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

A β encoder is an analog-to-digital (A/D) converter, proposed by Daubechies et al. in 2002, that outputs a truncated sequence of β expansion of an input value x. It is known that the conventional pulse code modulation (PCM) that outputs the binary expansion of x is sensitive to the offset of the threshold voltage, while a β encoder is robust to such an offset. We propose an algorithm that calculates the binary expansion of an interval that is identified by an output sequence from a β encoder. Such a method is referred to as a β-ary to binary converter. We generate sequences of random numbers, using a hardware β encoder followed by the β-ary to binary converter. The randomness of the generated binary random numbers is verified by the National Institute of Standards and Technology (NIST) statistical test suite.

DOI： http://doi.org/10.1587/nolta.7.38

Other Link： https://www.jstage.jst.go.jp/article/nolta/7/1/7_38/_article

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

An alternative to the use of higher order Quadrature Amplitude Modulation (QAM) that shows strong variations of output amplitude is the use of higher order Phase Shift Keying (PSK). The bit error probability of higher order PSK is sensitive to phase distortion that is caused by propagation delay and Doppler frequency estimation errors. Phase Updating Loop (PUL) is a generalization of a Phase Locked Loop (PLL) that can estimate the delay and the Doppler accurately. In order to realize a higher order PSK, we recently proposed a delay-Doppler Space Division Multiplexing (dD-SDM) method in which a parameter space consisting of delay and Doppler is partitioned into several sub-spaces and each subspace has its assigned signature codes. In this paper, digital PUL is defined. Simulation results show that by the use of the dD-SDM method together with digital PUL we can successfully demodulate 256PSK data.

DOI： 10.1007/978-3-319-10262-7_1

Other Link： http://link.springer.com/chapter/10.1007%2F978-3-319-10262-7_1

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

The timing synchronization method proposed by Schmidl and Cox for orthogonal frequency division multiplexing (OFDM) systems uses a reference block consisting of two identical parts, while the one proposed by Shi and Serpedin uses a reference block consisting of four parts with a sign pattern (+1,+1,−1,+1). The accuracy of estimated delays of the latter method is higher than the former. In this paper, the number of partitions is generalized as an integer number M. Two criteria for optimization are proposed. Optimal codes with code length 5≤M≤30 are investigated.

DOI： 10.1007/978-3-319-12325-7_23

Other Link： http://link.springer.com/chapter/10.1007/978-3-319-12325-7_23

Language：English  

DOI： 10.1007/978-3-319-03871-1_5

Other Link： http://link.springer.com/chapter/10.1007%2F978-3-319-03871-1_5

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

Synchronisation must be established in any communication systems. In multicarrier communications, time and frequency offsets are taken into account. We use cross-ambiguity function to evaluate synchronisation performance and the interference in a CDMA system with such two-dimensional offsets. Welch bound for one dimensional and discrete time cross correlation function is extended to the one for two dimensional and continuous time cross ambiguity functions. This bound is compared with an ambiguity function for continuous time signal generated from discrete time signal with rectangular chip waveforms.

Language：English   Publishing type：Research paper (bulletin of university, research institution)  

Other Link： http://www.kurims.kyoto-u.ac.jp/~kyodo/kokyuroku/contents/1742.html

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

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

Reduction of MAI in Asynchronous DS/CDMA Systems Using Post-Filter

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

DOI： 10.1049/el:20020276

Publishing type：Research paper (scientific journal)   Publisher：Physical Review Research  

Numerous biological and microscale systems exhibit synchronization in noisy environments. The theory of such noisy oscillators and their synchronization has been developed and experimentally demonstrated, but inferring the noise intensity and phase response is not always straightforward. In this paper, we propose a useful formula that enables us to infer the noise intensity and phase response of a noisy oscillator synchronized with periodic external forcing. Through asymptotic approximations for small noise, we show that noisy synchronous oscillators satisfy a simple relationship among the noise intensity and measurable quantities, i.e., the stationary distribution of the oscillation phase and stationary probability current obtained as the average phase velocity, which is verified through systematic numerical analysis. The proposed formula facilitates a unified analysis and design of synchronous oscillators in weakly noisy environments.

DOI： 10.1103/PhysRevResearch.7.013076

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

<p>We assess how well the recently created MRI reconstruction technique, Multi-Resolution Convolutional Neural Network (MRCNN), performs in the core medical vision field (classification). The primary goal of MRCNN is to identify the best k-space undersampling patterns to accelerate the MRI. In this study, we use the Figshare brain tumor dataset for MRI classification with 3064 T1-weighted contrast-enhanced MRI (CE-MRI) over three categories: meningioma, glioma, and pituitary tumors. We apply MRCNN to the dataset, which is a method to reconstruct high-quality images from under-sampled k-space signals. Next, we employ the pre-trained VGG16 model, which is a Deep Neural Network (DNN) based image classifier to the MRCNN restored MRIs to classify the brain tumors. Our experiments showed that in the case of MRCNN restored data, the proposed brain tumor classifier achieved 92.79% classification accuracy for a 10% sampling rate, which is slightly higher than that of SRCNN, MoDL, and Zero-filling methods have 91.89%, 91.89%, and 90.98% respectively. Note that our classifier was trained using the dataset consisting of the images with full sampling and their labels, which can be regarded as a model of the usual human diagnostician. Hence our results would suggest MRCNN is useful for human diagnosis. In conclusion, MRCNN significantly enhances the accuracy of the brain tumor classification system based on the tumor location using under-sampled k-space signals.</p>

DOI： 10.1587/transinf.2022edp7198

Web of Science

Scopus

CiNii Research

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Publishing type：Research paper (international conference proceedings)   Publisher：Proceedings of the 11th International Japan-Africa Conference on Electronics, Communications, and Computations, JAC-ECC 2023  

User terminal collaboration is an emerging strategy for realizing spectrum- and energy-efficient wireless communication systems while improving positioning accuracy for advanced location-aware services. In this paper, we evaluate the achievable performance of a received signal strength (RSS)-based cooperative positioning scheme with user terminal collaboration, where the RSS is shared among users through direct inter-user communication at a higher frequency band. Simulation results show that user terminal collaboration significantly improves positioning accuracy in various evaluation scenarios.

DOI： 10.1109/JAC-ECC61002.2023.10479642

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Authorship：Lead author,　Last author,　Corresponding author   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE International Symposium on Information Theory - Proceedings  

The error exponent of fixed-length lossy source coding was established by Marton. Ahlswede showed that this exponent can be discontinuous at a rate R, depending on the probability distribution P of the given information source and the distortion measure d(x, y). The reason for the discontinuity in the error exponent is that there exists (d, ) such that the rate-distortion function R(|P) is neither concave nor quasi-concave with respect to P. Arimoto's algorithm for computing the error exponent in lossy source coding is based on Blahut's parametric representation of the error exponent. However, Blahut's parametric representation is a lower convex envelope of Marton's exponent, and the two do not generally agree. The contribution of this paper is to provide a parametric representation that perfectly matches the inverse function of Marton's exponent, thus avoiding the problem of the rate-distortion function being nonconvex with respect to P. The optimal distribution for fixed parameters can be obtained using Arimoto's algorithm. Performing a nonconvex optimization over the parameters successfully yields the inverse function of Marton's exponent.

DOI： 10.1109/ISIT54713.2023.10206938

Scopus

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Other Link： https://dblp.uni-trier.de/db/conf/isit/isit2023.html#Jitsumatsu23

Publishing type：Research paper (scientific journal)  

An accurate delay and Doppler estimation method for a radar system using time
and frequency-shifted pulses with pseudo-random numbers is proposed. The
ambiguity function of the transmitted signal has a strong peak at the origin
and is close to zero if delay and Doppler are more than the inverses of the
bandwidth and time-width. A two-dimensional (2D) sinc function gives a good
approximation of the ambiguity function around the origin, by which fractional
delay and Doppler are accurately estimated.

DOI： 10.48550/arXiv.2312.04969

arXiv

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

Other Link： https://www.journal.ieice.org/summary.php?id=k105_6_509

The error exponent of a discrete memoryless channel is expressed in two
forms. One is Gallager's expression with a positive slope parameter and the
other is Csiszar and Korner's information-theoretic representation expressed
using the mutual information and the relative entropy. They differ in
appearance, and existing methods to prove their agreement are not elementary,
as they require an evaluation of the KKT conditions that the optimal
distribution must satisfy. Similarly, there are two types of expressions for
the strong converse exponent. They are Arimoto's expression with a negative
slope parameter and Dueck and Korner's information-theoretic expression. The
purpose of this paper is to clarify the relation between two ways of
representing exponents, i.e., representations using slope parameters and those
using information-theoretic quantities, from the viewpoint of algorithms for
computing exponents. Arimoto's algorithm is based on expression using slope
parameters, while the authors' and Tridenski and Zamir's algorithms are based
on Dueck and Korner's information-theoretic expression. An algorithm family
that includes the above two algorithms as special cases was recently proposed.
This paper clarifies that the convergence of Tridenski and Zamir's algorithm
proves the match of Arimoto's and Dueck and Korner's exponents. We discuss
another family of algorithms and, using the surrogate objective function used
therein, prove that the two expressions of the error exponent coincide.
Evaluation of the KKT condition is not needed in this proof. We then discuss
the computation of the error and correct decoding probability exponents in
lossy source coding. A new algorithm family for computing the source coding
strong converse exponent is defined. The convergence of a member of the
algorithm family implies the match of the two expressions of the strong
converse exponent.

DOI： 10.48550/arXiv.2205.06027

arXiv

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

Information leakage in Wyner’s wiretap channel model is usually defined as the mutual information between the secret message and the eavesdropper’s received signal. We define a new quantity called “conditional information leakage given the eavesdropper’s received signals,” which expresses the amount of information that an eavesdropper gains from his/her received signal. A benefit of introducing this quantity is that we can develop a fast algorithm for computing the conditional information leakage, which has linear complexity in the code length n, while the complexity for computing the usual information leakage is exponential in n. Validity of such a conditional information leakage as a security criterion is confirmed by studying the cases of binary symmetric channels and binary erasure channels.

DOI： 10.1587/transfun.2020EAP1017

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

Dueck and Körner's reliability function for discrete memoryless channels for rates above the capacity coincides with Arimoto's exponent of correct decoding probability. The two exponent functions are described by seemingly different optimization problems over the space of probability distributions. Arimoto gave an iterative algorithm for solving the optimization problem that appears in his exponent function. However, no algorithm to solve the optimization problem that appears in Dueck and Körner's exponent has been proposed. This paper proposes a new iterative algorithm for solving the minimization problem in Dueck and Körner's exponent. In the proposed algorithm, a double minimization form with respect to two joint distributions on input and output symbols is introduced. This double minimization is connected to another double minimization that appears in Arimoto's algorithm. Such a connection leads to a quadruple minimization problem, by which the match of Arimoto and Dueck-Körner exponents is easily proved.

DOI： 10.1109/TIT.2019.2950678

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

© 2018 IEICE. Hayashi and Matsumoto gave two lower bounds for the secrecy exponent for wiretap channels in 2011 and 2016. They proved that the latter exponent function is greater than or equal to the former one for any positive rate, input distribution and conditional probability of wiretapper's channel. In this paper, we give a new and simple proof of the inequality between the two exponent functions. To prove the inequality we use non-negativity of Kullback-Leibler distance together with a lemma that was introduced by Arimoto to derive a computation algorithm for error and correct decoding probability exponent for discrete memoryless channels.

