Blind Multiuser Detection Algorithm Research Articles

Multiple access interference suppression for CDMA systems via [formula omitted]-minimization

A key problem in code-division multiple access (CDMA) system is to mitigate the multiple access interference (MAI) from other users while detecting the desired user. The performance of the conventional minimum output energy (MOE) multiuser detector for CDMA system significantly degrades in the presence of signature waveform distortions induced by multipath propagation or timing asynchronism. In this paper, a robust linear programming (ROLP) algorithm for blind multiuser detection is proposed. Different from the existing MOE-based multiuser detection techniques, the proposed ROLP minimizes the ℓ∞-norm of the output to exploit the non-Gaussianity of the communication signals. To achieve robustness against signature waveform mismatch, the proposed method constrains the magnitude response of any signature vector within a specified uncertainty set to exceed unity. The uncertainty set is modeled as a rhombus, which differs from the spherical uncertainty region widely taken in the existing robust multiuser detectors. The resulting optimization problem is reformulated into a linear programming program and hence can be solved efficiently. The proposed ROLP is computationally simpler than its robust counterparts that requires solving a second-order cone programming. Simulation results demonstrate the superiority of the ROLP over several robust detectors, which indicate that its performance approaches the optimal performance bound.

Investigation of Blind Multi-User Detection Technology

Blind multi-user detection algorithm is an effective method to overcome multi-access interference and influence of near-far effect. This paper briefly describes commonly used algorithms of blind multi-user detection technology, introduces the application of the least mean square algorithm (LMS) and compares the performance with other algorithms. Aiming at the shortcomings of the LMS algorithm, the variable step size LMS algorithm and the relatively low complexity LMK algorithm based on the change of the input signal vector are studied.

Blind Multiuser Detection in Massive MIMO Channels With Clustered Sparsity

In this letter, we propose a blind multiuser detection algorithm for massive MIMO systems equipped with a uniform planar antenna array. We model the channel in the angular domain as a sparse matrix with the non-zero coefficients forming clusters. The channel sparsity is described by a binary Markov random field (MRF). Then, we develop a turbo message passing framework by incorporating the MRF model into the bilinear generalized approximate message passing (BiGAMP) algorithm. We show that the proposed scheme considerably outperforms the schemes without exploiting the clustered sparsity of the channel.

The multi-user detection under fading channel

This paper proposes a method of blind multi-user detection algorithm based on signal sub-space estimation under the fading channels in the present of impulse noise. This algorithm adapts recursive least square (RLS) filter that can estimate the coefficients using only the signature waveform. In addition, to strengthen the ability of resisting the impulse noise, a new suppressive factor is induced, which can suppress the amplitude of the impulse, and improve the ability of convergence speed. Simulation results show that new RLS algorithm is more robust against consecutive impulse noise and have better convergence ability than conventional RLS. In addition, Compared to the least mean square (LMS) detector, the new robust RLS sub-space based method has better multi-address-inference (MAI) suppressing performance, especially, when channel degrades.

PERFORMANCE COMPARISON OF BLIND ADAPTIVE MULTIUSER DETECTION ALGORITHMS

Blind multiuser detection algorithms are used to el iminate the Multiple Access Interference (MAI) and the Near-Far effect in mobile communication systems. Four kinds of blind multiuse r detection algorithms applied to code-division multiple-access (CDMA) communication system are studied in this paper. Tho se algorithms are the Least Mean Squares (LMS), Rec ursive Least Squares (RLS), Kalman filter and subspace-based Kalman filt er algorithms. The resultant signal to interference ratio (SIR) at the output of the receivers controlled by the four kinds of multi-use r detection algorithm has been discussed in this pa per. Simulation results show that the subspace based Kalman filter algorithm outperfo rms all other three algorithms. Subspace-based Kalm an filter algorithm has faster convergence speed, more practical and the ca pability of CDMA system can be increased.

Fuzzy step size least mean square algorithm tuned linearly constrained constant modulus algorithm for multi‐carrier code division multiple access blind multiuser detector

ABSTRACTAdaptive fuzzy logic step size least mean square algorithm (FLCLMS) tuning unit is designed to adjust the step size of the linear constrained constant modulus algorithm for blind multiuser detection (MUD) in multi‐carrier code division multiple access (MC‐CDMA) systems is presented. In wireless communications system, the conventional constant modulus algorithm for blind MUD has some disadvantages such as slow convergence speed and phase rotation. To overcome these shortages, a modified constant modulus algorithm was developed for blind multiuser detector. On the basis of the deterministic behavior of the FLCLMS algorithm, it has also proposed simplification over the cost function calculation, obtaining more efficient algorithm and creating new perspective for the MUD implementation. The proposed algorithm ensures the algorithm convergence to the desired user and suppresses the multiple access interference in this cost function. Thus, the performance of the system is improved. The computational experiments show that the proposed FLCLMS not only can find optimal or closed‐to‐optimal solutions but also can obtain the low computation complexity both better and more robust results than existing algorithm reported recently in the literature. Copyright © 2013 John Wiley & Sons, Ltd.

