262-271, March 2020.

Language：English   Publishing type：Research paper (scientific journal)  

In massive MIMO (mMIMO) systems, large matrix inversion is a challenging problem due to the huge volume of users and antennas. Neumann series (NS) and successive over relaxation (SOR) are two typical methods that solve such a problem in linear precoding. NS expands the inverse of a matrix into a series of matrix vector multiplications, while SOR deals with the same problem as a system of linear equations and iteratively solves it. However, the required complexities for both methods are still high. In this paper, four new joint methods are presented to achieve faster convergence and lower complexity in matrix inversion to determine linear precoding weights for mMIMO systems, where both Chebyshev iteration (ChebI) and Newton iteration (NI) are investigated separately to speed up the convergence of NS and SOR. Firstly, joint Chebyshev and NS method (ChebI-NS) is proposed not only to accelerate the convergence in NS but also to achieve more accurate inversion. Secondly, new SOR-based approximate matrix inversion (SOR-AMI) is proposed to achieve a direct simplified matrix inversion with similar convergence characteristics to the conventional SOR. Finally, two improved SOR-AMI methods, NI-SOR-AMI and ChebI-SOR-AMI, are investigated for further convergence acceleration, where NI and ChebI approaches are combined with the SOR-AMI, respectively. These four proposed inversion methods provide near optimal bit error rate (BER) performance of zero forcing (ZF) case under uncorrelated and correlated mMIMO channel conditions. Simulation results verify that the proposed ChebI-NS has the highest convergence rate compared to the conventional NS with similar complexity. Similarly, ChebI-SOR-AMI and NI-SOR-AMI achieve faster convergence than the conventional SOR method. The order of the proposed methods according to the convergence speed are ChebI-SOR-AMI, NI-SOR-AMI, SOR-AMI, then ChebI-NS, respectively. ChebI-NS has a low convergence because NS has lower convergence than SOR. Although ChebI-SOR-AMI has the fastest convergence rate, NI-SOR-AMI is preferable than ChebI-SOR-AMI due to its lower complexity and close inversion result.

DOI： 10.1186/s13638-019-1631-x

Language：English   Publishing type：Research paper (scientific journal)  

Heterogeneous networks (HetNets) technology is expected to be applied in next generation cellular networks to boost system capacity. However, applying HetNets introduces a significant amount of interference among different tiers within the same cell. In this paper, we propose a weighted rank constrained rank minimization (WRCRM) based interference alignment (IA) approach for three-tier HetNets. The concept of RCRM is applied in a different way to deal with the basic characteristic of different tiers: Their different interference tolerance. In the proposed WRCRM approach, interference components at different tiers are weighted with different weighting factors (WFs) to reflect their vulnerability to interference. First, we derive an inner and a loose outer bound on the achievable degrees of freedom (DoF) for the three-tier system that is modeled as a three-user mutually interfering broadcast channel (MIBC). Then, the derived bounds along with the well-known IA feasibility conditions are used to show the effectiveness of the proposed WRCRM approach. Results show that there exist WF values that maximize the achievable interference-free dimensions. Moreover, adjusting the required number of DoF according to the derived bounds improves the performance of the WRCRM approach.

DOI： 10.1587/transcom.2019EBP3084

Language：English   Publishing type：Research paper (scientific journal)  

In this paper, we investigate the energy-efficient resource allocation problem in an uplink non-orthogonal multiple access (NOMA) millimeter wave system, where the fully-connected-based sparse radio frequency chain antenna structure is applied at the base station (BS). To relieve the pilot overhead for channel estimation, we propose a codebook-based analog beam design scheme, which only requires to obtain the equivalent channel gain. On this basis, users belonging to the same analog beam are served via NOMA. Meanwhile, an advanced NOMA decoding scheme is proposed by exploiting the global information available at the BS. Under predefined minimum rate and maximum transmit power constraints for each user, we formulate a max-min user energy efficiency (EE) optimization problem by jointly optimizing the detection matrix at the BS and transmit power at the users. We first transform the original fractional objective function into a subtractive one. Then, we propose a two-loop iterative algorithm to solve the reformulated problem. Specifically, the inner loop updates the detection matrix and transmit power iteratively, while the outer loop adopts the bi-section method. Meanwhile, to decrease the complexity of the inner loop, we propose a zero-forcing (ZF)-based iterative algorithm, where the detection matrix is designed via the ZF technique. Finally, simulation results show that the proposed schemes obtain a better performance in terms of spectral efficiency and EE than the conventional schemes.

DOI： 10.1109/TCOMM.2019.2942308

Language：English   Publishing type：Research paper (other academic)  

As a spectrum efficient multi-carrier modulation scheme, filter-bank based orthogonal frequency division multiplexing techniques using offset quadrature amplitude modulation (OFDM/OQAM) are investigated for future wireless communication systems, where a low-sidelobe spectrum is achieved by band-limiting each subcarrier while keeping their orthogonality. One of the technical issues in OFDM/OQAM is the suppression of the peak-to-average power ratio (PAPR). Since existing PAPR reduction schemes for traditional OFDM are not straightforwardly applicable to OFDM/OQAM systems, PAPR suppression for OFDM/OQAM is still a challenging issue. This paper proposes a partial scrambling overlapped selected mapping (PS-OSLM) technique for OFDM/OQAM systems, where a partial scrambling technique is applied to an overlapped SLM scheme which selects the best candidate sequence among possible overlapped candidate sequences so as to minimize the PAPR. It is verified by simulation that the proposed PS-OSLM effectively reduce PAPR of OFDM/OQAM signal without explicit side information while improving bit error rate (BER) performance compared with conventional schemes.

DOI： 10.1109/JAC-ECC48896.2019.9051096

Language：English   Publishing type：Research paper (other academic)  

In orthogonal frequency division multiplexing (OFDM) with massive multi-input multiple-output (mMIMO), the reduction of the high peak-to-average power ratio (PAPR) is a challenging problem. Recently, an adaptive peak cancellation is proposed to reduce the transmitted signalâ™s PAPR, while keeping the out-of-band leakage power (ACLR) as well as an in-band distortion power (EVM) below the predetermined and permissible value. In this paper, we propose an analytical method to evaluate achievable BER performance of downlink OFDM with the peak cancellation in massive multi-input-multioutput (mMIMO) systems using arbitrary numbers of transmit antennas and served users. In this method, bit error rate (BER) is derived based on the assumption that in-band distortion due to peak cancellation is approximated as random variable following Gaussian distribution, provided that variance of the Gaussian distribution in two user case is known. The results clarify that theoretical BER expressions for arbitrary numbers of transmit antennas and served users show good agreements with its simulation results. In addition, we clarified the impact of the increase of the number of transmit antennas on achievable BER and PAPR reduction capability in MRC precoded mMIMOOFDM system with the peak cancellation.

DOI： 10.1109/VTCFall.2019.8891444

Language：English   Publishing type：Research paper (other academic)  

In this paper, we propose a two-dimensional pilot allocation scheme over frequency- and delay-time domains (2D-PFD) for channel estimation in massive multiple-input multiple-output (MIMO)/time division duplex (TDD) system, where two- dimensional pilot resources are simultaneously allocated to each user for their uplink channel estimation. We evaluate bit error rate (BER) performance of massive MIMO/TDD system using the 2D-PFD scheme by computer simulation in order to clarify the effectiveness of the proposed pilot allocation compared with single dimensional pilot allocation over either delay-time domain or frequency domain, respectively.

DOI： 10.1109/VTCFall.2019.8891106

Language：English   Publishing type：Research paper (other academic)  

Properly designing scattered pilot pattern over orthogonal frequency division multiplexing (OFDM) subcarriers is important to improve the accuracy of the sparse channel estimation, while decreasing the number of the required pilots. In this paper, we propose a pilot-subcarrier allocation scheme that optimizes the pilot subcarrier patterns without any knowledge of channels, where channel estimation is done by interpolating the pilot- subcarriers scattered over frequency domain. The proposed pilot allocation scheme utilizes the mutual incoherence property (MIP) of the compressive sensing (CS) theory to formulate the pilot allocation problem into infinity norm problem. Then, MIP based weighted fast iterative shrinkage-thresholding algorithm (MIP-WFISTA) is proposed to solve the formulated problem. Simulation results validate that, compared with the conventional techniques, the proposed pilot design scheme achieves more accurate channel estimation and as a result better bit error rate (BER) performance while decreasing the number of the required pilots in frequency-selective fading environments.

DOI： 10.1109/VTCFall.2019.8891578

Language：English   Publishing type：Research paper (scientific journal)  

Nowadays, trust models of wireless sensor networks (WSNs) security have flourished due to the day-to-day attack challenges, which are most popular for internet of things (IoT). This article proposes a trust model based on non-zero-sum game approach for clustered-WSNs (CWSNs) security to maximise the data trustworthiness transmission. The proposed model is developed for two different attack-defence scenarios. In the first scenario, the trust model is used to face a denial-of-service (DoS) attack in which the attacker is able to drop or partially drop the delivered acknowledgments (ACKs) from a cluster member (CM) to the cluster head (CH). In the second scenario, the model target is to protect CWSNs from ON–OFF attack where the attacker is capable to frequently infect the CMs. Simulation results show improved performance of protecting the CWSNs against DoS/ON–OFF attacks and maximising data trustworthiness represented by the CMs compliance of sending the ACKs to the CH. Consequently, this mechanism can attain the appropriate security and performance for WSN-based IoT systems.

DOI： 10.1049/iet-wss.2018.5114

Language：English   Publishing type：Research paper (other academic)  

This paper presents performance analysis of power control (PC) based interference coordination for multiple-input multiple-output (MIMO) heterogeneous networks (HetNets). In this analysis, a PC-based approach is compared with a beamforming (BF) based approach to verify its advantages and limitation in managing a sort of interference in HetNets. As for the PC based approach, a non-cooperative game based PC scheme (NC-PC) is employed to coordinate co-tier and cross-tier interference, where the macro base station (MBS) and the small BS (SBS) are simultaneously competing to determine their transmit powers with equal priority for maximizing their sum rates. On the other hand, in the beamforming based scheme, interference cancellation is achieved by utilizing extra degree of freedom at MIMO technology, while multiple antennas are not necessary in the PC based technique. The performance of the NC-PC against MBS cancellation technique is evaluated with and without cotier interference cancellation scheme in terms of sum rate, the number of antennas, and diversity gain.

DOI： 10.1109/VTS-APWCS.2019.8851666

Language：English   Publishing type：Research paper (other academic)  

In this paper, a cross-tier interference mitigation framework based on interference alignment and coordinated beamforming (IA-CB) is investigated for downlink non-orthogonal multiple access (NOMA) heterogeneous networks (HetNets). In the proposed technique, named cross-tier IA-CB (CrIA-CB), the conventional IA-CB is extended to eliminate the cross-tier interference between the macro cell (MC) and the underlaid small cells (SC) in HetNets. The proposed CrIA-CB utilizes the degrees of freedom provided by the massive multiple input multiple output (mMIMO) technology for designing the transmit and receive beamforming vectors to null the cross-tier interference at the user side while decreasing the sharing channel state information (CSI) between SCs and MC. Simulation results validate the performance improvement of the proposed technique in terms of system sum rate over the conventional techniques.

DOI： 10.1109/VTCSpring.2019.8746524

Language：English   Publishing type：Research paper (other academic)  

In massive multi-input multi-output (mMIMO) orthogonal frequency division multiplexing (OFDM) systems, reduction of high peak-to-average power ratio (PAPR) is a challenging problem. Although deliberate amplitude peak limiting is a promising PAPR reduction approach, it causes un-desired nonlinear in-band distortion and out-of-band radiation. Thus, the joint use of a peak limiter and band-limitation filter such as clipping-and-filtering (CF) is required. The objective of this paper is to evaluate the effect of CF based PAPR reduction for mMIMO-OFDM systems, where a band-limitation filter is designed to limit out-of-band radiation due to clipping while mitigating peak amplitude regrowth due to filtering. We discuss the effect of utilizing extra degrees of freedom for compensating in-band distortion due to CF in mMIMO systems. Simulation results verified the effectiveness of the above approach in terms of instantaneous peak power, adjacent channel leakage power ratio (ACLR) and signal-to-distortion power ratio (SDR) in mMIMO-OFDM downlink.

DOI： 10.1109/JEC-ECC.2018.8679567

Language：English   Publishing type：Research paper (scientific journal)  

Orthogonal frequency division multiple access (OFDMA) is extensively utilized for the downlink of cellular systems such as long term evolution (LTE) and LTE advanced. In OFDMA cellular networks, orthogonal resource blocks can be used within each cell. However, the available resources are rare and so those resources have to be reused by adjacent cells in order to achieve high spectral efficiency. This leads to inter-cell interference (ICI). Thus, ICI coordination among neighboring cells is very important for the performance improvement of cellular systems. Fractional frequency reuse (FFR) has been widely adopted as an effective solution that improves the throughput performance of cell edge users. However, FFR does not account for the varying nature of the channel. Moreover, it exaggerates in caring about the cell edge users at the price of cell inner users. Therefore, effective frequency reuse approaches that consider the weak points of FFR should be considered. In this paper, we present an adaptive self-organizing frequency reuse approach that is based on dividing every cell into two regions, namely, cell-inner and cell-outer regions; and minimizing the total interference encountered by all users in every region. Unlike the traditional FFR schemes, the proposed approach adjusts itself to the varying nature of the wireless channel. Furthermore, we derive the optimal value of the inner radius at which the total throughput of the inner users of the home cell is as close as possible to the total throughput of its outer users. Simulation results show that the proposed adaptive approach has better total throughput of both home cell and all 19 cells than the counterparts of strict FFR, even when all cells are fully loaded, where other algorithms in the literature failed to outperform strict FFR. The improved throughput means that higher spectral efficiency can be achieved; i.e., the spectrum, which is the most precious resource in wireless communication, can be utilized efficiently. In addition, the proposed algorithm can provide significant power saving, that can reach 50% compared to strict FFR, while not penalizing the throughput performance.

DOI： 10.1007/s11276-017-1571-5

Language：English   Publishing type：Research paper (scientific journal)  

Pilot contamination due to pilot reuse in adjacent cells is a very serious problem in massive multi-input multiple-output (MIMO) systems. Therefore, proper pilot allocation is essential for improving system performance. In this paper, we formulate the pilot allocation optimization problem so as to maximize uplink sum rate of the system. To reduce the required complexity inherent in finding the optimum pilot allocation, we propose a low-complexity pilot allocation algorithm, where the formulated problem is decoupled into multiple subproblems; in each subproblem, the pilot allocation at a given cell is optimized while the pilot allocation in other cells id held fixed. This process is continued until the achievable sum rate converges. Through multiple iterations, the optimum pilot allocation is found. In addition, to improve users’ fairness, we formulate fairness-aware pilot allocation as maximization problem of sum of user’s logarithmic rate and solve the formulated problem using a similar algorithm. Simulation results show that the proposed algorithms match the good performance of the exhaustive search algorithm, meanwhile the users’ fairness is improved.

DOI： 10.1587/transcom.2017EBP3312

Language：English   Publishing type：Research paper (scientific journal)  

The rapid development of wireless sensor networks (WSNs) is a significant incentive to contribute to vulnerable applications such as cognitive radio (CR). This paper proposes a Stackelberg game approach to enhance the WSN-based CR security against the spectrum sensing data falsification (SSDF) attack and conserve the consequently lost power consumption. The attack aims to corrupt the spectrum decision by imposing interference power to the delivered reports from the sensor nodes (SNs) to the fusion center (FC) to make a protection level below a specific threshold. The proposed model utilizes the intelligent Stackelberg game features along with the matched filter (MF) to maximize the number of protected reports sent by the SNs to the FC leading to an accurate decision of the spectrum status. Furthermore, the TDMA protocol is utilized to resolve the complexity of employing MF for the spectrum detection to avoid the collision between the delivered reports. The proposed model aims to enhance the number of correctly received reports at the FC, and hence manage the lost energy of reports retransmission due to the malicious attack effect. Moreover, the model can conserve the lost power of the failed communication attempts due to the SSDF attack impact. Simulation results indicate the improved performance of the proposed protection model along with the MF over six different environments against the SSDF attack as compared to two defense schemes, namely, random and equal weight defense strategies.

DOI： 10.1109/ACCESS.2019.2940699

Language：English   Publishing type：Research paper (scientific journal)  

A spoofing attack is a critical issue in wireless communication in which a malicious transmitter outside a system attempts to be genuine. As a countermeasure against this, we propose a device-authentication method based on position identification using radio-propagation characteristics (RPCs). Not depending on information processing such as encryption technology, this method can be applied to sensing devices etc. which commonly have many resource restrictions. We call the space from which attacks achieve success as the “attack space.” In order to confine the attack space inside of the target system to prevent spoofing attacks from the outside, formulation of the relationship between combinations of transceivers and the attack space is necessary. In this research, we consider two RPCs, the received signal strength ratio (RSSR) and the time difference of arrival (TDoA), and construct the attack-space model which uses these RPCs simultaneously. We take a tire pressure monitoring system (TPMS) as a case study of this method and execute a security evaluation based on radio-wave-propagation simulation. The simulation results assuming multiple noise environments all indicate that it is possible to eliminate the attack possibility from a distant location.

