Hidekazu Murata

Cooperative relaying scheme with space time code for multihop communications among single antenna terminals

In mobile multihop communications, the diversity technique is important since the channel between mobile terminals may suffer from the effects of fading and the routes between terminals are normally created through several hops. Space-time coding using multiple transmit antennas is an effective countermeasure for fading. For terminals which have only one antenna, due to the size/cost limitations, user cooperation has been introduced as a diversity technique. In this paper, a space-time coded cooperative relaying scheme for a multihop communications scenario, in cases where the number of hops is more than two, is proposed in order to combat the effects of fading among single antenna terminals, without bandwidth expansion. The scheme utilizes a space-time code for cooperative relaying and is developed in both frequency-flat and frequency-selective fading channels. By computer simulations, it is shown that the proposed scheme provides diversity gain and more improvement of frame error rate as the number of hops increases. Furthermore, the effects of an error correcting code and co-channel interference are shown.

Space time coded cooperative relaying technique for multihop communications

In multihop wireless networks, the quality of communications is degraded due to the relay transmissions over fading channels. Space-time code using multiple transmit antennas is an effective countermeasure for fading. For terminals which have only one antenna due to size/cost limitations, user cooperation has been introduced as a diversity technique. A new cooperative relaying scheme is proposed in order to combat the effects of fading in multihop communications among single antenna terminals. This scheme utilizes space-time code for cooperative relaying and is developed in both frequency-flat and frequency-selective fading channels for exploiting space and path diversity gain. By computer simulations, it is shown that the scheme can achieve almost full spatial diversity in multihop communications by both non-regenerative relaying with SNR estimation and regenerative relaying with error detection.

FPGA implementation of 4/spl times/4 MIMO test-bed for spatial multiplexing systems

Multiple input multiple output (MIMO) transmission techniques hold the potential of dramatically increasing the data rates and spectral efficiency of wireless communication systems. However, since multiple transmitters and receivers are required, a large number of channel emulators are also required for in-lab experiments, resulting in an increase in equipment cost. This paper describes an implementation of received signal generator for a 4/spl times/4 MIMO transmission in one FPGA chip which can be utilized as a real-time MIMO spatial multiplexing system test-bed. Our experimental results demonstrate that the CDF and channel correlations of emulated Rayleigh fading under this fading channel approach the theoretical values.

Real-time MIMO received signal generator for spatial multiplexing systems

Multiple input multiple output (MIMO) transmission techniques hold the potential of dramatically increasing the data rates and spectral efficiency of wireless communication systems. However, since multiple transmitters and receivers are required, a large number of channel emulators are also required for in-lab experiments, resulting in an increase of equipment cost. The paper describes an implementation of a received signal generator for 4/spl times/4 MIMO transmission in one FPGA chip which can be utilized as a real-time MIMO spatial multiplexing system testbed. Our experimental results demonstrate that the CDF and channel correlations of emulated Rayleigh fading and the BER performance under this fading channel approach the theoretical values.

Iterative FDE for DD-Based Cooperative Relaying with FD-STBC in Quasi-Synchronous Networks

A cooperative diversity requires accurate synchronization for relaying in multihop communications. This paper presents an iterative equalizer for multihop networks with delay diversity, which is tolerant to asynchronous relaying. We introduce frequency-domain space-time coding suited for the equalizer. In addition, we employ cooperative spatial multiplexing to improve the system throughput. We demonstrate that cooperative diversity and multiplexing can offer high spectrum-efficiency even in frequency-selective and poor-scattering channels

Performance Analysis of Diversity Techniques for Multihop Cooperative Networks with Adaptive Transmission

Wireless multihop communications with the cooperation of multiple relay terminals at each hop gives diversity effect and shows a significant frame error rate improvement than that without cooperation. To improve the spectral efficiency of this communication networks, adaptive modulation method is applied in this paper. The performance of adaptive transmission schemes combined with diversity techniques in multihop cooperative networks is analyzed. Numerical results from the analysis show that the throughput performance of adaptive transmission combined with a selection diversity technique is superior to that of the STBC diversity technique

Adaptive MLSE Equalizer with Per-Survivor QR Decomposition for Trellis-Coded MIMO Transmission

A trellis-coded multiple-input multiple-output (MIMO) transmission technique, which exploits multiple-antenna elements at both transmitter and receiver sides and employs trellis-coded modulations (TCMs), has potential to significantly increase spectral efficiency in wireless communications. At the receiver, an adaptive equalizer based on maximum-likelihood sequence estimation (MLSE) deals with intersymbol interference (ISI) incurred in wideband transmissions and jointly decodes multiplexed TCM signals. Recently, a sphere-constrained maximum-likelihood detection, so-called sphere decoding, has drawn much attention for reducing the computational burden in MIMO transmission systems. This paper describes the super-trellis structured Viterbi algorithm applying per-survivor sphere decoding, and evaluates the effect of the complexity reduction in branch metric computations.

Spatial interleaving for vector Viterbi equalizer with super-trellis decoding in trellis-coded space-time transmission

This paper evaluates the effect of spatial interleaving in the Viterbi algorithm with combined intersymbol interference (ISI) equalization, trellis-coded modulation (TCM) decoding and multi-signal detection. Through computer simulations, it is confirmed that spatial interleaving provides substantial diversity gains in both frequency-flat and frequency-selective Rayleigh fading channels. In Nakagami-Rice fading channels, performance improvement is significant at low Rician factor because of overcoming the burst errors incurred by signal fading. Spatial interleaving does not require additional computational complexity, memory buffer and decoding delay, differently from time interleaving. Moreover, the optimum combined TCM and ISI maximum likelihood sequence estimation (MLSE) can employ interleaving with almost no extra complexity, and iteration between equalization and decoding is not needed through the use of spatial interleaving.

Performance of turbo equalizer employing MMSE filter and LDPC codes

The performance of the receiver combining a minimum mean square error (MMSE) filter and low-density parity-check (LDPC) codes is investigated. Spatial multiplexing techniques can improve spectral efficiency without channel information at the transmitter over rich scattering wireless channel environments. A multiuser scenario is assumed where different users transmit LDPC encoded information simultaneously at the same carrier frequency. The receiver separates the multiplexed signal into signals for each user by the MMSE filter. The log likelihood ratios (LLR) of these signals are updated by the LDPC decoder. From the LLR and channel information, soft replicas are generated. Soft interference cancellation is performed by subtracting interference components from the received signal. The MMSE filtering is applied to the resultant signal. The interference component is eliminated by an iterative process between the MMSE filter and LDPC decoders. The paper shows the performance of this scheme using feedback channel estimation assuming a 4/spl times/4 multiple-input multiple-output (MIMO) system.

Performance of LDPC based turbo equalization for spatial multiplexing

The performance of the turbo equalization algorithm combined minimum mean square error (MMSE) filter with low-density parity-check (LDPC) codes is investigated under frequency selective fading environment. Spatial multiplexing scheme can improve frequency efficiency without channel knowledge at the transmitter. In this system different users transmit LDPC encoded information on the same carrier frequency at the same time. The receiver separates multiplexed signals into individual signals of each user by MMSE filter. After that, each information bit is decoded by sum-product algorithm and log likelihood ratio (LLR) of them are updated. The soft replica is generated from its LLR. Interference components are subtracted from the received signal. The MMSE filtering is reapplied to the resultant signal. This paper shows the performance of this scheme in 4x4 multiple-input multiple-output (MIMO) system and reveals the effect of iteration and channel estimation on the bit error rate (BER) performance.