Robust Multiuser Detection Research Articles

An efficient and robust multi-user detection in IDMA system

Multi-user detection (MUD) is a popular method in wireless communication systems to enhance efficiency by together processing the signals received from all users. The complexity of MUD has been a great problem in practical scenario. Wiener (optimum) filter yields best estimate of the input signal from noisy observations. In this paper, using Wiener filtering, a less complex and robust MUD strategy is introduced in a new multiple access scheme called interleave-division multiple-access (IDMA) which supports MUD in a simple way. The proposed IDMA system helps in achieving lower bit error rate and manages multiple number of users easily when compared to other multiple access schemes.

FPGA Implementation of Multi-User Detection Genetic Algorithm Tool for SDMA-OFDM Systems

Robust multi-user detection (MUD) methods based on space division multiple access (SDMA) techniques are essential to efficiently exploit the electromagnetic spectrum. In this paper, an adaptive Genetic Algorithm-based tool for SDMA-OFDM Systems (GASOS) is developed to improve the performance and computational complexity in cases of fully-loaded and overloaded multi-user scenarios. The data flow in GASOS is appropriate in pipelining and parallelization to reduce operational time. A new GASOS-based MUD hardware design for SDMA-OFDM systems is proposed using FPGA architecture. The design details are presented together with their planned operational modules. Resource utilization is optimized, and the total number of clock cycles required is found to be 15 initially, in addition to one clock cycle per member of algorithm population. A clock frequency of 100 MHz is used and implementation is carried out on Xilinx® Virtex-6 FPGA, built in the development platform ML605 edition with JTAG Hardware Co-simulation. According to the results obtained from the developed algorithm and implementation tools, a high number of users can be physically possible and provided with support. Real-time based implementation of MUD systems has the potential to play a major role in next-generation communication systems.

A simple quantum-inspired bee colony algorithm for discrete optimisation problems

To design a novel intelligence algorithm for discrete optimisation problem, a simple quantum-inspired bee colony algorithm SQBCA is proposed. The proposed SQBCA applies the quantum computing theory to bee colony optimisation BCO, which is an effective discrete optimisation algorithm. Then the proposed simple quantum-inspired bee colony algorithm is used to solve benchmark functions and multiuser detection problems of code division multiple access CDMA system. By hybridising the bee colony optimisation and quantum computing theory, the quantum state and binary state of the quantum bees can be well evolved by simulated quantum rotation gate and simulated quantum not gate. The new robust multiuser detection based on SQBCA can search the global optimal solution. Simulation results for CDMA systems are provided to show that the proposed robust multiuser detection method is superior to the multiuser detection based on previous intelligence algorithms.

Robust blind multiuser detection based on PSO algorithm in the mismatch environment of receiver spreading codes

This paper deals with robust blind linear minimum mean square error (LMMSE) detection using the particle swarm optimization (PSO) algorithm in the presence of code mismatch. The paper shows that the PSO algorithm incorporating the linear system of the LMMSE detector, which is termed as LPSO, can significantly improve the bit error rate (BER) and the system capacity. As the code mismatch occurs, the output BER performance is vulnerable to degradation for LPSO. To remedy this problem, a blind LMMSE scheme is proposed and combined with PSO to form a robust blind LPSO (BLPSO) detector under code mismatch scenarios. Several computer simulations are provided to demonstrate the effectiveness of the proposed scheme.

Robust Multiuser Detection in Chaotic Communication Systems over Non-gaussian Fading Channels

In this article, we deal with the problem of robust code division multiple access (CDMA) signal detection in a chaotic communication system transmitting across a Non-gaussian fading channel. Since the performance of robust multiuser detector depends on the selection of M-estimator and the spreading sequences, a new influence function is used to derive an improved robust detector for the problem of data detection in CDMA impulsive fading channels using chaotic spreading. Numerical results show that the proposed robustification offers improved performance over Huber’s minimax detector and outperforms the DPSK decorrelating detector, particularly when the channel is highly impulsive.

