Tad Matsumoto

Accumulator-Assisted Distributed Turbo Codes for Relay Systems Exploiting Source-Relay Correlation

In relay systems, the probability of errors occurring in the source-relay (S-R) link can be viewed as representing correlation between the source and the relay. This letter proposes a very simple iterative decoding technique, accumulator-assisted distributed turbo code (ACC-DTC) using 2-state (memory-1) convolutional codes (CC), where the correlation knowledge between the source and the relay is estimated and exploited at the destination.

EXIT Chart-Aided Adaptive Coding for Multilevel BICM With Turbo Equalization in Frequency-Selective MIMO Channels

This paper proposes an adaptive coding (AC) scheme for multilevel bit-interleaved coded modulation (ML-BICM) with minimum mean-square error (MMSE) turbo equalization in frequency-selective multiple-input-multiple-output (MIMO) channels. The aim of this paper is to minimize the information rate loss due to the mismatch between channel realization and channel coding. With the aid of the knowledge about extrinsic information transfer characteristics at the receiver, code parameters such as code rates and/or generator polynomials are adaptively selected independently for each ML-BICM layer. Model-based simulation results show that an achievable average throughput can be significantly improved with the proposed AC technique over automatic repeat request with fixed coding rate. Furthermore, the advantageous points of the proposed scheme are verified through field-measurement-data-based simulations.

Iterative MIMO turbo multiuser detection and equalization for STTrC-coded systems with unknown interference

Iterative multiuser detection in a single-carrier broadband multiple-input multiple-output (MIMO) system is studied in this paper. A minimum mean squared error (MMSE) low-complexity multiuser receiver is derived for space-division multiple-access (SDMA) space-time trellis-coded (STTrC) systems in frequency-selective fading channels. The receiver uses MMSE filtering to jointly detect several transmit antennas of the user of interest, while the interference from the undetected transmit antennas, cochannel interference (CCI), and intersymbol interference (ISI) are all cancelled by the soft cancellation. The performances of two extreme receiver cases are evaluated. In the first case, only one transmit antenna of the user of interest is detected at a time and the remaining ones are cancelled by soft cancellation. In the second case, all the transmit antennas are detected jointly. The comparison of the two cases shows improvement with the latter one, both in single-user and multiuser communications and in the presence of unknown cochannel interference (UCCI). It is further shown that in the multiuser case, the proposed receivers approach the corresponding single-user bounds. The number of receive antenna elements required to achieve single-user bound is thereby equal to the number of users and not to the total number of transmit antennas.

Outage-based LDPC code design for SC/MMSE turbo-equalization

A semi-analytical EXIT chart analysis approach is presented to perform code design of low-density parity-check (LDPC) codes with a frequency-domain SC/MMSE turbo equalizer. The approach utilizes the equivalent channel assumption at the equalizer output to analytically compute the equalizer output mutual information. The analysis is used to compute the EXIT functions of the receiver for a sample set of random channel realizations. LDPC code design is then performed to match the channel code to the random convergence properties of the equalizer to obtain a desired outage probability. Substantial performance improvement is achieved with the code design compared to a standard regular LDPC code. Target block error probability is not reached, which is considered to be the result of some of the approximations made in the analysis and code design.

A computationally efficient MIMO turbo-equaliser

A reduced complexity version of the soft-interference cancelling MMSE turbo equalizer is proposed for single-carrier MIMO systems. In the receiver exact symbol-by-symbol interference covariance matrice inverses are replaced by time averages acquired through matrix inversion lemma iterations. Consequently, also the requirement to explicitly estimate signal-to-noise ratio is removed. After a number of iterations the equalizer is further simplified by utilizing the matched filter approximation. Remaining multipath and multiuser interference, in addition to receiver noise, are accounted for in the approximation. The performance of the receiver is verified through simulations with two MIMO radio network configurations.

Estimation of Observation Error Probability in Wireless Sensor Networks

In this letter, we first of all propose for a parallel wireless sensor network (WSN) a decoding technique that well exploits the correlation knowledge of the sensing data to be transmitted from each sensor to the fusion center (FC). This letter then derives an algorithm to estimate the observation error probabilities, representing the correlation, of the links between the sensing object and sensors. The convergence of the algorithm is also evaluated. Furthermore, the comparison of bit-error-rate (BER) performance between two cases, one uses estimated observation error probabilities, the other assumes the full knowledge of the observation error probabilities, is made. The simulation results show that the difference is only around 0.3-0.5 dB in per-link signal-to-noise power ratio (SNR), depending on the number of sensors.

