基于高阶累积量的盲自适应解相关检测器

基于高阶累积量,本文提出一种新的无约束优化准则,并且证明该优化准则有全局最小值,其及值点满足解相关条件,得到一种新的盲自适应解相关检测器。仿真结果表明,该检测器具有较强的干扰抑制能力。     

Noncoherent detection in asynchronous multiuser channels

The noncoherent demodulation of multiple differentially phase-shift-keyed signals transmitted simultaneously over an asynchronous code-division multiple-access (CDMA) channel with white Gaussian background noise is considered. A class of bilinear detectors is defined with the objective of obtaining the optimal bilinear detector. The optimality criterion considered is near-far resistance that denotes worst-case asymptotic efficiency over the signal energies and phases which are unknown at the receiver. The optimal bilinear detector is therefore obtained by solving a minimax optimization problem. In the finite packet length case, this detector is shown to be a time-varying multiinput multioutput linear decorrelating filter followed by differential decision logic. In the limit as packet lengths go to infinity, the time-varying decorrelating detector is replaced by a time-invariant multiinput multioutput decorrelating filter. Several properties of the optimally near-far resistant detector are established     

Adaptive path selective fuzzy decorrelating detector under impulsive noise for multipath fading CDMA systems

This letter proposes a novel adaptive path selective fuzzy decorrelating (APSFD) detector for direct-sequence code- division multiple-access (DS-CDMA), systems with time-varying multipath fading channels under impulsive noise. The proposed detector combines adaptive path selective decorrelating (APSD) detector with a fuzzy median filter which is based on fuzzy rank ordering of samples to eliminate the effect of impulsive noise. Simulation results clearly show that the proposed detector eliminates the effect of impulsive noise and improves the performance of APSD detector under high impulsive noise.     

RBF network assisted adaptive path selective decorrelating detector under impulsive noise for multipath fading CDMA systems

This paper proposes a novel radial basis function assisted adaptive path selective decorrelating detector for direct sequence code division multiple access systems with time-varying multipath fading channels under impulsive noise. The proposed detector combines adaptive path selective decorrelating detector (APSDD) with a radial basis function (RBF) network to eliminate the effect of impulsive noise. Simulation results clearly show that the proposed detector eliminates the effect of impulsive noise and improves the performance of APSDD under high impulsive noise.     

基于峰度的盲自适应多用户检测

基于四阶累积量,分析一种新的优化准则,即定向最小峰度(OMK:Oriented Minimum Kur-tosis)准则。理论分析表明:该准则函数具有全局最小值且极值点满足解相关条件。由此,通过求解该优化问题,能得到一种新的盲多用户接收方案。然后,利用最速下降法,给出盲多用户检测的自适应算法。仿真结果进一步验证了本文的结论。     

A New Multiuser Detector for Synchronous DS/CDMA System

1IntroductionInaCode-DivisionMultiple-Access(CDMA)system,severalindependentusersaccesssimulboeouslyacommonchannelbymodulatingpreassignedsignatUrewaveforms.Inthemobileradiochannels,MultipleAccessinterference(MAI)arises.Therefore,muchattelltionhasbeend...     

Extended-window decorrelating detector for asynchronous CDMAchannels and its performance analysis

We propose a new decorrelating detector for the asynchronous code-division multiple-access channels, called the extended-window decorrelating detector (EW-DD). The EW-DD helps to avoid the noncausality problem of the filter-type decorrelating detector and achieve a simplified detection by converting the asynchronous system into the synchronous one. It also helps to enhance the bit-error rate (BER) performances by utilizing one whole period of information of all users and by eliminating the multiple-access interference from the past data through feedback. Nevertheless, the computational complexity is kept lower than that of other existing decorrelating detectors. We carry out BER analysis of the EW-DD and demonstrate performance improvements of the EW-DD over other decorrelating detectors through computer simulations     

A low complexity multiuser detector for synchronous CDMA system

In a code-division multiple-access (CDMA) system, multiuser detection (MUD) can exploit the information of signals from other interfering users to increase the system capacity. However, the optimum MUD for CDMA systems requires the solution of an NP-hard combinatorial optimization problem. It is well known that the computational complexity of the optimum multiuser detector is exponential with the number of active users in the system. In this paper, we apply a hybrid algorithm to develop a suboptimal MUD strategy. The result of symmetric successive overrelaxation (SSOR) preconditioned conjugate-gradient method is first used to initialize the reduced-complexity recursive (RCR) multiuser detector. Then, RCR algorithm is applied to detect the received data bit by optimizing an objective function in relation with the linear system of decorrelating detector. Simulation results for the synchronous case show that the performance of our proposed SSOR-RCR multiuser detector is promising and outperform the decorrelator and linear minimum mean squared error multiuser detector with lower computational complexity.     