Robust Multiuser Detection in Synchronous DS-CDMA System with MRC Receive Diversity over Nakagami-<i>m</i> Fading Channel

This paper presents the robust multiuser detection in synchronous direct sequence-code division multiple access (DS-CDMA) systems with Maximal Ratio Combiner (MRC) receive diversity over frequency-nonselective, slowly fading Nakagami-m channels in a non-Gaussian environment. Average probability of error is derived for decorrelating detector over single path Nakagami-m fading channel. A new M-estimator proposed to robustify the detector is studied and analyzed. Simulation results show that the new M-estimator outperforms linear decorrelating detector, the Huber, and the Hampel estimator based detectors.

Successive interference cancelation for a CDMA system with diversity reception in non-Gaussian noise

SUMMARY A large class of physical phenomenon observed in practical wireless systems exhibits non-Gaussian behavior. The performance of many multiuser detectors can degrade substantially in the presence of such impulsive ambient noise. In this paper, multiuser detection of space coded MIMO and code division multiple access (CDMA) signals under impulsive noise with diversity reception are investigated. We analyze and derive the probability of bit error (Pb) performance of a successive interference cancelation (SIC) system under impulsive noise and maximal ratio combining. We use Middleton's class A model for the noise distribution. Furthermore, we employ post detection SIC as the robust multiuser detection technique for combating the impulsive noise at specific noise parameters in a CDMA setting. The performance of the system under power imbalance is also shown. Novel analytical derivations for both combining techniques are presented, and simulations were performed, which confirm the theoretical results. Copyright © 2011 John Wiley & Sons, Ltd.

Robust multiuser detection using Kalman filter and windowed projection approximation subspace tracking algorithm

The authors propose some robust adaptive multiuser detection schemes for direct-sequence code-division multiple-access multipath frequency-selective fading channels. Multiple access interference (MAI) and intersymbol interference (ISI) are presented in an identical format using expanded signal subspace, which facilitates multiuser detection in a symbol-by-symbol fashion. This study contributes to the theoretical aspect of adaptive multiuser detection by proving that the optimum linear multiuser detectors that achieve maximum signal-to-interference-plus-noise ratio (SINR) must exist in the signal subspace, and the theoretic SINR upper bound is also derived. Another contribution of this study is to propose the design of multiuser detectors in an expanded signal subspace, and introduce subspace estimation and Kalman filtering algorithms for their adaptive implementation. To robustify the adaptive detectors against subspace estimation and channel estimation errors, a modified projection approximation subspace tracking (PAST) algorithm is proposed for subspace tracking. It is demonstrated by simulations that these adaptive detectors effectively suppress both MAI and ISI and converge to the optimum SINR. They are robust against subspace estimation errors and channel estimation errors compared to the conventional Wiener minimum mean square error (MMSE) detector.

Robust multi-user detection based on quantum bee colony optimisation

To resolve local convergent difficulty of combinatorial optimisation algorithm, a quantum bee colony optimisation (QBCO) that employs novel evolutionary quantum equations is proposed. The proposed QBCO algorithm applies quantum coding and quantum rotation mechanism to evolutionary process of bee colony, which is a simple and effective discrete optimisation algorithm. Then, the proposed quantum bee colony optimisation algorithm is used to solve robust multi-user detection problem of code division multiple access (CDMA) system in the presence of impulsive noise. Furthermore, by hybridising the stochastic Hopfield neural network and quantum bee colony optimisation, the quantum state and measure state of the quantum bee are co-evolutionary in design of robust multi-user detection. The new multi-user detection algorithm can search global optimal solution in faster convergence rate. Simulation results for CDMA system are provided to show that the designed robust detectors are superior to some previous detectors in bit error rate (BER), multiple access interference and near-far resistance.

