分集接收混合遗传算法多用户检测器在异步CDMA移动通信中的应用研究

本文研究了将混合遗传法应用于码分多址扩频通信的多用户检测中，从而消除多址接入干扰的方法。本文先给出了在异步瑞利衰落信道下解调扩频信号的分集接收混合遗传算法多用户检测器的原理框图，然后分析了用混合遗传算法进行多用户检测的理论依据和实际性能。仿真结果表明无论是抗多址干扰还是抑制远近效应，分集接收混合遗传算法多用户检测器都明显优于传统接收机，其性能接近分集接收最佳多用户检测器。     

基于中继放大转发的多天线基站下行传输性能分析

研究基站具有多根天线、中继与用户具有单天线的中继放大转发多用户系统,利用正交空时分组编码和机会主义调度策略同时获得空间分集和多用户分集.针对自适应增益和固定增益转发策略,首先导出独立不同分布瑞利衰落下系统中断概率和误码率的闭合表达式;随后根据高信噪比下系统的渐近性能确定系统的分集阶数,分析空间分集和多用户分集对系统性能的联合影响,并与单跳多天线基站下行传输系统进行性能比较;最后利用计算机仿真验证理论分析结果的正确性.     

基于分布式中继选择的自适应协作传输方案

协作分集通过使网络用户共享彼此天线以形成虚拟多天线阵列,可以显著提高网络容量,然而针对网络拓扑的动态变化与无线传输的时变特性,仅靠协作分集并不能十分有效地解决这些问题,必须结合考虑相应的自适应传输策略.本文提出动态网络环境中协作中继的最佳选择准则,在此基础上给出最佳协作中继的分布式选择协议.根据协作中继与源节点间的无线信道质量,进一步提出一种自适应协作传输方案,以有效抵抗多用户网络环境中的无线衰落.此外,对自适应协作传输方案的误码性能,在瑞利衰落信道下进行相应的理论分析,得到了系统误比特率的解析表达式,据此给出数值仿真实验以进行性能比较.结果表明:相对于传统协作分集而言,本文提出的自适应协作传输方案获得了进一步的性能增益,误比特率显著下降.     

Rayleigh衰落信道中的CDMA多用户分集接收性能

本文针对频率选择性Ｒａｙｌｅｉｇｈ衰落信道，设计了一种ＣＤＭＡ多用户检测器分集结构，通过该结构，高斯信道多用户检测算法可以有效地应用到Ｒａｙｌｅｉｇｈ衰落信道中，仿真结果表明，分集合并实现的多用户中以显著改善衰落信道的误码性能，其处理多址干扰能力并不因分集而受到影响，另外，本文还对不同的合并以及不同的检测地作了性能上的比较。     

异步CDMA移动通信系统中采用分集接收的多用户检测器

在CDMA移动通信系统中,多址接入干扰可以通过多用户检测技术来消除,而分集接收可以减小信道衰落的影响。本文给出了一类应用解相关检测、天线分集、RAKE多径分集技术的接收机,并对这一类接收机的性能做了分析。结果表明,在上行链路中,应用多用户检测和分集接收能够极大地提高接收机的性能。     

相关衰落信道Turbo乘积编码MDPSK的分集接收

由于无线衰落信道中差分检测Turbo乘积编码调制具有良好的性能,文中研究了相关平坦Rayleigh衰落信道中差分检测Turbo乘积编码MDPSK信号的等增益分集,这种等增益分集接收无需任何信道状态信息.研究结果表明,等增益合并可以改善快衰落信道中TPC-MDPSK的错误平底效应,等增益分集合并的Turbo乘积编码的MDPSK信号在相关系数为0.5的平坦Rayleigh衰落信道中的性能和独立衰落信道中的系统性能相差仅1 dB.     

DS/CDMA系统决策反馈多用户检测算法之实验研究

多用户检测技术(MUD)是第三代移动通信系统IMT-2000中的一项关键技术.本文对非线性多用户检测器中盲自适应决策反馈检测器(DFBD)进行了性能分析和计算机仿真.通过与盲自适应多用户检测器(DB)及解相关决策反馈多用户检测器(DDFD)的比较,证实了盲自适应决策反馈检测器能够较好的实现多用户检测的功能.     

空间相关莱斯衰落信道下基于部分信道信息的多用户预编码与调度算法

在空间相关的莱斯衰落信道模型下,针对多用户MIMO(Multiple-Input Multiple-Output)系统潜在的多用户分集增益和空间分集增益,该文提出了一种基于部分信道信息的多用户预编码与调度算法。结合部分瞬时信道信息和统计信息,利用约束最大似然估计对各用户信道矢量进行估计,然后利用估计的各用户信道调度多个用户进行预编码。仿真结果表明,该方案以较少的反馈开销,获得了较大的性能增益。     

异步CDMA移动通信系统采用分集接收的多用户检测器

在ＣＤＭＡ移动通信系统中，多址接入干扰可以通过多用户检测技术来消除，而分集接收可以减小信道衰落的影响，本文给出了一类应用解相关检测，天线分集，ＲＡＫＥ多径分集技术的接收机，并对这一类接收机的性能做了分析，结果表明，在上行链路中，应用多用户检测和分集接收能够极大提高接收机的性能。     

平坦瑞利衰落信道中多用户检测器的性能分析

在采用传统信号检测方式的CDMA系统中,多址干扰限制了系统的容量和性能.本文分析了在精确估计信道的情况下平坦瑞利衰落信道中的判决反馈和线性解相关两种多用户检测器的性能,主要分析了二者的误码率性能和抗远近效应的能力,并首次分析了衰落信道中的渐近多用户效率(AME).结果表明,判决反馈多用户检测器的渐近多用户效率优于线性解相关检测器.     