Fast optimal and suboptimal any-time algorithms for CDMA multiuser detection based on branch and bound

A fast optimal algorithm based on the branch-and-bound (BBD) method is proposed for the joint detection of binary symbols of K users in a synchronous code-division multiple-access channel with Gaussian noise. Relationships between the proposed algorithms (depth-first BBD and fast BBD) and both the decorrelating decision-feedback (DF) detector and sphere-decoding algorithm are clearly drawn. It turns out that decorrelating DF detector corresponds to a "one-pass" depth-first BBD; sphere decoding is, in fact, a type of depth-first BBD, but one that can be improved considerably via tight upper bounds and user ordering, as in the fast BBD. A fast "any-time" suboptimal algorithm is also available by simply picking the "current-best" solution in the BBD method. Theoretical results are given on the computational complexity and the performance of the "current-best" suboptimal solution.     

Adaptive implementation of polynomial expansion detector formulti-user detection in DS-CDMA systems

The polynomial expansion (PE) multi-user detector was proposed to eliminate the computational complexity of matrix inversion involved in the decorrelating detector and the MMSE detector. Computation of the polynomial coefficients in a PE detector is, however, a complex task. A fast converging adaptive algorithm based on the Davidon-Fletcher-Powell (DFP) method is proposed for computing polynomial weights for a PE detector     

Analysis of DS-CDMA system supporting heterogeneous traffic with decorrelating detector

Single-cell and multiple-cell direct-sequence code-division multiple-access (DS-CDMA) systems supporting heterogeneous traffic are investigated when decorrelating detector is used at receiver. Theoretical analyses and numerical examples are presented to study the effect of imperfect power control on the system performance of the reverse link. As to the forward link, the system performance is analyzed and the power allocation problem at base stations is formulated as a constrained optimization problem. Two algorithms, namely, the optimal algorithm and the unit transmission power allocation (UTXPA) algorithm, are proposed to solve this optimization problem. Computer simulations are presented to compare the performance of the proposed algorithms.     

一种自适应分布式多用户检测算法

本文针对移动CDMA加性白高斯噪声和衰落信道 ,提出了一种自适应分布式多用户检测算法 .它由空间分集和解相关检测复合组成 .解相关检测器的性能近似最佳多用户检测器 ,且不依赖于其它用户的信号能量及衰落特性 .基于随机梯度技术的盲自适应分集合并方案由最佳似然比检验准则构成 .对其性能做了理论分析和数值估计 ,并与传统的选择法、等增益法及最大比值法做了比较 .所提出的方法易于实时实现 ,可以较大地提高接收机性能和系统容量增益     

Performance of a Multiuser Detector with Multicarrier Transmission for a DS/CDMA System

In this paper, a new multiuser detector combining decorrelating detector and multicarrier transmission scheme is proposed and analyzed in a frequency selective Rayleigh fading channel. The bit error probability and asymptotic multiuser efficiency are derived as performance measures. From numerical results, it is shown that the proposed detector achieves better BER performance and lower computational complexity compared to a conventional decorrelating detector. It is also shown that the proposed detector is robust to partial narrowband interference, and alleviates near-far problem effectively. The results in this paper can be applied to design of a wideband CDMA system.     

Blind adaptive decorrelating detector for DS-CDMA systems:auxiliary-vector detector

A blind adaptive decorrelating detector is proposed which consists of two vectors: one is the pre-assigned spreading code of the desired user and the other is orthogonal to it. The orthogonal vector is adjusted adaptively to minimise the multiple access interference (MAI). This blind adaptive detector requires no more knowledge than does the conventional single-user receiver. Simulation results show that the obtained performance is close to that of the decorrelator     

Analysis of an adaptive decorrelating detector for synchronous CDMAchannels

Multiuser detection allows for the efficient use of bandwidth in code-division multiple-access (CDMA) channels through mitigation of near-far effects and multiple-access noise limitations. The decorrelating detector, developed by Lupas and Verdu (1989), is a linear multiuser detector that is asymptotically optimal in terms of near-far resistance when certain communication parameters are completely known to the detector. In this paper, a simple adaptive decorrelating detector is developed by placing constraints on the set of spreading codes to be used by the active users. This adaptive detector has two modules: it first decorrelates the existing users, and then it determines the spreading code of a new user entering the network with or without the use of a training sequence. Maximum likelihood detection is proposed for determining the new user's spreading code. The performance of this algorithm is studied by investigating the probability of making an error in determining the new user's spreading code as a function of the number of samples used to make the determination, the number of users transmitting, and the signal to noise ratio of the new user with respect to the ambient Gaussian noise     

