Selective Multiuser Detection for Cellular CDMA Systems

Multiuser detection-oriented CDMA systems have been anticipated to significantly improve system capacity in third-generation W-CDMA-based systems. However, they are greatly limited by the computational complexity of multiuser receivers. In this work, we propose a new, computationally efficient approach to multiuser detection (MUD), consisting in MUD of the subset of preselected users, and conventional detection of the rest of users, called selective multiuser detection (SMD). It allows for full exploitation of available processing power at the receiver by use of MUD and provides remedy for computational complexity of MUD techniques when the number of active users increases beyond the processing capability. We propose and examine three different criteria for selection of users to be processed by the multiuser receiver and analyze the capacity for the single-cell and the multicell CDMA cellular system. The capacity improvement with respect to the conventional CDMA detector combines the gain from MUD and reduction of other-cell interference. We apply the analysis to two SMD schemes using decorrelator and successive interference canceller (SIC) as the multiuser receiver. The results indicate that the SMD is a promising alternative for MUD-oriented CDMA systems with large numbers of active users.     

Performance of Multiuser Detection in Multirate CDMA Systems

Multiuser detectors for asynchronous multirate code-division multiple-access (CDMA) systems are considered. A multirate CDMA system model able to fit several system concepts in the same framework is presented. The performance of the multi-code (MC) system with one processing gain and the multiple processing gain (MPG) system is compared. Upper bounds for the expected value of the asymptotic multiuser efficiency of the decorrelating detector for a synchronous multirate CDMA system with three effective users are derived for a system with one and two processing gains. The numerical results show that the performance of the decorrelating detector for MC and MPG systems do not differ significantly. The bit error rates (BER) of the decorrelating, parallel interference canceler (PIC) and groupwise serial interference canceler (GSIC) with either PIC or decorrelator within the group are compared. The results show that the decorrelating and the GSIC detectors yield the best performance. For all interference cancellation schemes the BER saturates at high SNRs due to decision errors degrading the multiple-access interference (MAI) estimates.     

码分多址系统中的多用户检测

CDMA通信系统是一个自干扰受限系统，如何克服CDMA系统中的多址干扰问题已成为提高CDMA系统容量的关键。多用户检测是克服CDMA多址干扰最有潜力的关键技术之一。本文研究了CDMA移动通信系统中几种常见的多用户检测技术，分析了他们的原理，并对各种多用户检测的优缺点进行了比较。     

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。     

CDMA多用户检测技术

首先分析了CDMA移动通信系统中采用多用户检测的必要性 ,然后介绍了各种多用户检测技术的工作原理 ,对各种多用户检测技术的特点进行了分析比较 ,最后提出了目前多用户检测技术的一些最新发展方向。     

一种子空间盲自适应多用户检测技术在天线阵CDMA系统中的应用

多用户检测技术是ＤＳ－ＣＤＭＡ中的一项关键技术,而天线阵也是一种减轻多用户干扰的方法,本文将两种技术结合在一起,提出了将子空间方法应用于天线阵多用户检测技术,这种技术可适用于低速移动台在慢衰落信道下的盲检测,仿真结果表明这种算法比单纯作最佳二维Ｒａｋｅ接收要好,和有训练序列的先做ＣＭＯＥ再做最佳合并的性能差不多。     

CDMA移动通信系统中的联合功率控制与多用户检测

功率控制和多用户检测是CDMA移动通信系统中克服远近效应、抑制多址干扰(MAI)的两项关键技术。这里简要介绍了CDMA移动通信系统中功率控制与多用户检测技术,阐述了联合功率控制与多用户检测技术的基本概念,重点综述了联合功率控制与线性多用户检测技术以及联合功率控制与非线性多用户检测技术的研究进展,并对今后的研究方向进行了概括性的描述。     

DS/CDMA系统中的多用户检测技术

多用户检测技术可抑制多址干扰（ＭＡＩ）,从而提高ＣＤＭＡ系统的容量和性能。介绍了多用户检测器的分类和自适应算法、盲算法在多用户检测中的应用。     

利用空间分组的CDMA系统多用户检测技术

多用户检测技术可以增加CDMA系统的用户容量。将天线阵列和空间滤波器运用于基站多用户检测之间的信号接收,并通过某一准则将不同方向上的用户分为互相关性很小以至可以忽略的不同想似组,进而忽略不同组的用户之间的多址干扰（MAI）,在此基础上再对各组分别进行信息检测,将能大大减小多用户检测的计算量,提高信号处理速度。     