DOI： 10.2197/ipsjjip.27.322

Language：English   Publishing type：Research paper (scientific journal)  

In this paper, a downlink cooperative channel estimation scheme is proposed for the three-dimensional massive multiple inputs multiple outputs (3D-mMIMO) system operating in the frequency division duplexing (FDD) mode. In the proposed cooperative scheme, users have to cooperate with each other via device-to-device (D2D) communication protocol to jointly exploit the sparsity structure property of the channel. Motivated by the sparsity property of the mMIMO channel in the angle-time domain, a parametric feedback scheme is proposed, where the feedback overhead is decreased by sending a limited version of the estimated coefficients rather than all the coefficients back to the BS. Then, a compressive sensing (CS) algorithm is proposed, which we named weighted fast iterative shrinkage thresholding (WFISTA). In the WFISTA, we first introduce new weights and threshold function to the original FISTA to enhance its sparsity-undersampling trade-off in the single measurement vector (SMV) case, then we extend the proposed WFISTA to the case of multiple measurement vector (MMV) problem by adopting ReMBo (reduce MMV and boost) strategy. The proposed WFISTA has the ability to estimate the mMIMO system's channel coefficients by exploiting the joint sparsity structure through cooperation among users' equipment (UEs). Complexity analysis and the probability of decreasing the feedback overhead are provided for the proposed cooperative estimation scheme. The simulation results verify the efficiency of the proposed cooperative algorithm scheme compared to several joint channel estimations.

DOI： 10.1109/ACCESS.2019.2920861

Language：English   Publishing type：Research paper (scientific journal)  

In this paper, we propose an enhanced selected mapping (e-SLM) technique to improve the performance of OFDM-PLC systems under impulsive noise. At the transmitter, the best transmit sequence is selected from among possible candidates so as to minimize the weighted sum of transmit signal peak power and the estimated receive one, where the received signal peak power is estimated at the transmitter using channel state information (CSI). At the receiver, a nonlinear blanking is applied to hold the impulsive noise under a given threshold, where impulsive noise detection accuracy is improved by the proposed e-SLM. We evaluate the probability of false alarms raised by impulsive noise detection and bit error rate (BER) of OFDM-PLC system using the proposed e-SLM. The results show the effectiveness of the proposed method in OFDM-PLC system compared with the conventional blanking technique.

DOI： 10.1587/transcom.2019EBP3081

Language：English   Publishing type：Research paper (other academic)  

In this paper, we present our recent studies on pilot allocation and interference coordination for heterogeneous networks (HetNets) using massive multi-input-multi-output (mMIMO) technology in time division duplex (TDD) mode, where the macro-cell base station (MBS) and overlaid small-cell base stations (SBSs) share the same time-frequency resources, and thus co-tier and cross-tier interferences occur. We investigate how to coordinate such undesirable interference for maximizing the system sum-rate under required constraints. As the first approach, we present an uplink pilot allocation scheme to enhance the downlink system sum-rate by coordinating downlink cross-tier interference to small-cell users (SUs) based on the estimated uplink channel state information. In this approach, we study the optimum pilot allocation against the trade-off between two degradation factors, i.e., uplink pilot overhead and downlink cross-tier interference. As the second approach, we present a dynamic SBS clustering scheme to mitigate dominant co-tier interference among small cells (SCs), where the SBS clustering is carried out based on potential mutual co-tier interference strength between two SCs. We also consider the SBS precoder design in each cluster to further improve the downlink sum rate of SCs under SBS power constraint. Simulation results show that our proposals are useful approaches to enhance the sum rate performance in TDD-mMIMO-HetNets.

DOI： 10.1109/ISPACS.2018.8923182

Language：English   Publishing type：Research paper (scientific journal)  

Tomoya Kageyama, Osamu Muta, ``Performance Analysis of Impulsive Noise Blanking for Multi-Carrier PLC Systems,'' IEICE Communications Express, Vol.7, no.9, pp.334-349, Sept. 2018.

Language：English   Publishing type：Research paper (scientific journal)  

Recently, attention has been paid to the integration of opportunistic communications, whether based on opportunistic user selection (OUS) or opportunistic antenna selection, with interference alignment (IA) in order to improve the performance of wireless networks. In OUS, users that have the best operational conditions are usually selected. However, fairness among users is another important aspect that should be considered in scheduling users. In this paper, a queue-aware two-stage opportunistic IA (OIA) algorithm is proposed for the downlink multicell multiuser multiple-input-multiple-output system. In the first stage, inter-cell interference is eliminated using one pair of precoding/postcoding matrices. Whereas in the second stage, two user selection polices are proposed namely, capacity-based selection (CBS) and queue-based scheduling (QBS), to select a group of users and minimize the inter-user interference among them using another pair of precoding/postcoding matrices. In the QBS-OIA case, a joint scheduling, resource allocation, and IA optimization problems are formulated, and a low complexity heuristic is proposed to solve it. Comparisons are conducted with other OIA algorithms in terms of achieved sum rate, achieved degrees-of-freedom (DoFs), number of served users, queue overflow probability, and computational complexity. Simulations show that the two proposed CBS-OIA and QBS-OIA algorithms outperform other schemes in terms of sum rate and DoFs. Moreover, the proposed QBS-OIA is capable of serving more users, in some cases, and achieves lower overflow probability with much reduced complexity on the expense of achieving a bit lower sum rate than the CBS-OIA in some cases.

DOI： 10.1109/ACCESS.2018.2869693

Language：English   Publishing type：Research paper (scientific journal)  

In this study, downlink channel estimation of three-dimensional massive multiple-input multiple-output (3D-MIMO) system operating in the frequency division duplexing (FDD) mode is considered. Inspired by the channel sparsity property, this study proposes a compressive sensing algorithm to exploit the channel sparsity structure in the angle-time domain. The proposed algorithm, named AMP-ADM, combines the multiple approximate message passing (M-AMP) algorithm with the alternative direction of multiplier (ADM) technique to efficiently exploit the sparsity structure of the 3D massive MIMO channel. First, the proposed AMP-ADM is implemented in the case of the conventional estimation for the FDD protocol where the channel is estimated individually at each user equipment. Then, building on this algorithm, a low complexity feedback AMPADM- T scheme at the transmitting base station (BS) side is proposed. In the proposed feedback AMP-ADM-T technique the users' channels are jointly estimated at the BS to fully exploit the common sparsity basis. Complexity and convergence analyses are provided for both the AMP-ADM and feedback AMP-ADM-T algorithms. Simulation results prove the improved performance of the proposed feedback AMP-ADM-T algorithm compared to different state-of-the-art joint channel estimation techniques.

DOI： 10.1049/iet-com.2017.0916

Language：English   Publishing type：Research paper (other academic)  

In this paper, we investigate pilot allocation problem in two-tier time division duplex (TDD) heterogeneous network (HetNet) with mMIMO. First, we propose a new pilot allocation scheme to maximize ergodic downlink sum rate of macro users (MUs) and small cell users (SUs), where the uplink pilot overhead and cross-tier interference are jointly considered. Then, we theoretically analyze the formulated problem and propose a low complexity one-dimensional search algorithm to obtain the optimum pilot allocation. In addition, we propose two suboptimal pilot allocation algorithms to simplify the computational process and improve SUs' fairness, respectively. Finally, simulation results show that the performance of the proposed scheme outperforms that of the traditional schemes.

DOI： 10.1109/VTCSpring.2018.8417620

Language：English   Publishing type：Research paper (other academic)  

In power line communication (PLC) systems using multi-carrier modulation such as orthogonal frequency division multiplexing (OFDM), reduction of peak-to-average power ratio (PAPR) of OFDM signal and mitigation of the influence of impulsive noise are challenging problems. To deal with these problems in PLC-OFDM systems, this paper proposes an enhanced selected mapping (e-SLM) technique that jointly achieves PAPR reduction on the transmitter side and impulsive noise detection accuracy improvement on the receiver side, where the transmitter selects the best transmit sequence among possible candidates so as to minimize the weighted sum of transmit signal peak power and the estimated receive one, provided that channel state information is available on the transmitter side. On the receiver side, a nonlinear filter is applied to suppress impulsive noise, where the received signal amplitudes exceeding a given threshold are blanked as impulsive noise. Using the proposed e-SLM, peak power of the received signal is reduced below a given threshold level, so that impulsive noise is effectively detected with high accuracy. We evaluate bit error rate (BER) performance of PLC-OFDM systems using the proposed e-SLM method under PLC channel in presence of impulsive noise. Simulation results show the effectiveness of the proposed method in OFDM PLC systems.

DOI： 10.1109/ISPLC.2018.8360223

Language：English   Publishing type：Research paper (other academic)  

A spoofing attack is a critical issue in wireless communication in embedded systems in which a malicious transmitter outside a system attempts to be genuine. As a countermeasure against this, we propose a device-authentication method based on position identification using radio-propagation characteristics (RPCs). Since RPCs are natural phenomena, this method does not depend on information processing such as encryption technology. We call the space from which attacks achieve success "attack space". By formulating the relationship between combinations of transceivers and the attack space, this method can be used in embedded systems. In this research, we consider two RPCs, the received signal strength ratio (RSSR) and the time difference of arrival (TDoA), and construct the attack-space model which use these RPCs simultaneously for preventing wireless spoofing-attacks. We explain the results of a validity evaluation for the proposed model based on radio-wave-propagation simulation assuming free space and a noisy environment.

DOI： 10.1109/DASC-PICom-DataCom-CyberSciTec.2017.94

Language：English   Publishing type：Research paper (other academic)  

In this paper, a dynamic autonomous frequency reuse strategy is adopted for resource allocation in uplink cellular networks. It is assumed that each cell is divided into inner and outer regions. The proposed approach is based on minimizing the total uplink interference at every eNB for all users in both the inner and outer regions in the network. The main advantage of the proposed scheme is that it adapts itself to the varying wireless channel. Simulation results show that the proposed approach provides better total network uplink throughput and average user uplink bit rate compared to the traditional fractional frequency reuse (FFR) regardless of the User Equipment (UE) transmit power, cell radius and user density within the cell.

DOI： 10.1109/ICCE.2018.8326341

Language：English   Publishing type：Research paper (scientific journal)  

In this paper, we propose game-theoretic approaches to model the cooperative spectrum sensing in cognitive radio environment with cognitive secondary users (SU) capable of energy harvesting. An evolutionary game model is considered in the first scenario, where distributed SUs are allowed to choose between two strategies, cooperate to sense the spectrum, or deny to be a free rider. The sensed data is sent to a fusion center (FC) to have a final decision about the existence of the primary user. In the second scenario, the Stackelberg game is applied to model the case when the FC participates as a leader in the game, with carefully designed incentives to SUs to encourage cooperation. Simulation results show the behavior of the two proposed game models and quantify the improvement due to the FC intervention in the Stackelberg game model.

DOI： 10.1109/ACCESS.2018.2810107

Language：English   Publishing type：Research paper (other academic)  

Fitting the huge number of pilots needed for massive multiple inputs multiple outputs antennas (MIMO) channel estimation within the time and frequency resources is a challenging problem. Generally, compressed sensing (CS) channel estimation algorithms face the dilemma of trading off the estimation accuracy and the computational complexity. In this paper, we propose a weighted fast iterative shrinkage thresholding algorithm (W-FISTA). The proposed algorithm provides higher estimation efficiency with the same complexity as the original FISTA. With low computational complexity, multiple measurement vectors (MMV) version of the W-FISTA is proposed to estimate the 3D massive MIMO channel. The proposed MMV-WFISTA estimate the channel coefficients by exploiting its joint sparsity structure in the angle-delay sparse domain. The complexity analysis and the simulation results indicate a clear improvement in the performance of the proposed MMV-WFISTA over joint estimation algorithms.

DOI： 10.1109/PIMRC.2017.8292556

Language：English   Publishing type：Research paper (scientific journal)  

In this paper, we investigate the power allocation problem in massive multiple-input-multiple-output cognitive radio networks. We propose an orthogonal pilot sharing scheme at pilot transmission phase, where secondary users are allowed to use pilots for channel estimation only when there are temporarily unused orthogonal pilots. Following this, we formulate the power allocation optimization problem of the secondary network (SN) to maximize the downlink sum rate of the SN subject to the total transmit power and primary users' signal-interference-plus-noise-ratio constraints. Next, we transform the original (nonconvex) problem into a convex one by using convex approximation techniques and propose an iterative algorithm to obtain the solution. Furthermore, we prove that the proposed algorithm converges to Karush-Kuhn-Tucker points of the original problem. Meanwhile, the impact of the number of the secondary base station (SBS) antennas or the primary BS (PBS) antennas on the downlink rate of the SN and primary network is theoretically studied. Finally, the numerical results present the downlink sum rate of the SN under different parameters through our proposed algorithm.

DOI： 10.1109/TVT.2017.2749599

Language：English   Publishing type：Research paper (other academic)  

Pilot contamination due to the pilot reuse in adjacent cells is a serious problem in time-division duplex (TDD) massive multi-input multiple-output (MIMO) system. Therefore, the pilot allocation is significant for improving the performance of the system. In this paper, we formulate the pilot allocation optimization problem for maximizing uplink sum rate of the system. To reduce the required complexity for finding the optimum pilot allocation, we propose a low-complexity pilot allocation algorithm, where the formulated problem is decoupled into multiple subproblems; in each subproblem, the pilot allocation at a given cell is optimized while fixing the pilot allocation in other cells. This process is continued until the achievable sum rate converges. Through multiple iterations, the optimum pilot allocation is found. In addition, to improve users' fairness, we formulate a fairness aware pilot allocation as maximization problem of sum of user's logarithmic rate and solve the formulated problem using a similar algorithm. Simulation results show that the proposed algorithms obtain good performance comparable to the exhaustive search algorithm, meanwhile the users' fairness is improved.

DOI： 10.1109/VTCFall.2017.8288098

Language：English   Publishing type：Research paper (scientific journal)  

Massive MIMO (mMIMO) is a promising technology for smart multimedia and wireless communication fields. In this paper, we investigate pilot allocation problem in two-tier time division duplex (TDD) heterogeneous network (HetNet) with mMIMO. First, we propose a new pilot allocation scheme for maximizing ergodic downlink sum rate of macro users (MUs) and small cell users (SUs), where the uplink pilot overhead and cross-tier interference are jointly considered. Then, we theoretically analyze the formulated problem and propose a low complexity onedimensional search algorithm to obtain the optimum pilot allocation. In addition, we propose two suboptimal pilot allocation algorithms to simplify the computational process and improve SUs' fairness, respectively. Finally, simulation results show that the performance of the proposed scheme outperforms that of the traditional schemes.

DOI： 10.1587/transfun.E100.A.2314

Language：English   Publishing type：Research paper (scientific journal)  

Osamu Muta, Yusuke Ohki, and Tomoya Kageyama, ``Partial Scrambling Selected Mapping for PAPR Reduction of OFDM Signals,'' IEICE Communications Express, Vol. 6 No. 9, pp.535-541, Sept. 2017.

Language：English   Publishing type：Research paper (other academic)  

Due to the fast boom of security threats in wireless sensor networks (WSNs) sensitive applications, we propose a game-theoretic protection approach for sensor nodes in a clustered WSN based on a repeated game. The proposed game model is developed for detecting malicious sensor nodes that drop the high priority packets (HPPs) aiming at maximizing the high priority data trustworthiness (HPT). Simulation results indicate the improved HPT of the proposed protection model which attains the Pareto optimal HPT as compared to a non-cooperative defense mechanism.

DOI： 10.1109/ISCC.2017.8024586

Language：English   Publishing type：Research paper (other academic)  

Wireless Sensor Networks (WSNs) security plays an intrinsic role to guarantee efficient data transmission, stable network topologies, and robust routing algorithms. In this paper, we propose a modified Stackelberg game of a previous work for high assurance of data trustworthiness in a Power Grid Network (PGN). The proposed approach is presented to mitigate a more severe attack scenario compared to that considered in the previous work; this attack scenario frequently manipulates sets of the deployed nodes in the PGN, which cannot be treated using the previously proposed approach. Our proposed scheme reduces the required number of nodes to be protected to achieve the desired data trustworthiness. Simulation results prove efficient detection for corrupted transmitted data based on limited number of nodes as compared to the previously proposed approach.

DOI： 10.1109/ISCC.2017.8024697

Language：English   Publishing type：Research paper (scientific journal)  

An optimization model for solving the channel assignment problem in multi-cell WLANs which is based on minimizing the maximum interference at access points in the network is proposed. The channel assignment problem is formulated as a mixed integer linear program. The main advantage of the proposed model is that it guarantees that the worst access point interference is minimized. Simulation results show that the proposed model provides both the least worst access point interference and the best fairness, compared to the pick-first greedy algorithm, the optimum model and the maxmin model.

