Soon Xin Ng

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

On the MIMO channel capacity of multidimensional signal sets

In this contribution, the capacity of multiple-input multiple-output (MIMO) systems using multidimensional phase-shift keying/quadratic-amplitude modulation signal sets is evaluated. It was shown that transmit diversity is capable of narrowing the gap between the capacity of the Rayleigh-fading channel and that of the additive white Gaussian noise channel. However, because this gap becomes narrower when the receiver diversity order is increased, for higher order receiver diversity, the performance advantage of transmit diversity diminishes. A MIMO system having full multiplexing gain has a higher achievable throughput than the corresponding MIMO system designed for full diversity gain, although this is attained at the cost of a higher complexity and a higher signal-to-noise ratio. The tradeoffs between diversity gain, multiplexing gain, complexity, and bandwidth are studied.

Reduced-Complexity Coherent Versus Non-Coherent QAM-Aided Space-Time Shift Keying

A novel reduced-complexity near-optimal detection algorithm is proposed for enhancing the recent Coherently-detected Space-Time Shift Keying (CSTSK) scheme employing arbitrary constellations, such as {\cal L}-point Phase-Shift Keying (PSK) and Quadrature Amplitude Modulation (QAM). The proposed detector relies on a modified Matched Filter (MF) concept. More specifically, we exploit both the constellation diagram of the modulation scheme employed as well as the Inter-Element-Interference (IEI)-free STSK architecture. Furthermore, we generalize the Pulse Amplitude Modulation (PAM)- or PSK-aided Differentially-encoded STSK (DSTSK) concept and conceive its more bandwidth-efficient QAM-aided counterpart. Then, the proposed reduced-complexity CSTSK detector is applied to the QAM-aided DSTSK scheme, which enables us to carry out low-complexity non-coherent detection, while dispensing with channel estimation. It is revealed that the proposed detector is capable of approaching the optimal Maximum Likelihood (ML) detectors performance, while avoiding the exhaustive ML search. Interestingly, our simulation results also demonstrate that the reduced-complexity detector advocated may achieve the same performance as that of the optimal ML detector for the specific STSK schemes parameters. Another novelty of this paper is that the star-QAM STSK scheme tends to outperform its square-QAM counterpart, especially for high number of dispersion matrices. Furthermore, we provided both the theoretical analysis and the simulations, in order to support this unexpected fact.

Efficient Computation of EXIT Functions for Nonbinary Iterative Decoding

The calculation of nonbinary extrinsic information transfer charts for the iterative decoding of concatenated index-based codes is addressed. We show that the extrinsic information at the output of a constituent a posteriori probability decoder can be calculated with very low complexity, where expensive histogram measurements are not required any more. An example for turbo trellis-coded modulation demonstrates the capabilities of the proposed approach

Hybrid iterative multiuser detection for channel coded space division multiple access OFDM systems

Space division multiple access (SDMA) aided orthogonal frequency division multiplexing (OFDM) systems assisted by efficient multiuser detection (MUD) techniques have recently attracted intensive research interests. The maximum likelihood detection (MLD) arrangement was found to attain the best performance, although this was achieved at the cost of a computational complexity, which increases exponentially both with the number of users and with the number of bits per symbol transmitted by higher order modulation schemes. By contrast, the minimum mean-square error (MMSE) SDMA-MUD exhibits a lower complexity at the cost of a performance loss. Forward error correction (FEC) schemes such as, for example, turbo trellis coded modulation (TTCM), may be efficiently combined with SDMA-OFDM systems for the sake of improving the achievable performance. Genetic algorithm (GA) based multiuser detection techniques have been shown to provide a good performance in MUD-aided code division multiple access (CDMA) systems. In this contribution, a GA-aided MMSE MUD is proposed for employment in a TTCM-assisted SDMA-OFDM system, which is capable of achieving a similar performance to that attained by its optimum MLD-aided counterpart at a significantly lower complexity, especially at high user loads. Moreover, when the proposed biased Q-function based mutation (BQM) assisted iterative GA (IGA) MUD is employed, the GA-aided systems performance can be further improved, for example, by reducing the bit error ratio (BER) measured at 3 dB by about five orders of magnitude in comparison to the TTCM-assisted MMSE-SDMA-OFDM benchmarker system, while still maintaining modest complexity.

Spatial Modulation and Space-Time Shift Keying: Optimal Performance at a Reduced Detection Complexity

In this paper, we propose a comprehensive reduced-complexity detector both for hard-decision-aided as well as for the soft-decision-assisted Spatial Modulation (SM)/Space-Time Shift Keying (STSK). More explicitly, the detection of the SM scheme, which activates a single one out of M antennas to transmit a single LPSK/QAM symbol, may be carried out by detecting the antenna activation index m and the LPSK/QAM symbol st separately, so that the detection complexity may be reduced from the order of O(M · L) to the lower bound of O(M + log2 L). However, the QAM aided STSK hard detection proposed in [1] results in a performance loss. Furthermore, the Max-Log-MAP algorithm proposed for soft STSK detection in [2] only takes into account the maximum a posteriori probabilities, which also imposed a performance degradation. Therefore, in this paper, we propose a novel solution for hard-decision-aided SM/STSK detection, which retains its optimal performance, despite its reduced detection complexity, when either LPSK or LQAM is employed. Furthermore, we propose the reduced-complexity Approx-Log-MAP algorithm conceived for the soft-decision-aided SM/STSK detector, in order to replace the suboptimal Max-Log-MAP algorithm.