DOI： 10.23919/ISITA.2018.8664377

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

© 2018 IEICE. One of the important tasks in wireless communications is propagation delay estimation. It has been found that the channel estimation accuracy of compressed sensing is superior to the existing method based on signal parameter estimation through MUltiple SIgnal Classification (MUSIC) and Estimation of Signal Parameters via Rotational Invariance Techniques (ESPRIT). However, there is a problem in the method that multipath delays may not be resolved if they span between the grids. This problem leads to inaccurate channel estimation. In this paper, we describe the Atomic Norm Minimization (ANM) that enables super resolution channel estimation. In additions, we propose ANM by using Spread Spectrum (SS) signal. In this study, we show new experiments using Gold code for Global Positioning System (GPS). We have also added a new experiment to check the performance of the ANM with SS signal.

DOI： 10.23919/ISITA.2018.8664379

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

Copyright © 2018 The Institute of Electronics, Information and Communication Engineers. Compressed Sensing (CS) is known to provide better channel estimation performance than the Least Square (LS) method for channel estimation. However, multipath delays may not be resolved if they span between the grids. This grid problem of CS is an obstacle to super resolution channel estimation. An Atomic Norm (AN) minimization is one of the methods for estimating continuous parameters. The AN minimization can successfully recover a spectrally sparse signal from a few time-domain samples even though the dictionary is continuous. There are studies showing that the AN minimization method has better resolution than conventional CS methods. In this paper, we propose a channel estimation method based on the AN minimization for Spread Spectrum (SS) systems. The accuracy of the proposed channel estimation is compared with the conventional LS method and Dantzig Selector (DS) of the CS. In addition to the application of channel estimation in wireless communication, we also show that the AN minimization can be applied to Global Positioning System (GPS) using Gold sequence.

DOI： 10.1587/transfun.E101.A.2141

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

Compressed Sensing (CS) is known to provide better channel estimation performance than the Least Square (LS) method for channel estimation. However, multipath delays may not be resolved if they span between the grids. This grid problem of CS is an obstacle to super resolution channel estimation. An Atomic Norm (AN) minimization is one of the methods for estimating continuous parameters. The AN minimization can successfully recover a spectrally sparse signal from a few time-domain samples even though the dictionary is continuous. There are studies showing that the AN minimization method has better resolution than conventional CS methods. In this paper, we propose a channel estimation method based on the AN minimization for Spread Spectrum (SS) systems. The accuracy of the proposed channel estimation is compared with the conventional LS method and Dantzig Selector (DS) of the CS. In addition to the application of channel estimation in wireless communication, we also show that the AN minimization can be applied to Global Positioning System (GPS) using Gold sequence.

DOI： 10.1587/transfun.E101.A.2141

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

© 2017 IEEE. Recently, Parizi, Telatar, and Merhav [1] determined the exact random coding secrecy exponents for a wiretap channel. In this study, we focus on the computation of such secrecy exponents. To obtain the exact random coding secrecy exponent for a constant composition random coding ensemble, optimization with respect to two stochastic matrices must be performed. Parizi et al. suggested that inner optimization is a convex optimization problem and therefore can be solved efficiently and that the outer optimization is not guaranteed to have convex structure and is solved by an exhaustive search. In this paper, we develop an efficient computation of the exact random coding secrecy exponent.

DOI： 10.1109/ISIT.2017.8006822

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

© 2017 DGON. Compressive sensing (CS) for radar signal processing is known to be capable of various applications. This signal processing technique shows excellent performance for detecting objects. However, the grid problem of CS is an obstacle to more precise performance. In this paper, we introduce two methods to overcome this grid problem and evaluate the performance of the methods. The first method is an up-sampled model, which is a method of dividing the grids into smaller pieces. The second method is an atomic norm minimization, which is a detectable method for continuous parameters.

DOI： 10.23919/IRS.2017.8008110

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

© 2016 IEEE. The form of Dueck and Körner's exponent function for correct decoding probability for discrete memoryless channels at rates above the capacity is similar to the form of Csiszár and Körner's exponent function for correct decoding probability in lossy source coding for discrete memoryless sources at rates below the rate distortion function. We recently gave a new algorithm for computing Dueck and Körner's exponent. In this paper, we give an algorithm for computing Csiszár and Körner's exponent. The proposed algorithm can also be used to compute cutoff rate and the rate distortion function.

DOI： 10.1109/ISIT.2016.7541555

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

© 2015 IEEE. Estimation of the channel distortion characteristics is of crucial importance for realizing a reliable communication. In order to estimate the channel, a received signal is sampled at some rate. The Nyquist rate is widely used notion to determine the sampling rate of the received signal. On the other hand, Vetterli introduced the concept of rate of innovation that is the degree of freedom of the signal space and proposed annihilating filter method, which solves a nonlinear simultaneous equation by means of finding roots of the characteristic polynomial of the equation. By using this technique, the number of samples can be reduced from the Nyquist rate. In this paper, we employ the annihilating filter method to perform the estimation of a multi-path channel. A spread spectrum signal with a wide bandwidth is transmitted, while the received signal is sampled at a very low sampling rate that is determined according to the rate of innovation.

DOI： 10.1109/VTCFall.2015.7390934

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

© 2015 IEEE. For a discrete memoryless channel, a lower bound for the correct decoding probability exponent was derived by Arimoto. He also gave an iterative algorithm for computing the exponent. Subsequently, Dueck and Körner determined the optimal exponent function of the correct decoding probability. In this paper, a new iterative algorithm that computes Dueck and Körner's exponent is presented.

DOI： 10.1109/ISIT.2015.7282590

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

© 2014 National Institute of Information and Communicatio. The timing synchronization method proposed by Shmidl and Cox uses a reference block consisting of two identical parts, while the one proposed by Shi and Serpedin uses a reference block consisting of four parts with the third part being multiplied by -1. The accuracy of estimated delays of the latter method is higher than the former. In this paper, the number of division is generalized as an integer number M. Optimal M is investigated for single- and multi-path channels. We conclude that a recommended M value is approximately given by √N/2 for both single- and muti-path channels, irrespectively of signal-to-noise ratio, where N is a length of the reference block.

DOI： 10.1109/WPMC.2014.7014808

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

A β-encoder, a non-binary analog-to-digital converter that is based on the β-expansion, is reported to be robust to large process variations and widespread environment fluctuations. However, the quantization error of the β-encoder is complicatedly distributed and hard to be estimated due to the chaotic nature of the β-transformation. In this work, we propose an analysis method for determining an upper bound of the mean squared error of the quantization. We also provide an evaluation of the signal-to-quantization-noise ratio, which is useful for designing β-encoders.

DOI： http://dx.doi.org/10.1587/nolta.6.99

Other Link： https://www.jstage.jst.go.jp/article/nolta/6/1/6_99/_article

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

© 2014 IEEE. The Separable Property (SP) condition for time and frequency synchronization compels us to determine phase correction terms in the Gabor Division/Spread Spectrum System (GD/S3). The phase correction technique has led us to design a GD/S3 receiver equipped with phase-tuned layers for Mary phase shift keying (MPSK). The resulting signal points of the time domain (TD) and frequency domain (FD) correlator outputs of each layer for M = 16 consist of only three lines, called a main-lobe with a layer-dependent phase angle and sidelobes with phase angle ±2π/16. The two sidelobes suggesting bit errors are removed by using code division multiple target (CDMT), inspired by code division multiple-access (CDMA) philosophy. The simulation result for 16PSK is confirmed.

DOI： 10.1109/WCNC.2014.6952051

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

Other Link： http://www.cscjournals.org/library/manuscriptinfo.php?mc=SPIJ-182

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

Other Link： http://www.cscjournals.org/csc/manuscriptinfo.php?ManuscriptCode=80.77.70.71.42.46.51.50.101&JCode=SPIJ&EJCode=77.74.67.68.104&Volume=5&Issue=5

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

Other Link： http://www.cscjournals.org/csc/manuscriptinfo.php?ManuscriptCode=78.75.68.69.40.44.47.52.103&JCode=SPIJ&EJCode=77.74.67.68.104&Volume=45.106&Issue=44.106

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

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

DOI： 10.1093/ietcom/e88-b.10.4047

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

Reduction of MAI in Asynchronous DS/CDMA Systems Using Post-Filter

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

We propose a post-filter (digital filter applied after the correlator) to reduce multiple-access interference (MAI) in the correlator output in asynchronous communications. Optimum filter coefficients are derived for Markov and i.i.d. codes. It is shown that post-filter is not needed for Markov case. Variance of MAI is reduced in i.i.d. codes and it becomes equal to that of Markov codes; thus, both will have the same bit error rate (BER) performance. This post-filter reduces level of MAI in the correlator output for Gold codes as well.

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

Exact and approximate methods based on a posteriori probability threshold rule for multiuser code acquisition, utilizing interference cancellation, in the reverse link of base station of a Direct Sequence Code Division Multiple Access (DS/CDMA) system are proposed. Expectation and variance of correlator output corresponding to a synchronization chip and otherwise are derived including effects of data and timing estimation errors. Applying central limit theorem, density functions for the two cases are obtained and this leads to formulation of a joint density function of correlator output data. After receiving an output, conditional probability of corresponding chip being the synchronization chip is updated and compared with a threshold value. If the updated value of a posteriori probability is greater than or equal to threshold value, acquisition is declared; otherwise, next correlator output is examined and the process carries on until acquisition is declared. Hence, upper bound on acquisition error probability is guaranteed beforehand. Accumulated data is used for decision making, unlike conventional threshold rules that use only current data. Computer simulations show significant gains in mean acquisition time and correct acquisition probability compared to a similar multiuser system with conventional threshold rule. An approximate method with substantially less complexity than the exact method is derived. Instead of exact value of correlator output variance, an approximation is used. Consequently, joint density function of correlator output is considerably simplified however, performance is only slightly degraded.

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

Conventional single user correlator for asynchronous DS/CDMA systems provides only one scalar value for each data period. Code acquisition is expected to be improved if sampling is performed once each chip time. This accurate code acqusition method is shown to require covariance matrix of SS codes, while the optimum method needs inversion of the covariance matrix. However, Markovian SS codes with eigenvalue -2 + √3 do not need matrix inversion, which is the same value needed to achieve minimum bit error rate.

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

The self-interference of spreading sequence (SS) codes for asynchronous direct sequence (DS)/code division multiple access (DS/CDMA) generated by a Markov chain, was discussed. The central limit theorem was applied and E_S and σ_S
² were averaged where E_S and σ_S
² denoted mean and variance of S_p
⁽ⁱ⁾/√N with respect to X⁽ⁱ⁾ respectively. An estimated bit error rate (BER) of a nearly synchronized correlation receiver was also obtained.

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

A study of the number of solutions for a class of piecewise-linear equations related to transistor circuits was performed. The equations were found to play a central role in the dc analysis of transistor circuits. Certain assumptions like conductance matrix of a resistive circuit as positive definite or v-i characteristics of nonlinear resistors as exponential functions were made.

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

This paper discusses the number of solutions for a class of piecewise-linear equations related to two-transistor circuits compised of transistors, linear passive resistors, and DC sources. By using Ebers-Moll model, a transistor is replaced by two nonlinear resistors and two linear current-controlled current sources. We assume in this paper that the nonlinear resistors are ideal diodes. Then a circuit equation for the above circuit is a piecewise-linear equation Ti + Gv = b where each component i_k and v_k of the vectors i and v respectively are subject to v_ki_k = 0, v_k < 0, and i_k > 0. We show that the number of solution for the equations is at most 5.

