Blind Adaptive Multiuser Detection Research Articles

Two approaches to multiuser detection over fading channels

In this paper, two different receiver structures to multiuser detection that are appropriate for the code-division multiple-access systems with antenna arrays in fading channels are investigated and compared. We analyze and compare the performance of the two different multiuser detection structures for uplink or downlink channels. The number of elements of receiving antenna array may be limited in the downlink channel due to the small size of receivers. We assume a synchronous system, but it can be easily extended to an asynchronous system. The first approach is based on the distributed decorrelator where the signal decorrelation is performed by each receiving antenna element independently and decorrelated outputs are combined according to the maximum ratio. The second approach is the central decorrelator where the signal decorrelation is performed once collectively on the outputs from all elements of receiving antenna array. Both decorrelators provide the same performance in the additive white Gaussian noise channels. The distributed decorrelator provides the better performance in flat fading channels. We employ the decorrelator to demonstrate our results. The results discussed in the present paper can be extended to other configurations such as the blind adaptive space-time multiuser detection.

A robust blind adaptive multiuser detection based on maximum correntropy criterion in satellite CDMA systems

AbstractSatellite code‐division multiple‐access systems use multiuser detection (MUD) methods to deal with multiple‐access interferences. Among the different kinds of MUD, blind adaptive MUD regarding the system as a state‐space model is widely used for its tracking capability and independence of training sequences. The innovation process noise of the state‐space model is usually assumed to follow the Gaussian distribution, and the minimum mean‐square error criterion is the default criterion for most conventional blind adaptive MUD methods. In the past few years, the impulsive noise of the innovation process has attracted attention, declaring that a Gaussian distribution is not suitable for simulating the impulsive noise. Thus, more criteria are proposed to enhance the robustness of the blind adaptive MUD. This paper improves the robustness of MUD methods under impulsive noise by bringing forward a new cost function based on the maximum correntropy criterion and deduces the expression of the blind adaptive detector. Simulation results show that the proposed method achieves superior performance in terms of bit error rate, convergence, and robustness compared with other methods.

Kalman Filter-Based Chip Differential Blind Adaptive Multiuser Detection for Variably Mobile Asynchronous Underwater Multiuser Communications

To mitigate the inter-symbol interference (ISI), multiple access interference (MAI), and the effect of different Doppler shifts within a data package incurred in variably mobile asynchronous underwater multiuser communications (VMAUMC), a Kalman filter-based chip differential blind adaptive multiuser detection (D-KF-BAMUD) algorithm is proposed in this paper. The Kalman filter-based blind adaptive multiuser detection (KF-BAMUD) algorithm has been adopted to combat ISI and MAI in the scenario of static users, and underwater and under-ice multiuser communication experiments have been carried out to verify the effectiveness of the KF-BAMUD algorithm. To tackle the more challenging VMAUMC, a differential modulation and demodulation technique operating at the chip level is proposed to reduce the impact of Doppler shift residues after the Doppler compensation with an average Doppler frequency offset within each data package. The technique is combined with the KF-BAMUD algorithm, leading to the D-KF-BAMUD algorithm, which is able to effectively handle ISI, MAI, and the effect of Doppler shift residues simultaneously in VMAUMC. This paper reports our experiments on VMAUMC carried out in Songhua River in April 2016 (seven users, data rate 7.87 bit/s, up to 2 m/s variably relative velocity in each data package, and horizontal distance 200-m shallow-water channel between transducer and hydrophone), and the encouraging experimental results demonstrate the effectiveness of the proposed system and the D-KF-BAMUD algorithm.