DOI： 10.1007/s11277-017-4129-z

Language：English   Publishing type：Research paper (scientific journal)  

In heterogenous networks (HetNets), the deployment of small cells with the reuse of limited frequency resources to improve the spectral efficiency results in cross- and co-tier interference. In addition, the excessive power usage in such networks is also a critical problem. In this paper, we propose precoding and postcoding schemes to tackle interference and energy efficiency (EE) challenges in the two-tier downlink multiple- input-multiple-output (MIMO) HetNets. We propose transmission strate- gies based on hierarchical partial coordination (HPC) of the macro cell and small cells to reduce channel state information (CSI) exchange and guaran- tee the quality of service (QoS) in the upper tier with any change of network deployment in the lower tier. We employ the interference alignment (IA) scheme to cancel cross- and co-tier interference. Additionally, to maximize the EE, power allocation schemes in each tier are proposed based on a combination of Dinkelbach's method and the bisection searching approach. To investigate insights on the optimization problem, a theoretical analysis on the relationship between the maximum achievable EE and the transmit power is derived. Simulation results prove the superior EE performance of the proposed EE maximization scheme over the sum rate maximization approach and confirm the validity of our theoretical findings.

DOI： 10.1587/transcom.2016EBP3247

Language：English   Publishing type：Research paper (scientific journal)  

The authors propose a game-theoretic approach using the Stackelberg game for securing cognitive radio sensor network (CRSN) against the spectrum sensing data falsification attack; this attack aims at corrupting the spectrum decisions communicated from the ambient sensor nodes (ASNs) to the fusion centre by imposing interference power. The proposed game approach is developed for two different attack-defence scenarios. In the first scenario, the attacker selects to attack a group of delivered reports of the ASNs that have a protection degree below a specific threshold. In the second scenario, the attacker applies its maximum attack interference power to the delivered reports of the ASNs that have been reported to be least protected in the previous round. Simulation results indicate the improved performance of the proposed protection model as compared with two baseline defence mechanisms, namely, the random and equal-protection defence mechanisms with static signal-to-noise ratio (SNR) and variable SNRs. Consequently, Stackelberg game features prove to be beneficial for securing communication over CRSN.

DOI： 10.1049/iet-com.2016.1336

Language：English   Publishing type：Research paper (scientific journal)  

Wanming Hao, Osamu Muta, Haris Gacanin, and Hiroshi Furukawa, ``Price-based Pilot Sharing for Spectrum Sharing Massive MIMO Networks,'' IEICE Communication Express, Vol. 6, No. 5, pp.213-218, May 2017

Language：English   Publishing type：Research paper (other academic)  

Energy-efficient resource allocation is considered for cognitive cooperative radio networks (CCRNs) with imperfect spectrum sensing. The optimization problem of maximizing energy efficiency (EE) is formulated over the transmission power and sensing time subject to some practical limitations, such as the individual power constraint for secondary source and relay, the quality of service (QoS) for the secondary system, and effective protection for the primary user (PU). Given the complexity of this problem, two simplified versions (i.e., perfect and imperfect sensing cases) are studied in this paper. We transform the considered problem in fractional form into an equivalent optimization problem in subtractive form. Then, for perfect sensing, the Lagrange dual decomposition and iterative algorithm are applied to acquire the optimal power allocation policy; for imperfect sensing, an exhaustive search and iterative algorithm are proposed to obtain the optimal sensing time and corresponding power allocation. Finally, numerical results show that the EE design greatly improves EE compared with the conventional spectrum-efficient design.

DOI： 10.1145/3033288.3033324

Language：English   Publishing type：Research paper (scientific journal)  

Mohamed Elwekeil, Masoud Alghoniemy, Osamu Muta, Adel Abdel-Rahman, Haris Gacanin, and Hiroshi Furukawa, ``A Dynamic Distributed Frequency Reuse Scheme for OFDMA Downlink Cellular Networks,'' IEICE Communications Express, vol. 5, no. 8, pp.248-253, Aug. 2016.

Language：English   Publishing type：Research paper (scientific journal)  

Energy-efficient resource allocation is considered in sensing-based spectrum sharing for cooperative cognitive radio networks (CCRNs). The secondary user first listens to the spectrum allocated to the primary user (PU) to detect the PU state and then initiates data transmission with two power levels based on the sensing decision (e.g., idle or busy). Under this model, the optimization problem of maximizing energy efficiency (EE) is formulated over the transmission power and sensing time subject to some practical limitations, such as the individual power constraint for secondary source and relay, the quality of service (QoS) for the secondary system, and effective protection for the PU. Given the complexity of this problem, two simplified versions (i.e., perfect and imperfect sensing cases) are studied in this paper. We transform the considered problem in fractional form into an equivalent optimization problem in subtractive form. Then, for perfect sensing, the Lagrange dual decomposition and iterative algorithm are applied to acquire the optimal power allocation policy; for imperfect sensing, an exhaustive search and iterative algorithm are proposed to obtain the optimal sensing time and corresponding power allocation strategy. Finally, numerical results show that the energy-efficient design greatly improves EE compared with the conventional spectrum-efficient design.

DOI： 10.1587/transcom.2015CCP0026

Language：English   Publishing type：Research paper (scientific journal)  

S. Elsayed, M. Elsabrouty, O. Muta and H. Furukawa, “Model-based quantization for perceptually weighted compressed video sensing," IEICE Communications Express, Vol. 5 No. 7, pp.216-222, July 2016.

Language：English   Publishing type：Research paper (scientific journal)  

We present a study of using game theory for protecting wireless sensor networks (WSNs) from selfish behavior or malicious nodes. Due to scalability, low complexity and disseminated nature of WSNs, malicious attacks can be modeled effectively using game theory. In this study, we survey the different game-theoretic defense strategies for WSNs. We present a taxonomy of the game theory approaches based on the nature of the attack, whether it is caused by an external attacker or it is the result of an internal node acting selfishly or maliciously. We also present a general trust model using game theory for decision making. We, finally, identify the significant role of evolutionary games for WSNs security against intelligent attacks; then, we list several prospect applications of game theory to enhance the data trustworthiness and node cooperation in different WSNs.

DOI： 10.3390/s16071003

Language：English   Publishing type：Research paper (scientific journal)  

A perceptual-based compressed sensing (CS), which focuses the measurements and the recovery on the visually important low-frequency coefficients, is applied for multi-view image signals. High correlation among different views is exploited to generate signal prediction using disparity estimation and compensation techniques. A residual-based recovery is utilised as a joint recovery for the nonreference images to enhance the reconstruction performance. The proposed framework shows remarkable performance improvement over the conventional CS with joint recovery as well as the perceptualbased CS with independent recovery.

DOI： 10.1049/el.2016.0477

Language：English   Publishing type：Research paper (other academic)  

The traditional K-best sphere decoder retains the best K-nodes at each level of the search tree; these K-nodes, include irrelevant nodes which increase the complexity without improving the performance. A variant of the K-best sphere decoding algorithm for ill-conditioned MIMO channels is proposed, namely, the ill-conditioned reduced complexity K-best algorithm (ill-RCKB). The ill-RCKB provides lower complexity than the traditional K-best algorithm without sacrificing its performance; this is achieved by discarding irrelevant nodes that have distance metrics greater than a pruned radius value, which depends on the channel condition number. A hybrid-RCKB decoder is also proposed in order to balance the performance and complexity in both well and ill-conditioned channels. Complexity analysis for the proposed algorithms is provided as well. Simulation results show that the ill-RCKB provides significant complexity reduction without compromising the performance.

DOI： 10.1109/CCNC.2016.7444753

Language：English   Publishing type：Research paper (other academic)  

In this paper, we propose a game-theoretic protection model for Wireless Sensor Network (WSN) nodes within a cluster based on a Stackelberg game. The proposed game approach is developed for two different attack-defense scenarios. In the first scenario, the attacker selects to attack a group of nodes that have a protection degree below a specific threshold. In the second scenario, the attacker targets the nodes that have been reported to be least protected in the previous round. Simulation results indicate the improved performance of the proposed protection model as compared to the no-defense case.

DOI： 10.1109/CCNC.2016.7444900

Language：English   Publishing type：Research paper (other academic)  

The innovative concept of Compressed Sensing (CS) presents a breakthrough that enables the acquisition of sparse signals at much lower sampling rates compared to the conventional Nyquist rate. The scope of CS is not limited only to sparse signal but it is also applicable to compressible signals, such as multimedia signals including audio signals. Representing the random samples from CS process using finite-precision is a crucial problem in communication systems. In this paper, we focus on 1-bit quantized CS. We propose to take into account the perceptual CS model for audio compression, where the perceptual properties are taken into account. We propose two models, the first applies perceptual effect at the transmitter side. In the other model, a modified Binary Iterative Hard Thresholding (BIHT) is proposed to improve the performance of 1-bit compressed sensing by taking the perceptual properties of the received audio signal into account. The Mean Opinion Score (MOS) is used to compare the perceptual quality of the received signal for the proposed 1-bit perceptual CS algorithms. Simulation results show that a better performance is achieved using the proposed algorithms.

DOI： 10.1109/ISCC.2015.7405560

Language：English   Publishing type：Research paper (other academic)  

Recently, an adaptive peak cancellation was proposed to reduce the high peak-to-average power ratio (PAPR), while keeping the out-of-band (OoB) power leakage as well as an in-band distortion power (EVM) below the pre-determined (permissible) level. However, the peak cancellation in MIMO-OFDM systems was not considered. In this paper, we propose a peak cancellation method for linearly pre-coded MIMO-OFDM systems using eigen-beam space division multiplexing (E-SDM). We evaluate and discuss the performance of the system using the proposed peak cancellation in terms of bit error rate (BER), complementary cum-mulative distribution function (CCDF) of PAPR and the system's computational complexity. Our results show the improvements with respect to both the achievable BER and PAPR with the proposed peak cancellation in E-SDM systems under the restriction of OoB power radiation.

DOI： 10.1109/PIMRC.2015.7343308

Language：English   Publishing type：Research paper (other academic)  

In this paper, we apply an efficient scaling strategy on layered scaled min-sum LDPC decoder. In addition, we propose a joint optimization strategy for the quantization and scaling parameters of layered scaled min-sum LDPC decoder. The study of our optimization results, for DVB-S2 LDPC codes with different constellation sizes and code rates, shows that each constellation size code rate pair has different optimal scaling and quantization parameters. In order to maximize the achievable performance, we propose using the different scaling and quantization parameters for each constellation size code rate pair. The simulation results show the performance improvement of separately using optimal scaling parameters or optimal quantization parameters, and the overall performance enhancement of using both optimal scaling and quantization parameters.

DOI： 10.1109/ISIT.2015.7282940

Language：English   Publishing type：Research paper (scientific journal)  

Sawsan Elsayed, Maha Elsabrouty, Osamu Muta, and Hiroshi Furukawa, ``Perceptual-based Compressed Video Sensing,'' IEICE Communications Express, Vol. 4 No. 8, pp.251-257, Aug. 2015.

Language：English   Publishing type：Research paper (scientific journal)  

An ACK based partial random selection (ACK-PRS) encoding algorithm for the uplink distributed low-density parity check network code of the generalised adaptive network coded cooperation is proposed. The proposed algorithm achieves good error correction performance and high system throughput, while maintaining the low complexity of the random selection algorithm. This good performance is achieved by a minor increase in the down link signalling. Simulation results for 5 and 20 uplink users verify the good performance of the proposed ACK-PRS.

DOI： 10.1049/el.2015.2132

Language：English   Publishing type：Research paper (other academic)  

Analog-to-digital (A/D) converter (ADC) and related analog hardware designs are important factors to simplify the transceiver circuits in wireless communication systems. In order to mitigate the nonlinearity of a low-resolution ADC that reduces the required analog hardware complexity, we have investigated two nonlinearity mitigation techniques for A/D conversion, i.e., the dither-ADC and the hysteresis-ADC. In this paper, we evaluate the effect of the nonlinearity mitigated A/D conversion techniques on the achievable performance in single carrier offset- quadrature-amplitude-modulation (OQAM)and QAM systems, where the receiver adopts either the dither-ADC or the hysteresis-ADC. Simulation results prove that both the dither-ADC and the hysteresis-ADC are effective in improving BER performance of both OQAM and QAM systems affected by the nonlinearity of ADC, while the transmitter employs a selected mapping technique that achieves a low peak-to-average power ratio (PAPR).

DOI： 10.1109/VTCSpring.2015.7145796

Language：English   Publishing type：Research paper (other academic)  

Compressed Sensing (CS) has been widely used for multimedia processing to reduce the number of the measurements required to acquire signals that are spare or compressible sparse in some basis. CS provides good quality of the restored signal even when the signal is not completely sparse and even also at high compression ratio. However, classical CS assumes that the measurements are real-valued and have infinite-bit precision that requires impractical hardware implementation. Quantized CS provides a solution to this problem. Different quantized compressed sensing techniques are developed in literature and recovery is possible even if only 1-bit is used for the quantization. In this work, we propose using different quantization vlaues, including 1-bit compressed sensing for perceptual audio signal compression in perceptual systems in order to clarify the effect of the quantization process on the achievable quality of audio signal. Mean Opinion Score (MOS) is used as metric to compare the perceived quality of audio signal of 1-bit CS and classical CS. Simulations results show that reasonable performance is achieved for different quantization CS compared to quantized classical CS.

DOI： 10.1109/DCC.2015.52

Language：English   Publishing type：Research paper (other academic)  

Interference Alignment (IA) emerged on the communication scene as a solution to the interference problem in all interference-limited networks, including heterogeneous cellular systems. However, the performance of IA is greatly related to the accuracy of the channel state information at transmitters (CSIT), namely the number of feedback bits. Accordingly, in order to improve the performance of IA, it would be useful to analyze the number of feedback bits with respect to the sum rate loss. Motivated by that, this paper studies a limited feedback-based IA scheme suitable for two tier macrocell-femtocell heterogeneous networks. First, an approximate analytical expression for the upper bound on the total sum rate loss due to limited feedback in the studied IA system, is derived. Then, a simulation based evaluation of the sum-rate loss due to the implementation of limited feedback IA in heterogeneous networks is obtained. Simulation results conrmed the severe effect of quantization of CSI on the interference alignment performance.

DOI： 10.1109/VTCSpring.2015.7145883

Language：English   Publishing type：Research paper (scientific journal)  

This paper presents a downlink interference mitigation framework for two-tier heterogeneous networks, that consist of spectrumsharing macrocells and femtocells^∗ . This framework establishes cooperation between the two tiers through two algorithms, namely, the restricted waterfilling (RWF) algorithm and iterative reweighted least squares interference alignment (IRLS-IA) algorithm. The proposed framework models the macrocell-femtocell two-tier cellular system as an overlay cognitive radio system in which the macrocell system plays the role of the primary user (PU) while the femtocell networks play the role of the cognitive secondary users (SUs). Through the RWF algorithm, the macrocell basestation (MBS) cooperates with the femtocell basestations (FBSs) by releasing some of its eigenmodes to the FBSs to do their transmissions even if the traffic is heavy and the MBS's signal to noise power ratio (SNR) is high. Then, the FBSs are expected to achieve a near optimum sum rate through employing the IRLS-IA algorithm to mitigate both the co-tier and cross-tier interference at the femtocell users' (FUs) receivers. Simulation results show that the proposed IRLS-IA approach provides an improved sum rate for the femtocell users compared to the conventional IA techniques, such as the leakage minimization approach and the nuclear norm based rank constraint rank minimization approach. Additionally, the proposed framework involving both IRLS-IA and RWF algorithms provides an improved total system sum rate compared with the legacy approaches for the case of multiple femtocell networks.

DOI： 10.1587/transcom.E98.B.467

Language：English   Publishing type：Research paper (scientific journal)  

Mahmoud M. Selim, Osamu Muta, Hossam M. H. Shalaby, and Hiroshi Furukawa, ``Chunk-based Resource Allocation in Multi-Cell OFDMA Systems with Fairness Guarantee,'' IEICE Communications Express, Vol.4, no.2, pp.31-37, February 2015.

Language：English   Publishing type：Research paper (scientific journal)  

Ibrahim Al-Nahhal, Ahmed Emran, Hossam Kasem, Adel B.Abd El-Rahman, Osamu Muta, and Hiroshi Furukawa, ``Flexible Fractional K-best Sphere Decoding for Uncoded MIMO Channels,'' IEICE Communications Express, Vol.4, No.1, pp.20-25, January 2015.

Language：English   Publishing type：Research paper (scientific journal)  

Mohamed Rihan, Maha Elsabrouty, Osamu Muta, and Hiroshi Furukawa, ``Iterative Reweighted Least Squares Interference Alignment Approach for Multicell MIMO Networks,'' IEICE Communications Express, Vol.4, No.1, pp.1-7, January 2015.

Language：English   Publishing type：Research paper (other academic)  

In this paper, an optimization model for solving the channel assignment problem in multi-cell WLANs is proposed. This model is based on maximizing the minimum distance between access points (APs) that work on the same channel. The proposed model is formulated in the form of a mixed integer linear program (MILP). The main advantage of the proposed algorithm is that it ensures non-overlapping channel assignment with no overhead power measurements. The proposed channel assignment algorithm can be implemented within practical time frames for different topology sizes. Simulation results indicate that the proposed algorithm exhibits better performance than that of the pick-first greedy algorithm and the single channel assignment method.