Robust multiuser detection based on variable loading RLS technique

A variable loading recursive least squares (VLRLS) multiuser detection based on the generalized sidelobe canceller is presented to realize the suppression of multiple access interference in code division multiple access (CDMA) systems. In conjunction with a subweight partition approach, the VLRLS detector demonstrates the advantages of insensitivity to dynamic estimate modeling error, less computational load, and more robust to against spreading code mismatches compared to the conventional VLRLS and RLS-based detectors. Simulation results illustrate the effectiveness of the proposed detector.

A new m-estimator based robust multiuser detection in flat-fading non-gaussian channels

We have proposed a new M-estimator based structure for noncoherent demodulation of differentially phase-shift keyed (DPSK) signals transmitted simultaneously via direct sequence code division multiple access (CDMA) flat-fading channel and embedded in impulsive noise. The approach is also corroborated with simulation results to show the efficacy of the proposed detector with the proposed M-estimator in synchronous flat-fading non-Gaussian channels. The gross error sensitivity for the proposed estimator is analyzed. Further, lower bounds for the explosion and implosion breakdown points of the proposed estimator are derived.

Robust Multiuser Detection in Synchronous Chaotic Modulation Systems

In reality, many wireless channels exhibit marked departure from Gaussian noise assumption, causing significant performance loss when linear multiuser detectors, which are optimum in the case of Gaussian noise, are used for detection of code division multiple access signals. In this article, we propose a new influence function-based M-estimator and its application to the problem of robust multiuser detection of code division multiple access signals in chaotic modulation systems, in which user data are modulated by an analog chaotic series rather than periodic binary spreading sequences, against non-Gaussian background noise. The solution to this robust detection problem is not in closed form and requires an iterative procedure, which is a limitation in its practical use. However, it causes a little attendant increase in computational complexity in practical applications. Robustness analysis and simulation results show that the proposed detector offers significant performance gains over least-squares and Huber M-estimator-based detectors in chaotic modulation systems in non-Gaussian noise.

Robust multiuser detection based on least p-norm state space filtering model

Alpha stable distribution is better for modeling impulsive noises than Gaussian distribution in signal processing. This class of process has no closed form of probability density function and finite second order moments. In general, Wiener filter theory is not meaningful in SaSG environments because the expectations may be unbounded. We proposed a new adaptive recursive least p-norm Kalman filtering algorithm based on least p-norm of innovation process with infinite variances, and a new robust multiuser detection method based on least p-norm Kalman filtering. The simulation experiments show that the proposed new algorithm is more robust than the conventional Kalman filtering multiuser detection algorithm.

Improved Robust Techniques for Multiuser Detection in Non-Gaussian Channels

In many physical channels where multiuser detection techniques are to be applied, the ambient channel noise is known through experimental measurements to be decidedly non-Gaussian, due largely to impulsive phenomena. This is due to the impulsive nature of man-made electromagnetic interference and a great deal of natural noise. This paper presents a robust multiuser detector for combating multiple access interference and impulsive noise in code division multiple access (CDMA) communication systems. A new M-estimator is proposed for "robustifying" the detector. The approach is corroborated with simulation results to evaluate the performance of the proposed robust multiuser detector compared with that of the linear decorrelating detector, and the Huber and the Hampel M-estimator based detectors. Simulation results show that the proposed detector with significant performance gain outperforms the linear decorrelating detector, and the Huber and the Hampel M-estimator based detectors. This paper also presents an improved robust blind multiuser detection technique based on a subspace approach, which requires only the signature waveform and the timing of the desired user to demodulate that user's signal. Finally, we show that the robust multiuser detection technique and its blind adaptive version can be applied to both synchronous and asynchronous CDMA channels.