Blind adaptive multi-user detection for under-ice acoustic communications with mobile interfering users

The Least Mean Squares Blind Adaptive Multi-user Detection algorithm, the Recursive Least Squares Blind Adaptive Multi-user Detection algorithm, and the Kalman Filter Blind Adaptive Multi-user Detection algorithm, for under-ice communication networks with rising and diving interfering users, are investigated in this paper. Under-ice random asynchronous multi-user communication experiments with rising and diving interfering users were carried out (7 users, 15.7 bit/s per user, 1.2 km under-ice acoustic channels in the Bohai Sea). Good experimental results verified the feasibility and effectiveness of the proposed algorithms in mitigating inter-symbol interference and multiple access interference.

A Kalman Filter-Based Blind Adaptive Multi-User Detection Algorithm for Underwater Acoustic Networks

An underwater acoustic Kalman filter-based blind adaptive multi-user detection algorithm, suitable for underwater acoustic communication networks, is proposed in this paper. The algorithm can be employed to effectively improve the system capacity of multi-user communication in underwater acoustic sensor networks, reduce transmitting power and costs on power control, extend the multi-user communication distance, weaken or eliminate intersymbol interference, multiple access interference and near-far effect, thus effectively utilizing limited underwater frequency band resource. First, the dynamic model of underwater acoustic multi-user communication system and the optimal filter equation of the proposed algorithm are found. Second, computation complexity is analyzed, and convergence analysis is carried out in terms of excess mean output energy. Finally, pool, river, sea, and under-ice asynchronous communication experiments have been carried out for both the scalar and the vector hydrophones. Good experimental results verify the effectiveness of the proposed algorithm.

The Kalman Filtering Blind Adaptive Multi-user Detector Based on Tracking Algorithm of Signal Subspace

Multi-user detection is an effective method to reduce multiple access interference in code division multiple access (CDMA) systems. This paper discusses a signal subspace based blind adaptive multiuser detector and a Kalman filtering blind adaptive multiuser detector. Combining them together, a new Kalman filtering blind adaptive multiuser detector based on a tracking algorithm of the signal subspace is proposed. Analysis and simulation show that the proposed blind multiuser detector achieves better suppression of multiple access interference and has a higher convergence rate.

Analysys of Blind adaptive multiuser detection receivers

In this paper, blind adaptive multiuser detection with Mean Output Energy (MOE) are designed in receivers for synchronous MC-DS-CDMA systems in Rayleigh fading channels. Pre and post detection in multiuser detectors are implemented in the system to detect their effects in the outputs. On the basic of the delayed received signals, we proposed Affine Projection Algorithm-link multiuser detector (APA) and its performance is evaluated with the existing multiuser blind detectors (Normalized blind LMS and Kalman Filter). Compared to existing multiuser detectors APA-link detector outperformed the BER performance and provided a tradeoff between performance and computation cost. The analysis if further extended by implementing, decorrelating multiuser detector based receivers in SC-DS-CDMA and MC-DS-CDMA to eliminate the MAI caused by other users.

LMS Blind Adaptive Multiuser Detection for Underwater Acoustic Communication with MMSE and MOE Criteria

In order to solve detection of multi-user detection in underwater acoustic communication networks, blind adaptive multiuser detection method using LMS algorithm was proposed to solve the MAI problem of multi-user detection in underwater acoustic communication channel when users increase. Two type simulations were executed, including synchronous and asynchronous multi-user simulation analysis, to verify the validity of LMS multi-user detection algorithm and inspection machine. The verification of the effectiveness of the MMSE and MOE algorithm for LMS multi-user detection algorithm was done by simulation.

A Low Complexity and Effective Rapid Channel Tracking Scheme for UWB Multiple-Access Systems

In this paper, the applicability of the subspace-based blind adaptive algorithm in multiple access ultra-wideband systems is investigated. However, in the multiuser transmission environment, multiple access interference becomes a serious issue and results in the degradation of system performance. In order to overcome this shortcoming, we propose a novel and low complexity decision mechanism, termed the decision timing instant (DTI). A major advantage of the DTI algorithm is that it admits an adaptive implementation with low computational complexity instead of singular value decomposition. In the present paper, we exploit the joint blind multiuser detection in UWB systems, a combined scheme is proposed, which couples the minimum-mean-square-error and the DTI subspace tracking algorithm under UWB time-variant channels. Simulation results show that DTI is able to fast and precisely trace the variation of the channel environment and to improve the performance of the blind adaptive multiuser detection with a subspace approach over time-varying channels.