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

This paper discusses the number of solutions for a class of piecewise-linear equations related to two-transistor circuits composed of transistors, linear passive resistors, and DC sources. By using Ebers-Moll model, a transistor is replaced by two nonlinear resistors and two linear current-controlled current sources. We assume in this paper that the nonlinear resistors are ideal diodes. Then a circuit equation for the above circuit is a piecewise-linear equation Ti + Gv = b where each component i_k and v_k of the vectors i and v respectively are subject to v_ki_k = 0, v_k ≤ 0, and i_k ≥ 0. We show that the number of solutions for the equation is at most 5.

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

We consider a circuit composed of linear capacitors, nonlinear resistors, and dc voltage sources and show the possibility that the total energy dissipated at resistors in the above circuit is smaller than the energy stored at capacitors. Linear passive circuits cannot possess such a property.

Event date： 2017.11 - 2017.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：新潟県   Country：Japan  

On computation of secrecy exponent functions

Other Link： http://www.ieice.org/ess/sita/SITA2017/program/index_e.html

Event date： 2017.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Prague   Country：Czech Republic  

Other Link： http://www.dgon-irs.org/fileadmin/templates/dokumente_irs/Programme_IRS-2017-Online.pdf

Event date： 2017.6

Language：English   Presentation type：Oral presentation (general)  

Venue：aachen   Country：Germany  

Other Link： http://www.isit2017.org/

Event date： 2016.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Yugawara   Country：Japan  

Other Link： http://www.epapers.org/nolta2016/ESR/session_sched_view.php?sched_id=1

Event date： 2016.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Yugawara   Country：Japan  

Other Link： http://www.epapers.org/nolta2016/ESR/session_sched_view.php?sched_id=1

Event date： 2016.8

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Other Link： http://apwcs2016.cn.tcu.ac.jp/program.html

Event date： 2016.7

Language：English   Presentation type：Oral presentation (general)  

Venue：BARCELONA   Country：Spain  

The form of
Dueck and K\"orner's exponent function for
correct decoding probability for discrete memoryless channels
at rates above the capacity
is similar to
the form of
Csisz\'ar and K\"orner's exponent function for
correct decoding probability i

Other Link： http://www.isit2016.org/

Event date： 2015.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山   Country：Japan  

Event date： 2015.9

Language：English   Presentation type：Oral presentation (general)  

Venue：New York   Country：United States  

Estimation of Multi-path Channels by Using the Annihilating Filter Method

Other Link： http://www.ieeevtc.org/vtc2015fall/

Event date： 2015.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Hong Kong  

For a discrete memoryless channel,
a lower bound for the correct decoding
probability exponent
was derived by Arimoto.
He also gave an iterative algorithm for computing
the exponent.
Subsequently, Dueck and K\"orner determined the optimal
exponent function of the correct decoding probability.
In this paper, a new iterative algorithm that
computes Dueck and K\"orner's exponent is presented.

Other Link： http://isit2015.org/

Event date： 2014.11

Language：English  

Venue：Melbourne   Country：Australia  

Other Link： http://www.springer.com/gp/book/9783319123240

Event date： 2014.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Sydney   Country：Australia  

Other Link： https://wpmc2014.org/

Event date： 2014.4

Language：English   Presentation type：Oral presentation (general)  

Venue：Istanbul   Country：Turkey  

Event date： 2013.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Vilnius   Country：Other  

Other Link： http://www.macom.ws/

Event date： 2013.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Tampere   Country：Finland  

Other Link： http://www.cs.tut.fi/RABAN/

Event date： 2013.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Lyon   Country：France  

Other Link： http://conferences.computer.org/wimob2013/

Event date： 2013.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Sevilla   Country：Spain  

Other Link： http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=6691301&sortType%3Ddesc_p_Publication_Year%26queryText%3DYutaka+Jitsumatsu

Event date： 2013.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Las Vegas   Country：United States  

Other Link： http://www.ieeevtc.org/vtc2013fall/index.php

Event date： 2013.8

Language：English  

Venue：Ilmenau   Country：Germany  

Other Link： http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=6629786&sortType%3Ddesc_p_Publication_Year%26queryText%3DYutaka+Jitsumatsu

Event date： 2013.6

Language：English  

Venue：Dresden   Country：Germany  

Other Link： http://www.irs-2013.de/welcome

Event date： 2012.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Anaheim   Country：United States  

Event date： 2011.9 - 2011.10

Presentation type：Oral presentation (general)  

Venue：Bologna   Country：Italy  

Event date： 2011.5

Venue：Prague   Country：Czech Republic  

Event date： 2010.10

Venue：Taichung   Country：Taiwan, Province of China  

Event date： 2008.11 - 2008.12

Presentation type：Oral presentation (general)  

Venue：New Orleans   Country：United States  

Event date： 2008.8

Presentation type：Oral presentation (general)  

Venue：Bologna   Country：Italy  

Event date： 2008.7

Presentation type：Oral presentation (general)  

Venue：TORONTO   Country：Canada  

Presentation type：Oral presentation (general)  

Country：France  

Presentation type：Oral presentation (general)  

Venue：Seattle,   Country：United States  

Presentation type：Oral presentation (general)  

Venue：Beijing   Country：China  

Presentation type：Oral presentation (general)  

Venue：San Francisco,   Country：United States  

Event date： 2024.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Fukuoka   Country：Japan  

Other Link： https://joint.imi.kyushu-u.ac.jp/post-15347/

Event date： 2024.9

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Other Link： https://ken.ieice.org/ken/paper/20240925Hc4E/eng/

Event date： 2024.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Sapporo   Country：Japan  

Other Link： https://ken.ieice.org/ken/paper/202407197cEI/eng/

Event date： 2024.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Utrecht   Country：Netherlands  

Other Link： https://numeration-2024.sciencesconf.org/

Event date： 2024.1

Language：Japanese   Presentation type：Oral presentation (general)  

Other Link： https://ken.ieice.org/ken/paper/20240119pCZJ/eng/

Event date： 2023.11 - 2023.12

Language：English   Presentation type：Poster presentation  

Venue：Yamaguchi   Country：Japan  

Event date： 2023.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Fukuoka  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Osaka   Country：Japan  

Other Link： https://ken.ieice.org/ken/paper/20230908FCwu/

Event date： 2023.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Kyoto   Country：Japan  

Other Link： https://ken.ieice.org/ken/paper/20230511wCUr/eng/

Event date： 2022.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Kobe   Country：Japan  

Other Link： https://www.ieice.org/ess/sita/SITA2021/program/index_e.html

Event date： 2022.11 - 2022.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Noboribetsu   Country：Japan  

Other Link： https://www.ieice.org/ess/sita/SITA2022/

Event date： 2022.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Ehime   Country：Japan  

Other Link： https://ken.ieice.org/ken/paper/20221028cCNA/eng/

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Other Link： https://confit.atlas.jp/guide/event/jsmrm2022/subject/_OS02-6/date?cryptoId=

Event date： 2022.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

Other Link： https://ken.ieice.org/ken/paper/20220802zCME/eng/

Event date： 2022.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Okayama   Country：Japan  

Other Link： https://ken.ieice.org/ken/paper/20220721NCKz/eng/

Event date： 2022.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Kumamoto   Country：Japan  

Other Link： https://ken.ieice.org/ken/paper/20220519MCKb/eng/

Event date： 2022.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Other Link： https://ken.ieice.org/ken/paper/20220303vCiK/eng/

Event date： 2021.5

Language：Japanese  

Country：Japan  

Other Link： https://ci.nii.ac.jp/naid/40022264980/en/

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Other Link： https://ken.ieice.org/ken/paper/20210316GC2W/eng/

Event date： 2020.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Other Link： https://ken.ieice.org/ken/paper/20201202zCBd/eng/

Event date： 2020.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Other Link： https://ken.ieice.org/ken/paper/20201203fCBH/eng/

Event date： 2020.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Other Link： https://ken.ieice.org/ken/paper/2020052931Yl/eng/

Event date： 2020.3

Language：English   Presentation type：Oral presentation (general)  

Venue：Kyoto   Country：Japan  

Other Link： https://ken.ieice.org/ken/paper/20200311T1XT/eng

Event date： 2020.2

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.2

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Other Link： https://jglobal.jst.go.jp/en/detail?JGLOBAL_ID=202002271261005580

Event date： 2019.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：霧島市，鹿児島県   Country：Japan  

Event date： 2019.11

Language：Japanese   Presentation type：Symposium, workshop panel (public)  

Venue：霧島市，鹿児島県   Country：Japan  

Event date： 2019.10

Language：Japanese  

Country：Japan  

Event date： 2019.3

Language：Japanese  

Country：Japan  

Event date： 2019.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京都   Country：Japan  

Event date： 2018.10

Language：English  

Venue：Singapore   Country：Singapore  

Hayashi and Matsumoto gave two lower bounds for the secrecy exponent for wiretap channels in 2011 and 2016. They proved that the latter exponent function is greater than or equal to the former one for any positive rate, input distribution and conditional probability of wiretapper's channel. In this paper, we give a new and simple proof of the inequality between the two exponent functions. To prove the inequality we use non-negativity of Kullback-Leibler distance together with a lemma that was introduced by Arimoto to derive a computation algorithm for error and correct decoding probability exponent for discrete memoryless channels.

Event date： 2018.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Singapore   Country：Singapore  

Other Link： https://ieeexplore.ieee.org/document/8664377

Event date： 2018.10

Language：English  

Venue：Singapore   Country：Singapore  

One of the important tasks in wireless communications is propagation delay estimation. It has been found that the channel estimation accuracy of compressed sensing is superior to the existing method based on signal parameter estimation through MUltiple SIgnal Classification (MUSIC) and Estimation of Signal Parameters via Rotational Invariance Techniques (ESPRIT). However, there is a problem in the method that multipath delays may not be resolved if they span between the grids. This problem leads to inaccurate channel estimation. In this paper, we describe the Atomic Norm Minimization (ANM) that enables super resolution channel estimation. In additions, we propose ANM by using Spread Spectrum (SS) signal. In this study, we show new experiments using Gold code for Global Positioning System (GPS). We have also added a new experiment to check the performance of the ANM with SS signal.

Event date： 2018.9

Language：Japanese  

Country：Japan  

Event date： 2017.6

Language：English  

Venue：Prague   Country：Czech Republic  

Compressive sensing (CS) for radar signal processing is known to be capable of various applications. This signal processing technique shows excellent performance for detecting objects. However, the grid problem of CS is an obstacle to more precise performance. In this paper, we introduce two methods to overcome this grid problem and evaluate the performance of the methods. The first method is an up-sampled model, which is a method of dividing the grids into smaller pieces. The second method is an atomic norm minimization, which is a detectable method for continuous parameters.

Event date： 2017.6

Language：English  

Venue：Aachen   Country：Germany  

Recently, Parizi, Telatar, and Merhav [1] determined the exact random coding secrecy exponents for a wiretap channel. In this study, we focus on the computation of such secrecy exponents. To obtain the exact random coding secrecy exponent for a constant composition random coding ensemble, optimization with respect to two stochastic matrices must be performed. Parizi et al. suggested that inner optimization is a convex optimization problem and therefore can be solved efficiently and that the outer optimization is not guaranteed to have convex structure and is solved by an exhaustive search. In this paper, we develop an efficient computation of the exact random coding secrecy exponent.

