Full-Rate, Full-Diversity Adaptive Space Time Block Coding for Transmission over Rayleigh Fading Channels

A full-rate, full-diversity Adaptive Space Time Block Coding (ASTBC) scheme based on Singular Value Decomposition (SVD) is proposed for transmission over Rayleigh fading channels. The ASTBC-SVD scheme advocated is capable of providing both full-rate and full-diversity for any number of transmit antennas, Nt, provided that the number of receive antennas, Nr, equals to Nt. Furthermore, the ASTBC-SVD scheme may achieve an additional coding gain due to its higher product distance with the aid of the block code employed. In conjunction with SVD, the “water-filling” approach can be employed for adaptively distributing the transmitted power to the various antennas transmit according to the channel conditions, in order to further enhance the attainable performance. Since a codeword constituted by Nt symbols is transmitted in a single time slot by mapping the Nt symbols to the Nt transmit antennas in the spatial domain, the attainable performance of the ASTBC-SVD scheme does not degrade, when the channel impulse response values vary from one time slot to the next. Hence, the proposed ASTBC-SVD scheme is attractive in the context of both uncorrelated and correlated Rayleigh fading channels. The performance of the proposed scheme was evaluated, when communicating over uncorrelated Rayleigh fading channels. Explicitly, an Eb/N0 gain of 2.5 dB was achieved by the proposed ASTBC-SVD scheme against Alamouti’s scheme [1], when employing Nt = Nr = 2 in conjunction with 8PSK

Concatenated Space Time Block Codes and TCM, Turbo TCM Convolutional as well as Turbo Codes

Space-time block codes provide substantial diversity advantages for multiple transmit antenna systems at a low decoding complexity. In this paper, we concatenate space-time codes with Convolutional Codes (CC), Turbo Convolutional codes (TC), Turbo BCH codes (TBCH), Trellis Coded Modulation (TCM) and Turbo Trellis Coded Modulation (TTCM) schemes for achieving a high coding gain. The associated performance and complexity of the coding schemes is compared

Non-Iterative Joint Channel Equalisation and Channel Decoding

A non-iterative turbo equaliser scheme is proposed, which outperforms the iterative turbo equaliser by about 0.7 dB at a BER of 10E-3 over a symbol-spaced two-path channel and by about 3.4dB at a BER of 10e-3 over a five-path Gaussian channel

Reduced Complexity I/Q Turbo Detection for Space-Time Trellis-Coded Systems

A reduced-complexity turbo-detection scheme, referred to here as the R-TD arrangement, is proposed for employment in space-time trellis-coded (STTC) systems using the inphase/quadrature-phase (I/Q) cancellation technique that was previously developed for single-transmitter and single-receiver systems. The R-TD scheme decomposes the received signal into its constituent I and Q signal components and detects these components separately; hence, reducing the number of possible signal combinations to be “tested” by the detector. The R-TD scheme is capable of approaching the performance of the conventional turbo detector (F-TD), while achieving a complexity reduction factor of 3 and 862 for a four-phase-shift-keying 32-state STTC system, denoted as STTC(4,32), communicating over two- and five-path Rayleigh-fading channels, respectively, exhibiting a symbol-spaced and equal-tap-weight channel-impulse response. In order to investigate the benefits of employing channel coding in conjunction with STTC schemes, the R-TD principle was also invoked in convolutional-coding-aided STTC schemes. It was observed that, at a given throughput, the turbo-detected “nonchannel-coded” STTC(4,32) system required a similar signal-to-noise ratio to that of the R = 1/2 and constraint length K = 7 convolutional-coded STTC(16,16) scheme for achievingthe bit error rate (BER) of 10-5. At a higher target, BER of 10-3, the “nonchannel-coded” STTC(4,16) and STTC(4,32) schemes outperformed the channel-coded STTC(16,16) system by 0.8 and 2.3 dB, despite having a factor of 19 or 11 lower complexity, respectively. Index Terms—Inphase, iterative equalization and decoding, quadrature phase, reduced complexity, serial concatenated codes, space–time trellis coding(STTC), turbo equalization/detection

