CDMA系统中一种新的基于MMSE多用户检测的自适应功率控制算法

功率控制技术是CDMA通信系统中克服“远一近效应”，降低多址干扰、增大系统容量的一项关键技术。第三代移动通信系统对功率控制提出了新的研究课题。在本文提出CDMA系统中一种新的白适应功率控制和MMSE多用户检测的联合优化的算法，仿真结果表明，这种新的联合优化算法对提高系统容量，改善系统性能有很大的作用。     

CDMA系统中联合功率控制、波束赋形与多用户检测

应用功率控制、波束赋形和多用户检测可以有效地消除和减少CDMA系统中的干扰。本文结合波束赋形和多用户检测的特性，提出一种应用波束赋形增益和多用户相关矩阵的解相关算法。基于算法的复杂性，提出一种区分聚集用户进行多用户检测的的算法。由于波束赋形能够消减主瓣波束之外的多用户干扰，对聚集移动台采用解相关检测达到减少运算量和消除多用户干扰的目的。对算法进行了仿真分析，证明了本算法的优越性。     

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

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 (P_b) 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.     

多速率CDMA系统自适应接收机

随着移动通信的发展，多速率数据通信业务越来越多。第三代移动通信系统能够支持可变服务质量的不同数据速率业务。因此，多速率接收机的研究也越来越引起重视。多速率系统中，当干扰信号具有不同速率参数时，不同用户的周期平稳性不同，单速率自适应FIR接收机的性能会严重下降。提出了一种适合于多速率多址干扰下的自适应滤波器组接收机，仿真结果表明，自适应滤波器组接收机能够更有效地消除多种模式的多址干扰，比单速率接收机具有更好的性能。     

The LSCM_SUB algorithm for blind multiuser detection in multipath CDMA channels

1 Introduction Multiuser detection (MUD) is applied mainly in CDMA to cancel the multiaccess interference. The single-user matched filter or RAKE receiver treats interference from other users as noise, but MUD takes advantage of other user’s interference…     

多径CDMA信道下的一种改进的盲空时多用户检测

该文在多径CDMA信道下基于Rosen梯度投影实现的最小均方盲空时多用户检测方法的基础上提出了一种改进的方法,该方法与原有的方法相比,运算量有所降低、对系统的要求降低,但通过仿真结果比较表明,该方法的检测性能与原有的方法大致相当,因而更加具有竞争力。     

Asynchronous block-based minimum mean square error (B-MMSE) CDMA multi-user detection

This paper introduces a novel asynchronous CDMA multi-user detector, the block-based MMSE (B-MMSE) multi-user detector, in which the data stream is segmented into blocks by inserting zero bits and detection takes place block-by-block without compromising the MMSE detection efficiency. The BER performance of the B-MMSE detector is studied and the results are compared with those of the decorrelating detector. It is shown that the B-MMSE detector offers promising detection efficiency at a much lower implementation complexity, which is linear in the product of number of users and block size, than that of the traditional MMSE detector. © 1998 John Wiley & Sons, Ltd.     

Simplified Iterative MMSE Multiuser Detector Using Polynomial-Expansion Approximation

We propose to simplify the inverse matrix computation of the iterative MMSE multiuser detector by using a low-complexity polynomial-expansion matrix approximation. This approximation is an application of the polynomial-expansion multiuser detector. The number of stages is set to the number of users to obtain a linear complexity. Simulations under AWGN and asynchronous multipath channels show that the approximation performs as well as the exact inverse implementation for iterative MMSE multiuser detector.     

基于NLMS的CDMA盲自适应多用户检测算法研究

多用户检测是抑制DS-CDMA系统多址干扰最有效的技术之一。由于所需的先验知识仪有期望用户的地址码,盲多用户检测技术的研究尤受重视。最小输出能量(MOE)准则被广泛用于盲线性多用户检测。目前已提出的该类检测器多采用LMS或RLS算法。本文则研究基于NLMS算法的盲自适应检测技术,并进一步提出盲自适应变步长NLMS检测器和参数可变的盲自适应变步长NLMS检测器。它们具备很好的收敛速度和跟踪能力,以及较高的输出信干比,同时计算复杂度仅为O(3N)或O(4N),非常适合硬件实现。     

自适应部分干扰抵消多用户接收机

在DS/CDMA系统中,采用多用户检测技术可以有效地克服多址干扰(MAI,MultipleaccessInterference)及远近效应。本文提出了一种自适应部分干扰抵消(APPIC,AdaptivePartialParallelInterferencecancellation)算法,根据匹配滤波器输出的判决统计对多址干扰进行选通抵消,以提高系统性能。同时本文给出了自适应部分干扰抵消接收机的非相干实现方案,并给出了仿真结果。     

