Adaptive linearly constrained minimum variance beamforming for multiuser cooperative relaying using the kalman filter

In this paper, we consider a wireless communication scenario with multiple source-destination pairs communicating through several cooperative amplify-and-forward relay terminals. The relays are equipped with multiple antennas that receive the source signals and transmit them to the destination nodes. We develop two iterative relay beamforming algorithms that can be applied in real-time. In both algorithms, the relay beamforming matrices are jointly designed by minimizing the received power at all the destination nodes while preserving the desired signal at each destination. The first algorithm requires the existence of a local processing center that computes the beamforming coefficients of all the relays. In the second algorithm, each relay can compute its beamforming coefficients locally with the help of some common information that is broadcasted from the other relays. This is achieved at the expense of enforcing the desired signal preservation constraints non-cooperatively. We provide two extensions of the proposed algorithms that allow the relays to control their transmission power and to modify the quality of service provided to different sources. Simulation results are presented validating the ability of the proposed algorithms to perform their beamforming tasks efficiently and to track rapid changes in the operating environment.     

多径条件下最小方差空时多用户检测的性能分析

本文研究和分析了在一般多径信道条件下，CDMA阵列接收机对于多址干扰和符号间串扰的联合抑制。文中推广了多用户检测的正则表示，利用最小最大原理实现了广义正则开式的最小方差空时多用户检测器：进一步分析并改进了空时信道的估计方法；最后定量分析了系统的干扰抑制能力。     

基于约束最小均方的噪声抑制MOE盲多用户检测

针对最小输出能量(minimum output energy,MOE)检测器的权向量由于受到噪声的影响而导致性能下降的问题,设计了一种新的MOE检测器,并且利用约束最小均方(least mean square,LMS)算法得到权向量,提出DS-CDMA系统下一种基于约束LMS的MOE盲噪声抑制多用户检测算法.该算法将权向量和噪声子空间正交,消除了权向量中的噪声分量,降低了噪声输出能量,从而使系统的性能优于常规的LMS盲多用户检测.仿真结果证明了所提算法的有效性和优越性.     

Spatio-temporal blind adaptive multiuser detection

We propose blind multiuser detection schemes with antenna arrays, which is based on signal subspace estimation. They are a multichannel extension of the decorrelating and minimum mean-square-error detectors, and therefore they share their immunity to near-far effects. The blind scheme may be seen as an extension of the results in of Wang and Poor (see IEEE Trans. Inform. Theory, vol.44, p.677-90, 1998). However, it is seen that compared with the latter results when spatial diversity is considered, the proposed spatio-temporal detectors offer, with little attendant increase in computational complexity, a better performance. A blind adaptive implementation based on a new orthogonal PAST (projection approximation subspace tracking) algorithm, which is shown to be efficient for subspace tracking, is proposed. Also, we develop a blind estimation of the spatial signature based on the orthogonality between noise and signal subspaces. It is seen that the blind adaptive multiuser detection and blind spatio-temporal signature estimation can he integrated jointly     

Probabilistic algorithms for blind adaptive multiuser detection

Two probabilistic adaptive algorithms for jointly detecting active users in a DS-CDMA system are reported. The first one, which is based on the theory of hidden Markov models (HMMs) and the Baum-Welch (1070) algorithm, is proposed within the CDMA scenario and compared with the second one, which is a previously developed Viterbi-based algorithm. Both techniques are completely blind in the sense that no knowledge of the signatures, channel state information, or training sequences is required for any user. Once convergence has been achieved, an estimate of the signature of each user convolved with its physical channel response (CR) and estimated data sequences are provided. This CR estimate can be used to switch to any decision-directed (DD) adaptation scheme. Performance of the algorithms is verified via simulations as well as on experimental data obtained in an underwater acoustics (UWA) environment. In both cases, performance is found to be highly satisfactory, showing the near-far resistance of the analyzed algorithms     

Subspace blind adaptive detection for multiuser CDMA

Direct adaptive realizations of the linear minimum mean-square error (MMSE) receiver for direct-sequence code-division multiple access possess the attractive feature of not requiring any explicit information of interference parameters such as timing, amplitudes, or spreading sequences; however, they need a training sequence for the desired user. Previously, a new blind adaptive receiver was proposed based on an anchored least mean-squared (LMS) algorithm that requires only the spreading code and symbol timing of the desired user but obviates the need for a training sequence. In this work, it is analytically demonstrated that the blind LMS algorithm always provides (nominally) faster convergence than the training driven LMS-MMSE receiver of but at the cost of increased tap-weight fluctuations or misadjustment. Second, the property that the optimal MMSE or minimum-output energy filter coefficients lies in the signal subspace is exploited to propose a new efficient blind adaptive receiver requiring fewer adaptive coefficients. Improved detector characteristics (superior convergence rates and steady-state signal-to-interference-plus-noise ratios) is indicated by analysis and supported by simulation     