Event date： 2017.3 - 2007.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2017.2

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：佐賀県唐津市   Country：Japan  

Other Link： http://www.ma.is.saga-u.ac.jp/~hirotomo/ica2017/

Event date： 2017.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪   Country：Japan  

Other Link： http://www.ieice.org/ken/paper/20170120mbPD/

Event date： 2017.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪   Country：Japan  

Other Link： http://www.ieice.org/ken/paper/20170120mbPD/

Event date： 2016.7

Language：English  

Venue：Barcelona   Country：Spain  

The form of Dueck and Körner's exponent function for correct decoding probability for discrete memoryless channels at rates above the capacity is similar to the form of Csiszár and Körner's exponent function for correct decoding probability in lossy source coding for discrete memoryless sources at rates below the rate distortion function. We recently gave a new algorithm for computing Dueck and Körner's exponent. In this paper, we give an algorithm for computing Csiszár and Körner's exponent. The proposed algorithm can also be used to compute cutoff rate and the rate distortion function.

Event date： 2016.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Fukuoka   Country：Japan  

Event date： 2016.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Fukuoka   Country：Japan  

レーダーは電波を発信し検出すべき物体からの反射波を観測することで，
物体の速度と位置を検出する装置である．近年，圧縮センシングの枠組
みを利用してレーダーの解像度を向上させる研究が行われている．圧縮セン
シングの解法を利用するためには，位置と速度のパラメータ空間を離散化
する必要がある．しかし，真のパラメータの値が離散化されたグリッドの
中間に位置すると，物体の見逃しや誤検出を引き起こす問題があった．
この問題に対し，Tangらはatomic
normという新しいノルムの概念を導入し，パラメータ空間の離散

Event date： 2016.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Event date： 2016.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Event date： 2015.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Hong　Kong  

Other Link： http://www.nolta2015.org/

Event date： 2015.9

Language：English  

Venue：Boston   Country：United States  

Estimation of the channel distortion characteristics is of crucial importance for realizing a reliable communication. In order to estimate the channel, a received signal is sampled at some rate. The Nyquist rate is widely used notion to determine the sampling rate of the received signal. On the other hand, Vetterli introduced the concept of rate of innovation that is the degree of freedom of the signal space and proposed annihilating filter method, which solves a nonlinear simultaneous equation by means of finding roots of the characteristic polynomial of the equation. By using this technique, the number of samples can be reduced from the Nyquist rate. In this paper, we employ the annihilating filter method to perform the estimation of a multi-path channel. A spread spectrum signal with a wide bandwidth is transmitted, while the received signal is sampled at a very low sampling rate that is determined according to the rate of innovation.

Event date： 2015.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京工業大学   Country：Japan  

A new method for estimating a real-valued radix in an A/D converter.

Other Link： http://www.ieice.org/ken/paper/20150714XbBD/

Event date： 2015.6

Language：English  

Venue：Hong Kong  

For a discrete memoryless channel, a lower bound for the correct decoding probability exponent was derived by Arimoto. He also gave an iterative algorithm for computing the exponent. Subsequently, Dueck and Körner determined the optimal exponent function of the correct decoding probability. In this paper, a new iterative algorithm that computes Dueck and Körner's exponent is presented.

Event date： 2015.3

Language：English   Presentation type：Oral presentation (general)  

Venue：Fukuoka   Country：Japan  

Other Link： https://sites.google.com/a/ejust.kyushu-u.ac.jp/3ed-jec-ecc-2015/

Event date： 2015.3

Language：English   Presentation type：Oral presentation (general)  

Venue：Fukuoka   Country：Japan  

Other Link： http://www.imi.kyushu-u.ac.jp/publishes/pub_inner/id:2

Event date： 2014.9

Language：English  

Venue：Sydney   Country：Australia  

The timing synchronization method proposed by Shmidl and Cox uses a reference block consisting of two identical parts, while the one proposed by Shi and Serpedin uses a reference block consisting of four parts with the third part being multiplied by -1. The accuracy of estimated delays of the latter method is higher than the former. In this paper, the number of division is generalized as an integer number M. Optimal M is investigated for single- and multi-path channels. We conclude that a recommended M value is approximately given by √N/2 for both single- and muti-path channels, irrespectively of signal-to-noise ratio, where N is a length of the reference block.

Event date： 2014.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Halmstad   Country：Sweden  

Other Link： http://www.springer.com/gp/book/9783319102610#

Event date： 2014.4

Language：English  

Venue：Istanbul   Country：Turkey  

The Separable Property (SP) condition for time and frequency synchronization compels us to determine phase correction terms in the Gabor Division/Spread Spectrum System (GD/S³). The phase correction technique has led us to design a GD/S³ receiver equipped with phase-tuned layers for Mary phase shift keying (MPSK). The resulting signal points of the time domain (TD) and frequency domain (FD) correlator outputs of each layer for M = 16 consist of only three lines, called a main-lobe with a layer-dependent phase angle and sidelobes with phase angle ±2π/16. The two sidelobes suggesting bit errors are removed by using code division multiple target (CDMT), inspired by code division multiple-access (CDMA) philosophy. The simulation result for 16PSK is confirmed.

Event date： 2014.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡市   Country：Japan  

Event date： 2014.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡市   Country：Japan  

Event date： 2014.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：金沢市   Country：Japan  

Event date： 2013.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京都   Country：Japan  

Event date： 2013.11

Language：English  

Venue：Tampere   Country：Finland  

Non-coherent signal with unknown delay and Doppler is recovered by Gabor Division/Spread Spectrum System (GD/S³) with bipolar data. Separable Property (SP) condition for time and frequency synchronization leads us to determine phase correction terms in GD/S³ receiver. The receiver of GD/S³ is applicable for MPSK communications by introducing e ^{-j2π k-1/M} phase-tuned layers (for k = 1, 2,..., M)¹⁾.

Event date： 2013.10

Language：English  

Venue：Lyon   Country：France  

Non-coherent signal with unknown delay and Doppler is recovered by Gabor division/spread spectrum system. Separable property (SP) condition for time and frequency synchronization leads us to determine delay and Doppler precisely. This paper gives an enlargement of acceptable delay and Doppler region by using multiple codes and their associated receivers simultaneously without increasing computation time. As its application, two-target simultaneous determination is discussed.

Event date： 2013.9

Language：English  

Venue：Seville   Country：Spain  

Delay and Doppler determination of a time-delayed and frequency-shifted signal is one of fundamental problems in communication. The two-parameter estimation is reduced to two one-parameter estimation problems in time- and frequency-domain signals. Motivated by Gabor's communication theory, we proceed further parallelism between time- and frequency-domain signals and solve the two problems individually and cooperatively. Simulation results without prescribed information are reported.

Event date： 2013.9

Language：English  

Venue：Las Vegas, NV   Country：United States  

Recently proposed new Time-Domain (TD) synchronization using frequency integration and TD Spread Spectrum (SS) codes has been shown to be robust to frequency offset, that has its dual Frequency-Domain (FD) synchronization using time integration and FD SS codes which is robust to timing offset. Separable Property (SP) is defined for time-frequency synchronization under the condition containing time and frequency deviations to be performed separately and cooperatively. The SP compels us to design phase correction on SS codes and transmitted data.

Event date： 2013.8

Language：English  

Venue：Ilmenau   Country：Germany  

We have recently given a time-frequency synchronization method, called a Phase Updating Loop (PUL), in which a delay and a Doppler can be acquired separately and cooperatively by using a strategy to determine a phase term satisfying Time Frequency Symmetry (TFS) in time and frequency domains. In active and passive PULs, phase distortions caused by the delay and the Doppler are compensated for by the transmitter and the receiver, respectively. Phase correction terms for the PULs are shown to be effective for synchronization.

Event date： 2013.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京都   Country：Japan  

Event date： 2013.8

Language：English  

Venue：Egham   Country：United Kingdom  

An alternative to the use of higher order Quadrature Amplitude Modulation (QAM) that shows strong variations of output amplitude is the use of higher order Phase Shift Keying (PSK). The bit error probability of higher order PSK is sensitive to phase distortion that is caused by propagation delay and Doppler frequency estimation errors. Phase Updating Loop (PUL) is a generalization of a Phase Locked Loop (PLL) that can estimate the delay and the Doppler accurately. In order to realize a higher order PSK, we recently proposed a delay-Doppler Space Division Multiplexing (dD-SDM) method in which a parameter space consisting of delay and Doppler is partitioned into several subspaces and each subspace has its assigned signature codes. In this paper, digital PUL is defined. Simulation results show that by the use of the dDSDM method together with digital PUL we can successfully demodulate 256PSK data.

Event date： 2013.6

Language：English  

Venue：Dresden   Country：Germany  

Recently proposed new time synchronization using frequency domain (FD) integration and time domain (TD) spread spectrum (SS) codes has been shown to be robust to frequency offset, that has its dual frequency synchronization using TD integration and FD SS codes which is robust to timing offset. Separable property (SP) is defined for time-frequency synchronization under the condition containing time and frequency deviations is to be performed separately and cooperatively. The SP comples us to design phase corrections on SS codes and transmitted data.

Event date： 2013.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡市   Country：Japan  

Event date： 2013.5

Language：English  

Venue：Beijing   Country：China  

A non-binary analog-to-digital converter (ADC) based on β-expansion, called a β-encoder, can reportedly achieve robustness against large process variation and widespread environment change. The quantization error of the β-encoder is not uniformly distributed, which makes mean squared error (MSE) evaluation difficult. In this work, an analysis method for giving the upper bound of the MSE of the quantization error is proposed. We also gave an evaluation of signal-to-noise-ratio (SNR), which is effective for designing β-encoders^*.

Event date： 2013.5

Language：English   Presentation type：Oral presentation (general)  

Venue：北京   Country：China  

Event date： 2012.11

Presentation type：Oral presentation (general)  

Venue：宮古島   Country：Japan  

Event date： 2012.8

Language：English  

Venue：Paris   Country：France  

Timing synchronisation is achieved by time (T)-division spread spectrum (SS) code acquisition. Frequency (F)-domain SS code acquisition method is proposed for the recently proposed F-division SS system (FD/S³), which uses T-domain correlation and permits frequency offset. Frequency dual of this method gives a new T-domain code acquisition with F-domain correlation, which is more resistant to frequency offset than the conventional one with T-domain correlation.

Event date： 2012.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Paris   Country：France  

Event date： 2012.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Waterloo   Country：Canada  

Event date： 2012.6

Language：English  

Venue：Waterloo, ON   Country：Canada  

Synchronisation must be established in any communication systems. In multicarrier communications, time and frequency offsets are taken into account. We use cross-ambiguity function to evaluate synchronisation performance and the interference in a CDMA system with such two-dimensional offsets. Welch bound for one dimensional and discrete time cross correlation function is extended to the one for two dimensional and continuous time cross ambiguity functions. This bound is compared with an ambiguity function for continuous time signal generated from discrete time signal with rectangular chip waveforms.