Language：English   Publishing type：Research paper (other academic)  

Although the amplify-and-forward (AF) relaying is an effective and simple technique for cooperative communication networks, it introduces a noise enhancement problem. This problem occurs when the effects of interference and the multipath fades are amplified during the transmission from the source to the relay. AF is usually used with the multiple access broadcast (MABC) protocol which is a two phases transmission (2P) analog network coding (ANC) protocol for the half-duplex (HD) communication mode. However, MABC is not designed to utilize the direct link (DL) signal no matter how strong it is. To utilize the DL signal, a three transmission phases protocol known as time-division broadcast protocol (TDBC) was proposed at which both end nodes transmit their message at consecutive time slots and the relay nodes broadcasts a combined signal at the 3^rd time slot. To deal with the noise enhancement problem and improve the system performance, this paper proposes a zero-forcing based relay power allocation (ZF-RPA) scheme to be used with TDBC protocol, where the noise enhancement is mitigated by introducing adaptive ZF gains at the relay node that inverses the channels effects between sources and relay when the signal is constructed to be transmitted at the third phase of the TDBC. Analytical results of the ZF-RPA scheme is compared to the traditional variable-gain (VG-RPA) scheme under the same nodes power allocation. Simulation results show that the ZF-RPA is superior for all channel qualities in terms of the outage probability compared to the traditional VG-RPA. The total system sum rate comparison reveals that the ZF-RPA scheme could outperform the VG-RPA scheme as long as the channel qualities of the relay-transceiver links are less than certain threshold. This paper also clarifies that it is effective to select either ZF or VG-RPA according to the channel qualities and it can be implemented with VHDL by introducing an adaptive control unit (ACU).

DOI： 10.1109/InfoSEEE.2014.6947792

Language：English   Publishing type：Research paper (other academic)  

In this paper, cooperative compressive spectrum sensing is considered to enable accurate sensing of the wide-band spectrum. The proposed algorithm is based on compressive sensing theory and aims to reduce the hardware complexity of the cognitive radio receiver by distributing the sensing work among groups of sensing nodes. The proposed algorithm classies the cooperated sensing nodes into different sensing groups depending on the quality of the reporting channel between the sensing node and the fusion center (FC). To sense the wide- band analog signal and take a global decision about spectrum occupancy, each node uses its local sensing matrix, which is assigned to its sensing group and a part of a global sensing matrix at the FC. The size of the local sensing matrix of each sensing node,and consequently the contribution of this node in the overall measurement vector, depends on its sensing group. The FC classies and rearranges the compressed data to formulate one global measurement vector which is used with a global sensing matrix to estimate the wide-band signal spectrum. The receiver operation characteristics (ROC) of the overall spectrum sensing system show that the proposed receiver provides more protection to primary users (higher detection probability) at the same secondary user throughput (probability of false alarm).

DOI： 10.1109/VTCFall.2014.6966230

Language：English   Publishing type：Research paper (scientific journal)  

Underlay cognitive radio (CR) permits unlicensed secondary users (SUs) to transmit their own data over the licensed spectrum unless the interference from the SUs on the licensed primary user (PU) exceeds an acceptable level. This paper proposes two generalized interference alignment (IA)-based distributed optimization designs for multiple secondary transceivers in the underlay CR case with channel uncertainty under assumption that the actual channel error norm is below a certain bound. One of the designs is an extension to an existing method and the other one is a new design. In these methods, the precoding and power allocation matrices for each SU are either independently or jointly optimized for imperfect channel knowledge to maximize the secondary rates and to hold the secondary interference on the primary receiver under an acceptable limit that is determined by the primary receiver. Numerical results prove the ability of the proposed methods to support significant secondary rates provided that the PU is protected from extra interference from SUs, even in presence of channel uncertainty.

DOI： 10.1587/transcom.E97.B.2543

Language：English   Publishing type：Research paper (other academic)  

In cellular networks, fractional frequency reuse (FFR) is an effective inter-cell interference mitigation technique to achieve significant coverage improvement for cell edge users. Area Spectral Efficiency (ASE) is an important and vital factor to be improved in cellular networks and is defined as the number of transmitted information bits per unit area per unit time per unit bandwidth (i.e., bps/Hz/m²). In this paper, we compare ASE of different downlink FFR schemes in MIMO Heterogeneous cellular networks (MIMO HetNets), where the base station (BS) locations are modeled using Poission Point Process (PPP). Stochastic PPP is widely used in the design and analysis of signal processing algorithms especially for communication systems. ASEs are evaluated based on coverage probability functions for Strict FFR and Soft Frequency Reuse (SFR) in MIMO HetNets for both closed and open access cases. In the same time we illustrate not only the role but also the benefits of utilizing PPP in modeling the BS locations for analytical evaluation of two main types of FFR deployments. Numerical results show that, for SFR in both open and closed access cases, it is better to use MIMO HetNets than other techniques due to large interference resulted from utilizing the whole bandwidth inside the cell. Also, in SFR case, ASE is directly proportional to the power control factor β_k. For Strict FFR MIMO HetNet open access case, SDMA with large numbers of antenna provides higher ASE at the expense of system complexity. For better ASE in MIMO HetNet system, it is recommended to use adaptive technique between strict FFR MIMO and MU-MIMO in terms of target threshold value of signal-to-interference ratio (SIR).

DOI： 10.1109/InfoSEEE.2014.6947820

Language：English   Publishing type：Research paper (other academic)  

The deployment of femtocells in current and future communication systems promises an effective solution for limited indoor coverage problem and a possible gateway for mobile data offloading. In this paper, we cast a cognitive interference alignment approach (IA) suitable for heterogeneous cellular networks with a mixed macrocell and femtocell deployment Specifically, in our approach a restricted waterfilling (RWF) algorithm is used to maximize the downlink data rate, while reserving some eigenmodes for giving the femtocell basestations the opportunity to do their transmissions even at high signal-to-noise power ratio (SNR) for the macrocell basestation. Additionally, both the cross-tier and co-tier interference is to be aligned at each femtocell user's receiver using an Iterative Reweighted Least Squares(IRLS) algorithm. The simulation results show that the proposed IA approach provides an improved sum rate for the femtocell users, compared to the conventional IA techniques, like, the leakage minimization approach and the nuclear norm based rank constraint rank minimization approach.

DOI： 10.1109/ISWCS.2014.6933435

Language：English   Publishing type：Research paper (scientific journal)  

Mahmoud M. Selim, Osamu Muta, Hossam M. H. Shalaby, and Hiroshi Furukawa, ``Low Complexity QoS-aware Subcarrier Allocation forMISO-OFDMA Systems,'' IEICE Communications Express, Vol. 3 No. 8, pp. 235-240, Aug. 2014.

Language：English   Publishing type：Research paper (other academic)  

In MIMO space division multIPlexing (SDM) systems, the peak power of the transmit signal at each antenna element is increased by the precoder and hence it causes the power efficiency degradation and/or nonlinear distortion at the power amplifier. To solve this problem, this paper present a peak power aware precoding scheme for MIMO-SDM systems, where the precoder is designed to mitigate the peak output power at each antenna element so that peak amplitude of the transmit signal at each antenna is reduced while minimizing the performance degradation caused by the peak power restriction. The proposed system employs an aLTErnative iterative optimization algorithm that determines the precoding matrix so that the precoding and virtual post-coding matrices are aLTErnatively optimized under the constraint of peak output at each antenna element. Simulation results show that the proposed method is effective in restricting the peak transmission power at each antenna within a permissible level while mitigating performance degradation in bit error rate (BER) performance of the precoded SDM systems.

DOI： 10.1109/PIMRC.2014.7136197

Language：English   Publishing type：Research paper (scientific journal)  

Mohamed Elwekeil, Masoud Alghoniemy, Osamu Muta, Adel Abdel-Rahman, and Hiroshi Furukawa, ``A Maxmin Approach for Channel Assignment in Multi-cell WLANs,'' IEICE Communications Express, Vol.3, No.5, pp.175-181, May 2014.

Language：English   Publishing type：Research paper (other academic)  

A radio relay multi-hop transmission using Multi-Input Multi-Output (MIMO) is a promising technique to construct indoor wireless communication systems. To improve power efficiency at the power amplifier on the transmitter side, this paper considers MIMO constant envelope modulation (CEM) transceiver. On the other hand, the resolution of A/D converter (ADC) affects hardware complexity on MIMO receiver circuits. Although analog hardware complexity on MIMO receiver circuits can be reduced by decreasing the resolution of ADC, it causes severe ADC nonlinearity which affects achievable performance, i.e., there a trade-off between hardware complexity and non-linearity on ADC circuits for MIMO receiver. The objective of this paper is to investigate the influence of ADC nonlinearity on achievable performance in MIMO differential encoded Gaussian minimum shift keying (D-GMSK) systems using a reduced-state modified maximum sequence estimation (MLSE) equalization. In the MLSE equalization for D-GMSK systems, the influence of ADC nonlinearity is mitigated by approximating the received signal in presence of quantization error. Computer simulation results show that the MLSE equalization scheme approximating the influence of ADC nonlinearity improves BER performance of MIMO and SISO D-GMSK systems using a low resolution ADC compared to cases without using the above approximation in multi-path Rayleigh fading conditions.

DOI： 10.1109/ICOIN.2014.6799738

Language：English   Publishing type：Research paper (other academic)  

This paper investigates an iterative algorithm to control weighting coefficients of transmit/receive spatial filters in a frequency-division duplex (FDD) based eigen-mode space division multiplexing (E-SDM/FDD) system. In this system, weighting matrices of transmit/receive spatial filters are optimized using an iterative algorithm that minimizes the mean square error (MSE) of the virtual received signal, where the receiver feeds back relative channel characteristic information of the forward-link to the transmitter. This paper also presents an alternative feedback control method for optimizing the weighting coefficients of the transmit spatial filter in presence of feedback bit errors; the receiver determines the weighting coefficients at the transmitter and sends back relative information of them to the transmitter. This method will be able to mitigate the performance degradation caused by the feedback bit error. Simulation results of bit error rate (BER) performance proves the effectiveness of the proposed algorithm in the E-SDM/FDD 4 × 2 MIMO systems.

DOI： 10.1109/ICCS.2014.7024872

Language：English   Publishing type：Research paper (other academic)  

In this paper, we investigate the performance of offset quadrature amplitude modulation based orthogonal frequency division multiplexing (OQAM-OFDM) systems using an adjacent channel leakage power ratio (ACLR) and error vector magnitude (EVM) restricted peak amplitude cancellation scheme for peak-to-average power ratio (PAPR) reduction, where peak amplitude of the transmit signal that exceeds a give threshold level is iteratively suppressed by adding a peak cancellation (PC) signal which exhibits sharp peak amplitude at the midpoint of pulse waveform in time domain. In addition, using this scheme, both ACLR and EVM are automatically adjusted so as to meet a given requirement. In the proposed scheme, both PAPR reduction performance and system requirements such as out-of-band spectrum radiation and in-band distortion are simultaneously taken into consideration. Through computer simulation results, it is demonstrated that the proposed PAPR reduction scheme is effective in reducing PAPR of pulse shaped OQAM-OFDM signals, while both ACLR and EVM requirements are simultaneously fulfilled.

DOI： 10.1109/ICCS.2014.7024837

Language：English   Publishing type：Research paper (scientific journal)  

Wireless Local Area Networks (WLANs) are widely deployed for internet access. Multiple interfering Access Points (APs) lead to a significant increase in collisions, that reduces throughput and affects media traffic. Thus, interference mitigation among different APs becomes a crucial issue in Multi-Cell WLAN systems. One solution to this issue is to assign a different frequency channel to each AP so as to prevent neighboring cells from operating on the same channel. However, most of the existing WLANs today operate in the unlicensed 2.4 GHz Industrial, Scientific and Medical (ISM) band, which suffers from lack of the available channels. Therefore, effective channel assignment to minimize the interference in Multi-Cell WLANs is necessary. In this article, we formulate the channel assignment problem as a mixed integer linear programming (MILP) problem that minimizes the worst case total interference power. The main advantage of this algorithm is that it provides a global solution and at the same time guarantees a non-overlapping channel assignment. We also propose a Lagrangian relaxation approach to transform the MILP into a low complexity linear program which can be solved efficiently in real time, even for large sized networks. Simulation results reveal that both the MILP algorithm and the Lagrangian relaxation approach provide a total interference reduction below the default setting of having all APs assigned the same channel. In addition, simulation results on cumulative density function (CDF) of the SINR at the user level prove the validity of the proposed algorithms.

DOI： 10.1587/transfun.E97.A.1761

Language：English   Publishing type：Research paper (other academic)  

In this paper, a novel one bit resolution ADC for wireless communication devices is presented. If we use a conventional one bit resolution ADC for wireless communication devices, the communication quality becomes worse due to heavy non-linearity. To overcome this problem, we proposed a novel one bit resolution ADC circuit with linearity enhancement technique, which uses a S/H and a hysteresis comparator. By using hysteresis effect, the periodicity of one bit resolution ADC output signal can be reduced. Signal-to-Quantization-Noise Ratio (SQNR) can be improved by 6.4dB, thanks to the proposed technique.

DOI： 10.1109/ISCE.2014.6884368

Language：English   Publishing type：Research paper (scientific journal)  

The multiple access broadcast (MABC) is an effective two phases transmission (2P) ANC protocol for the half-duplex (HD) communication mode. However, MABC does not make use of channel gain of the direct link (DL) no matter how strong it is. On the other hand, the time division broadcast (TDBC) is known as a three phases transmission (3P) protocol which enables transceivers to utilize DL and thus offers the possibility to achieve higher performance compared with the MABC at the expense of a reduced spectral efficiency due to the one extra transmission phase. In this paper, we investigate a joint single relay selection and power allocation schemes for energy-efficient wireless communication systems with analog network coding (ANC) for TDBC, where two-way relay channel with two end nodes and N parallel relay nodes is considered under an assumption of perfect channel-state information (CSI). Our objective is to minimize the total system transmit power consumption under quality-of-service (QoS) constraints for TDBC protocol with joint single relay selection and nodes power allocation. In addition, a zero-forcing based relay signal combining technique that combines the signals received at the 1st and 2nd transmission phases, also known as zero-forcing relay power allocation (ZF-RPA), is also investigated. Numerical simulation shows that the traditional VG-RPA is more energy-efficient than the ZF-RPA scheme for TDBC in cases with and without utilizing DL.

DOI： 10.1109/VTCSpring.2014.7022964

Language：English   Publishing type：Research paper (other academic)  

Resource allocation (RA) in multi-cell OFDMA systems is very important for maximizing system throughput. Although sub-channel RA is optimal in terms of system throughput, more interest is given to chunk-based RA so as to simplify allocation algorithms and minimize required signalling. In this paper, we propose a fairness-aware chunk-based RA algorithm for the downlink transmission of multi-cell OFDMA system with fractional frequency reuse (FFR) adoption. Simulation results reveal that our proposed algorithm outperforms two reference algorithms in literature in terms of some system metrics such as average system spectral efficiency (SE), users fairness and rates of cell-edge users.

DOI： 10.1109/ICCVE.2014.7297707

Language：English   Publishing type：Research paper (other academic)  

In two-way relay network (TWRN), end nodes may have different quality-of-service (QoS) requirements according to their priority, traffic demand, and/or their downlink and uplink split ratio. In this paper, the heterogeneity among network users that have different traffic load/demands is considered by assuming a weighted fairness between the two end nodes. An energy efficient design is proposed for two-way relaying (TWR) with time division broadcast (TDBC) protocol that minimizes the allocated power to the two transceivers and the relay node under a weighted quality-of-service (QoS) bidirectional data rates requirement with weighting factor (a). This design utilizes the signal combining process at the relay node in TDBC, also known as relay power allocation (RPA), to provide a new simpler way to ensure the weighted rates without increasing the complexity to control different power allocation of the three nodes. Adaptive calculation of the relay power allocation factor, e, is adopted for combining the two received signals to satisfy the QoS requirements. Simulation results show an improvement in the efficiency in terms of the average allocated power and an improved users' fairness compared with scenarios where a predetermined fixed value of e is used.

DOI： 10.1109/ICCVE.2014.7297702

Language：English   Publishing type：Research paper (other academic)  

Fractional Frequency Reuse (FFR) is an efficient mitigation technique for modern cellular networks because of its low complexity and coordination requirements and resource allocation flexibility. This work considers the use of FFR in the cellular uplink where we analyze the uplink worst case Signal to Interference Ratio (SIR) for two main FFR schemes; which are strict FFR and Soft FFR. A closed form expression is derived analytically for the worst SIR and for the best inner radius. This analytical technique is utilized to configure a FFR solution for the uplink of OFDMA cellular system. The analysis is performed using two-tier cellular network with uniform user density and for three different cases of FFR. The effect of power control exponent on both FFR schemes is also studied. The inner radius configuration depends on equalizing the worst SIR for both inner and outer edges of the cell. Numerical results show that FFR with reuse four yields the highest SIR. It is noticed that power control exponent doesn't affect strict FFR but affects SFR as it reduces its SIR and inner radius.

