Bee Leong Yeap

Turbo Coding, Turbo Equalisation and Space-Time Coding: EXIT-Chart-Aided Near-Capacity Designs for Wireless Channels

Covering the full range of channel codes from the most conventional through to the most advanced, the second edition of Turbo Coding, Turbo Equalisation and Space-Time Coding is a self-contained reference on channel coding for wireless channels. The book commences with a historical perspective on the topic, which leads to two basic component codes, convolutional and block codes. It then moves on to turbo codes which exploit iterative decoding by using algorithms, such as the Maximum-A-Posteriori (MAP), Log-MAP and Soft Output Viterbi Algorithm (SOVA), comparing their performance. It also compares Trellis Coded Modulation (TCM), Turbo Trellis Coded Modulation (TTCM), Bit-Interleaved Coded Modulation (BICM) and Iterative BICM (BICM-ID) under various channel conditions.The horizon of the content is then extended to incorporate topics which have found their way into diverse standard systems. These include space-time block and trellis codes, as well as other Multiple-Input Multiple-Output (MIMO) schemes and near-instantaneously Adaptive Quadrature Amplitude Modulation (AQAM). The book also elaborates on turbo equalisation by providing a detailed portrayal of recent advances in partial response modulation schemes using diverse channel codes.A radically new aspect for this second edition is the discussion of multi-level coding and sphere-packing schemes, Extrinsic Information Transfer (EXIT) charts, as well as an introduction to the family of Generalized Low Density Parity Check codes.This new edition includes recent advances in near-capacity turbo-transceivers as well as new sections on multi-level coding schemes and of Generalized Low Density Parity Check codesComparatively studies diverse channel coded and turbo detected systems to give all-inclusive information for researchers, engineers and students Details EXIT-chart based irregular transceiver designs Uses rich performance comparisons as well as diverse near-capacity design examples

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. (1995). 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.

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/sup -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.

Comparative study of turbo equalization schemes using convolutional, convolutional turbo, and block-turbo codes

Turbo equalizers have been shown to be successful in mitigating the effects of inter-symbol interference introduced by partial response modems and by dispersive channels for code rates of R/spl les/ 1/2. We comparatively studied the performance of a range of binary phase-shift keying turbo equalizers employing block-turbo codes, namely Bose-Chaudhuri-Hocquenghen (1960, 1959) turbo codes, convolutional codes, and convolutional turbo codes having high code rates, such as R=3/4 and R=5/6, over a dispersive five-path Gaussian channel and an equally weighted symbol-spaced five-path Rayleigh fading channel. These turbo equalization schemes were combined with an iterative channel estimation scheme in order to characterize a realistic scenario. The simulation results demonstrated that the turbo-equalized system using convolutional turbo codes was the most robust system for all code rates investigated.

Comparative study of space time block codes and various concatenated turbo coding schemes

Space-time block codes provide substantial diversity advantages in multiple transmit antenna assisted systems at a low decoding complexity. In this contribution, we concatenate space-time codes with three turbo coding schemes, namely turbo BCH (TBCH) codes, turbo convolutional (TC) codes and turbo trellis coded modulation (TTCM) schemes for the sake of achieving significant coding gain. The issues of mapping coded bits of the TBCH and TC schemes to different protection classes of various multilevel modulation schemes is also addressed. Finally, the performance and associated complexity of the three turbo schemes is compared.

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. 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 the coding schemes is compared.

Wideband burst-by-burst adaptive modulation with turbo equalization and iterative channel estimation

The performance of adaptive modulation-applied in conjunction with turbo equalization (TE)-is characterized in a noise limited environment over a slowly varying wideband multi-path Rayleigh fading channel. The iterative structure of the turbo equalizer was also exploited in order to invoke an iterative least mean square (LMS) channel estimator. Finally, the throughput performance of the adaptive modulation scheme was compared to that of its constituent modulation modes, where a gain of 1.5 dB to 1.7 dB was recorded.

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 as (STBC-SP), has shown useful performance improvements over Alamoutis conventional orthogonal design. In recent years, iterative decoding algorithms have attained substantial performance improvements in the context of wireless communication systems. We demonstrate that the performance of STBC-SP 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 are 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/sup -5/, the proposed turbo-detected STBC-SP scheme employing optimum mapping, is capable of achieving a coding gain of approximately 19 dB over the identical-throughput 1 bit/symbol uncoded STBC-SP benchmarker scheme. The proposed scheme also achieved a coding gain of approximately 2 dB over the 1 bit/symbol channel-coded STBC-SP benchmarker scheme that employed Gray mapping.

Comparative study of turbo equalisers using convolutional codes and block-based turbo codes for GMSK modulation

In contrast to previously proposed turbo equalisers, where typically non-iterative channel decoders were used, this paper compares the performance of partial-response GMSK turbo equalisers using two different encoders, namely block BCH turbo codes and convolutional codes. The BER performance is assessed over non-dispersive Gaussian channels, and dispersive Rayleigh fading channels.

Reduced complexity in-phase/quadrature-phase turbo equalisation using iterative channel estimation

A novel reduced complexity trellis-based equaliser, referred to as the in-phase/quadrature-phase equaliser (I/Q-EQ), is proposed. The I/Q-EQ is employed in the context of turbo equalisation (TEQ-IQ) and with the aid of iterative channel estimation. The performance of the TEQ-IQ is characterized in a noise limited environment over an equally-weighted, symbol-spaced three-path Rayleigh fading channel. The TEQ-IQ achieved the same performance as the conventional turbo equaliser, while achieving a complexity reduction by a factor of 1.25 and 7.17 for 4-QAM and 16-QAM, respectively.