Shuang Tan

Adaptive minimum error-rate filtering design: A review

Adaptive filtering has been an enabling technology and has found ever-increasing applications in various state-of-the-art communication systems. Traditionally, adaptive filtering has been developed based on the Wiener or minimum mean square error (MMSE) approach, and the famous least mean square algorithm with its low computational complexity readily meets the fast real-time computational constraint of modern high-speed communication systems. For a communication system, however, it is the systems bit error rate (BER), not the mean square error (MSE), that really matters. It has been recognised that minimising the MSE criterion does not necessarily produce the minimum BER (MBER) performance. The introduction of the novel MBER design has opened up a whole new chapter in the optimisation of communication systems, and its design trade-offs have to be documented in contrast to those of the classic but actually still unexhausted MMSE and other often-used optimisation criteria. This contribution continues this theme, and we provide a generic framework for adaptive minimum error-probability filter design suitable for the employment in a variety of communication systems. Advantages and disadvantages of the adaptive minimum error-probability filter design are analysed extensively, in comparison with the classic Wiener filter design.

Symmetric Complex-Valued RBF Receiver for Multiple-Antenna-Aided Wireless Systems

A nonlinear beamforming assisted detector is proposed for multiple-antenna-aided wireless systems employing complex-valued quadrature phase shift-keying modulation. By exploiting the inherent symmetry of the optimal Bayesian detection solution, a novel complex-valued symmetric radial basis function (SRBF)-network-based detector is developed, which is capable of approaching the optimal Bayesian performance using channel-impaired training data. In the uplink case, adaptive nonlinear beamforming can be efficiently implemented by estimating the systems channel matrix based on the least squares channel estimate. Adaptive implementation of nonlinear beamforming in the downlink case by contrast is much more challenging, and we adopt a cluster-variation enhanced clustering algorithm to directly identify the SRBF center vectors required for realizing the optimal Bayesian detector. A simulation example is included to demonstrate the achievable performance improvement by the proposed adaptive nonlinear beamforming solution over the theoretical linear minimum bit error rate beamforming benchmark.

Minimum bit error rate multiuser transmission designs using particle swarm optimisation

We consider the downlink of a multiuser system equipped with multiple antennas transmitting to multiple single-antenna mobile receivers. Particle swarm optimisation (PSO) is invoked to solve the constrained nonlinear optimisation problem for the minimum bit error rate (MBER) multiuser transmitter (MUT). The proposed PSO aided symbol-specific MBER-MUT and average MBER-MUT schemes provide improved performance in comparison to the conventional minimum mean-square-error MUT scheme, while imposing a reduced complexity compared to the state-of-the-art sequential quadratic programming based symbol-specific MBER-MUT and average MBER-MUT schemes, respectively.

On Multi-User EXIT Chart Analysis Aided Turbo-Detected MBER Beamformer Designs

This paper studies the mutual information transfer characteristics of a novel iterative soft interference cancellation (SIC) aided beamforming receiver communicating over both additive white Gaussian noise (AWGN) and multipath slow fading channels. Based on the extrinsic information transfer (EXIT) chart technique, we investigate the convergence behavior of an iterative minimum bit error rate (MBER) multiuser detection (MUD) scheme as a function of both the system parameters and channel conditions in comparison to the SIC aided minimum mean square error (SIC-MMSE) MUD. Our simulation results show that the EXIT chart analysis is sufficiently accurate for the MBER MUD. Quantitatively, a two-antenna system was capable of supporting up to K=6 users at Eb/Na=3dB, even when their angular separation was relatively low, potentially below 20deg.

Particle Swarm Optimisation Aided Minimum Bit Error Rate Multiuser Transmission

We consider the downlink of multiuser system from a transmitter equipped with multiple antennas to multiple non-cooperative single-antenna mobile receivers. Particle swarm optimisation (PSO) algorithm is invoked to solve the constrained nonlinear optimisation problem for the minimum bit error rate (MBER) multiuser transmission (MUT). The proposed PSO aided MBER-MUT scheme provides much better performance over the conventional minimum mean-square-error MUT scheme, and it achieves a much lower complexity compared to the state-of-the-art sequential quadratic programming based MBER MUT.