Language：English   Publishing type：Research paper (other academic)  

Underlay cognitive radio (CR) permits unlicensed secondary users (SUs) to transmit their own data over the licensed spectrum unless the interference from the SUs on the licensed primary user (PU) exceeds an acceptable level. This paper proposes two interference alignment (IA)-based distributed optimization designs for multiple secondary transceivers in underlay cognitive radio case with channel uncertainty. The precoding and power allocation matrices for each SU are either independently or jointly optimized for imperfect channel knowledge to maximize the secondary rates and to control the secondary interference on the primary receiver to be below the acceptable limit that is determined by the primary receiver. Numerical results prove the ability of the proposed methods to support significant secondary rates and to protect the PU from extra interference, within the acceptable primary range, even in presence of channel uncertainty case. In addition, joint optimization design has higher secondary performance than the independent optimization design.

DOI： 10.1109/PIMRC.2013.6666287

Language：English   Publishing type：Research paper (other academic)  

Fractional Frequency Reuse (FFR) is an efficient method to mitigate Inter Cell Interference in multicellular Orthogonal Frequency Division Multiple Access (OFDMA) systems. In this paper, we analyze the downlink worst case Signal to Interference Ratio for FFR schemes. A closed form expression is derived analytically for the worst SIR, outage probability, and Spectral Efficiency (SE). The proposed analytical technique is used to configure a FFR solution for the downlink of OFDMA cellular system. The analysis is performed using two-tiers cellular network with uniform user density and for three different cases of FFR, namely, Frequency Reuse Factor (FRF) = 3, FRF=4 and sectored FFR. The inner radius configuration depends on equalizing the worst SIR for both inner and outer edges of the cell. Numerical results show that sectored FFR yields the highest SE and low outage probability. Sectored FFR highly balances the needs of interference reduction and resource efficiency.

DOI： 10.1109/PIMRC.2013.6666210

Language：English   Publishing type：Research paper (other academic)  

Frequency reuse schemes are an interference management techniques well suited to OFDMA-based cellular networks. In this paper, analytical expressions are derived for the worst case Signal to Interference Ratio (SIR) ratio for both Fractional Frequency Reuse (FFR), and Soft Frequency Reuse (SFR). Also, analytical expressions are derived for the best inner radius using the worst SIR in both FFR, and SFR schemes. The analysis is performed in cellular network using exponent path loss model. The results showed that FFR with reuse four has the smallest interference hence better edge spectral effiency than SFR with different power ratios. For SFR it is better to use power ratios between 2, 4 as they achieve reasonable inner radii than other power ratios. The analysis showed that there is tradeoff aspect between capacity and coverage related to SFR and FFR respectively.

Language：English   Publishing type：Research paper (other academic)  

The Channel assignment problem for multi-cell WLANs is important due to the lack of free available channels. Usually, this problem can be formulated as a mixed integer linear program (MILP) which requires high combinatorial complexity. In this paper, a lagrangian relaxation technique is used in order to transform the MILP into a low complexity linear program. Simulation results show that the proposed channel assignment algorithm provides significant reduction in complexity compared to the MILP counterpart at the expense of insignificant increase in total interference-sum at Access Points (APs). It is also suggested that the benefits of reduced complexity outweigh the increased interference.

DOI： 10.1109/ICCNC.2013.6504069

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (other academic)  

This paper investigates the interference alignment (IA) solution for a K-user static flat-fading multiple input multiple output (MIMO) interference channel. Optimal users' precoders and postcoders are designed through a rank constraint rank minimization (RCRM) framework with IA conditions inserted within the constraints and the cost function of a complex matrix optimization problem. With RCRM formulation, the interference is forced to span the lowest dimensional subspace possible, under the condition that the useful signal subspaces span all available spatial dimensions. Using the recent advances in matrix completion theory and low rank matrix recovery theory, we propose an Iterative Reweighted Least Squares (IRLS) approach to IA. Through this approach, we provide an adequate relaxation for the rank function which in some cases attain the same results obtained using the standard nuclear norm with lower elapsed time per iteration and lower number of iterations and in some cases perform better than any of the previous approaches.

DOI： 10.1109/WD.2013.6686521

Language：English   Publishing type：Research paper (other academic)  

In this paper, we propose a peak-to-average power ratio (PAPR) reduction scheme based on adaptive peak amplitude cancellation for multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems, where peak amplitude of OFDM signal is iteratively suppressed by adding a specific peak cancellation (PC) signal which has flat frequency spectrum over signal bandwidth in frequency domain and sharp peak amplitude at the midpoint of pulse waveform in time domain. In the proposed scheme, both adjacent channel leakage power ratio (ACLR) and error vector magnitude (EVM) are automatically adjusted so as to meet a given requirement. In the proposed scheme, both PAPR reduction performance and system requirements such as out-of-band spectrum radiation and in-band distortion are simultaneously taken into consideration; both ACLR and EVM are automatically controlled to meet the requirements. Computer simulation results prove that the proposed PAPR suppression scheme effectively reduce PAPR of the OFDM signal in MIMO systems, while both ACLR and BER requirements are simultaneously fulfilled.

DOI： 10.1109/PIMRC.2012.6362676

Language：English   Publishing type：Research paper (other academic)  

In this paper, we propose a new formulation for solving the channel assignment problem for Multi-cell WLANs as a mixed integer linear programming (MILP) problem. The objective is to minimize the total interference seen by all Access Points (APs). The main advantage of the proposed algorithm is that it provides a global solution and at the same time guarantees non-overlapping channel assignment. The proposed channel assignment formulation can be used for different topologies of WLAN as demonstrated in the simulation. Simulation results show that the proposed algorithm outperforms the pick-first greedy algorithm and the single channel assignment method. The proposed channel assignment technique reduces the total interference at all APs which leads to an improved throughput.

Language：English   Publishing type：Research paper (other academic)  

The authors have proposed constant envelope modulation (CEM) systems that enable to use a power-efficient nonlinear power amplifier on the transmitter side and a low resolution analog-to-digital converter (ADC) on the receiving side, where power consumption at the analog devices is effectively reduced by employing a low resolution ADC at the receiver. In such a receiver, the received signal is seriously affected by severe quantization error by the ADC and therefore BER performance is degraded. As a solution to performance degradation at the CEM receiver affected by quantization error, in this paper, we propose efficient nonlinear (Viterbi) equalization schemes that estimate both inter-symbol interference in multi-path channel and quantization error in ADC, where quantization error is estimated by using a simple function that models the relation between the received signal level and the resulting quantization error. In addition, the proposed scheme effectively reduces the number of states in Viterbi equalization to achieve computational complexity reduction for equalizations. Computer simulation results show that the proposed nonlinear equalization scheme improves BER performance of CEM receiver seriously affected by quantization error, while computational complexity is effectively reduced.

DOI： 10.1109/JEC-ECC.2012.6186969

Language：English   Publishing type：Research paper (other academic)  

The authors have proposed Multi-Input Multi-Output (MIMO) constant envelope modulation (CEM) systems that enable to use a power-efficient nonlinear power amplifier on the transmitter side and a low resolution analog-to-digital converter (ADC) on the receiver side, where power consumption at the analog devices is effectively reduced by employing a low resolution ADC at the receiver. In such a receiver, the received signal is seriously affected by severe quantization error by the ADC and therefore BER performance is degraded. As a solution to performance degradation at the MIMO-CEM receiver affected by quantization error, in this paper, we propose efficient nonlinear (Viterbi) equalization schemes that estimate both inter-symbol interference in multi-path channel and quantization error in ADC, where quantization error is estimated by using a simple function that models the relation between the received signal level and the resulting quantization error. In addition, the proposed scheme effectively reduces the number of states in Viterbi equalization to achieve computational complexity reduction for equalizations. Computer simulation results show that the proposal nonlinear equalization scheme improves BER performance of MIMO-CEM receiver seriously affected by quantization error, while computational complexity is effectively reduced.

DOI： 10.1109/ICOIN.2012.6164391

Language：English   Publishing type：Research paper (scientific journal)  

The authors have proposed Multi-Input Multi-Output (MIMO)-Constant Envelope Modulation, (MIMO-CEM), as a power and complexity efficient alternative to MIMO-OFDM, suitable for wireless backhaul networks in which relay nodes are fixed in their positions. One of the major problems hindering the real application of MIMO-CEM is to estimate MIMO channel characteristics. MIMO-CEM is based upon two contrary schemes; one is nonlinear equalization such as maximum likelihood sequence estimator, which needs accurate channel information to replicate the received signal passing through it. The other is a low resolution analog-to-digital converter (ADC), e.g., 1-bit in the default operation that removes the received signal amplitude fluctuation. In this paper, as a solution to the channel estimation problem in MIMO-CEM with low resolution ADC receiver, we propose an adaptive MIMO-CEM channel estimation scheme where iterative adaptive channel estimation is carried out to minimize the error between the received preamble signal and the replicated one. We also prove that Code Division Multiplexing (CDM) preamble transmission is effective in estimating MIMO channel parameters in the presence of large quantization noise. Computer simulation results show that MIMO-CEM with the proposed channel estimator using CDM preambles achieves identical BER performance to that with the ideal channel estimation even in presence of severe quantization noise caused by a low resolution ADC.

DOI： 10.1587/transcom.E95.B.2393

Language：English   Publishing type：Research paper (other academic)  

Multi-Input Multi-Output (MIMO) Vector coding (VC) transmission with adaptive modulation is an effective technique to enhance transmission performance in frequency selective wireless channels. The VC is a kind of code-division multiplexing (CDM) by which eigenvectors of channel autocorrelation matrix are used as spreading code. A major disadvantage of the VC is that the transmit signal exhibits high peak-to average power ratio (PAPR), which causes nonlinear distortion and/or power efficiency degradation at a power amplifier, similarly to OFDM and CDM systems. As a solution to this problem, selected mapping (SLM) PAPR reduction techniques have been studied. This paper presents a partial scrambling SLM PAPR reduction method for multi-code VC transmission in adaptive modulated MIMO systems. In this method, PAPR of the transmit signal is reduced to scramble bit sequence mapped on limited number of code vectors in VC systems. In addition, the maximum amplitude of transmit signal in each transmission block is reduced only when the maximum peak amplitude exceeds a given threshold value. Simulation results clarify that the partial scrambling method achieves better average throughput performance than the conventional method, although almost identical PAPR reduction performance is obtained for MIMO VC systems in an attenuated six-path Rayleigh fading condition.

Language：English   Publishing type：Research paper (scientific journal)  

As a solution to high peak-to-average power ratio (PAPR) problems in vector coding (VC) systems, phase controlbased methods such as selected mapping (SLM) and partial transmit sequence have been investigated. As described in this study, a phase sequence blind estimation method is presented for PAPR reduction based on phase control in multi-input multi-output (MIMO) adaptive modulated VC systems, where turbo code is employed. On the receiver side, the phase sequence component is estimated using a maximum likelihood method that selects the most likely sequence among all candidate sequences by exploiting soft-output information of the decoder. Computer simulation results show that when the number of candidate sequences in SLM is M = 16, instantaneous power of the transmit signal at the complementary cumulative distribution function of 10^-5 can be reduced by about 4.0 and 3.5 dB for single-input single-output and MIMO cases as compared with the case without PAPR reduction, although almost identical block error rate performance and the same throughput performance as in the case of perfect phase sequence estimation are achieved in an attenuated six-path Rayleigh fading condition.

DOI： 10.1049/iet-com.2012.0139

Language：English   Publishing type：Research paper (other academic)  

Wireless backhaul systems have been considered as a promising candidate of beyond 3G wireless broadband system for mobile communications. The achievable transmission performance over radio relay channel depends on antenna directivity and radiation patterns of each antenna element. To improve the transmission performance and keep radio relay channel in an acceptable condition, it is effective to control the antenna directivity by employing multi-antenna signal transmission and reception. For this purpose, we have proposed a simple method to extend the existing single antenna relay node based on IEEE802.11a to multi-antenna system, where a cross configuration multi-antenna is applied to the existing relay nodes as external equipment. The multi-antenna system is controlled by detecting the antenna control information assigned to the lengths of the packets transmitted from the existing node. In this paper, to clarify the effectiveness of multi-antenna system in wireless multi-hop networks, we show an indoor radio propagation model based on two dimensional ray-tracing that provides realistic indoor channel characteristics and evaluate throughput performance by system level simulations. Simulation results ensure that application of directional antenna to multi-hop networks with highly efficient packet forwarding protocol, called Intermittent Periodic Transmit (IPT), improves throughput performance of the radio relay transmission in wireless backhaul.

DOI： 10.1109/JEC-ECC.2012.6186954

Language：English   Publishing type：Research paper (other academic)  

As a solution to high peak-to-average power ratio (PAPR) problems in vector coding (VC) systems, phase control based methods such as selected mapping and partial transmit sequence have been investigated. In this paper, a phase sequence blind estimation method is presented for PAPR reduction based on phase control in multi-input multi-output (MIMO) adaptive modulated vector coding systems, where Turbo code is employed. On the receiver side, the phase sequence component is estimated using a maximum likelihood method which selects the most likelihood sequence among all candidate ones by exploiting soft-output information of the decoder. Computer simulation results show that when the number of candidate sequences in SLM is M 16, instantaneous power of the transmit signal at the CCDF of 10 ⁶ can be reduced by about 4.5dB and 3.4dB for SISO and MIMO cases as compared to case without PAPR reduction, while almost the same block error rate (BLER) performance and the same throughput performance as case of the prefect phase sequence estimation are achieved in attenuated 6-path Rayleigh fading condition.

DOI： 10.1109/WCSP.2011.6096816

Language：English   Publishing type：Research paper (other academic)  

The authors have proposed Multi-Input Multi-Output (MIMO)-Constant Envelope Modulation (MIMO-CEM), as power and complexity efficient alternative to MIMO-OFDM, suitable for wireless backhaul networks. One of the major problems to withstand real application of MIMO-CEM is to estimate MIMO channel characteristics. The MIMO-CEM is based upon two contrary schemes; one is nonlinear Maximum Likelihood Sequence Estimator (MLSE), which needs accurate channel information to replicate the received signal passing through it. The other is a low resolution analog-to-digital converter (ADC), e.g., 1-bit in the default operation that removes the received signal amplitude fluctuation. This paper considers channel estimation problem in MIMO-CEM. First, we propose a MIMO-CEM adaptive channel estimator, in static and quasi-static channel conditions, based upon Code Division Multiplexing (CDM) preambles transmission, where channel parameters are iteratively estimated by observing the received MIMO preambles. Then, we extended the proposed CDM preamble method to Decision Directed Channel Estimation (DDCE) to track MIMO-CEM channel in high Doppler frequency conditions and clarify the effectiveness of MIMO-CEM in dynamic channel conditions.

DOI： 10.1109/GLOCOMW.2011.6162510

Language：English   Publishing type：Research paper (other academic)  

Major drawback in orthogonal frequency division multiplexing (OFDM) systems is that the transmit signal exhibits high peak-to-average power ratio (PAPR). In this paper, a phase sequence blind estimation method is presented for PAPR reduction based on a selected mapping (SLM) or a partial transmit sequence (PTS) in multi-input multi-output (MIMO) coded OFDM systems, where low density parity check (LDPC) code is employed. On the receiver side, the selected phase sequence information is estimated using a maximum likelihood method which selects the most likelihood sequence among all candidate sequences by exploiting soft-output information of the decoder. Computer simulation results show that when the number of candidate sequences in SLM is M = 256, instantaneous power of the transmit signal at the CCDF of 10 ^-6 can be reduced by about 3.9dB as compared to case without PAPR reduction, while almost the same bit error rate (BER) performance as case of the prefect phase sequence estimation is achieved in attenuated 12-path Rayleigh fading condition.

DOI： 10.1109/ICSPCS.2011.6140821

Language：English   Publishing type：Research paper (other academic)  

The authors have proposed Multi-Input Multi-Output (MIMO)-Constant Envelope Modulation, (MIMO-CEM), as power and complexity efficient alternative to MIMO-OFDM, suitable for wireless backhaul network in which relay nodes are fixed in their positions. One of the major problems to withstand real application of MIMO-CEM is to estimate MIMO channel characteristics. The MIMO-CEM is based upon two contrary schemes; one is the nonlinear CEM modified Maximum Likelihood Sequence Estimator (MLSE) proposed by the authors, which needs accurate channel information to replicate the received signal passing through channel. The other is low resolution analog-to-digital converter (ADC), i.e., 1-bit in the default operation and 2 or 3 bits in the optional operations, which means that the received channel amplitude information may be completely or partially destroyed. These two contrary demands make MIMO-CEM channel estimation a big challenge; how we can accurately estimate the channel in these severe low ADC resolution conditions. We consider this issue through designing an efficient MIMO-CEM channel estimator based upon a block based adaptive filter. In addition, in order to speed up the parameter convergence rate in the proposed adaptive estimator, we design a correlator estimator as initial channel state estimation used in the adaptive estimator. We prove the effectiveness of the proposed MIMO-CEM channel estimation under different channel scenarios and different low ADC resolutions such as 1, 2 and 3-bit.