一种新的抗远近效应的盲DS-CDMA接收机

本文研究多径频率选择性衰落信道下直接序列扩频码分多址(DS-CDMA)信号的处理问题,提出了一种新型的盲接收机.该接收机不需预知多址干扰用户的扩频码,不需预知信道参数,只需已知期望用户的扩频码和粗略的定时,就可以完成用户的盲检测.同时,该接收机通过降维自适应去相关滤波和基于判决指导的自适应多径合并,来获得低成本和良好的抗衰落、抗远近效应性能.仿真结果验证了本文提出的接收机的优良性能.     

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     

A Soft-Input Soft-Output Decorrelating Block Decision-Feedback Multiuser Detector for Turbo-Coded DS-CDMA Systems

Previously, a decorrelating decision-feedback multiuser detector for direct-sequence code-division multiple-access (DS-CDMA) systems normally produces only hard-decision outputs of users' data. In turbo-coded DS-CDMA systems, such a multiuser detector does not match well with the soft-input soft-output nature of a turbo-decoding algorithm, thereby resulting in some extent of performance loss. In this paper, a soft-input soft-output decorrelating block decision-feedback multiuser detector is proposed to perform joint multiuser detection and turbo decoding in an iterative manner. This multiuser detector partitions the received users' data into a number of blocks appropriately and then detects the users' data on a block-by-block basis, where the soft-decision outputs are generated based on the maximum a posteriori criterion and the decision outputs of a stronger block (with a higher energy) are fed back for use in making decisions of those weaker ones. Computer simulation results show that the proposed iterative multiuser detector with turbo decoding significantly improves the bit error rate performance of a DS-CDMA receiver.     

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.     

一种新的适用于多径信道的基于LMK准则的盲自适应多用户检测及其收敛性分析

基于最小平均峰度(Least MeanKurtosis,LMK)准则],该文提出了一种适用于同步直扩码分多址(DS/CDMA)系统多径慢衰落信道中的线性盲自适应多用户检测算法。这种算法基于高阶统计量(High Order Statistics,HOS)特性,算法复杂度相对较低。文中分析了算法在多径信道中无噪声情况下的收敛特性,指出在这种情况下,算法具有全局最小点,此时算法满足解相关条件。仿真结果表明,文中给出的检测器具有较强的多址干扰抑制性能。     

Multichannel joint detection of multicarrier 16-QAM DS/CDMA system for high-speed data transmission

We propose a multichannel joint detector which eliminates other user, multipath, and intercarrier interference through a decorrelating process in a multicarrier 16-QAM direct-sequence code-division multiple-access system. The performance of the proposed detector under a frequency-selective fading channel is analytically derived and compared to that of a conventional single-user detector. The symbol error ratio curve of the proposed detector does not show the error floor that is seen in the conventional detector, and the resultant performance is close to that of a multicarrier 16-QAM system without any interference.     

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     

Neural network techniques for adaptive multiuser demodulation

Adaptive methods for performing multiuser demodulation in a direct-sequence spread-spectrum multiple-access (DS/SSMA) communication environment are investigated. In this scenario, the noise is characterized as being the sum of the interfering users' signals and additive Gaussian noise. The optimal receiver for DS/SSMA systems has a complexity that is exponential in the number of users. This prohibitive complexity has spawned the area of research on suboptimal receivers with moderate complexity. Adaptive algorithms for detection allow for reception when the communication environment is either unknown or changing. Motivated by previous work with radial basis functions (RBF's) for performing equalization, RBF networks that operate with knowledge of only a subset of the system parameters are studied. Although this form of detection has been previously studied (group detection) when the system parameters are known, in this work, neural network techniques are employed to adaptively determine unknown system parameters. This approach is further bolstered by the fact that the optimal detector in the synchronous case can be implemented by a RBF network when all of the system parameters are known. The RBF network's performance (with estimated parameters) is compared with the optimal synchronous detector, the decorrelating detector and the single layer perceptron detector. Clustering techniques and adaptive least mean squares methods are investigated to determine the unknown system parameters. This work shows that the adaptive radial basis function network attains near optimal performance and is robust in realistic communication environments     

一种基于ML准则的适用于频率选择性多径衰落的多用户检测算法

本文采用ML准则得出了适于频率选择性衰落的线性解相关算法。仿真表明本方法性能优于Zvonar提出的先解相关再最大比值合并的算法;且该方法由于采用等价扩频序列实现,硬件耗费也较少。