Robust adaptive MMSE/DFE multiuser detection in multipath fading channel with impulse noise

The direct-sequence code-division multiple-access (DS/CDMA) technique is extensively used for cellular, personal, and mobile radio communication systems. However, the conventional channel estimators cannot provide accurate channel information for multiuser detection in the presence of impulsive noise and Doppler spread, especially in the time-varying fading channel. We propose a linear-trend tracking method for estimating the impulse response of the time-varying channel via a robust Kalman filtering with a scheme that can automatically adjust the variance of the driving noise. The proposed method need not identify the parameters of the channel model and is insensitive to the speed of channel variation. Following channel estimation, a robust multiuser detection algorithm is developed via a Kalman-based decision feedback equalization (DFE). A nonlinear limitation function is incorporated to mitigate the effects of channel estimation error and impulsive noise and to prevent severe error propagation. Simulation results conclude that the performance of the DS/CDMA system is improved by using the proposed receiver.

Robust Blind Multiuser Detection for Synchronous CDMA Systems Using Worst-Case Performance Optimization

The performance of blind multiuser detection methods is known to degrade severely in the presence of even small mismatches between the actual and the presumed desired user signatures. Such mismatches may occur in practical situations due to an imperfect knowledge of the channel impulse response. We propose a new robust approach to blind multiuser detection in the presence of unknown arbitrary-type mismatches of the desired user signature. Two different formulations of a robust multiuser receiver are considered. The proposed formulations are based on the explicit modeling of uncertainties in the covariance matrix of the desired user signature and/or data covariance matrix and optimization of the worst-case performance. Simple closed-form solutions to the considered robust multiuser detection problems are derived. The proposed methods have a computational complexity comparable to that of the traditional blind multiuser detection algorithms, and, at the same time, offer an improved robustness and faster convergence rates.

Adaptive transmitter optimization for blind and group-blind multiuser detection

The linear subspace-based blind and group-blind multiuser detectors recently developed represent a robust and efficient adaptive multiuser detection technique for code-division multiple-access (CDMA) systems. In this paper, we consider adaptive transmitter optimization strategies for CDMA systems operating in fading multipath environments in which these detectors are employed. We make use of more recent results on the analytical performance of these blind and group-blind receivers in the design and analysis of the transmitter optimization techniques. In particular, we develop a maximum-eigenvector-based method of optimizing spreading codes for given channel conditions and a utility-based power control algorithm for CDMA systems with blind or group-blind multiuser detection. We also design a receiver incorporating joint optimization of spreading codes and transmitter power by combining these algorithms in an iterative configuration. We will see that the utility-based power control algorithm allows us to efficiently set performance goals through utility functions for users in heterogeneous traffic environments and that spreading code optimization allows us to achieve these goals with lower transmit power. The signal processing algorithms presented here maintain the blind (or group-blind) nature of the receiver and are distributed, i.e., all power and spreading code adjustments can be made using only locally available information.

Robust multiuser detection in frequency-selective non-Gaussian channels

This paper addresses the problem of multiuser detection in multipath fading code division multiple-access channels with non-Gaussian noise. A robust multipath decorrelator with equal-gain combining for differential coherent detection of differential phase-shift keying signals is proposed to mitigate multiple-access interference and multipath interference, and to ameliorate non-Gaussian ambient noise. The asymptotic (i.e., large processing gain) performance of the proposed multiuser detector is derived and compared with that of the linear multipath decorrelator for differential coherent detection. Computer simulations are carried out to corroborate the asymptotic results. These results show that, in highly impulsive noise and under slow fading conditions, the robust multipath decorrelator assures substantial performance improvement over the linear multipath decorrelator for a wide range of values of signal-to-noise ratio, with little attendant increase in the algorithmic complexity. Copyright © 2003 AEI.

Robust multiuser detection in frequency-selective non-Gaussian channels

Robust multiuser detection in frequency-selective non-Gaussian channels

Turbo decoding for robust multiuser detection in impulsive noise channels

A more robust version of the nonlinear M-decorrelating detector through iterative (turbo) decoding is proposed. The turbo code performance in the linear decorrelating detector is also studied. Simulation results indicate that combined nonlinear signal processing and turbo decoding can achieve highly robust performance in impulsive noise.