DOI： 10.1109/IWCMC.2011.5982749

Language：English   Publishing type：Research paper (other academic)  

The authors have proposed Multi-Input Multi-Output (MIMO)-Constant Envelope Modulation, MIMO-CEM, as power and complexity efficient alternative to MIMO-OFDM, suitable for wireless backhaul networks. Because MIMO-CEM receiver employs 1-bit ADC, MIMO-CEM channel estimation is one of the major challenges toward its real application. The authors have proposed adaptive channel estimator in static and quasi-static channel conditions. Although wireless backhaul channel conditions are theoretically considered as static and quasi-static, it suffers from some channel fluctuations in real applications. Hence, the objective of this paper is to present a decision directed channel estimation (DDCE) to track channel fluctuation in high Doppler frequency condition, and clarify the effectiveness of our method under dynamic channel. For the purpose of comparison, the performance of DDCE is compared with that of a pilot assisted linear interpolation channel tracking for MIMO-CEM. Different Doppler frequencies are assumed to prove the effectiveness of the scheme even in high channel variations.

DOI： 10.1007/978-3-642-21984-9_51

Language：English   Publishing type：Research paper (other academic)  

Adaptive predistorter is an effective technique to compensate for nonlinear distortion in a power amplifier. As a method to improve the parameter convergence speed in the predistorter, a series expansion technique with an orthogonal polynomials has been investigated. In this paper, we present an adaptive predistortion linearization method based on orthogonal polynomial expansion for a nonlinear power amplifier affected by memory effect in OFDM systems, where both memory and memoryless predistorter are constructed by the weighted sum of orthogonal polynomials. In addition, to achieve the parameter optimization speed improvement of the predistorter, we propose a method to determine step-size in a recursive calculation. The parameter convergence performance of the predistorter is investigated in OFDM systems with and without peak-to-average power ratio (PAPR) reduction, where the partial transmit sequence (PTS) technique is employed to reduce PAPR. Computer simulation results show that the proposed adaptive predistorter achieves faster parameter convergence time than that of non-orthogonal one in OFDM systems with nonlinear power amplifier affected by memory effect, even though PAPR of OFDM signal is reduced by using PTS. It is also confirmed that power added efficiency is further improved by combining the adaptive predistortion with PAPR reduction technique.

DOI： 10.1109/ICCSP.2011.5739374

Language：English   Publishing type：Research paper (scientific journal)  

A major drawback in OFDM systems is that the transmitsignal exhibits a high Peak-to-Average Power Ratio (PAPR) which causes nonlinear distortion at the output of power amplifier. To achieve high efficiency in OFDM systems, it is important to suppress PAPR of the transmit signal. In IEEE802.16e (mobile WiMAX) based systems, it is desirable to employ a simple PAPR reduction method such as clipping & filtering (C&F) or peak windowing (PW). The purpose of this paper is to evaluate PAPR reduction performance of C&F and PW and compare them in an IEEE802.16e based OFDM system. In addition, we also show a repeated PW method which reduces PAPR by repeatedly applying a smooth window function to the transmit signal. Computer simulation results show that the repeated PW can achieve almost the same PAPR reduction performance as that of the repeated C&F with significantly lower computational complexity.

DOI： 10.1587/transcom.E94.B.1467

Language：English   Publishing type：Research paper (other academic)  

Wireless backhaul systems have been considered as a promising candidate of beyond 3G wireless broadband system for mobile communications. The achievable transmission performance over radio relay channel depends on antenna directivity and radiation patterns of each antenna element. To improve the transmission performance and keep radio relay channel in an acceptable condition, it is effective to control the antenna directivity by employing multi-antenna signal transmission and reception. In this paper, we propose a simple method to extend the existing single antenna relay node based on IEEE802.11a to multi-antenna system, where a cross polarized multi-antenna is applied to the existing relay nodes as external equipment. The multi-antenna system is controlled by detecting the antenna control information assigned to the lengths of the packets transmitted from the existing node. The proposed method does not require special change of the existing system such as hardware design on multi-antenna configuration. We also developed a prototype base/relay node with optional multi-antenna equipment and confirmed the effectiveness of the proposed method by experiment. To clarify the effectiveness of the proposed multi-antenna system in wireless backhaul networks, we evaluate throughput performance by system level simulations. Simulation results ensure that the proposed multi-antenna system with highly efficient packet forwarding protocol, called Intermittent Periodic Transmit (IPT), improves throughput performance of the radio relay transmission in wireless backhaul as compared with conventional omni-directional antenna system.

DOI： 10.1109/ICCSP.2011.5739365

Language：English   Publishing type：Research paper (other academic)  

OFDMA (Orthogonal frequency division multiple access) based systems have been considered as a candidate for future wireless communication systems. In such a system, it is important to provide high data rate services for users with high mobility. For this purpose, decision-directed channel tracking (DDCT) techniques have been investigated for OFDM systems in high mobility environments. The performance of the DDCT in OFDMA systems depends on the assigned channel condition, and therefore it is important to allocate a proper channel to each user. The purpose of this paper is to propose an adaptive channel assignment method which enhances the DDCT improvement in an OFDMA system, where the former numbered resource blocks (RBs) in OFDMA frame are preferentially allocated to the users moving at a high speed. Computer simulation results show that the proposed method is effective in improving throughput performance of OFDMA systems in a high Doppler frequency condition.

DOI： 10.1109/ICSPCS.2010.5709724

Language：English   Publishing type：Research paper (scientific journal)  

As described in this paper, construction and blind estimation methods of phase sequences are proposed for subcarrier-phase control based peak-to-average power ratio (PAPR) reduction in low-density paritycheck (LDPC)-coded orthogonal frequency division multiplexing (OFDM) systems. On the transmitter side, phase sequence patterns are constructed based on a given parity-check matrix. The PAPR of the OFDM signal is reduced by multiplying the constructed phase sequence selected from the same number of candidates as the number of weighting factor (WF) combinations in a partial transmit sequence (PTS) method. On the receiver side, the phase sequence is estimated blindly using the decoding function, i.e., the most likely phase sequence among a limited number of possible phase sequence candidates is inferred by comparing the sum-product calculation results of each candidate. Computer simulation results show that PAPR of QPSK-OFDM and 16QAM-OFDM signals can be reduced respectively by about 3.7 dB and 4.0 dB without marked degradation of the block error rate (BLER) performance as compared to perfect estimation in an attenuated 12-path Rayleigh fading condition.

DOI： 10.1587/transfun.E93.A.2130

Language：English   Publishing type：Research paper (other academic)  

In this paper, a subcarrier-phase control based peak-to-average power (PAPR) reduction scheme without side-information transmission is proposed for LDPC coded OFDM systems. On the transmitter side, peak power of OFDM signal is reduced by multiplying the selected phase-sequence. On the receiver side, the phase sequence used for PAPR reduction is estimated without side information by utilizing the decoding property of LDPC code, i.e., based on the decoding information in single iteration sum-product calculation, limited number of candidate sequences is selected from all possible phase sequence patterns and the correct phase-sequence can be estimated by comparing the decoding results corresponding to these selected candidate sequences. Computer simulation results show that, when LDPC code with code-rate of R ≈ 1/2 is used, PAPR of OFDM signal can be reduced by about 2.4dB without significant degradation in BLER performance as compared to perfect WF estimation in attenuated 12-path Rayleigh fading condition.

DOI： 10.1109/PIMRC.2009.5450116

Language：English   Publishing type：Research paper (scientific journal)  

As a method to realize a high-speed communication in the home network, the power-line communication (PLC) technique is known. A problem of PLC is that leakage radiation interferes with existing systems. When OFDM is used in a PLC system, the leakage radiation is not sufficiently reduced, even if the subcarriers corresponding to the frequencyband of the existing system are never used, because the signal is not strictly band-limited. To solve this problem, each subcarrier must be bandlimited. In this paper, we apply the OQAM based multi-carrier transmission (OQAM-MCT) to a high-speed PLC system, where each subcarrier is individually band-limited. We also propose a pilot-symbol sequence suitable for frequency offset estimation, symbol-timing detection and channel estimation in the OQAM-MCT system. In this method, the pilot signalsequence consists of a repeated series of the same data symbol. With this method, the pilot sequence approximately becomes equivalent to OFDM sequence and therefore existing pilot-assisted methods for OFDM are also applicable to OQAM-MCT system. Computer simulation results show that the OQAM-MCT system achieves both good transmission rate performance and low out-of-band radiation in PLC channels. It is also shown that the proposed pilot-sequence improves frequency offset estimation, symboltiming detection and channel estimation performance as compared with the case of using pseudo-noise sequence.

DOI： 10.1587/transcom.E92.B.473

Language：English   Publishing type：Research paper (other academic)  

An iterative optimization method of transmit/receive frequency domain equalization (FDE) is proposed for single carrier transmission systems, where both transmit and receive FDE weights are iteratively determined with a recursive algorithm so as to minimize the error signal at a virtual receiver. The computer simulation results show that SC systems using the proposed transmit/receive equalization method achieves better BER performance than those using the conventional receive FDE. BER performance of SC systems using the proposed method was improved by about 2.7dB at BER=10^-3 compared to case of those using conventional receive FDE in attenuated 6-path quasistatic Rayleigh fading with normalized delay spread value of τ/T = 0.769. In addition, when decision feedback equalizer (DFE) with sufficient number of feedback taps is adopted in both systems, the proposed system achieves better BER performance than the conventional system in a low E_b/N region and BER performance of the proposed system becomes close to that of the conventional one as E_b/N₀ increases in the above channel condition.

DOI： 10.1109/VETECF.2008.200

Language：English   Publishing type：Research paper (scientific journal)  

In this paper, we propose a weighting factor (WF) estimation method for peak power reduction (PPR) based on adaptive flipping of parity carriers in a turbo-coded orthogonal frequency-division multiplexing (OFDM) system. In this PPR scheme, the peak-to-average power ratio of a turbo-coded OFDM signal is reduced with adaptive flipping of the phase of the parity carriers corresponding to the WFs. At the receiver, the WFs are estimated at a turbo decoder by exploiting the redundancy of an error-correcting code using no extra side information. The proposed WF estimation method is based on an iterative decoding of the turbo code, i.e., the turbo decoder provides not only error correction capability but the WF estimation function as well. When the proposed WF estimation method is used for the system using a turbo code with constraint length K = 4 and a code rate of R = 1/2, the instantaneous power of the OFDM signal at the complementary cumulative distribution function of 10^-4 can be reduced by about 2.1 dB through the application of the PPR scheme. When the bit error rate (BER) performance is evaluated as a function of the peak signal-to-noise power ratio (PSNR), the proposed method achieves better BER performance than the case without the PPR in an attenuated 12-path Rayleigh fading condition. The improvements in BER performance as a function of PSNR are about 1.1, 2.0, and 2.1 dB at BER = 10^-4 for turbo-coded OFDM signals using QPSK, 16-state quadrature amplitude modulation (QAM), and 64-state QAM schemes, respectively.

DOI： 10.1109/TVT.2008.918729

Language：English   Publishing type：Research paper (other academic)  

In this paper, we propose a weighting factor (WF) iterative estimation method for a turbo-coded multi-carrier code division multiplexing (MC-CDM) system using partial-transmit sequence (PTS) based peak-to-average power (PAPR) reduction, where the transmitter structure in the proposed system is an extended version of the PTS and the systematic bits of turbo-code is adaptively flipped by multiplying WFs so as to reduce PAPR of MC-CDM signal. On the receiver side, WF estimation and error correction are jointly performed with turbo decoding, where WFs are estimated by exploiting the decoding results of two data streams using different spreading code. When PTS like PAPR reduction using 9 clusters is applied to MC-CDM signal with spreading factor of 16, PAPR of the transmit signal at the CCDF of 10^-4 can be reduced by about 2.0dB, where the number of multiplexed codes is 8. With the proposed method, WF estimation accuracy is improved as the subcarrier modulation level increases. The degradation in block error rate (BLER) performance as compared with case of the perfect WF estimation is about 0.7dB at BLER=10^-2 for QPSK-MC-CDM signal with PAPR reduction using 5 clusters in attenuated 12-path Rayleigh fading condition. In the MC-CDM system using 64QAM, the proposed method achieves almost the same BLER performance as case of the perfect WF estimation, even when the number of clusters is L = 9.

DOI： 10.1109/VETECF.2008.201

Language：English   Publishing type：Research paper (scientific journal)  

Power-line communication (PLC) technique is one method to realize high-speed communications in a home network. In PLC channels, the transmission signal quality is degraded by colored non-Gaussian noise as well as frequency-selectivity of the channels. In this paper, we describe our investigation of the performance of a OQAM-MCT system in which a noise canceller is used jointly with a time-domain persubcarrier adaptive equalizer. Furthermore, we propose a noise cancellation method designed for the OQAM-MCT system. The performance of the OQAM-MCT system is evaluated in PLC channels with measured impulse responses in the presence of measured noise. Computer simulation results show that the bit rate of the OQAM-MCT system is improved using both an adaptive equalizer and noise canceller, and that the OQAM-MCT system achieves better performance than an OFDM system with an insufficient length of the guard interval.

DOI： 10.1093/ietfec/e91-a.11.3112

Language：English   Publishing type：Research paper (other academic)  

As a method to realize a high-speed communication in home network, the power-line communication (PLC) technique is known. In PLC channels, transmission signal quality is degraded by colored non-Gaussian noise with uncommon characteristics as well as frequency-selectivity of channels. In this paper, we investigate the performance of the OQAM-MCT system with a small number of subcarriers where noise canceller is jointly used with time-domain per-subcarrier adaptive equalizer. In addition, we propose a modified noise cancellation method designed for OQAM-MCT system. The performance of the OQAM-MCT system is evaluated in PLC channels with measured impulse responses in presence of measured noise. Computer simulation results show that transmission rate of the OQAM-MCT system is improved by using both adaptive equalizer and noise canceller and also the OQAMMCT system achieves better performance than OFDM system with insufficient length of guard interval.

DOI： 10.1109/ISPLC.2008.4510458

Language：English   Publishing type：Research paper (other academic)  

MIMO system is a technology to realize high data rates and high capacity. Among various MIMO systems, Eigenbeam MIMO (E-MIMO) system achieves the theoretical maximum capacity. The E-MIMO system uses eigenvectors of channel autocorrelation matrix as transmit and receive weights. As a method to find these eigenvectors, eigenvalue decomposition or singular value decomposition (SVD) are generally well-known. In this paper, we propose a least mean square (LMS) based algorithm to find the transmit and receive weights without significant increase of computational complexity for E-MIMO system. Computer simulation shows that the proposed algorithm gives almost the same performance as that of SVD.

DOI： 10.1109/VETECS.2008.171

Language：English   Publishing type：Research paper (other academic)  

As a method to realize an orthogonal multicarrier transmission, Offset Quadrature Amplitude Modulation based Multi-Carrier Modulation (OQAM-MCM) has been known, where each subcarrier is strictly band-limited by a filter. Objective of this paper is to discuss the use of OQAM-MCM system instead of Orthogonal Frequency Division Multiplexing (OFDM) system as a countermeasure against frequency-selective fading. We investigate the performance of OQAM-MCM system with a small number of subcarriers employing a simplified time-domain per-subcarrier equalizer. Computer simulation results show that OQAM-MCM system can achieve both better spectrum efficiency and lower Bit Error Rate (BER) performance than those of OFDM systems with insufficient Guard Interval (GI), when a time-domain per-subcarrier equalizer is used in both systems.

DOI： 10.1109/VETECS.2008.91

Language：English   Publishing type：Research paper (scientific journal)  

The adaptive predistorter and the negative feedback system are known as methods to compensate for the nonlinear distortion of a power amplifier. Although the feedback method is a simple technique, its instability impedes the capability of high-feedback gain to achieve a highcompensation effect. On the other hand, the predistorter requires a long time for convergence of the adaptive predistorters. In this paper, we propose a nonlinear distortion compensation method for a narrow-band signal. In this method, an adaptive predistorter and negative feedback are combined. In addition, to shorten the convergence time to minimize nonlinear distortion, a variable step-size (VS) method is also applied to the algorithm to determine the parameters of the adaptive predistorter. Using computer simulations, we show that the proposed scheme achieves both five times faster convergence speed than that of the predistorter and three times higher permissible delay time in the feedback amplifier than that of a negative feedback only amplifier.