Improved blind multiuser detection algorithm based on minimum output energy

Based on minimum output energy, an improved blind multiuser detection algorithm is proposed by the use of Hopfield neural network. Compared with traditional algorithms, the proposed algorithm does not need the circuit for constraints. The resources are greatly saved and the complexity is reduced as well. The simulation results show that the performance of the improved algorithm is similar to that of the optimal multiuser detection algorithm which is not suitable for the mobile station. Compared with the traditional gradient blind multiuser detection algorithm, the convergence speed of the improved algorithm is quickened.

Performance of constrained blind adaptive DS-CDMA UWB multiuser detector in multipath channel with IEEE 802.11a interference

Ultra wideband wireless systems are supposed to coexist with other spectrally overlapping narrowband wireless systems especially IEEE 802.11a wireless LAN. Presence of narrowband interference degrades the performance of UWB. In this paper we study bit error probability performance of the constrained blind DS-CDMA UWB multi-user detection algorithms in the presence of IEEE 802.11a OFDM narrowband interference. The constrained blind adaptive algorithm is implemented using both least mean square and recursive least square algorithm and the bit error probability performance is compared with Rake matched filter receiver. The constrained blind receiver does not require spreading code knowledge of all users other than that of the user of interest. Simulation results show that the constrained blind detector cancels IEEE 802.11a interference significantly in comparison with that of the Rake matched filter in the UWB multipath channel.

The Subspace-Based Linear Conjugate CMA in BPSK-Modulated MC-CDMA Systems

A subspace-based linear conjugate constant modulus algorithm (CMA) for blind adaptive multiuser detection in BPSK-Modulated MC-CDMA systems is proposed. First, a linear conjugate CMA algorithm is presented which jointly elaborates the received signal and its complex conjugate to utilize the information contained in the pseudo-autocorrelation of the observable, thus is capable of achieving much better performance. Second, to further improve the performance, the subspace method is applied to the linear conjugate CMA algorithm to obtain a subspace-based linear conjugate CMA algorithm, which mitigates the influence of the noise subspace. Finally, an improved projection approximation subspace tracking with deflation algorithm is proposed for adaptive signal subspace estimation to reduce the computational complexity. The proposed algorithm provides an improved robustness against the signature waveform mismatch, good tracking capability in dynamic environment and better output signal-to-interference-plus-noise-ratio and bit error rate performance. The superiority of the proposed algorithm is demonstrated through computer simulations.

A Low Complexity RLS-PASTd Algorithm for Blind Multiuser Detection in Dispersive CDMA Channels

For joint blind channel estimation and multiuser detection in direct-sequence code division multiple access (DS-CDMA) systems, a combined scheme is proposed, which couples the recursive least-squares (RLS) adaptations and the PASTd subspace tracking algorithm. A major advantage of the RLS-PASTd algorithm is that it admits an adaptive implementation with low computational complexity instead of singular value decomposition. Simulation results demonstrate the fast tracking capability and high steady-state estimation accuracy of the proposed algorithm in both the time-invariant and time-variant environments

Blind Multiuser Detection by Kurtosis Maximization for Asynchronous Multirate DS/CDMA Systems

Chi et al. proposed a fast kurtosis maximization algorithm (FKMA) for blind equalization/deconvolution of multiple-input multiple-output (MIMO) linear time-invariant systems. This algorithm has been applied to blind multiuser detection of single-rate direct-sequence/code-division multiple-access (DS/CDMA) systems and blind source separation (or independent component analysis). In this paper, the FKMA is further applied to blind multiuser detection for multirate DS/CDMA systems. The ideas are to properly formulate discrete-time MIMO signal models by converting real multirate users into single-rate virtual users, followed by the use of FKMA for extraction of virtual users' data sequences associated with the desired user, and recovery of the data sequence of the desired user from estimated virtual users' data sequences. Assuming that all the users' spreading sequences are given a priori, two multirate blind multiuser detection algorithms (with either a single receive antenna or multiple antennas), which also enjoy the merits of superexponential convergence rate and guaranteed convergence of the FKMA, are proposed in the paper, one based on a convolutional MIMO signal model and the other based on an instantaneous MIMO signal model. Some simulation results are then presented to demonstrate their effectiveness and to provide a performance comparison with some existing algorithms.