Event date： 2012.5

Language：English  

Venue：Yantai   Country：China  

This paper presents a method which can estimate frequency, power and phase of received signal corrupted with additive white Gaussian noise (AWGN) in large frequency offset environment. Proposed method consists of two loops, each loop is similar to a phase-locked loop (PLL). Proposed structure solves the problems of conventional PLL such as limited estimation range, long settling time, overshoot, high frequency ripples and instability. Traditional inability of PLL to synchronize signals with large frequency offset is also removed in this method. Furthermore, proposed architecture along with providing stability, ensures fast tracking of any changes in input frequency. Proposed method is also implemented using field programmable gate array (FPGA), it consumes 201 mW and works at 197 MHz.

Event date： 2012.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Yantai   Country：China  

This paper presents a method which can estimate frequency, power and phase of received signal corrupted with additive white Gaussian noise (AWGN) in large frequency offset environment. Proposed method consists of two loops, each loop is similar to a phase-locked loop (PLL). Proposed structure solves the problems of conventional PLL such as limited estimation range, long settling time, overshoot, high frequency ripples and instability. Traditional inability of PLL to synchronize signals with large frequency offset is also removed in this method. Furthermore, proposed architecture along with providing stability, ensures fast tracking of any changes in input frequency. Proposed method is also implemented using field programmable gate array (FPGA), it consumes 201 mW and works at 197 MHz.

Other Link： http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=6223346&sortType%3Ddesc_p_Publication_Year%26queryText%3DYutaka+Jitsumatsu

Event date： 2011.11 - 2011.12

Presentation type：Oral presentation (general)  

Venue：岩手   Country：Japan  

Event date： 2011.9

Language：English  

Venue：Bologna   Country：Italy  

Gabor-division (GD) code division multiple access (CDMA) communication, which can provide almost flat power spectrum, has been recently proposed. Using a UWB Gaussian pulse generator implemented by CMOS technology as a fundamental component generating a chip waveform, we apply the GD-CDMA system for UWB communications. Time-frequency two dimensional spread spectrum (SS) codes with Markovity are employed. How Markovian SS codes flatten the spectrum of the transmitted signal is explained.

Event date： 2011.5

Language：English  

Venue：Prague   Country：Czech Republic  

We propose a Gabor division (GD)-CDMA system which permits time and frequency offsets. Negatively correlated time- and frequency-domain spreading codes have shown to reduce the variances of mutual- and self-interferences. In this paper, we show that such negatively correlated spreading codes have another important property that they flatten the time-frequency energy distributions of signals in GD-CDMA system.

Event date： 2011.3

Presentation type：Oral presentation (general)  

Venue：大阪   Country：Japan  

Event date： 2011.2 - 2011.3

Country：Japan  

Event date： 2011.1

Presentation type：Oral presentation (general)  

Venue：熊本   Country：Japan  

Event date： 2010.11 - 2010.12

Presentation type：Oral presentation (general)  

Venue：松代   Country：Japan  

Event date： 2010.11 - 2010.12

Presentation type：Oral presentation (general)  

Venue：松代   Country：Japan  

Event date： 2010.11 - 2010.12

Venue：松代   Country：Japan  

Event date： 2010.11

Language：English  

Venue：Fukuoka   Country：Japan  

We propose a phase-locked loop (PLL) architecture, which reduces the double frequency ripple without increasing the order of loop filter. Proposed architecture uses quadrature numerically-controlled oscillator (NCO) to provide two output signals with phase difference of π/2. One of them is subtracted from the input signal before multiplying with the other output of NCO. The system also provides stability in case the input signal has noise in amplitude or phase. The proposed structure is implemented using field programmable gate array (FPGA), which dissipates 15.44mw and works at clock frequency of 155.8 MHz.

Event date： 2010.11

Presentation type：Oral presentation (general)  

Venue：Fukuoka   Country：Japan  

Event date： 2010.10

Language：English  

Venue：Taichung   Country：Taiwan, Province of China  

This paper proposes a low power architecture for second order digital phase-locked loop (DPLL). High power consumption of DPLL results from using a look-up table (LUT) in implementing the numerically controlled oscillator (NCO). A new design for NCO is presented in which no LUT is used. Proposed architecture implemented using field programmable gate array (FPGA) consumed 15.44 mw at 100 MHz clock frequency which means a more than 25% saving in power consumption compared to traditional NCO. Furthermore, proposed method also saves FPGA resources and works at faster clock frequency.

Event date： 2010.10

Presentation type：Oral presentation (general)  

Venue：Taichung   Country：Taiwan, Province of China  

Event date： 2010.10

Language：English  

Venue：Taichung   Country：Taiwan, Province of China  

We propose a CDMA system which is regarded as a frequency dual of a chip-asynchronous DS/CDMA system. In such a system, each user's signal may have a frequency offset, i.e. users' carrier frequencies are not synchronised completely. We show that the variance of multiple access interference (MAI) is reduced when frequency offsets are introduced. Such an MAI can be further reduced if we employ Markovian frequency-domain spreading codes.

Event date： 2010.9

Presentation type：Oral presentation (general)  

Venue：Krakow   Country：Poland  

Event date： 2010.5

Presentation type：Oral presentation (general)  

Venue：徳島   Country：Japan  

Event date： 2009.10 - 2010.5

Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Event date： 2009.10

Language：English  

Venue：Fukuoka   Country：Japan  

A low power architecture to compute arctangent function which is suitable for broad-band communication applications is presented. This architecture aims to avoid high power consumption and long latency which are the main disadvantages to other methods based on CORDIC algorithm or conventional LUT methods or polynomial approximation. The architecture is implemented using FPGA, computes arctangent function with 3 clock pulses, and it is power dissipation is lower than Cordic algorithm by 80%.

Event date： 2009.10

Presentation type：Oral presentation (general)  

Venue：Fukuoka   Country：Japan  

Event date： 2009.3

Presentation type：Oral presentation (general)  

Venue：函館   Country：Japan  

Markovian Coded Gaussian Filter with its application to Filterbanks

Other Link： http://www.ieice.org/ken/paper/20090309va8A/

Event date： 2008.11 - 2008.12

Language：English  

Venue：New Orleans, LA   Country：United States  

It is believed that the dimension of the signal space with interval T and bandwidth W is 2WT, while we cannot make the out-of-band and out-of-time energies of any waveform zero. We propose a Gaussian pulse shaping for multi-carrier CDMA systems to utilize the time and frequency resources effectively. Gaussian pulses have ICI and ISI; they are not orthogonal. Markovity of spreading codes save the drawback of ICI and ISI. Overlapped Gaussian pulses increase the spectral efficiency.

Event date： 2008.11

Presentation type：Oral presentation (general)  

Venue：別府，大分県   Country：Japan  

Event date： 2008.10

Venue：Kinugawa   Country：Japan  

Event date： 2008.9

Language：English  

Venue：Krakow   Country：Poland  

The performances of Sleplan's PSWF and Gaussian chip waveforms are compared in asynchronous CDMA systems, where Markov spreading codes are employed. Bit error rate of Gaussian and PSWF filters are significantly better than RRC filters. Implementation of the pulse shaping filters and Markov code generators by an FPGA will be reported at the conference.

Event date： 2008.9

Presentation type：Oral presentation (general)  

Venue：Krakow   Country：Poland  

Event date： 2008.9

Presentation type：Oral presentation (general)  

Venue：Budapest   Country：Hungary  

Event date： 2008.8

Language：English  

Venue：Bologna   Country：Italy  

A Gaussian pulse has inter-symbol-interference, which degrades signal to interference ratio (SIR). In asynchronous CDMA system, however, Markov codes with negative correlation recover the SIR of Gaussian pulses. The improvement over i.i.d. codes is 2.3dB and Gaussian pulse achieves almost same SIR and bandwidth as a root raised cosine (RRC) pulse. The filter length of Gaussian pulse is only a quarter of the RRC one.

Event date： 2008.7

Language：English  

Venue：Toronto, ON   Country：Canada  

Slepian's prolate spheroidal wave function (PSWF) is optimum in energy concentration within given frequency bandwidth and time-width. However it is not employed in communications mainly because its inter-symbol interference is unfavorable. We show that introducing Markovian spreading codes makes PSWF be a strong candidate for the chip waveform in CDMA systems. For design tractability, Gaussian waveform is recommended.

Event date： 2007.6

Language：English  

Venue：Nice   Country：France  

Pulse shaping filters are commonly implemented by FIR filters. Motivated by Slepian's philosophy of discrete prolate spheroidal sequences (DPSS), we investigate Welch's lower bound on aperiodic auto- and cross-correlations for oversampled sequences. An oversampled sequence set having minimum cross-correlations in chip-asynchronous CDMA system is provided under a given bandwidth condition.

Event date： 2006.11 - 2006.12

Language：English  

Venue：San Francisco, CA   Country：United States  

Performance of chip-asynchronous DS/CDMA system depends on chip waveform as well as spread spectrum (SS) codes. In case of rectangular chip waveform, SS codes generated by a Markov chain were shown to improve bit error rate (BER) performance. However, in commercial CDMA systems, a band-limited root raised cosine (RRC) pulse is used, where the superiority of Markov codes is reduced. RRC pulse fulfills inter-chip interference (ICI)-free condition. In CDMA systems, multiple-access interference (MAI) is of crucial importance. Gaussian pulse used in conjunction with Markovian codes reduces MAI although it does not has the ICI-free property. Computer simulations show that Gaussian pulse with same excess bandwidth energy as the RRC pulse significantly reduces BER.

Event date： 2006.9

Language：English  

Venue：Beijing   Country：China  

We give a quadratic form expression of the mean squared multiple-access interference (MAI) averaged over relative time delays for chip-asynchronous DS/CDMA systems. A lower bound on the mean squared MAI is referred to as chip-asynchronous version of Welch bound, which depends on chip pulse shapes. Real analysis tells us that a pair of rectangular and sine functions is one of Fourier transform and its inverse Fourier transform and vice versa. On the other hand, Gaussian pulses have the self-duality property. Gaussian chip pulses sacrifice inter-symbol interference, however, they give smaller mean squared MAI, as well as lower bit error rate, than the conventional Nyquist pulses.

Event date： 2006.7

Language：English  

Venue：Seattle, WA   Country：United States  

Multiple-access interference (MAI) depends on chip pulse shapes in chip-asynchronous direct sequence/code division multiple access (DS/CDMA) systems. The mean squared MAI averaged over relative time delays is expressed in a quadratic form, where a coefficient matrix is derived from the pulse shapes, while a variable vector consists of aperiodic autocorrelation functions of the signature sequences. This quadratic form gives a lower bound of the mean squared MAI, which is equivalent to the Welch bound if the pulse shape is a delta function. For any continuous pulse shapes, however, the mean squared MAI is shown to be reduced beyond the Welch bound. In case of rectangular pulse, the mean squared MAI is reduced by 13.4%, whereas the reduction ratio is 5.2% for band-limited pulses with excess bandwidth 0.5.

Event date： 2006.5

Language：English  

Venue：Kos   Country：Greece  

It is known that spreading codes generated by a Markov chain improve bit error rate performance of direct sequence/code division multiple access (DS/CDMA) systems if the chip pulse is rectangular. Real analysis tells us that a pair of the rectangular and sine functions is one of Fourier transform and its inverse Fourier transform and vice versa. On the other hand, Gaussian pulses have the self-duality property: they have the same expression in both time and frequency domains. Gaussian chip pulses sacrifice inter-symbol interference. However, the use of Markovian codes together with a Gaussian pulse increases the system performance approximately 30 % in terms of the number of users.