A blind adaptive decorrelating detector for CDMA systems

The decorrelating detector is known to eliminate multiaccess interference when the signature sequences of the users are linearly independent, at the cost of enhancing the Gaussian receiver noise. We present a blind adaptive decorrelating detector which is based on the observation of readily available statistics. The algorithm recursively updates the filter coefficients of a desired user by using the output of the current filter. Due to the randomness of the information bits transmitted and the ambient Gaussian channel noise, the filter coefficients evolve stochastically. We prove the convergence of the filter coefficients to a decorrelating detector in the mean squared error (MSE) sense. We develop lower and upper bounds on the MSE of the receiver filter from the convergence point and show that with a fixed step size sequence, the MSE can be made arbitrarily small by choosing a small enough step size. With a time-varying step size sequence, the MSE converges to zero implying an exact convergence. The proposed algorithm is distributed, in the sense that no information about the interfering users such as their signature sequences or power levels is needed. The algorithm requires the knowledge of only two parameters for the construction of the receiver filter of a desired user: the desired user's signature sequence and the variance of the additive white Gaussian (AWG) receiver noise. This detector, for an asynchronous code division multiple access (CDMA) channel, converges to the one-shot decorrelating detector     

An adaptive multiuser receiver for CDMA systems

A new real-time, digital adaptive multiuser receiver structure is proposed for the uplink in a mobile communications system employing code division multiple access (CDMA). The receiver efficiently implements the decorrelating detector of Lupas and Verdu (1989) and can be adapted to incorporate decision feedback to further improve the detector performance. While the basic receiver design is presented for synchronous CDMA over AWGN channels, experimental evaluation of the receiver for the asynchronous case verifies its robustness for cases when the relative user delays are small compared to the symbol duration as in microcellular scenarios. An efficient decorrelating RAKE combiner for frequency-selective multipath channels is also proposed and analyzed. Performance evaluation of the detector via computer simulation scenarios is conducted in support of analytical results to substantiate its potential for real-time operation     

Decision-feedback blind adaptive multiuser detector for synchronousCDMA system

We develop a blind adaptive multiuser detector for synchronous code-division multiple access (CDMA) with a noise-whitening filter. The triangular structure of the noise-whitened model ensures complete resolution of detection ambiguities. To further improve the symbol error probability performance, we introduce decision feedback in our detector similar to the decorrelating derision-feedback detector (DDFD), thus forming the decision-feedback blind adaptive multiuser detector (DFBD). Simulations indicate that the performance of the DFBD is very close to that of the DDFD in additive white Gaussian noise (AWGN) channels. In Rician fading channels, the DFBD can track the slowly varying channels well and has a symbol error probability performance approaching that of the DDFD, which requires the knowledge of users' energies. The blind adaptive and decision-feedback blind adaptive multiuser detectors proposed here do not, however, require that knowledge     

Asymptotic analysis of the MMSE multiuser detector fornonorthogonal multipulse modulation

We develop the minimum mean-squared-error (MMSE) multiuser detector for nonorthogonal multipulse modulation over the noncoherent additive white Gaussian noise channel. We analyze the asymptotic performance of the detector and show that, unlike the case of linear modulation, the MMSE detector does not generally approach the generalized maximum-likelihood (GML) detection rule as the noise power vanishes. It does, however, approach a detector which nulls out the multiaccess interference. This detector is termed the multipulse decorrelating detector due to its similarity to the linear decorrelating detector. The probability of error for this detector is derived and used to find the asymptotic multiuser efficiencies of both the multipulse decorrelating detector and the MMSE detector. It is shown that for noncoherent binary signaling, in which the multipulse modulation is two-dimensional, the multipulse decorrelating detector is superior to the GML detector asymptotically. This result does not generalize to larger dimensionality signal sets     

一种简化的解相关检测器及其性能分析

基于矩阵求逆的一阶近似提出了一种简化的解相关检测器,当用户间的相关系数较小时,这种检测器可以相当准确地逼近解相关检测器,文中分析了这种检测器的误码率性能。数值结果表明该检测器的性能远优于传统的多用户检测器,具有较好的抗远近性能,与解相关检测器相比,它的复杂度大大降低,使其有可能用于实际的 Ｃ Ｄ Ｍ Ａ 通信系统中。