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.

Blind adaptive receiver based on RLS-CMA for TH-UWB system

A novel receiver is proposed in this paper that uses the blind adaptive multi-user detection (MUD) technique to deal with the presence of multiple-access interference (MAI) and inter-symbol interference (ISI) in terms of high speed time-hopping ultra-wideband (TH-UWB) system. The receiver firstly adopts constrained recursive least squares constant modulus algorithm (RLS-CMA) to conduct adaptive decorrelation for eliminating MAI and ISI, and then uses projection approximation subspace tracking with deflation (PASTd) algorithm to launch channel estimation, do maximal ratio combining (MRC) and improve signal to interference plus noise ratio (SINR). The simulation results show that the proposed receiver can go to convergence rapidly under all four IEEE's UWB channel models, the bit error ratio (BER) performance is better than that of the traditional receiver and rake receiver.

A novel subspace tracking algorithm and its application to blind multiuser detection in cellular CDMA systems

In this paper, we propose and develop a new algorithm for the principle subspace tracking by orthonormalizing the eigenvectors using an approximation of Gram-Schmidt procedure. We carry out a novel mathematical derivation to show that when this approximated version of Gram-Schmidt procedure is added to a modified form of projection approximation subspace tracking deflation (PASTd) algorithm, the eigenvectors can be orthonormalized within a linear computational complexity. While the PASTd algorithm tries to extracts orthonormalized eigenvectors, the new scheme orthonormalizes the eigenvectors after their extraction, yielding much more tacking efficiency. We apply the new tracking scheme for blind adaptive multiuser detection for non-stationary cellular CDMA environment and use extensive simulation results to demonstrate the performance improvement of the proposed scheme.

Fixed-point blind adaptive multiuser detection algorithm for IR UWB systems in multipath channel

Using the hypothesis that data transmitted by different users are statistically independent of each other, this paper proposes a fixed-point blind adaptive multiuser detection algorithm for Time-Hopping (TH) Impulse Radio (IR) Ultra Wide Band (UWB) systems in multipath channel, which is based on Independent Component Analysis (ICA) idea. The proposed algorithm employs maximizing negentropy criterion to separate the data packets of different users. Then the user characteristic sequences are utilized to identify the data packet order of the desired user. This algorithm only needs the desired user’s characteristic sequence instead of channel information, power information and time-hoping code of any user. Due to using hypothesis of statistical independence among users, the proposed algorithm has the outstanding Bit Error Rate (BER) performance and the excellent ability of near-far resistance. Simulation results demonstrate that this algorithm has the performance close to that of Maximum-Likelihood (ML) algorithm and is a suboptimum blind adaptive multiuser detection algorithm of excellent near-far resistance and low complexity.

Blind adaptive affine projection algorithm-based multiuser detector over a multipath fading channel

In this paper, we propose a novel blind adaptive multiuser detector based on the affine projection algorithm (APA) for asynchronous direct-sequence code-division multiple-access (DS-CDMA) systems over a multipath fading channel. Computational complexities of least mean-squares (LMS), Kalman filter and APA-based blind adaptive multiuser detector are compared. The proposed detector is shown to outperform the LMS detector and has similar convergence and detection properties as the Kalman filtering with much reduced computation cost.

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.

Steady-state performance analysis of HOS-based blind adaptive multiuser detection

The blind adaptive multiuser detections based on higher-order statistics (HOS) can obtain higher steady-state decorrelating performance than the conventional linear algorithm under the high SNR condition. However, the closed-form analysis for this steady-state performance is scarce due to the complication of analyzing the nonlinear updates of the adaptive algorithm. An analysis approach based on ordinary differential equation (ODE) method is proposed to get the closed-form excess mean-square error (EMSE) expression of the HOS-based multiuser detections. The simulation and the comparison verify the results of the analysis.