Two Schemes of Blind MMSE Multiuser Receiver for Space-Time Coded CDMA Systems

1　IntroductionIthasbeenshownthatthecapacityofwirelesscommunicationsystemscanbeincreaseddramatical lybyemployingmultipletransmittingandreceivingantennas.Space timecodinghasbeenpaidmoreat tentionrecentlybecauseitisaneffectivewaytoex ploitspatialandtemporaldiversity[1～2 ] .Despitealossincodingadvantage,space timeblockcodingcanofferthemaximumdiversitygainbasedononlythelinearprocessingatthereceiver[3～ 4] andhasbeenproposedtobeusedin 3Gsystems.InterferencesuppressionismorechallenginginCDMAsyste…     

Adaptive Interference Suppression for the Downlink of a Direct Sequence CDMA System with Long Spreading Sequences

A simple approach for adaptive interference suppression for the downlink (base-to-mobile link) of a direct sequence (DS) based cellular communication system is presented. The base station transmits the sum of the signals destined for the different mobiles, typically attempting to avoid intra-cell interference by employing orthogonal spreading sequences for different mobiles. However, the signal reaching any given mobile passes through a dispersive channel, thus destroying the orthogonality. In this paper, we propose an adaptive linear equalizer at the mobile that reduces interference by approximately restoring orthogonality. The adaptive equalizer uses the pilot's spreading sequence (which observes the same channel as the spreading sequence for the desired mobile) as training. Simulation results for the linear Minimum Mean Squared Error (MMSE) equalizer are presented, demonstrating substantial performance gains over the RAKE receiver. Long spreading sequences (which vary from symbol to symbol) are employed, so that the equalizer adapts not to the time-varying spreading sequences, but to the slowly varying downlink channel. Since the inter-cell interference from any other base station also has the structure of many superposed signals passing through a single channel, the adaptive equalizer can also suppress inter-cell interference, with the tradeoff between suppression of intra- and inter-cell interference and noise enhancement depending on their impact on the Mean Squared Error (MSE).     

Fast Converging Adaptive MMSE Multiuser Detector for DS-CDMA System

A fast converging adaptive minimum-mean-squared-error (MMSE) multiuser detector is proposed for direct-sequence code-division multiple-access (DS-CDMA) systems with severe near-far problem where the convergence rate of adaptive MMSE detectors for distinct users can be very different. It is shown that by successively cancelling the interference signals of strong power users, the convergence rate of the proposed detectors for weak power users can be significantly increased, which helps to reduce the length of training sequence for tracking. It is also shown that the order of cancellation and several important parameters required for interference cancellation can be determined from the convergence behavior of the proposed detector. Numerical results are presented to show that the proposed detector offers improved performance in various DS-CDMA environments.Zhiwei Mao received the B.Sc. degrees from Beijing University of Posts and Telecommunications (BUPT), Beijing, China in 1996 and 1999, respectively. Since 2000, she had been a Research Assistant and graduate student in the Department of Electrical and Coumputer Engineering, University of Victoria, Victoria, BC, Canada. She received the Ph.D. degree in electrical engineering in 2003. Currently, she is an Assistant Professor at Lakehead University, Thunder Bay, Ontario, Canada.Her research interests include wireless communications, multiuser detection, digital communications and digital singal processing.Vijay K. Bhargava received the B.Sc., M.Sc., and Ph.D. degree from Queens University, Kingston, ON, Canada in 1970, 1972 and 1974 respectively.Currently, he is a Professor and Head of the Department of Electrical and Computer Engineering at the University of British Columbia, Vancouver, Canada. Previously he was with the Univeristy of Victoria (1984–2003) and with Concordia University in Montréal (1976–1984). He is a co-author of the book Digital Communications by Satellite (New York: Wiley, 1981), co-editor of Reed-Solomon Codes and Their Applications (New York: IEEE, 1994) and co-editor of Communications, Information and Network Security (Boston: Kluwer, 2002). His research interest are in wireless communications.Dr. Bhargava is a Fellow of the B.C. Advanced Systems Institute, Engineering Institute of Canada (EIC), the IEEE, the Canadian Academy of Engineering and the Royal Society of Canada. He is a recipient of the IEEE Centennial Medal (1984), IEEE Canadas McNaughton Gold Medal (1995), the IEEE Haraden Pratt Award (1999), the IEEE Third Millennium Medal (2000), IEEE Graduate Teaching Award (2002), and the Eadie Medal of the Royal Society of Canada (2004).Dr. Bhargava is very active in the IEEE and was nominated by the IEEE Board of Director for the Office of IEEE President-Elect. Currently he serves on the Board of Communications Society. He is an Editor for the IEEE Transactions on Wireless Communications. He is a Past President of the IEEE Information Theory Society.     