The LSCM_SUB algorithm for blind multiuser detection in multipath CDMA channels

In this article, the least square constant modulus algorithm (LSCMA) is combined with the subspace approach and a LSCM_SUB (Subspace) blind adaptive multiuser detection in multipath code division multiple access (CDMA) channels is presented. The poor performance of LSCMA in the low signal to noise ratio (SNR) is improved by the LSCM_SUB algorithm. The performance of the proposed LSCM_SUB algorithm is compared with that of LSCMA. Simulation results show that the LSCM_SUB algorithm is superior to the LSCMA, especially in the low SNR.

A generalized blind adaptive multi-user detection algorithm for multipath Rayleigh fading channel employed in a MIMO system

In this paper, a generalized blind adaptive algorithm is introduced for multi-user detection of direct sequence code division multiple access (DS-CDMA) wireless communication systems. The main property of the proposed algorithm is its ability to resolve the multipath fading channel resulting in inter symbol interference (ISI) as well as multiple access interference (MAI). Other remarkable properties are its low complexity and mitigation to the near-far problem as well as its insensitivity to asynchronous transmission. The proposed system is based on the minimization of the output energy and convergence to the minimum mean square error (MMSE) detector. It is blind in the sense that it needs no knowledge of the other users' signatures, only the intended user signature and timing are required. Furthermore, the convergence of the minimum output energy (MOE) detector to the MMSE detector is analytically proven in case of M-ary PSK. Depicted results show that the performance of the generalized system dominates those previously considered. Further improvements are obtained when multiple input multiple output (MIMO) technique is employed.

A pre-processing blind multiuser detection algorithm based on LSCM using antenna array

A pre-processing blind multiuser detection algorithms based on the least squares constant modulus (PLSCMA) using antenna array is proposed in this paper. It first uses the signals received from every antenna to correlate with the conjugation of the DoA vector of the expected user, and then applies the pre-processed signals to the LSCMA. We simulate and compare the proposed algorithm with the conventional LSCMA. Simulation results show that the proposed algorithm is superior to LSCMA.

New LSCM blind multiuser detection algorithm for antenna array CDMA system

Two blind multiuser detection algorithms for antenna array in Code Division Multiple Access (CDMA) system which apply the linearly constrained condition to the Least Squares Constant Modulus Algorithm (LSCMA) are proposed in this paper. One is the Linearly Constrained LSCMA (LC-LSCMA), the other is the Preprocessing LC-LSCMA (PLC-LSCMA). The two algorithms are compared with the conventional LSCMA. The results show that the two algorithms proposed in this paper are superior to the conventional LSCMA and the best one is PLC-LSCMA.

Blind multiuser detection of STBC signals using hybrid constant modulus and subspace methods

A blind multi-user detection algorithm for space-time block coded (STBC) signals is proposed based upon subspace methods and constant modulus algorithms for multiple antenna based receivers. The subspace method is used to determine blindly the multiuser detector required for the mitigation of multi-user interference and to coherently combine multipath and multiple receive antenna signals. It is shown that this subspace method for STBC could however, solve this problem only up to a matrix ambiguity and the structure of this ambiguity matrix looks like a channel matrix obtained for a single user STBC system with frequency non-selective channel. Hence, the remaining problem is shown to be equivalent to blind equalisation of a single user STBC in flat fading channels. A tap constrained constant modulus algorithm is proposed to solve the remaining problem. In this blind method, only the signature waveform of the user of interest is assumed to be known, and the signature waveforms of all other users in addition to the channel impulse responses of all the users are assumed to be unknown. Simulation results confirm superior performance of the proposed method over conventional non-blind matched filters.

Blind adaptive multiuser detection based on affine projection algorithm

In this letter, we introduce a novel blind multiuser detector based on the affine projection algorithm (APA) for direct-sequence code-division multiple-access (DS-CDMA) systems. Computational complexities of least mean-squares (LMS), recursive least squares (RLS), Kalman, and APA-based blind multiuser detection algorithms are compared. The proposed technique has similar convergence and tracking properties as the RLS algorithm with much reduced computational cost. Simulation results are presented to compare our APA-based algorithm with the blind LMS, RLS, and Kalman schemes.

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.

Blind Adaptive Kalman Filter-Based Multiuser Detector Over a Multipath Fading Channel

An adaptive blind multiuser detection algorithm is proposed for asynchronous direct-sequence code-division multiple-access (DS-CDMA) systems based on a modified constrained Kalman filter over a multipath fading channel. This detector is shown to outperform the present least mean squares filter in bit-error-rate and convergence rate, and it is shown to have a better tracking capability under a dynamic environment where the number of users will change frequently with time.

Modified linearly constrained CMA for blind adaptive multiuser detector in DS∕CDMA systems

A modified linearly constrained constant modulus algorithm for blind adaptive multiuser detection in DS/CDMA systems is presented. By selecting a suitable linearly constrained cost function, the performance of the proposed algorithm is improved in terms of the capability of suppressing multiple access interference. Simulation results indicate that the proposed algorithm provides a faster convergence and steady-state performance.