A multidimensional phase-locked loop for blind multiuser detection

This paper concerns the problem of blind multiuser detection, a special case of the blind source separation problem in which the source signals have finite alphabets. Specifically, we address the problem of identifying and resolving the n/spl times/n unitary matrix ambiguity U that results from whitening the receiver observations, where n is the number of sources. We propose the multidimensional phase-locked loop (MPLL) as a generalization of a scalar decision-directed PLL to vector-valued signals. The MPLL adapts an estimate of U according to the recursion U/spl circ//sub k+1/=U/spl circ//sub k/R/sub k/, where R/sub k/ is an n-dimensional Householder-like rotation depending on only the kth receiver observation. The O(n/sup 2/) complexity of an efficient implementation of the algorithm is extremely low. Nevertheless, simulation results demonstrate good convergence properties and superior steady-state performance when compared with prior techniques. The algorithm is also able to accommodate large alphabets and shaped alphabets.     

一种新的盲自适应多用户检测算法

多址干扰引发严重的远 /近问题。本文提出一种新的代价函数 :差分平均输出能量(DMOE) ,并设计了适用于DS/CDMA系统的盲多用户检测算法。理论分析和数值模拟表明该算法的收敛性能及误码性能均优于MOE检测器     

一种基于约束最小误码率的多用户检测算法

针对多用户检测器误码率函数具有多个局部极小点的缺陷,本文提出一组新的约束条件,在约束的检测器解空间里,误码率函数具有唯一的最小点.同时,本文还提出了一种有效的阻碍共轭梯度算法来求解约束最小点.仿真结果表明,本文的提出的约束最小误码率检测器性能接近理想的线性最小误码率检测器,明显优于最小均方误差检测器.     

Single-antenna blind receiver for multiuser detection in unknowncorrelated noise

The problem of blind multiuser detection for direct-sequence code-division multiple-access systems operating over fading dispersive channels and in the presence of additive Gaussian noise with unknown temporal correlation function is considered. Such a problem has been addressed by Wang and Poor (1999) and solved by employing a receiver with two well-separated antennas, such that the noise is spatially uncorrelated. A new method, which enables blind multiuser detection in correlated noise with just one antenna (and thus can be implemented in mobile transceivers), is proposed here. The effectiveness of the new procedure is tested through computer simulations, and its performance is compared to that of the algorithms developed by Wang and Poor (1999) and Wang and Host-Madsen (1999). Numerical results demonstrate that the newly proposed method, while relying on halved hardware resources, incurs a performance loss of only a few decibels with respect to the two-antenna based procedures     

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.     

一种新的CMA盲多用户检测算法

该文提出了一种新的盲自适应多用户检测算法,这种算法的计算复杂度为O(NL),其中N为扩频因子,L为取样数据窗长度。仿真分析表明,该文提出的算法稳态性能好,收敛速度特别快,且能适应环境的变化,是一种较好的多用户检测算法。     

Asymptotic analysis of blind multiuser detection with blind channel estimation

The analytical performance of the subspace-based blind linear minimum mean-square error (MMSE) multiuser detection algorithm in general multipath multi-antenna code-division multiple-access (CDMA) systems is investigated. In blind multiuser detection, the linear MMSE detector of a given user is estimated from the received signals, based on the knowledge of only the spreading sequence of that user. Typically, the channel of that user must be estimated first, based on the orthogonality between the signal and noise subspaces. An asymptotic limit theorem for the estimate of the blind linear detector (when the received signal sample size is large) is obtained, based on which approximate expressions of the average output signal-to-inference plus noise ratios (SINRs) and bit error rates (BERs) for both binary phase-shift keying (BPSK) and quaternary phase-shift keying (QPSK) modulations are given. Corresponding results for group-blind multiuser detectors are also obtained. Examples are provided to demonstrate the excellent match between the theory developed in this paper and the simulation results.     