Event date： 2005.10

Language：English  

Venue：Perth, Western Australia   Country：Australia  

Conventional code acquisition techniques don't exploit the entire available information for decision making but only use a part of it. A maximum a posteriori probability (MAP) code acquisition scheme is proposed which efficiently utilizes all the available information by exploiting statistical properties of spreading codes. Computer simulations show significant performance improvements over conventional schemes.

Event date： 2005.5

Language：English  

Venue：Kobe   Country：Japan  

In terms of Bit error rate (BER) and synchronization performances, Markovian codes are superior to i.i.d. codes in asynchronous mode, for singleuser case. Their BER performance is better than i.i.d. codes in case of multiuser detection (MUD) also. This paper shows that a simple code acquisition scheme based on statistical properties of spread spectrum (SS) codes efficiently makes performance of Markov codes to be superior to i.i.d. codes in asynchronous MUD systems. Hence, Markov codes are a strong candidate for being SS codes in MUD case as well. Furthermore, the proposed code acquisition scheme significantly outperforms conventional schemes.

Event date： 2005.5

Language：English  

Venue：Kobe   Country：Japan  

Variance of multiple access interference (MAI) is separated into two independent variables; one is spread spectrum (SS) codes and the other is chip waveforms used in transmitter and receiver. For given SS codes, chip waveform optimization problem is formulated to minimize variance of MAI. One possible answer is provided under some assumptions.

Event date： 2004.8 - 2004.9

Language：English  

Venue：Sydney   Country：Australia  

In spread spectrum (SS)-based digital watermarking systems, watermark information is spread by a pseudo-random code and added to the original information signal. On the other hand, we have proposed another watermarking system having one watermark channel and several image transmission channels. Information data is modulated by SS codes with variable code length according to its significance. This paper inspects bit error rate of such a watermarking system for both watermark channel and image transmission channels.

Event date： 2003.10

Language：English  

Venue：Honolulu   Country：United States  

Multiuser code acquisition system based on Interference Cancellation (IC) is proposed for the reverse link of base station of Direct Sequence Code Division Multiple Access (DSKDMA) systems. Explicit expressions for the variance and density function of correlator output are derived incorporating data and timing estimation errors. Consequently, a threshold rule based on a posteriori probability can be applied which guarantees an upper bound on acquisition error probability beforehand, a very important system performance criterion. Computer simulation results show that acquisition error probability is below the upper limit; system capacity and mean acquisition time performance are also promising.

Event date： 2003.6 - 2003.7

Language：English  

Venue：Yokohama   Country：Japan  

We propose a decorrelator for chip-synchronous DS/CDMA systems using Markovian SS codes, which makes observed data at each chip-time uncorrelated. Moreover, using the decorrelator output a posteriori probability can be calculated by applying a very simple expression.

Event date： 2003.5

Language：English  

Venue：Bangkok   Country：Thailand  

The spread-spectrum Markovian-code acquisition in asynchronous DS/CDMA systems was discussed. The success rate of acquisition and bit error rate (BER) of the correlator using an accumulated version of the serial search acquisition were analyzed. The analysis showed that in a quasi-synchronous state Markov sequences were inferior to Gold sequences in terms of both the acquisition rate and BER.

Presentation type：Oral presentation (general)  

Venue：京都大学   Country：Japan  

Difficulties for aquiring a synchronization in multiple access communications.

Presentation type：Oral presentation (general)  

Venue：神戸   Country：Japan  

Autocorrelation Functions of SS Codes based on Markov Chains

Presentation type：Oral presentation (general)  

Venue：Lausanne   Country：Switzerland  

Presentation type：Oral presentation (general)  

Venue：Prague   Country：Czech Republic  

Presentation type：Oral presentation (general)  

Venue：bangkok   Country：Thailand  

Presentation type：Oral presentation (general)  

Venue：Yokohama   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Presentation type：Oral presentation (general)  

Country：Japan  

Presentation type：Oral presentation (general)  

Venue：Milan   Country：Italy  

Presentation type：Oral presentation (general)  

Venue：Vancouver   Country：Canada  

Presentation type：Oral presentation (general)  

Venue：Sydney   Country：Australia  

Venue：Seoul,   Country：Korea, Republic of  

Presentation type：Oral presentation (general)  

Venue：Kobe   Country：Japan  

Presentation type：Oral presentation (general)  

Country：Japan  

Presentation type：Oral presentation (general)  

Venue：Kobe   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：Kobe   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：Perth,   Country：Australia  

Presentation type：Oral presentation (general)  

Country：Japan  

Presentation type：Oral presentation (general)  

Venue：Okinawa   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：Okinawa   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：名古屋   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：Island of Kos   Country：Greece  

Presentation type：Oral presentation (general)  

Venue：San Diego   Country：United States  

Presentation type：Oral presentation (general)  

Venue：群馬大学（桐生市）   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：三重県　賢島   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Sendai  

Other Link： https://ken.ieice.org/ken/paper/20240119pCZJ/eng/

Language：Others  

The error exponent of fixed-length lossy source coding was established by
Marton. Ahlswede showed that this exponent can be discontinuous at a rate $R$,
depending on the probability distribution $P$ of the given information source
and the distortion measure $d(x,y)$. The reason for the discontinuity in the
error exponent is that there exists $(d,\Delta)$ such that the rate-distortion
function $R(\Delta|P)$ is neither concave nor quasi-concave with respect to
$P$. Arimoto's algorithm for computing the error exponent in lossy source
coding is based on Blahut's parametric representation of the error exponent.
However, Blahut's parametric representation is a lower convex envelope of
Marton's exponent, and the two do not generally agree. The contribution of this
paper is to provide a parametric representation that perfectly matches with the
inverse function of Marton's exponent, thus avoiding the problem of the
rate-distortion function being non-convex with respect to $P$. The optimal
distribution for fixed parameters can be obtained using Arimoto's algorithm.
Performing a nonconvex optimization over the parameters successfully yields the
inverse function of Marton's exponent.

DOI： 10.48550/arXiv.2304.11558

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Other Link： http://arxiv.org/pdf/2304.11558v1

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CiNii Books

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Language：Japanese   Publisher：東京 : 映像情報メディア学会  

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Language：Japanese  

Estimations of the Elastic wave velocities of rocks by convolutional neural networks

Language：Japanese  

Sparse superposition codes in massive machine type communications

Language：Japanese  

Examination of Arrangement of Jammers in a Cooperative Jamming Network

Language：Japanese  

The distribution of the conditional information leakage in binary symmetric erasure wiretap channels

Language：Japanese  

MRI Acceleration by Super Resolution

Language：Japanese  

Performance Evaluation of Random Number Generation Algorithm Based on a β-ary/Binary Conversion

Language：Japanese  

Performance Evaluation of Line Spectral Estimation Method Using the Atomic Norm

Language：Japanese  

A-8-21 Comparison of Methods of Compressed Sensing for Continuous Parameter Estimation

Language：Japanese  

A-8-20 Parameter Discritization Problem in Channel Estimation Method Based on Compressed Sensing

Language：Others  

An Iterative Algorithm for Computing the Optimal Exponent of Correct Decoding Probability for Rates below the Rate Distortion Function
The form of Dueck and K"orner&#039;s exponent function for correct decoding<br />
probability for discrete memoryless channels at rates above the capacity is<br />
similar to the form of Csisz&#039;ar and K"orner&#039;s exponent function for correct<br />
decoding probability in lossy source coding for discrete memoryless sources at<br />
rates below the rate distortion function. We recently gave a new algorithm for<br />
computing Dueck and K"orner&#039;s exponent. In this paper, we give an algorithm<br />
for computing Csisz&#039;ar and K"orner&#039;s exponent. The proposed algorithm can be<br />
also used to compute cutoff rate and the rate distortion function.

Language：Japanese  

A new method for estimating a real-valued radix in an A/D converter

Language：Japanese  

Theoretical Analysis on Quantization Error of β-Encoder
Theoretical evaluation of last{the quantization} error of the β-encoder, that is a non-binary analog-to-digital converter (ADC) based on β-expansion, is given. Although a β-encoder is considered to be robust against large process variation and wide last{spread} environment change, its mean-squared-error has not yet been analyzed theoretically, due to non-uniform distribution of the quantization error. In this study, we propose a new method to calculate the upper bound of the mean-squared-error caused by the quantization of β-encoder. Based on this method, we provide a theoretical evaluation of signal-to-noise ratio of the β-encoder.

Language：Japanese  

Theoretical Analysis on Quantization Error of β-Encoder

Language：Japanese  

Theoretical Analysis on Quantization Error of β-Encoder

Language：Japanese  

Theoretical Analysis on Quantization Error of β-Encoder
Theoretical evaluation of last{the quantization} error of the β-encoder, that is a non-binary analog-to-digital converter (ADC) based on β-expansion, is given. Although a β-encoder is considered to be robust against large process variation and wide last{spread} environment change, its mean-squared-error has not yet been analyzed theoretically, due to non-uniform distribution of the quantization error. In this study, we propose a new method to calculate the upper bound of the mean-squared-error caused by the quantization of β-encoder. Based on this method, we provide a theoretical evaluation of signal-to-noise ratio of the β-encoder.

Language：Japanese  

Separable Property for time and frequency synchronization in communications
Synchronization of time and frequency is necessary for any communication system, and determination of delay and Doppler of a channel is a fundamental problem in radar. The authors have recently proposed a delay and Doppler determination method which works in large delay and Doppler dispersions. Using a notion of templates, a two-parameter determination problem is separated into two one-parameter determination problems. A time-frequency synchronization method is said to satisfy Separable Property (SP), if delay and Doppler can be acquired separately and cooperatively. In this paper, we show that Gabor division/spread spectrum system (GD/S^3) satisfies the SP condition.

Language：Japanese  

Separable Property for time and frequency synchronization in communications

Language：Japanese  

The tolerance of TD/S^3 reciever for frequancy offset
In the conventional direct sequence/spread spectrum (DS/SS), a time delay of a channel can be estimated by time-domain code acquisition using a correlation reciever. In a recently proposed time division/spread spectrum system (TD/S^3), frequency-domain correlator that performs a pattern matching between the Fourier transform of received signal and an frequency domain template is employed. In this report, we investigate the tolerance of frequency domain correlator against frequency offset.

Language：Japanese  

The tolerance of TD/S3 reciever for frequency offset

Language：Japanese  

Sequences generated by chaos and optimum sequences for asynchronous CDMA system
Pseudorandom numbers generated from chaos are applied to spread spectrum communications. Kohda and Fujisaki showed that chaos-based pseudorandom numbers generated from Marcov map decrease bit error rate (BER) compared with pseudorandom numbers based on i.i.d. and shift register sequense. However, this fact is not recognized very well in the field of communications. One of the famous criteria in designing spread spectrum is the Welch bound, which is a lower bound on total squared correlations. In this paper, we discuss the defference between chip-asynchronous CDMA system and chip-synchronous one and show that for the chip-asynchronous CDMA systems, chaos-based pseudorandom numbers is superior in terms of total square asynchronous correlations.