On the Performance and Complexity of Irregular Variable Length Codes for Near-Capacity Joint Source and Channel Coding

In this paper we propose a novel irregular variable length coding (IrVLC) scheme for near-capacity joint source and channel coding. We employ a number of component variable length coding (VLC) codebooks having different coding rates for encoding particular fractions of the input source symbol stream. These fractions may be chosen with the aid of extrinsic information transfer (EXIT) charts in order to shape the inverted EXIT curve of the IrVLC codec for ensuring that it does not cross the EXIT curve of a serially concatenated channel codec. In this way, an open EXIT chart tunnel may be created even at low Eb/N0 values that are close to the capacity bound of the channel. We propose iteratively decoded serially concatenated IrVLC designs amalgamated with Trellis coded modulation (TCM). These schemes are shown to be capable of operating within 0.6 dB of the uncorrelated narrowband Rayleigh fading channels capacity bound using an average interleaver length of 217,500 bits and an effective bandwidth efficiency of 1.56 bit/s/Hz, assuming ideal Nyquist filtering. By contrast, the equivalent-rate regular VLC-based bench-marker schemes were found to be capable of operating at a higher distance of 1.1 dB from the capacity bound, which is nearly twice that of the proposed IrVLC-TCM scheme. Additionally, an irregular convolutional coiling (IrCC) based bench-marker was found to be capable of operating at 0.8 dB from the capacity bound, owing to its slightly eroded performance when operating with the considered interleaver length.

On the MIMO channel capacity of multi-dimensional signal sets

In this paper two general formulae were derived for the capacity evaluation of multi-input multi-output (MIMO) systems using multi-dimensional signal sets, different modulation schemes and an arbitrary number of transmit as well as receive antennas. It was shown that transmit diversity is capable of narrowing the gap between the capacity of the Rayleigh-fading channel and the AWGN channel. However since this gap becomes narrower when the receiver diversity order is increased, for higher-order receiver diversity the performance advantage of transmit diversity diminishes. A MIMO system having full multiplexing gain has a higher achievable capacity than the corresponding MIMO system designed for achieving full diversity gain, provided that the channel SNR is sufficiently high.

Distributed Turbo Trellis Coded Modulation for Cooperative Communications

In this contribution, we propose a Distributed Turbo Trellis Coded Modulation (DTTCM) scheme for cooperative communications. The DTTCM scheme is designed based on its decoding convergence with the aid of non-binary Extrinsic Information Transfer (EXIT) charts. The source node transmits TTCM symbols to both the relay and the destination nodes during the first transmission period. The relay performs TTCM decoding and re-encodes the information bits using a Recursive Systematic Convolutional (RSC) code regardless whether the relay can decode correctly or not. Only the parity bits are transmitted from the relay node to the destination node during the second transmission period. The resultant symbols transmitted from the source and relay nodes can be viewed as the coded symbols of a three-component parallel-concatenated TTCM scheme. At the destination node, a novel three-component TTCM decoding is performed. It is shown that the performance of the DTTCM matches exactly the EXIT chart analysis. It also performs very closely to its idealised counterpart that assumes perfect decoding at the relay.

Quantum Search Algorithms, Quantum Wireless, and a Low-Complexity Maximum Likelihood Iterative Quantum Multi-User Detector Design

The high complexity of numerous optimal classic communication schemes, such as the maximum likelihood (ML) multiuser detector (MUD), often prevents their practical implementation. In this paper, we present an extensive review and tutorial on quantum search algorithms (QSA) and their potential applications, and we employ a QSA that finds the minimum of a function in order to perform optimal hard MUD with a quadratic reduction in the computational complexity when compared to that of the ML MUD. Furthermore, we follow a quantum approach to achieve the same performance as the optimal soft-input soft-output classic detectors by replacing them with a quantum algorithm, which estimates the weighted sum of a functions evaluations. We propose a soft-input soft-output quantum-assisted MUD (QMUD) scheme, which is the quantum-domain equivalent of the ML MUD. We then demonstrate its application using the design example of a direct-sequence code division multiple access system employing bit-interleaved coded modulation relying on iterative decoding, and compare it with the optimal ML MUD in terms of its performance and complexity. Both our extrinsic information transfer charts and bit error ratio curves show that the performance of the proposed QMUD and that of the optimal classic MUD are equivalent, but the QMUDs computational complexity is significantly lower.