Sequential detection CDMA multi‐user receiver

This paper proposes a sequential detection technique for a multi‐user receiver that is constructed over a CDMA system. In this system, the transmitter transmits a symbol made by spreading the spectrum with an enveloped sequence protected by guard sequences, and a receiver de‐modulates the core‐sequence part of the received symbol with either a de‐correlating detector or an MMSE detector. The advantage is that performance is improved without reducing the number of the active users. This sequential detection system estimates the best user signal from all of the soft outputs, which are obtained by solving a de‐correlating system of equations. Once detected, the best user component is removed from the received symbol. The resultant symbol composed of the remaining user signals is then sequentially detected by repeating the method stated above. A computer simulation of this system reveals a remarkable improvement in the bit‐error rate performance compared to conventional systems. Copyright © 2005 John Wiley & Sons, Ltd.     

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.     

多径CDMA信道下基于指数加权最小二乘盲空时多用户检测

本文首先在码片匹配滤波的基础上为多径CDMA信道下的接收机提出四种数据选择方案，分析了各种数据方案对多址干扰与码间干扰的影响；接着提出了基于Rosen梯度投影实现的指数加权最小二乘盲空时多用户检测方法并分析了四种数据选择方案对其运算复杂度的影响；最后通过仿真实验结果表明：本文所提出盲空时多用户检测方法在运算量、收敛速度以及接收性能具有一定的优势。     

Three novel simple beamforming algorithms for CDMA communication systems

To apply a beamforming algorithm with a linear array of N antennas in real wireless communication systems, two main issues should be addressed: Algorithm complexity and number of antennas. In this paper, we propose three simple beamforming algorithms for direct sequence code division multiple access systems. We first propose a new framework to obtain the updating equation for the weight vector using PCA. Then, using this framework, four different objective functions are used as examples to illustrate how to obtain new adaptive algorithms. We demonstrate that these objective functions lead to three novel blind algorithms, with two of them resulting in the same algorithm. Moreover, they have considerably low complexities, requiring only 2N–1 complex additions and either 2N+1 or 2N complex multiplications for a single run. We evaluate the performances of these algorithms in estimating the angle‐of‐arrival of the desired signal and in producing the array beam pattern, and in alleviating the BER in Rayleigh fading and AWGN channels. In summary, these new beamforming algorithms obtained based on the proposed framework operate as blind algorithms, have low computational complexities, and offer desirable performances even if N is restricted.Copyright © 2012 John Wiley & Sons, Ltd.     

A new hybrid heuristic multiuser detector for DS‐CDMA communication systems

In this work, we present a new multiuser detection (MUD) structure which results from incorporating the tabu search (TS) heuristic algorithm with the local search (LS) heuristic algorithm. The new proposed structure brings much improvement when compared to both the conventional (matched filter) detector and the decorrelating detector. Moreover, the new TS‐LS‐detector proposed here approximates well the performance of the optimal MUD detector but with a very low computational complexity. Copyright © 2008 John Wiley & Sons, Ltd.     

Multiuser detection and diversity reception for asynchronous CDMA mobile communication

In CDMA mobile communication systems, multiple access interference can be canceled by multiuser detection technique. The Degradation by channel fading can be reduced by diversity reception. This paper investigates a family of multiuser receivers that combined decor-relating detection, antenna diversity and RAKE multipath diversity. The performance of the multiuser receivers is analyzed. The results demonstrate a significant increase in the performance of the receivers by using multiuser detection and diversity reception.     

A multipath interference cancellation technique for WCDMA downlink receivers

In this paper, we present a simple interference cancellation technique for the downlink of wideband code‐division multiple‐access (WCDMA) systems in multipath environment. With the same knowledge required by a RAKE receiver, the present method acts as an equalizer and cancels the interfering multipath signals from the received signal to retrieve the orthogonality property of the received signal. The present receiver has a simple structure and it has significant performance gain against the RAKE receiver. In addition, the noise enhancement is negligible when there is a line of sight path or the channel power delay profile has an exponential decaying form. Copyright © 2006 John Wiley & Sons, Ltd.