Iterative Multiuser Minimum Symbol Error Rate Beamforming Aided QAM Receiver

A novel iterative soft interference cancellation (SIC) aided beamforming receiver is developed for high-throughput quadrature amplitude modulation systems. The proposed SIC-based minimum symbol error rate (MSER) multiuser detection scheme guarantees the direct and explicit minimization of the symbol error rate at the output of the detector. Adopting the extrinsic information transfer (EXIT) chart technique, we compare the EXIT characteristics of an iterative MSER multiuser detector (MUD) with those of the conventional minimum mean-squared error (MMSE) detector. As expected, the proposed SIC-MSER MUD outperforms the SIC-MMSE MUD.

Three-Stage Turbo MBER Multiuser Beamforming Receiver Using Irregular Convolutional Codes

Based on extrinsic information transfer (EXIT) charts, the convergence behavior of a three-stage serially concatenated multiuser beamforming receiver is presented. This system uses a linear minimum bit error rate (BER) multiuser detector as the inner module. Due to the nonrecursive nature of this inner module, a unity-rate memory-1 recursive precoder is placed in front of the channel to provide the required recursive structure. Irregular convolutional codes (IRCCs) are constructed to be used as the outer code to achieve near-capacity performance. Our simulations show that this system outperforms the traditional two-component iterative structure and is capable of significantly reducing the error floor.

MBER Turbo Multiuser Beamforming Aided QPSK Receiver Design Using EXIT Chart Analysis

This paper studies the mutual information transfer characteristics of a novel iterative soft interference cancellation (SIC) aided beamforming receiver designed for quadrature phase shift keying (QPSK) modulated systems communicating over additive white Gaussian noise (AWGN) channels. Based on the extrinsic information transfer (EXIT) chart technique, we investigate the convergence behaviour of an iterative minimum bit error rate (MBER) multiuser detection scheme as a function of the system parameters and channel conditions. We also compare the achievable performance and convergence behaviour of different multiuser detectors (MUD) and channel decoders. Our simulation results show that the EXIT chart analysis is sufficiently accurate for reliably predicting the performance of the MBER MUD, despite its potentially non-Gaussian output distribution because we invoke the histogram-based approximation of the true distribution. As expected, the proposed SIC- MBER MUD outperforms the SIC aided minimum mean square error (SIC-MMSE) MUD.

Adaptive beamforming for binary phase shift keying communication systems

The paper revisits adaptive beamforming assisted receiver for multiple antenna aided multiuser systems that employ binary phase shift keying (BPSK) modulation. The standard minimum mean square error (MMSE) design is based on the criterion of minimising the mean square error (MSE) between the beamformers desired output and complex-valued beamformers output. Since the desired output for BPSK systems is real-valued, minimising the MSE between the beamformers desired output and real-part of the beamformers output can significantly improve the bit error rate (BER) performance, and we refer to this alternative MMSE design as the real-valued MMSE (RV-MMSE) to contrast to the standard complex-valued MMSE (CV-MMSE) design. The minimum BER (MBER) design however still outperforms the RV-MMSE solution, particularly for overloaded systems where degree of freedom of the antenna array is smaller than the number of BPSK users. Adaptive implementation of this RV-MMSE beamforming design is realised using a least mean square (LMS) type adaptive algorithm, which we refer to as the RV-LMS, in comparison to the standard CV-LMS algorithm. The RV-LMS adaptive beamformer is shown to have a similar computational complexity as the adaptive MBER beamforming implementation known as the least bit error rate (LBER), imposing only half of the computational requirements of the CV-LMS algorithm.

Nonlinear Beamforming for Multiple-Antenna Assisted QPSK Wireless Systems

A nonlinear beamforming aided detector is proposed for multiple-antenna assisted quadrature phase shift keying systems. By exploiting the inherent symmetry of the optimal Bayesian detection solution, a symmetric radial basis function (SRBF) detector is developed which is capable of approaching the optimal Bayesian performance using channel-impaired training data. In the uplink case, adaptive nonlinear beamforming can be implemented effectively by estimating the channel matrix based on the least squares channel estimate. Adaptive implementation of nonlinear beamforming in the downlink case by contrast is much more challenging, and we adopt a cluster-variation enhanced clustering algorithm to directly identify the SRBF centre vectors required for realising the optimal Bayesian detector.