Radial Basis Function Assisted Turbo Equalization

This paper presents a turbo equalization (TEQ) scheme, which employs a radial basis function (RBF)-based equalizer instead of the conventional trellis-based equalizer of Douillard et al. Structural, computational complexity, and performance comparisons of the RBF-based and trellis-based TEQs are provided. The decision feedback-assisted RBF TEQ is capable of attaining a similar performance to the logarithmic maximum $a posteriori$ scheme in the context of both binary phase-shift keying (BPSK) and quaternary phase-shift keying (QPSK) modulation, while achieving a factor 2.5 and 3 lower computational complexity, respectively. However, there is a 2.5-dB performance loss in the context of 16 quadrature amplitude modulation (QAM), which suffers more dramatically from the phenomenon of erroneous decision-feedback effects. A novel element of our design, in order to further reduce the computational complexity of the RBF TEQ, is that symbol equalizations are invoked at current iterations only if the decoded symbol has a high error probability. This techniques provides 37% and 54% computational complexity reduction compared to the full-complexity RBF TEQ for the BPSK RBF TEQ and 16QAM RBF TEQ, respectively, with little performance degradation, when communicating over dispersive Rayleigh fading channels. Index Terms—Decision-feedback equalizer (DFE), Jacobian logarithm, neural network, radial basis function (RBF), turbo coding, turbo equalization (TEQ)

Reduced Complexity In-Phase/Quadrature-Phase M-QAM Turbo Equalization Using Iterative Channel Estimation

A reduced complexity trellis-based turbo equalizer known as the in-phase (I)/quadrature-phase (Q) turbo equalizer (TEQ-IQ) invoking iterative channel impulse response (CIR) estimation is proposed. The underlying principle of TEQ-IQ is based on equalizing the I and Q component of the transmitted signal independently. This requires the equalization of a reduced set of separate I and Q signal components in comparison to all of the possible I/Q phasor combinations considered by the conventional trellis-based equalizer. It was observed that the TEQ-IQ operating in conjunction with iterative CIR estimation was capable of achieving the same performance as the full-complexity conventional turbo equalizer (TEQ-CT) benefiting from perfect CIR information for both 4- and 16-quadrature amplitude modulation (QAM) transmissions, while attaining a complexity reduction factor of 1.1 and 12.2, respectively. For 64-QAM, the TEQ-CT receiver was too complex to be investigated by simulation. However, by assuming that only two turbo equalization iterations were required, which is the lowest possible number of iterations, the complexity of the TEQ-IQ was estimated to be a factor of 51.5 lower than that of the TEQ-CT. Furthermore, at BER = 10-3 the performance of the TEQ-IQ 64-QAM receiver using iterative CIR estimation was only 1.5 dB away from the associated decoding performance curve of the nondispersive Gaussian channel. <br/

Turbo Detection of Channel-Coded Space-Time Signals Using Sphere Packing Modulation

A recently proposed space-time signal construction method that combines orthogonal design with sphere packing, referred to here as (STBC-SP), has shown useful performance improvements over Alamouti’s conventional orthogonal design. In recent years, iterative decoding algorithms have attained substantial performance improvements in the context of wireless communication systems. In this paper, we demonstrate that the performance of STBCSP systems can be further improved by concatenating sphere packing aided modulation with channel coding and performing demapping as well as channel decoding iteratively. The sphere packing demapper is modified for the sake of accepting a priori information that is obtained from the channel decoder. Bit-wise mutual information measures were also employed for the sake of searching for the optimum bits-to-symbol mapping. We present simulation results for the proposed scheme communicating over a correlated Rayleigh fading channel. At a BER of 10?5, the proposed turbo-detected STBC-SP scheme employing the optimum mapping was capable of achieving a coding gain of approximately 19dB over the identical-throughput 1 bit/symbol uncoded STBC-SP benchmarker scheme. The proposed scheme also achieved a coding gain of approximately 2dB over the 1 bit/symbol channelcoded STBC-SP benchmarker scheme that employed Gray mapping