DOI： 10.1093/ietcom/e91-b.7.2331

Language：English   Publishing type：Research paper (scientific journal)  

In this paper, we propose a simple peak power reduction (PPR) method based on adaptive inversion of parity-check block of codeword in BCH-coded OFDM system. In the proposed method, the entire parity-check block of the codeword is adaptively inversed by multiplying weighting factors (WFs) so as to minimize PAPR of the OFDM signal, symbol-by-symbol. At the receiver, these WFs are estimated based on the property of BCH decoding. When the primitive BCH code with single error correction such as (31,26) code is used, to estimate the WFs, the proposed method employs a significant bit protection method which assigns a significant bit to the best subcarrier selected among all possible subcarriers. With computer simulation, when (31,26), (31,21 ) and (32,21 ) BCH codes are employed, PAPR of the OFDM signal at the CCDF (Complementary Cumulative Distribution Function) of 10^-4 is reduced by about 1.9, 2.5 and 2.5 dB by applying the PPR method, while achieving the BER performance comparable to the case with the perfect WF estimation in exponentially decaying 12-path Rayleigh fading condition

DOI： 10.1093/ietcom/e91-b.5.1454

Language：English   Publishing type：Research paper (scientific journal)  

Seiichiro Horikawa, Osamu Muta, Yoshihiko Akaiwa, ``Adaptive Guard Symbol Insertion Method for One-Cell Reuse TDMA Cellular Systems,'' IEICE Transactions on Communications, Vol.E90-B, No.12, pp.3724-3728, Dec. 2007.

Language：English   Publishing type：Research paper (other academic)  

Adaptive predistorter is an effective technique to compensate nonlinear distortion in a power amplifier. As a method to improve the parameter convergence speed in the predistorter, a series expansion technique with an orthogonal polynomials has been proposed. In this paper, we propose an adaptive predistorter based on orthogonal polynomial for the power amplifier with memory effect, where the parameters of predistorter are determined so as to minimize out-of-band radiation components detected by high pass filter (HPF). With computer simulation using the Advanced Design System (ADS) software, we show that the adaptive predisterter using orthogonal polynomials achieves faster convergence time than that with that of non-orthogonal one, while nonlinear distortion is compensated by memory predistorter using orthogonal polynomials.

DOI： 10.1109/PIMRC.2007.4394716

Language：English   Publishing type：Research paper (other academic)  

In this paper, we propose a peak power reduction method for LDPC coded OFDM system, where transmit data sequence is grouped into several clusters based on structure of a low density parity-check matrix and the phase of each cluster is adjusted so as to minimize PAPR of OFDM signal by multiplying weighting factors (WFs). At the receiver, WFs are estimated with sufficient accuracy by exploiting the decoding property of LDPC code. The proposed method can be applied to not only systematic coded signal but also non-systematic one. Computer simulation results show that, when LDPC code with code-rate of R ≈ 1/2 is used, PAPR of OFDM signal can be reduced by about 2.4dB without significant degradation in BLER performance as compared to perfect WF estimation in attenuated 12-path Rayleigh fading condition.

DOI： 10.1109/VETECS.2007.583

Language：English   Publishing type：Research paper (scientific journal)  

In this paper, we propose an adaptive guard symbol insertion method for one-cell reuse TDMA cellular systems in which cochannel interference is reduced by adaptively selecting the best transmitpulse waveform with different guard (null-) symbols according to the average error power (AEP) corresponding to signal-to-interference and noise power ratio (SINR), even though the same frequency channel is used at all base stations. Using the proposed system, current TDMA-based systems are readily extensible to one-cell reuse systems, which achieves higher spectrum efficiency. The system capacity is enhanced using the proposed method; moreover, the required qualities such as blocking probability and outage probability are retained.

DOI： 10.1093/ietcom/e90-b.12.3724

Language：English   Publishing type：Research paper (other academic)  

As a method to realize a high-speed communication in home network, the power-line communication (PLC) technique is known. A problem of the PLC is that leakage radiation interferes to existing systems. When OFDM is used in PLC system, the leakage radiation is not sufficiently reduced, even if the subcarriers corresponding to frequency-band of the existing system are never used, because the signal is not strictly band-limited. To solve this problem, each subcarrier must be band-limited. In this paper, we apply the OQAM based multi-carrier transmission (OQAM-MCT) to high-speed PLC system, where each subcarrier is individually band-limited. We also propose a pilot-symbol sequence for frequency offset estimation, symbol-timing detection and channel estimation in the OQAM-MCT system. In this method, the pilot signal-sequence consists of the succession of the same data symbol. Computer simulation results show that the OQAM-MCT system achieves both good transmission rate performance and low out-of-band radiation in the PLC channels. It is also shown that the proposed pilot-sequence improves frequency offset estimation, symbol-timing detection and channel estimation performance as compared with the case of using pseudo-noise sequence.

DOI： 10.1109/ISPLC.2007.371139

Language：English   Publishing type：Research paper (other academic)  

As a method to compensate for the nonlinear distortion of a power amplifier, the adaptive predistorter and the negative feed-back system are known. Although the feed-back method is a simple technique, its instability becomes a problem for a high feedback gain to achieve a high compensation effect. On the other hand, the predistorter needs long time to calculate the suitable parameters. In this paper, we propose a nonlinear distortion compensation method for a narrow-band signal. In this method, adaptive predistorter and negative feedback are combined. With computer simulations, we show that the proposed scheme achieves both five times faster convergence speed than that of the predistorter and three times longer permissible delay time in the feed-back amplifier than that of a negative feed-back only amplifier, while keeping the required compensation performance.

DOI： 10.1109/VTCF.2006.603

Language：English   Publishing type：Research paper (other academic)  

In this paper, we propose a weighting factor (WF) estimation scheme for phase-control based peak power reduction (PPR) of turbo-coded OFDM signal. In this PPR scheme, the peak power of OFDM signal is reduced by adjusting the phase of parity-carriers by multiplying WFs. At the receiver, WFs are estimated at turbo-decoder without using any side-information. The proposed WF estimation scheme is based on an iterative decoding of turbo-code, i.e. the turbo decoder provides not only error correction capability but also WF estimation function. When a turbo-code of the constraint length of K = 4 and the code rate of R = 1/2 is employed, PAPR of OFDM signal at the CCDF of 10^-4 can be reduced by about 2.1dB by applying the PPR scheme. The proposed scheme achieves good BER performance comparable to the case of perfect WF estimation in attenuated 12-path Rayleigh fading condition. The degradation in BER performance is about 1.0dB, 0.4dB and 0.2dB at BER=10^-4 for turbo-coded OFDM signals using QPSK, 16QAM and 64QAM, respectively.

Language：English   Publishing type：Research paper (other academic)  

A problem with the OFCDM (Orthogonal Frequency and Code Division Multiplexing) system is that PA PR (Peak to Average Power Ratio) of the signal becomes high. In this paper, we propose a novel peak reduction method which suppresses the inter-signal interference caused by peak power limitation for OFCDM signal. In the proposed method, peak power is reduced by adding the peak reducing signal generated with peak components detected by soft-clipping function. At the receiver, the inter-signal interference is compensated by estimating the peak components removed at the transmitter from the received signal. Performance of a total system including modulation, peak-limiter, predistorter, a model of 2GHz class A/B power amplifier and the receiver is investigated by computer simulation. Computer simulation results show the peak power reduction performance is improved about 1.4dB as compared with that of the conventional PRSA (peak reducing signal addition) method.

DOI： 10.1109/VTCF.2006.172

Language：English   Publishing type：Research paper (other academic)  

In a current TDMA cellular system, the same frequency channel is reused at separated cells to avoid co-channel interference from other cells. From the view point of the spectrum efficiency, one-cell reuse system where all base stations use the same frequency channel is desirable. However, in such a system, co-channel interference severely degrades BER performance, in addition to the degradation caused by signal distortion due to frequency-selective fading. In this paper, we propose a one-cell reuse TDMA cellular system, where co-channel interference is reduced by adaptively controlling the duration of guard time according to signal to interference and noise ratio (SINR), while the same frequency channel is used at all base-stations. With the proposed system, a current TDMA system is easily extended to one-cell reuse system which achieves higher spectrum efficiency. The system capacity is enhanced with the proposed scheme, while the required qualities such as blocking rate and outage rate are kept.

DOI： 10.1109/VETECF.2005.1558460

Language：English   Publishing type：Research paper (scientific journal)  

The OFCDM (Orthogonal Frequency and Code Division Multiplexing) system is receiving attention to achieve a high data rate transmission for multimedia communication. A problem with the system is that PAPR (Peak to Average Power Ratio) of the OFCDM signal increases as the number of carriers increases. In this paper, we investigate peak reducing methods for OFCDM system with a predistorter power amplifier. We show that the peak reduction scheme and adaptive predistortion gives a high power efficiency and high linearity in power amplification of OFCDM signal.

Language：English   Publishing type：Research paper (scientific journal)  

In this paper, we propose a peak power reduction (PPR) scheme based on reversal of parity-bits for a block-coded OFDM signal. In our PPR scheme, the entire parity-check block of codeword is adaptively reversed symbol-by-symbol, so as to minimize PAPR of the OFDM-signal. At the receiver, the original codeword can be restored with sufficient accuracy by checking the Syndrome of received codeword and protecting a significant-bit of code-word from transmission error. When (7,4), (31,21) and (31,26) BCH code are employed, PAPR of the OFDM signal at the CCDF (Complementary Cumulative Distribution Function) of 10^-4 can be reduced by about 2.8, 2.5 and 2.0dB by applying PPR scheme while achieving approximately the same BER performance as the case without PPR in exponentially decaying 6-path Rayleigh fading condition.

Language：English   Publishing type：Research paper (scientific journal)  

In this paper, we propose a peak-power-reduction (PPR) scheme for a systematic block-coded OFDM signal. In this scheme, peak power of OFDM signal is reduced by adjusting the phase of cluster, which contains only parity-carriers, so as to minimize the peak-to-average power ratio (PAPR) at the transmitter. At the receiver, original signal of parity-carrier is replicated using decided-value of receive data-carriers corresponding to data-bits of code-word. Thus, phase rotation value of the cluster is estimated by comparing the receive signal of parity-carrier and its replica. A reduction of about 2.5dB in peak power and approximately the same BER performance as the case of the ideal decoding are achieved by applying the PPR scheme to an OFDM system with 126 subcarriers in multipath fading condition.

Language：English   Publishing type：Research paper (scientific journal)  

We propose a peak-power-reduction (PPR) scheme that never sacrifices spectrum efficiency for a multicarrier transmission (MCT) system where subchannels are band-limited by filtering before the multiplexing. In this scheme, the transmit pulse power before filtering is decreased whenever the envelope peak amplitude is above a given threshold level. A reduction of 75% in peak power is achieved with a slight degradation in BER performance by applying the PPR scheme to an MCT system with eight subchannels under flat fading conditions. The proposed scheme is also investigated with an adaptive transmit power control, and the average transmit power and peak-to-mean power ratio (PMPR) are reduced.

DOI： 10.1002/ecja.1098

Language：English   Publishing type：Research paper (scientific journal)  

In this paper, we propose a frequency-domain channel estimation scheme using co-phased pilot-signals for a multi-carrier modulation (MCM) system with bandlimited subcarriers: pilot signals are inserted periodically in each subcarrier and are added up (multiplexed) to be in-phase at the midpoint of the pilot-symbol duration at the transmitter. Then, the multiplexed pilot signal exhibits a sharp peak amplitude at the midpoint of the pilot-symbol duration. Thus, the channel characteristics can be estimated with a high time resolution of the pilot signal. We evaluated the performance of an MCM system with a frequency-domain equalizer using the proposed scheme by computer simulation. The BER performance was improved with the channel estimation scheme.

Language：English   Publishing type：Research paper (scientific journal)  

This paper proposes a method which reduces the peak-to-mean power ratio (PMPR) of the multicarrier modulation signal by providing a subcarrier for peak power reduction outside the information band. The proposed method includes the addition of a redundant signal, that is, parity carrier, in order to reduce the peak power of the multicarrier signal when its envelope exceeds a given threshold. The parity carrier for peak power reduction is placed outside the band of the multicarrier signal and can be easily removed in the receiver. It is shown by a computer simulation that when two carriers for peak power reduction are added to the multicarrier signal with eight carriers, the PMPR after the peak power reduction approaches 4.7 dB. It is also shown for the case in which the power amplifier has little nonlinearity that an outband spectrum density of -50 dB can be achieved by applying the proposed method for a back-off of 4.7 dB.

DOI： 10.1002/ecja.1116

Language：English   Publishing type：Research paper (scientific journal)  

In this paper, we propose a pilot-signal assisted channel estimation (PSCE) scheme for a multi-carrier modulation (MCM) system where a pilot signal bandwidth is restricted in the subcarrier. In this scheme, at the receiver, the pilot signals of each subcarrier are added up to be inphase at midpoint of pilot-symbol duration, then pilot signal exhibits sharp peak amplitude. Thus channel impulse response can be estimated with a high time-resolution. A simple channel equalization is done using the estimated channel characteristic and BER performance is improved by applying the PSCE scheme to an MCM system under Rayleigh two-path fading condition.

Language：English   Publishing type：Research paper (scientific journal)  

A major disadvantage of multi-carrier transmission (MCT) is increase of peak power. In this paper, we propose a peak power suppression scheme for MCT system based on generating peak power suppressing signals at extra carrier (parity carrier). This scheme has an advantage that it can be applied to any MCT system and the suppressing signal can be easily spilt at the demodulator. In the case of 8 subcarriers, peak power can be reduced by about 5 dB by the proposed scheme. When nonlinearity of the power amplifier is small, out-of-band radiation is decreased to -50 dB below the in-band spectral with this scheme.

Language：English   Publishing type：Research paper (other academic)  

This paper proposes an adaptive channel selection method that reduces signal distortion due to frequency selective fading and thereby improving the performance of mobile communication. In this method a channel is adaptively selected by estimating current channel condition with mean square decision error as a measure. This selected frequency channel corresponds to the channel in which the delayed signals add-up inphase. Hence, BER performance is improved with the proposed scheme. Computer simulation results show the effectiveness of the proposed scheme for a system with multiple terminals and also for a multiple base station (cellular) system.

DOI： 10.1109/ICC.1999.765582

Language：English   Publishing type：Research paper (other academic)  

In this paper, we propose a peak-power-suppression (PPS) scheme for a multi carrier transmission (MCT) system where subchannels are band-limited by filtering before the multiplexer. In this scheme, transmit pulse power before filtering is decreased whenever envelope-peak amplitude is above a given threshold level. A reduction of 75% in peak power is achieved with a little, but insignificant, degradation in BER performance by applying the PPS scheme to an MCT system with 8 subchannels under flat fading conditions. The proposed scheme is also investigated with an adaptive transmit power control, and average transmit power and peak-to-mean power ratio (PMPR) are reduced.

Event date： 2013.5 - 2012.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Sarajevo   Country：Bosnia and Herzegovina  

PAPR Reduction and Related Techniques for Power Efficient Multi-Carrier/Multi-Code Communication Systems

Other Link： http://www.ieice-europe.org/ictf/

Event date： 2025.3

Language：Japanese   Presentation type：Oral presentation (general)  

Event date： 2025.3

Language：English   Presentation type：Oral presentation (general)  

Event date： 2024.12

Language：English   Presentation type：Oral presentation (general)  

Event date： 2024.11

Language：English   Presentation type：Oral presentation (general)  

Venue：RWTH Aachen University   Country：Germany  

Event date： 2024.11

Language：English   Presentation type：Oral presentation (general)  

Venue：RWTH Aachen University   Country：Germany  

Event date： 2024.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山コンベンションセンター   Country：Japan  

Event date： 2024.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Paris   Country：France  

Other Link： http://www.wimob.org/wimob2024/

Event date： 2024.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：電気通信大学   Country：Japan  

Event date： 2024.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Washington DC   Country：United States  

Event date： 2024.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Washington DC   Country：United States  

Event date： 2024.9

Language：English  

Venue： 函館市民会館  

Event date： 2024.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：日本工業大学   Country：Japan  

Event date： 2024.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：日本工業大学   Country：Japan  

Event date： 2024.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島大学   Country：Japan  

Event date： 2024.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島大学   Country：Japan  

Event date： 2023.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Alexandria   Country：Egypt  

Tanemasa Asano, Hideaki Iwahori, Ahmed Allam, Osamu Muta, Haruichi Kanaya and Adel B. Abdel-Rahman, "Experimental Study on Microwave Heating of Soil for Nematode Control," International Japan-Africa Conference on Electronics, Communications and Computations (JAC-ECC) 2023, Dec. 2023.

Event date： 2023.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Alexandria   Country：Egypt  

Zhuoran Li, Osamu Muta and Yutaka Jitsumatsu, "Performance Evaluation of Cooperative Positioning with User-Terminal Collaboration," International Japan-Africa Conference on Electronics, Communications and Computations (JAC-ECC) 2023, Dec. 2023.

Event date： 2023.12

Language：English   Presentation type：Oral presentation (general)  

Venue：九州工業大学   Country：Japan  

Event date： 2023.11 - 2023.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Sapporo   Country：Japan  

Osamu Muta, "Experimental Analysis of Indoor Localization Using Channel State Information in WLAN Systems," International Conference on Emerging Technologies for Communications (ICETC) 2023, Dec. 2023.

Event date： 2023.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Da Nang   Country：Viet Nam  

Takuto Suzuki, Salah Berra, Kazuki Maruta, and Osamu Muta, "Multiuser Scheduling to Improve Iterative Interference Replica Subtraction with Partial Zeroization for Massive MIMO Systems," 2023 International Conference On Advanced Technologies For Communications (ATC2023), Oct. 2023.