Blind Multiuser Detection in Frequency Domain for MC-CDMA Systems Using Particle Swarm Optimization

In digital communication systems, the constant modulus algorithm (CMA) for blind multiuser detector has some disadvantage such as slow convergence speed and weight phase rotation. In this paper, we put forward a novel receiver, which combines CMA blind adaptive multiuser detection and particle swarm optimization (PSO) technique in frequency domain for multi-carrier direct sequence code division multiple access (MC DS-CDMA) systems. By this approach we present an adaptive multistage structure based on PSO technique. In this structure, the weights are obtained by PSO technique between the received signal and its estimate through a CMA. The resulting weights contain reliability information for the hard decisions made in the previous stage. The simulation results show that BER performance of the PSO-based CMA blind multiuser detector is superior to that of steepest decreasing constant modulus algorithm (SDCMA), linearly constrained constant modulus algorithm (LCCMA), CMA based multiuser detection and is worthy due to its significant detection performance to achieve desirable improvement in convergence speed and tractability.

Blind Adaptive Multiuser Detection for the MC-CDMA Systems Using Orthogonalized Subspace Tracking

In this paper, we study the performance of subspace-based multiuser detection techniques for multicarrier code-division multiple access (MC-CDMA) systems. We propose an improvement in the PASTd algorithm by cascading it with the classical Gram-Schmidt procedure to orthonormalize the eigenvectors after their sequential extraction. The tracking of signal subspace using this algorithm, which we call OPASTd, has a faster convergence as the eigenvectors are orthonormalized at each discrete time sample. This improved PASTd algorithm is then used to implement the subspace blind adaptive multiuser detection for MC-CDMA. We also show that, for multiuser detection, the complexity of the proposed scheme is lower than that of many other orthogonalization schemes found in the literature. Extensive simulation results are presented and discussed to demonstrate the performance of the proposed scheme.

A Blind Adaptive MMSE Multiuser Detector over Multipath CDMA Channels and its Analysis

Based on the refinement-only fast subspace tracking (RO-FST) algorithm to adaptively estimate the signal sub-space, a blind adaptive SVD-based minimum-mean-square-error (MMSE) multiuser detector is proposed in this paper for asynchronous direct-sequence code-division-multiple-access (DS-CDMA) systems over multipath fading channels. Numerical results show that the proposed detector gives low computational complexity and good performance in terms of signal-to-interference-plus-noise ratio (SINR) and bit-error-rate (BER). In addition, we apply the perturbation analysis of the proposed adaptive detector to derive the closed-form expressions for the mean-square error (MSE) and SINR. The analytical results are shown to match well with the simulation results.

Multiuser channel estimation using robust recursive filters for CDMA system

In this paper, we present a novel blind adaptive multiuser detector structure and three robust recursive filters to improve the performance in CDMA environments: Sigma point kalman filter (SPKF), particle filter (PF), and Gaussian mixture sigma point particle filter (GMSPPF). Our proposed robust recursive filters have superior performance over a conventional extended Kalman filter (EKF). The proposed multiuser detector algorithms initially use Kalman prediction form to estimated channel parameters, and unknown data symbol be predicted. Second, based on this predicted data symbol, the robust recursive filters (e.g., GMSPPF) is a refined estimation of joint multipaths and time delays. With these estimated multipaths and time delays, data symbol detection is carried out (Kalman correction form). Computer simulations show that the proposed algorithms outperform the conventional blind multiuser detector with the EKF. Also we can see it provides a more viable means for tracking time-varying amplitudes and time delays in CDMA communication systems, compared to that of the EKF for near-far ratio of 20 dB. For this reason, it is believed that the proposed channel estimators can replace well-known filter such as the EKF.