Very Simple BICM-ID Using Repetition Code and Extended Mapping with Doped Accumulator

This paper proposes very simple bit-interleaved coded modulation with iterative detection (BICM-ID) as a spectrally efficient signal transmission scheme, where irregular repetition code and extended mapping with rate-1 doped accumulator (ACC) are combined to achieve a clear turbo-cliff. Doped ACC is used for close matching of the demapper and decoder’s extrinsic information transfer curves. Although the proposed BICM-ID system is very simple, it can achieve excellent performances and completely eliminate bit-error-rate floor. An exemplifying result for extended non-Gray mapped 4-quadrature amplitude modulation symbol shows that with 0.916 bits/channel use, turbo-cliff happens at 1.27 dB away from the Shannon limit.

Spatially Concatenated Codes With Turbo Equalization for Correlated Sources

This paper proposes for single carrier signaling a simple structure that combines turbo equalization and decoding of correlated sources in multipath-rich multiuser Rayleigh fading multiple access channels (MAC), where the correlation between the sources is exploited by vertical iterations (VI) between the decoders. The bit-flipping model with a flipping probability pe is used to express the correlation ρ between the sources as ρ = 1-2pe. The proposed simple structure, spatially concatenated codes (SpCC), can achieve turbo-like performance over MAC channels suffering from severe inter-symbol interference (ISI), even though it uses short memory convolutional codes. First of all, to achieve turbo-like performance we introduce VIs to exploit the knowledge about the source correlation by exchanging extrinsic log-likelihood ratio (LLR) between the two decoders. We then add a rate-1 doped accumulator (D-ACC) to flexibly adapt for the variation of correlations between the sources. The results of computer simulations and extrinsic information transfer (EXIT) analysis confirm that in multipath-rich environments the proposed structure can achieve excellent performances, 1.02-1.28 dB away from the Slepian-Wolf-Shannon limit, at 1% outage probability for 0 <; ρ ≤ 1.

Nonlinear frequency domain MMSE turbo equalization using probabilistic data association

This letter proposes a new frequency domain turbo equalization algorithm based on nonlinear minimum-mean- squared-error (MMSE) estimation. The conceptual basis of the proposed equalizer is the probabilistic data association (PDA) filtering. It is shown that by performing internal equalizer iterations, of which structure is resulted from the algorithm derivation according to the PDA concept, the convergence properties, analytical and verified by simulations, can be significantly improved over conventional MMSE turbo equalization techniques. Results of the simulations conducted to demonstrate the superiority of the proposed algorithm and to verify the accuracy of the analysis are presented in this letter.

Adaptive Transmission With Single-Carrier Multilevel BICM

In this paper, we introduce adaptive link control techniques for multiple-input multiple-output (MIMO) systems with broadband single-carrier signaling. Soft cancellation and minimum mean squared error turbo equalization is assumed, where matching between coding and equalization plays crucial roles to achieve high throughput. This paper uses multilevel coded bit-interleaved coded modulation (ML-BICM) with linear mapping as a core part of the transmission, on top of which this paper applies automatic repeat request (ARQ) with adaptive coding (AC) for link control. The reason behind the use of the linear mapping ML-BICM is the separability between the layers in the modulation format: This should bring us a significant benefit in designing the link control strategies because each layer has its own reliability, and the adaptive link control should be optimized based on the each layers reliabilities. For ARQ with ML-BICM, we introduce layer-by-layer retransmission control, where turbo equalization and retransmission control can be performed independently over the layers because of the layer-separability. The layer-by-layer concept is then applied to AC with ML-BICM, where the code parameters such as code rate and generator polynomials are chosen so that after several iterations the mutual information between the transmitted and the soft-input soft-output decoder output information can reach a value very close to one while minimizing the rate loss due to the mismatch between the equalization and decoder. Extrinsic information transfer analysis is performed for the MIMO channel realization being given. The transmitter is notified of the selected codes for the each layer via the feedback channel, and uses the selected codes for the following transmission, assuming that the channel state information (CSI) stays the same at least over two consecutive frames. Finally, this paper evaluates the throughput performances of the ML-BICM ARQ and AC techniques using multidimensional field measurement data. The performance tendencies are correlated with propagation properties, obtained as results of the high-resolution channel analysis, such as spatial spreads at the transmitter and receiver sides.