Event date： 2023.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：香川大学   Country：Japan  

Event date： 2023.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Hong-Kong   Country：China  

Shunsuke Shimizu, Osamu Muta, Kazuki Noguchi, Junsuke Izumi, Tomoki Murakami, and Shinya Otsuki, "Experimental Evaluation of MIMO-WLAN-based Object Detection with Reflectors," Proc. IEEE Vehicular Technology Conference 2023 Fall (VTC2023-Fall), Oct. 2023.

Event date： 2023.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：沖縄県市町村自治会館   Country：Japan  

Event date： 2023.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：沖縄県市町村自治会館   Country：Japan  

Event date： 2023.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Hong-Kong   Country：China  

Shunsuke Shimizu, Osamu Muta, Kazuki Noguchi, Tomoki Murakami, and Shinya Otsuki, "Performance of WLAN-based Object Detection with Distributed Antenna and Spatially Concatenated CSI," IEEE VTC2023-Fall Workshop (Workshop on Integrated Sensing, Communication, and Computation towards 6G held at VTC2023-Fall), Oct. 2023.

Event date： 2023.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Doha, Qatar   Country：Other  

Boniface Uwizeyimana, Ahmed H. Abd El-Malek, Osamu Muta, Mohammed Abo-Zahhad, Maha Elsabrouty, "A Multi-agent Multi-armed Bandit Approach for User Pairing in UAV-assisted NOMA-Networks," Proc. the 10th International Symposium on Networks, Computers and Communications (ISNCC'23), Oct. 2023.

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋大学   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋大学   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋大学   Country：Japan  

Event date： 2023.8 - 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：天神岬スポーツ公園   Country：Japan  

Event date： 2023.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：八丈町商工会   Country：Japan  

Event date： 2023.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北海道大学   Country：Japan  

Event date： 2023.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北海道大学   Country：Japan  

Event date： 2023.6 - 2023.5

Language：English   Presentation type：Oral presentation (general)  

Venue：北海道大学   Country：Japan  

Event date： 2023.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：慶應義塾大学   Country：Japan  

Takuto Suzuki, Salah Berra, Kazuki Maruta, Osamu Muta, "Improving Iterative Interference Replica Subtraction based Precoding for Massive MIMO Systems by Partial Zeroization", IEICE RCS national conference, May 2023.

Event date： 2023.4 - 2024.4

Language：English   Presentation type：Oral presentation (general)  

Venue：Dubai   Country：United Arab Emirates  

Simon Kaboyo, Ahmed Hassan Abd El-Malek, Osamu Muta, Mohammed Abo-Zahhad, Maha Elsabrouty, "Age of Information Analysis for Full Duplex Cooperative SWIPT NOMA System," IEEE Wireless Communications and Networking Conference (WCNC2024), April 2024.

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：芝浦工業大学   Country：Japan  

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北九州国際会議場   Country：Japan  

Event date： 2023.1

Language：English   Presentation type：Oral presentation (general)  

Venue：Las Vegas   Country：United States  

Takuto Suzuki, Salah Berra, Kazuki Maruta, and Osamu Muta, "Improving Iterative Interference Replica Subtraction based Precoding for Massive MIMO Systems by Partial Zeroization," 2023 IEEE 20th Consumer Communications & Networking Conference (CCNC).

Event date： 2022.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Alexandria   Country：Egypt  

Osamu Muta, "Experimental Analysis of CSI-based Indoor Localization Toward Joint Communications and Sensing"
International Japan-Africa Conference on Electronics, Communications and Computations 2022, Dec. 2022.

Event date： 2022.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋工業大学   Country：Japan  

Event date： 2022.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋工業大学   Country：Japan  

Event date： 2022.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Alexandria   Country：Egypt  

Tanemasa Asano, Ahmed Allam, Osamu Muta, Haruichi Kanaya, Adel B. Abdel-Rahman, "Investigation on Microwave Heating Characteristic of Watery Object Buried in Soil," International Japan-Africa Conference on Electronics, Communications and Computations 2022, Dec. 2022.

Event date： 2022.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Alexandria   Country：Egypt  

Boniface Uwizeyimana, Ahmed Abd El-Malek, Osamu Muta, Mohammed Abo-Zahhad and Maha Elsabrouty,
Multi-Armed Bandit and Repeated Auction Approaches for User Admission and Channel Allocation in 5G HetNets ,"
International Japan-Africa Conference on Electronics, Communications and Computations 2022, Dec. 2022.

Event date： 2022.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Arcrea HIMEJI (Himeji Culture and Convention Center)   Country：Japan  

Chenglong Shao, Osamu Muta, "Heterogeneous Carrier-Sense Multiple Access for Improved Energy Fairness in LoRaWAN,"
The Tenth International Symposium on Computing and Networking (CANDAR) 2022, Nov. 2022.

Event date： 2022.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Event date： 2022.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：愛媛大学   Country：Japan  

Event date： 2022.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：愛媛大学   Country：Japan  

Event date： 2022.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：新潟市民プラザ   Country：Japan  

Event date： 2022.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：新潟市民プラザ   Country：Japan  

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北海道立道民活動センター   Country：Japan  

Event date： 2022.9

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Gendia Ahmad, Muta Osamu, Hashima Sherief, Hatano Kohei, "UAV Positioning with Joint NOMA Power Allocation and Receiver Node Activation," IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC) 2022, Sept. 2022.

Event date： 2022.9

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Riku NOJIMA, Osamu MUTA, Tomofumi MAKITA, Kazuki MARUTA, "Joint Peak Cancellation and In-band Distortion Compensation Scheme for Precoded Massive MIMO-OFDM with Uniform Planar Array," IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC) 2022, Sept. 2022.

Event date： 2022.9

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Kyosuke Nakano, Osamu Muta, Takahiro Inoue, Takuto Watanabe, Naohiro Ikeda, "Experimental Evaluation of Floor Height Estimation Using Unlicensed-Band LPWA Signals Toward Three-Dimensional NLOS Indoor Positioning," IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC) 2022, Sept. 2022.

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Event date： 2022.9

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Event date： 2022.9 - 2022.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Event date： 2022.8

Language：English   Presentation type：Oral presentation (general)  

Venue：函館市亀田交流プラザ   Country：Japan  

Event date： 2022.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：金沢歌劇座   Country：Japan  

Event date： 2022.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Helsinki   Country：Finland  

Event date： 2022.5

Language：English   Presentation type：Oral presentation (general)  

Venue：慶應義塾大学   Country：Japan  

Event date： 2022.3

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Event date： 2022.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Event date： 2021.12

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Osamu Muta,
[Invited] Enhanced Selected Mapping for Impulsive Noise Blanking in Multi-Carrier Power-line Communication Systems
2021 International Conference on Emerging Technologies for Communications (ICETC 2021), Dec. 2021.

Event date： 2021.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Hiroki HASE, and Osamu MUTA,
Adaptive In-band Distortion Compensation for Spatially Precoded Massive MU-MIMO Systems with Deep Peak Cancellation
2021 International Conference on Emerging Technologies for Communications (ICETC 2021), Dec. 2021.

Event date： 2021.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Chenglong SHAO and Osamu MUTA
VirCh: Virtual Mobile Charger-basedWireless Power Transfer for Large-Scale Internet-of-Things Systems
2021 International Conference on Emerging Technologies for Communications (ICETC 2021), Dec. 2021.

Event date： 2021.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Event date： 2021.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Event date： 2021.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Event date： 2021.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Event date： 2021.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Event date： 2021.10

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Event date： 2021.9

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Tomofumi Makita and Osamu Muta, "QoS-aware Low-complexity User Pairing Based on Compressed Sensing in Downlink NOMA,' IEEE Vehicular Technology Conference Fall 2021, Sept. 2021.

Event date： 2021.9

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Kazuki Noguchi, Osamu Muta, Tomoki Murakami, and Shinya Otsuki
A CSI-based Object Detection Scheme using Interleaved Subcarrier Selection in Wireless LAN Systems with Distributed Antennas
Vehicular Technology Conference Fall 2021, Sept. 2021.

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Event date： 2021.9

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Event date： 2021.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Event date： 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Event date： 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Event date： 2021.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Online   Country：Other  

Chenglong Shao and Osamu Muta,
``Dude, Are You Approaching Me? Detecting Close Physical Contact via Unlicensed LPWAN Signals,''
IEEE ICC 2021 Workshop - IoMT, June 2021.

Event date： 2021.3

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Event date： 2021.1

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Event date： 2021.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Event date： 2021.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Event date： 2020.12

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Kazuki MUKAI, Kazuki MARUTA, Osamu MUTA, and Chang-Jun AHN, ``Improving Low Complexity Inter-User Interference Cancellation for Massive MIMO Systems,'' International Conference on Emerging Technologies for Communications (ICETC 2020), Dec. 2020.

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Event date： 2020.10

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Event date： 2020.9

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

Neural Network-Based PAPR Reduction of OFDM Signals

Event date： 2020.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン開催   Country：Japan  

A machine learning-based object detection utilizing CSI in WLAN

Event date： 2020.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島大学   Country：Japan  

Event date： 2020.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島大学   Country：Japan  

Event date： 2020.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島大学   Country：Japan  

Event date： 2020.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島大学   Country：Japan  

Event date： 2020.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京工業大学   Country：Japan  

Event date： 2020.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島市青少年センター   Country：Japan  

Event date： 2019.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Alexandria   Country：Egypt  

A Partial Scrambling Overlapped Selected Mapping PAPR Reduction Scheme for OFDM/OQAM Systems

Event date： 2019.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Alexandria   Country：Egypt  

Event date： 2019.10 - 2019.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：霧島ホテル   Country：Japan  

Event date： 2019.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：横須賀リサーチパーク   Country：Japan  

Event date： 2019.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：横須賀リサーチパーク   Country：Japan  

Event date： 2019.10

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：横須賀リサーチパーク   Country：Japan  

Event date： 2019.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Honolulu   Country：United States  

Event date： 2019.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Hawaii   Country：United States  

Two-dimensional Pilot Allocation for Massive MIMO/TDD Systems

Event date： 2019.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Hawaii   Country：United States  

Pilot-Assisted Sparse Channel Estimation Based on Mutual Incoherence Property

Event date： 2019.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Honolulu   Country：United States  

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪大学   Country：Japan  

Event date： 2019.9

Language：English   Presentation type：Oral presentation (general)  

Venue：大阪大学   Country：Japan  

Event date： 2019.9

Language：English   Presentation type：Oral presentation (general)  

Venue：大阪大学   Country：Japan  

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪大学   Country：Japan  

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪大学   Country：Japan  

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪大学   Country：Japan  

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪大学   Country：Japan  

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪大学   Country：Japan  

Event date： 2019.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Singapore   Country：Singapore  

Performance Analysis of Power Control Based Interference Coordination for Downlink MIMO HetNets

Event date： 2019.8

Language：Japanese  

Venue：函館   Country：Japan  

Event date： 2019.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：函館   Country：Japan  

Event date： 2019.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋大学   Country：Japan  

Event date： 2019.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪府立大学   Country：Japan  

An in-band distortion compensation scheme utilizing extra antennas under EVM requirements for massive MIMO-OFDM with peak cancellation

Event date： 2019.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：奄美市社会福祉センター   Country：Japan  

A study on BER improvement with peak power control and extra antenna for non-linear pre-coded massive MIMO systems

Event date： 2019.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：奄美市社会福祉センター   Country：Japan  

A study on peak cancellation and in-band distortion compensation for massive MIMO-OFDM

Event date： 2019.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：奄美市社会福祉センター   Country：Japan  

A study on spatial pre-coding method considering antenna correlation under peak power constraint

Event date： 2019.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島市立大学   Country：Japan  

Event date： 2019.4 - 2019.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Kuala Lumpur   Country：Malaysia  

Cross-Tier Interference Management Scheme for Downlink mMIMIO-NOMA HetNet

Event date： 2019.4

Language：English   Presentation type：Oral presentation (general)  

Venue：登別グランドホテル   Country：Japan  

Event date： 2019.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：早稲田大学   Country：Japan  

Event date： 2019.3

Language：English   Presentation type：Oral presentation (general)  

Venue：早稲田大学   Country：Japan  

Event date： 2019.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：早稲田大学   Country：Japan  

Event date： 2019.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：早稲田大学   Country：Japan  

Event date： 2019.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：湘南工科大学   Country：Japan  

Event date： 2019.3

Language：English   Presentation type：Oral presentation (general)  

Venue：湘南工科大学   Country：Japan  

Event date： 2019.3

Language：English   Presentation type：Oral presentation (general)  

Venue：横須賀リサーチパーク   Country：Japan  

Event date： 2019.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：横須賀リサーチパーク   Country：Japan  

Event date： 2019.1 - 2019.2

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪大学   Country：Japan  

Event date： 2018.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京理科大学   Country：Japan  

Event date： 2018.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Alexandria   Country：Egypt  

Tomoya Kageyama, Osamu Muta, Cheng-Ming Chen and SofiePollin, ``Effect of Limiter based PAPR Reduction for Massive MIMO Systems,'' International Japan-Africa Conference on Electronics, Communications and Computations 2018, Dec. 2018.

Event date： 2018.11

Language：English   Presentation type：Oral presentation (general)  

Venue：沖縄県 石垣市   Country：Japan  

Osamu Muta, Wanming Hao, Haris Gacanin, ``Pilot Allocation and Interference Coordination for Heterogeneous Network with Massive MIMO/TDD, '' 2018 International Symposium on Intelligent Signal Processing and Communication Systems, Nov. 2018.

Event date： 2018.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：沖縄県 那覇市   Country：Japan  

A Study on Interference Mitigation for Downlink MIMO Heterogeneous Networks

Event date： 2018.11

Language：English   Presentation type：Oral presentation (general)  

Venue：愛媛県 松山市   Country：Japan  

A Competition based Power Allocation Scheme for Downlink NOMA HetNet

Event date： 2018.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：愛媛県 松山市   Country：Japan  

Effect of Limiter based PAPR Reduction for Massive MIMO Systems

Event date： 2018.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：機械振興会館   Country：Japan  

A hierarchical interference alignment and coordinated beamforming scheme for downlink NOMA-HetNet with massive MIMO

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大分大学   Country：Japan  

Bit Error Rate Evaluation of massive MIMO-OFDM-SDMA Systems with Peak Cancellation

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大分大学   Country：Japan  

A Study on Frequency-domain and Delay-time domain Pilot Allocations for Uplink Channel Estimation in Massive MIMO Systems

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Bit Error Rate Evaluation of massive MIMO-OFDM-SDMA Systems with Peak Cancellation, Part II

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

BER Evaluation of MRC-Precoded MIMO-SDMA with Peak Cancellation

Event date： 2018.9

Language：English   Presentation type：Oral presentation (general)  

Venue：金沢大学   Country：Japan  

A Competition based Power Allocation Scheme for Downlink NOMA HetNet

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Porte   Country：Portugal  

Event date： 2018.5

Language：English   Presentation type：Oral presentation (general)  

Venue：慶應義塾大学   Country：Japan  

Capacity-Based Opportunistic User Selection for Downlink Interference Alignment in MU-MIMO Cellular Systems

Event date： 2018.4

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：湯田温泉   Country：Japan  

Event date： 2018.4

Language：English   Presentation type：Oral presentation (general)  

Venue：Manchester   Country：United Kingdom  

An Enhanced Selected Mapping Technique for Joint PAPR Reduction and Impulsive Noise Suppression in Multi-Carrier Powerline Communications Systems

Event date： 2018.3

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：東京電機大学   Country：Japan  

Event date： 2018.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京電機大学   Country：Japan  

Event date： 2018.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京電機大学   Country：Japan  

Event date： 2018.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京電機大学   Country：Japan  

Event date： 2018.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Event date： 2018.3

Language：English   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Weighted Rank Constrained Rank Minimization Interference Alignment for 3-Tier Downlink Heterogeneous Networks

Event date： 2018.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Event date： 2018.2 - 2018.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：横須賀リサーチパーク   Country：Japan  

Performance of Massive MIMO Cognitive Radio Networks With Pilot Sharing Under SINR Requirements of Primary Users

Event date： 2018.2 - 2018.3

Language：Japanese  

Venue：横須賀リサーチパーク   Country：Japan  

Peak detection threshold selection method and its achievable performance for peak cancellation in MIMO-OFDM systems, Part. II

Event date： 2018.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：愛媛大学   Country：Japan  

Event date： 2018.1

Language：English   Presentation type：Oral presentation (general)  

Country：United States  

Event date： 2017.11 - 2017.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋大学   Country：Japan  

Event date： 2017.11 - 2017.12

Language：English   Presentation type：Oral presentation (general)  

Venue：名古屋大学   Country：Japan  

Event date： 2017.11

Language：English   Presentation type：Oral presentation (general)  

Venue：阿蘇プラザホテル   Country：Japan  

Event date： 2017.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡大学   Country：Japan  

Event date： 2017.11

Language：English   Presentation type：Oral presentation (general)  

Venue：福岡大学   Country：Japan  

Event date： 2017.11

Language：English   Presentation type：Oral presentation (general)  

Venue：福岡大学   Country：Japan  

Event date： 2017.11