两类多用户检测技术

从技术角度比较了以美国和日本为研究重点的两类多用户检测技术,指出了它们的优缺点和当前国内外的研究状况,并给出了工程实现上的建议。     

异步编码CDMA系统中基于因子图的迭代多用户接收器

针对异步编码CDMA系统,本文提出了一种基于因子图的迭代多用户接收器,它是将用户信息比特对接收端噪声白化滤波器输出的条件后验概率分布用因子图表示,并采用和-积算法,经过有限次迭代获得用户信息比特的估计值．为降低计算复杂度,本文还提出一种简化算法．仿真结果表明,本文提出的迭代多用户接收器在经过几次迭代后的比特误码性能接近单用户系统;同时,简化算法的性能接近完全算法,但算法复杂度有明显改善．     

一种空时CDMA系统的多用户检测算法

多用户检测技术在实际应用中,难以解决的问题是在减少计算复杂度的同时又提高系统性能。本文针对空时CDMA系统设计了一种多用户检测算法,即附带噪声梯度的最速下降算法。此算法利用变步长迭代的思想实现多用户检测,避免了最小均方误差(MMSE)多用户检测庞大而复杂的求逆运算和固定步长收敛速度较慢的问题。计算机仿真结果表明,在空时CDMA系统中使用本文算法,收敛速度大大增加,同时在保持系统性能的前提下能够容纳较多的用户。     

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。     

Link and System Level Performance of Multiuser Detection CDMA Uplink

The link level performance and the cellular systemcapacity in the uplink direction of a CDMA cellularsystem utilising multiuser detection base stationreceivers is analysed by simulation. In the receiver,parallel multistage multiuser detection is employedtogether with two-antenna diversity reception and fastclosed-loop power control. A system level simulator isbuilt to utilise the link level simulation results andto show the increase in cellular capacity obtained byusing multiuser detection. The capacity is studied inurban micro and macro-cell environments utilising thechannel models developed in the European CODITproject. The modelling of the environment specific andCDMA specific features is considered in the systemsimulator. The system level simulator is calibratedwith analytical capacity calculations.     

空时CDMA多用户信号检测

本文利用最小均方误差(MMSE)和最大似然(ML)准则,推导了空时CDMA多用户检测算法,分析了空时多用户检测与单用户检测的关系,并提出一种空时CDMA多用户检测接收机结构.计算机仿真结果说明了本文提出的空时CDMA多用户检测算法,与单用户检测方法相比其误码性能有相当的改进.     

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.     

Asynchronous QR-RLS-CMOE Blind Multiuser Detection

DS/CDMA communication systems are widelyused because of their obvious advantages, such as softcapacity, soft handover, higher spectral efficiency andthe ability to mitigate the effects of multi-path fading.However, the multiple access interference (MAI) andnear-far problem in DS/CDMA limit the furtherapplications of this technique. The structure of the conventional single-userdetector (CD), which neglects the presence of MAI, issimple, but its performance is limited, and the receiversuf…     

The Complex Bootstrap Algorithm for Blind Separation of QAM Multiuser CDMA Signals

The bootstrap separator for multiuser signals is principally composed of cancelers, each one using the output of the other cancelers to facilitate control of its adaptive weight. In fact, such a structure performs as a signal separator rather than an interference canceler. Since for its separation there is no need for a reference signal (as in LMS cancelers), it is sometimes justifiably called a Blind Separator. However, for its operation the bootstrap separator requires a signal distinguisher termed discriminator. The algorithm was used in the past in applications such as dually polarized satellite communications and microwave terrestrial links. It was particularly reported for multiuser CDMA signal separating, with the signum function as discriminator. Especially for QAM signals, complex presentation is important. Therefore, we will concentrate in this report on what we call the Complex Bootstrap Algorithm. It is an extension to the previously reported bootstrap structure of [5]. We will examine its performance and emphasize the hardware saving in its implementation, and the ease of using it in simulation.     

多用户检测CDMA系统中的功率控制性能及其在系统设计中的应用

我们分析了在瑞利衰落信道下，在天线分集的相干多用户检测器的性能。由于多用户检测器是抗远／近效应的，我们将基于ＳＮＲ的功率控制引入多用户检测器以提高系统的性能。最后，我们给出了在系统设计时，基于ＳＮＲ的功率控制的参数的选取。     

异步多径条件下空时CDMA多用户检测

本文利用最小均方误差准则,推导了异步多径条件下空时CDMA多用户检测算法,分析了多用户检测与单用户检测关系,提出空时CDMA多用户检测接收机结构。基于SAGE迭代算法进行空时多用户检测,并利用CDMA信号的有限字符特性和上行信道的导频信息对SAGE算法提出改进。仿真结果说明了本文提出的空时CDMA多用户检测算法性能。