Language：Japanese  

空間ゆらぎのある連想記憶におけるS/N解析

Language：English  

Asynchrony, Markov, Interference (Dynamical Systems : Theories to Applications and Applications to Theories)

Language：Japanese  

Performance evaluation of MC-CDMA system which permits time and frequency offsets
In code division multiple access (CDMA) systems, spreading code is introduced as the third axis in addition to the time and the frequency axes. CDMA is a flexible communication system where interferences between users are admissible. In place of the current CDMA, orthogonal frequency division multiple access (OFDMA) was adopted for the downlink in the cellular phone system of the 3.9th generation that is called LTE(long term evolution). Communication systems using orthogonal multi-carriers, the signals of each subcarriers overlap in the frequency domain. Hence the interference between carriers increases rapidly when the frequency offset is caused by Doppler effect. Not only the efficiency of transmission but also robustness to an inevitable time and frequency synchronization errors are required for communication systems. In this paper, we review the Gabor's two dimensional expression of time and frequency plane, and propose multi-carrier CDMA system which permits time and frequency offsets using a Gaussian waveform. The bit error rate (BER) and signal to interference ratio (SIR) of the proposed system are evaluated.

Language：Japanese  

Performance evaluation of MC-CDMA system which permits time and frequency offsets
In code division multiple access (CDMA) systems, spreading code is introduced as the third axis in addition to the time and the frequency axes. CDMA is a flexible communication system where interferences between users are admissible. In place of the current CDMA, orthogonal frequency division multiple access (OFDMA) was adopted for the downlink in the cellular phone system of the 3.9th generation that is called LTE(long term evolution). Communication systems using orthogonal multi-carriers, the signals of each subcarriers overlap in the frequency domain. Hence the interference between carriers increases rapidly when the frequency offset is caused by Doppler effect. Not only the efficiency of transmission but also robustness to an inevitable time and frequency synchronization errors are required for communication systems. In this paper, we review the Gabor's two dimensional expression of time and frequency plane, and propose multi-carrier CDMA system which permits time and frequency offsets using a Gaussian waveform. The bit error rate (BER) and signal to interference ratio (SIR) of the proposed system are evaluated.

Language：Japanese  

Performance evaluation of MC-CDMA system which permits time and frequency offsets
In code division multiple access (CDMA) systems, spreading code is introduced as the third axis in addition to the time and the frequency axes. CDMA is a flexible communication system where interferences between users are admissible. In place of the current CDMA, orthogonal frequency division multiple access (OFDMA) was adopted for the downlink in the cellular phone system of the 3.9th generation that is called LTE(long term evolution). Communication systems using orthogonal multi-carriers, the signals of each subcarriers overlap in the frequency domain. Hence the interference between carriers increases rapidly when the frequency offset is caused by Doppler effect. Not only the efficiency of transmission but also robustness to an inevitable time and frequency synchronization errors are required for communication systems. In this paper, we review the Gabor's two dimensional expression of time and frequency plane, and propose multi-carrier CDMA system which permits time and frequency offsets using a Gaussian waveform. The bit error rate (BER) and signal to interference ratio (SIR) of the proposed system are evaluated.

Language：Japanese  

Optimization of Spreading Code for Bandlimited CDMA with Fractional Time Delays
The performance of asynchronous CDMA systems can be measured by total square asynchronous correlations (TSAC). Ulukus and Yates gave a lower bound on TSAC for a chip-synchronous system. TSAC for a chip-asynchronous system depends on chip waveform. In this paper, we give a lower bound on TSAC for a chip-asynchronous system with a sine chip waveform.

Language：Japanese  

揺らぎのあるニューラルネットワークにおける連想記憶

Language：Japanese  

FD‐based CDMAにおけるMAIの分散の評価

Language：Japanese  

チップ非同期CDMAにおける相互相関の二乗の総和について

Language：Japanese  

Associative memory in a neural network with fluctuation
Associative memory is one of the applications of neural networks, where information is stored in many neurons distributedly and we can retrieve a necessary data using its partial information as a trigger. Associative memory realizes a parallel and distributed storage which can work almost properly even if its small part is damaged. In this report, we pay attention to the point that the model of associative memory resembles with the model of CDMA systems. The bit error rate of a CDMA system, is improved by introducing asynchrony to the user's time delay and replacing i.i.d. spreading codes with Markov codes. We show that such techniques are effective in associative memory as well.

Language：Japanese  

Markovian Coded Gaussian Filter with its application to Filterbanks
In code division multiple access (CDMA) systems, spreading code is introduced as the third axis in addition to the time and the frequency axes. The CDMA is a flexible communication system where interferences between users are admissible. In place of the current CDMA, orthogonal frequency division multiple access (OFDMA) is expected to be adopted for the downlink in the cellular phone system of the 3.9th generation that is called LTE (long term evolution). In the orthogonal carrier method, the signals of each subcarriers overlap in the frequency domain. Hence the interference between carriers increases rapidly when the frequency offset is caused by Doppler effect. Not only the efficiency of transmission but also robustness to an inevitable time and frequency synchronization errors is required for communication systems. In this paper, we go back to the Gabor's two dimensional expression of time and frequency plane. A multi-carrier CDMA system using a Gaussian waveform is proposed. The interference between carriers and the bit error rate of the proposed system are evaluated. The Gaussian waveform is not orthogonal therefore the inter-carrier interference exists even when there is no frequency offset. However, the increasing rate of the inter-carrier interference to the frequency offset is very small compared with the rectangular wave.

Language：Japanese  

Markovian Coded Gaussian Filter with its application to Filterbanks
In code division multiple access (CDMA) systems, spreading code is introduced as the third axis in addition to the time and the frequency axes. The CDMA is a flexible communication system where interferences between users are admissible. In place of the current CDMA, orthogonal frequency division multiple access (OFDMA) is expected to be adopted for the downlink in the cellular phone system of the 3.9th generation that is called LTE (long term evolution). In the orthogonal carrier method, the signals of each subcarriers overlap in the frequency domain. Hence the interference between carriers increases rapidly when the frequency offset is caused by Doppler effect. Not only the efficiency of transmission but also robustness to an inevitable time and frequency synchronization errors is required for communication systems. In this paper, we go back to the Gabor's two dimensional expression of time and frequency plane. A multi-carrier CDMA system using a Gaussian waveform is proposed. The interference between carriers and the bit error rate of the proposed system are evaluated. The Gaussian waveform is not orthogonal therefore the inter-carrier interference exists even when there is no frequency offset. However, the increasing rate of the inter-carrier interference to the frequency offset is very small compared with the rectangular wave.

Language：Japanese  

Markovian Coded Gaussian Filter with its application to Filterbanks
In code division multiple access (CDMA) systems, spreading code is introduced as the third axis in addition to the time and the frequency axes. The CDMA is a flexible communication system where interferences between users are admissible. In place of the current CDMA, orthogonal frequency division multiple access (OFDMA) is expected to be adopted for the downlink in the cellular phone system of the 3.9th generation that is called LTE (long term evolution). In the orthogonal carrier method, the signals of each subcarriers overlap in the frequency domain. Hence the interference between carriers increases rapidly when the frequency offset is caused by Doppler effect. Not only the efficiency of transmission but also robustness to an inevitable time and frequency synchronization errors is required for communication systems. In this paper, we go back to the Gabor's two dimensional expression of time and frequency plane. A multi-carrier CDMA system using a Gaussian waveform is proposed. The interference between carriers and the bit error rate of the proposed system are evaluated. The Gaussian waveform is not orthogonal therefore the inter-carrier interference exists even when there is no frequency offset. However, the increasing rate of the inter-carrier interference to the frequency offset is very small compared with the rectangular wave.

Language：English  

Spreading sequences for CDMA channels with ISI.

Language：English  

Slepian's prolate spheroidal wave functions revisited.

Language：Japanese  

Reduction of Energy Function by Bit Flipping for Multi-User Detection
In CDMA communications, both decorrelator and MMSE do not achieve the minimum bit error rate(BER).because hard decisions are made on their outputs multiplied by the inverse of correlation matrix. Hence MMSE receiver does not give the minimum bit error rate(BER). On the other hand, maximum a posteriori probability(MAP) receiver minimize BER, but MAP receiver is not feasible because the calculation time is proportional to exponent of the number of users. We show that neighborhood search method using energy function is useful to reduce BER determined by correlator output. This receiver achieves lower BER than decorrelator and MMSE receiver and its calculation time is considerably less than that of MAP receiver.

Language：Japanese  

Reduction of Energy Function by Bit Flipping for Multi-User Detection
In CDMA communications, both decorrelator and MMSE do not achieve the minimum bit error rate(BER).because hard decisions are made on their outputs multiplied by the inverse of correlation matrix. Hence MMSE receiver does not give the minimum bit error rate(BER). On the other hand, maximum a posteriori probability(MAP) receiver minimize BER, but MAP receiver is not feasible because the calculation time is proportional to exponent of the number of users. We show that neighborhood search method using energy function is useful to reduce BER determined by correlator output. This receiver achieves lower BER than decorrelator and MMSE receiver and its calculation time is considerably less than that of MAP receiver.

Language：Japanese  

Reduction of Energy Function by Bit Flipping for Multi-User Detection
In CDMA communications, both decorrelator and MMSE do not achieve the minimum bit error rate(BER).because hard decisions are made on their outputs multiplied by the inverse of correlation matrix. Hence MMSE receiver does not give the minimum bit error rate(BER). On the other hand, maximum a posteriori probability(MAP) receiver minimize BER, but MAP receiver is not feasible because the calculation time is proportional to exponent of the number of users. We show that neighborhood search method using energy function is useful to reduce BER determined by correlator output. This receiver achieves lower BER than decorrelator and MMSE receiver and its calculation time is considerably less than that of MAP receiver.

Language：English  

Cross Correlation Matrices for Multiuser Chip-Asynchronous DS/CDMA Systems
It is shown that asynchronous direct sequence/code division multiple access (DS/CDMA) systems are analogous to associative memories with asynchronously overlapping connections. Strategies to design the connection weight matrices of associative memory are observed to be closely related to the kinds of CDMA receivers, such as correlator, decorrelator and minimum mean square error (MMSE) receiver. Simulation results show that such associative memory models can memorize Markov patterns with smaller error rate than i.i.d. patterns.

Language：Japanese  

Weighted Connection of Neural Networks Derived from Asynchronously CDMA Systems

Language：English  

Variance of Average Interference Parameter for LFSR and Random Markov Codes

Language：English  

Associative Memories with Asynchronously Overlapping Connections Learn Markov Pattern Better than I.I.D.

Language：English  

A detector based on calculation of a posteriori probability is proposed for code acquisition in singleuser direct sequence code division multiple access (DS/CDMA) systems. Available information is used for decision making, unlike conventional methods which only use a part of it. Although this increases the overhead in terms of additional memory and computational complexity, significant performance improvements are achieved. The frame work is extended to multiuser systems and again mean acquisition time/correct acquisition probability performance is superior to the conventional systems although computational complexity is high. An approximate multiuser method with significantly less complexity is also derived.

DOI： 10.1093/ietcom/e88-b.10.4047

Language：English  

A detector based on calculation of a posteriori probability is proposed for code acquisition in singleuser direct sequence code division multiple access (DS/CDMA) systems. Available information is used for decision making, unlike conventional methods which only use a part of it. Although this increases the overhead in terms of additional memory and computational complexity, significant performance improvements are achieved. The frame work is extended to multiuser systems and again mean acquisition time/correct acquisition probability performance is superior to the conventional systems although computational complexity is high. An approximate multiuser method with significantly less complexity is also derived.