Space-time blind multiuser detection for multirate DS/CDMA signals

Multiuser detection for multirate direct-sequence code-division multiple access (DS/CDMA) has been an active area of research. For example, nonblind low-rate (LR) and high-rate (HR) decorrelators have been proposed and analyzed in the literature for synchronous dual-rate systems with single receive antenna. Inspired by the subspace-based space-time (ST) blind linear detectors for synchronous single-rate systems, this paper extends the existing results and proposes the subspace-based ST-LR and ST-HR blind linear detectors, i.e., blind decorrelators and blind minimum mean-squared error (mmse) detectors, for synchronous dual-rate DS/CDMA. It is shown that: 1) ST-LR blind linear detectors can support no less users than ST-HR blind linear detectors as long as the desired spatial signature is identifiable (assuming that all the other system parameters are the same) and 2) the bit-error rate performance of ST-LR blind decorrelator is not inferior to that of its HR counterpart. The above conclusions are generalized to synchronous multirate systems. The extension to asynchronous systems is also described. Finally, the two-stage ST dual-rate blind detectors, which combine the adaptive purely temporal dual-rate blind mmse detectors with the nonadaptive beamformer, are presented.     

非线性调制下MMSE盲自适应多用户接收机

主要介绍三种面向非正交多脉冲调制(NMM)系统的非相干最小均方误差(MMSE)多用户检测器,它们均采用MMSE预滤波器(per-filter),但分别满足三种不同的非相干判决准则。其中最简单的判决准则是最大(MM)准则,另外两种则需要考虑MMSE滤波后的残余多用户干扰(MAI)的二阶统计量。然后介绍一种基于随机估计方法的盲自适应算法。最后对这三种判决准则进行性能分析。     

An improved subspace tracking algorithm for blind adaptive multiuser detection

As the Projection Approximation Subspace Tracking with deflation(PASTd) algorithm is sensitive to impulsive noise, an improved subspace tracking algorithm is proposed and applied to blind adaptive multi-user detection. Simulation results show that the improved PASTd algorithm not only remains the properties of the conventional PASTd algorithm, but also has good Bit Error Rate(BER) performance in impulsive noise environment, thus it can effectively improve the system performance.     

Direct blind multiuser detection for CDMA in multipath withoutchannel estimation

We consider the blind multiuser detection problem for asynchronous DS-CDMA systems operating in a multipath environment. Using only the spreading code of the desired user, we first estimate the column vector subspace of the channel matrix by multiple linear prediction. Then, zero-forcing detectors and MMSE detectors with arbitrary delay can be obtained without explicit channel estimation. This avoids any channel estimation error, and the resulting methods are therefore more robust and more accurate. Corresponding batch algorithms and adaptive algorithms are developed. The new algorithms are extremely near-far resistant. Simulations demonstrate the effectiveness of these methods     

Block modulus precoding for blind multiuser detection of DS-CDMA signals

We propose a blind multiuser detector based on a new data precoding technique for direct-sequence code-division multiple-access signals. The modulus of all users' data is block encoded, using a sequence that is unique for each user. This precoding method, together with the analytical constant modulus algorithm for detection, enables a closed-form, one-shot detection of the desired user's signal in a multipath channel using one or more antennas. The detection process does not involve or require a channel estimation step. The proposed detector is shown to be extremely near-far resistant, and can operate properly in the presence of severe carrier frequency offset.     

基于最小二乘恒模算法及子空间方法的盲多用户检测算法

恒模算法（CMA)是一种广泛应用于阵列处理、均衡、多用户检测中的盲算法。最小二乘恒模算法(LSCMA)由于其全局收敛性及稳定性受到关注，但是它在信噪比较低时性能不是很理想。本文将最小二乘恒模算法与子空间方法相结合，提出一种基于子空间分解的恒模算法，称为LSCM_SUB算法。仿真结果表明这种算法的收敛性能比LSCMA要好，尤其是在信噪比低的时候。     

Joint spatial-frequency blind multiuser detection based on LCCMA

Multicarrier code division multiple access (MC-CDMA) has the ability to combat with frequency selective fading and antenna array can enhance the performance of system. The paper proposes a novel joint spatial-frequency blind multiuser detection for antenna array MC-CDMA based on linear constraint constant modulation algorithm (LCCMA), which has robust performance and can ensue the weight vectors to converge to that of the desired user. Simulation indicates the proposed algorithm has better bit error ratio (BER) performance than that of the traditional beamforming-based two-step algorithm.