DOI： 10.1093/ietcom/e88-b.10.4047

Language：English  

Acquisition of Markovian SS Codes in Chip-Asynchronous DS/CDMA Systems
G. Mazzini et al. [1] showed that Spread Spectrum (SS) codes with Markovity give lower bit error rate (BER) than the conventional linear feedback shift register (LFSR) sequences such as Kasami and Gold codes, as well as independent and identically distributed (i.i.d.) codes in asynchronous DS/CDMA (direct sequence/code division multiple access) systems. However, SS codes are required to have not only low BER but also quick code acquisition performance. We have proposed a code acquisition method based on a posteriori probability for chip-synchronous DS/CDMA systems [9]. This report extends this acquisition method for asynchronous (or, chip-asynchronous) systems and shows Markovian SS codes have a good property in code acquisition as well, i.e., Markian SS codes makes calculation of a posteriori probability easier.

Language：English  

Acquisition of Markovian SS Codes in Chip-Asynchronous DS/CDMA Systems
G. Mazzini et al. [1] showed that Spread Spectrum (SS) codes with Markovity give lower bit error rate (BER) than the conventional linear feedback shift register (LFSR) sequences such as Kasami and Gold codes, as well as independent and identically distributed (i.i.d.) codes in asynchronous DS/CDMA (direct sequence/code division multiple access) systems. However, SS codes are required to have not only low BER but also quick code acquisition performance. We have proposed a code acquisition method based on a posteriori probability for chip-synchronous DS/CDMA systems [9]. This report extends this acquisition method for asynchronous (or, chip-asynchronous) systems and shows Markovian SS codes have a good property in code acquisition as well, i.e., Markian SS codes makes calculation of a posteriori probability easier.

Language：English  

Acquisition of Markovian SS Codes in Chip-Asynchronous DS/CDMA Systems
G. Mazzini et al. [1] showed that Spread Spectrum (SS) codes with Markovity give lower bit error rate (BER) than the conventional linear feedback shift register (LFSR) sequences such as Kasami and Gold codes, as well as independent and identically distributed (i.i.d.) codes in asynchronous DS/CDMA (direct sequence/code division multiple access) systems. However, SS codes are required to have not only low BER but also quick code acquisition performance. We have proposed a code acquisition method based on a posteriori probability for chip-synchronous DS/CDMA systems [9]. This report extends this acquisition method for asynchronous (or, chip-asynchronous) systems and shows Markovian SS codes have a good property in code acquisition as well, i.e., Markian SS codes makes calculation of a posteriori probability easier.

Language：English  

Acquisition of Markovian SS Codes in Chip-Asynchronous DS/CDMA Systems

Language：English  

Acquisition of Markovian SS Codes in Chip-Asynchronous DS/CDMA Systems

Language：English  

Acquisition of Markovian SS Codes in Chip-Asynchronous DS/CDMA Systems

Language：English  

Code Acquisition in Asynchronous DS/CDMA Systems
Synchronized users signals are subtracted from received signal at the base station of a direct sequence code division multiple access (DS/CDMA) system to aid code acquisition of new users. Expressions for expectation and variance of the correlator output corresponding to a synchronization chip and otherwise are derived for the asynchronous environment. A novel detector based on a posteriori probability threshold rule is proposed for code acquisition. Computer simulations show significant performance improvements over conventional code acquisition methods. The technique is also applicable for signals modulated by Markov codes and computer simulations show superiority of Markov codes over independent and identically distributed (i.i.d.) codes.

Language：English  

We propose a post-filter (digital filter applied after the correlator) to reduce multiple-access interference (MAI) in the correlator output in asynchronous communications. Optimum filter coefficients are derived for Markov and i.i.d. codes. It is shown that post-filter is not needed for Markov case. Variance of MAI is reduced in i.i.d. codes and it becomes equal to that of Markov codes; thus, both will have the same bit error rate (BER) performance. This post-filter reduces level of MAI in the correlator output for Gold codes as well.

Language：English  

Code Acquisition of Markovian SS codes in a chip-synchronous DS/CDMA system
Studies on spread spectrum (SS) communication using pseudorandom sequences generated by a chaotic map as spreading codes have proceeded for more than one decade. Chaotic binary sequences, especially ones generated by Markov piece wise linear (PL) maps, have attracted researchers' attention since it was proven that some class of such sequences is superior to conventional linear feedback shift register (LFSR) sequences in terms of bit error rate (BER). In order to apply such sequences to asynchronous SS communications, it is required that code acquisition of them must be possible in addition to having low BER. However, it is not clear so far whether code acquisition of chaotic sequences with Markovity is as easy as that of LFSR sequences. We propose a decorrelator for chip-synchronous DS/CDMA systems using Markovian SS codes, which makes observed data at each chip-time uncorrelated. Moreover, using the decorrelator output a posteriori probability can be calculated by applying a very simple expression.

Language：English  

The distribution of self-interferences of an incompletely synchronised correlator within a fraction of a chip in an asynchronous DS/CDMA system using spreading sequences (SS) codes generated by Markov chains is considered The resulting expressions for BER lead to a conclusion that SS codes with Markovity look promising.

DOI： 10.1049/el:20020276

Language：English  

The distribution of self-interferences of an incompletely synchronised correlator within a fraction of a chip in an asynchronous DS/CDMA system using spreading sequences (SS) codes generated by Markov chains is considered The resulting expressions for BER lead to a conclusion that SS codes with Markovity look promising.

DOI： 10.1049/el:20020276

Language：Japanese  

On Autocorrelation Functions of Spreading Sequences Based on Markov Chains

Language：English  

On a Synchronization Problem in Asynchronous DS/CDMA System (5th Workshop on Stochastic Numerics)

Language：English  

We show some results concerning the number of solutions of the equation y + Ax = b (y(T)x = 0, y greater than or equal to 0, x less than or equal to 0) which plays a central role in the de analysis of transistor circuits. In particular, we give sufficient conditions for the equation to possess exactly 2(l) (l less than or equal to n) solutions, where to is the dimension of the vector x.

Language：Japanese  

On tradeoffs between MAI and acquisition performance in an asynchronous DS/CDMA system
In code division multiple access based on direct sequence spectrum technique(DS-CDMA), spreading sequences play an important role. As spreading sequences, linear feedback shift register(LFSR)sequences have often been used. It is reported recently that for an asynchronous DS-CDMA system, the variance of the distributions of cross-correlation values of some sequences generated by class of Markov information sources(Markov sequences)is lower than that of LFSR sequences. However the variance of the distributions of self-correlation values of Markov sequences is higher than LFSR sequences. A preservation of a synchronization seems to be more difficult when using Markov sequences than using LFSR sequences. In this article, we evaluate the variance of self-correlation values of Mardov binary sequences for a asynchronous DS-CDMA system to estimate the bit error rate of the system and discuss the difficulties of a synchronization

Language：Japanese  

On tradeoffs between MAI and acquisition performance in an asynchronous DS/CDMA system.

Language：Japanese  

A sufficient condition for piecewise-linear equations including n ideal diode functions to have 2^l (l≦n) solutions
The maximum number of dc operating points for a circuit consisting of m transistors, linear passive resistors, and dc sources attracts much attention in the field of nonlinear circuits. Using Ebers-Moll's equivalent circuit, a circuit equation for the above circuit can be written in the form: f_k(x_k)+a_<k1>x_1+・・・+a_<kn>x_n=b_k(k=1,2,・・・n), where n=2m. Usually f_k(x_k) is a monotone increasing function. In this paper we consider f_k(x_k) to be a ideal diode function. Then the circuit equation is described by a piecewise linear equation with 2^n subregions. We discuss the number of solutions for this equation and show that the equation has exactly 2^l solutions (0〓l〓n) if the matrix obtained by multiplying arbitrary l columns of [a_<ij>] by -1 is a diagonally dominant matrix.

Language：Japanese  

An Upper Bound for the Number of Solutions of a Piecewise-linear Equation Related to Two-transistor Circuits
This paper discusses the number of solutions for a class of piecewise-linear equations related to two-transistor circuits composed of transistors, linear passive resistors, and DC sources. By using Ebers-Moll model, a transistor is replaced by two nonlinear resistors and two linear current-controlled current sources. We assume in this paper that the nonlinear resistors are ideal diodes. Then a circuit equation for the above circuit is a piecewise-linear equation Ti + Gv = b where each component ik and vk of the vectors i and v respectively are subject to vkik = 0, vk < 0, and ik > 0. We show that the number of solutions for the equation is at most 5.

DOI： 10.15017/1515724

Language：Japanese  

A sufficient condition for piecewise-linear equations including n ideal diode functions to have 2l (l.LEQ.n) solutions.

Language：English  

We consider a circuit composed of linear capacitors, nonlinear resistors, and de voltage sources and show the possibility that the total energy dissipated at resistors in the above circuit is smaller than the energy stored at capacitors. Linear passive circuits cannot possess such a property.

Language：Japanese  

On a dissipated energy of a circuit composed of one capacitor, ideal diodes, linear resistors, and dc voltage sources
It is well-known that the dissipated energy in equal to the stored energy of a capacitor 1/2CE^2 when we charge a capacitor C by the voltage source E. We may conjecture from this fact that when we store some amount of energy in capacitors, the same amount of energy inevitably be dissipated at resistors for general circuits. However the above ralation does not hold for circuits containing nonlinear resistors. In this paper, we consider the dissipated energy of circuits composed of one capacitor, ideal diodes, linear resistors, and dc voltage sources. And we show dissipated energy can be reduced to 1/3 compared with the linear case when using 2 voltage sources and can be redued to 1/7 when using 3 voltage sources. Further we give circuits having small dissipated energy containing n(>3) voltages sources.

Language：Japanese  

On a dissipated energy of a circuit composed of one capacitor, ideal diodes, linear resistors, and dc voltage sources
It is well-known that the dissipated energy is equal to the stored energy of a capacitor 1/2CE^2 when we charge a capacitor C by the voltage source E. We may conjecture from this fact that when we store some amount of energy in capacitors, the same amount of energy must inevitably be dissipated at resistors for general circuits. However the above ralation does not hold for circuits containing nonlinear resistors. In this paper, we consider the dissipated energy of circuits composed of one capacitor, ideal diodes, linear resistors, and dc voltage sources. And we show dissipated energy can be reduced to 1/3 compared with the linear case when using 2 voltage sources and can be redued to 1/7 when using 3 voltage sources. Further we give circuits having small dissipated energy containing n(>3) voltages sources.

Language：Japanese  

Maximum Number of Solutions for a Kind of Nonlinear Simultaneous Equatioonswith 2 Variables
本論文では, 非線形連立方程式 e^<x_i>+a_<i1>x_1+a_<i2>x_2+b_i=0 (i=1,2) において, a_<ij>, b_iが任意の実数をとるとき, 実数解の最大個数がちょうど5個であることを示す.

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：2

Proceedings of International Conference Number of peer-reviewed papers：4

Type：Competition, symposium, etc. 

Number of participants：236

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：3

Number of peer-reviewed articles in Japanese journals：2

Proceedings of International Conference Number of peer-reviewed papers：3

Proceedings of domestic conference Number of peer-reviewed papers：2

Type：Competition, symposium, etc. 

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：2

Number of peer-reviewed articles in Japanese journals：1

Proceedings of International Conference Number of peer-reviewed papers：0

Proceedings of domestic conference Number of peer-reviewed papers：2

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Number of participants：20

Type：Competition, symposium, etc. 

Number of participants：40

Type：Competition, symposium, etc. 

Number of participants：20

Type：Competition, symposium, etc. 

Number of participants：300

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Number of participants：500

Type：Competition, symposium, etc.