DS/CDMA多用户检测盲自适应梯度算法的改进

本文在直接序列/码分多址(DS/CDMA)系统盲检测自适应梯度算法(BAG)的基础上,提出了一种多用户检测盲自适应梯度算法的改进算法(IBAG).BAG算法包括自适应梯度算法(TBAG)和时变自适应梯度算法(TIBAG),TBAG算法的跟踪特性较好,但起始收敛特性不好;TIBAG算法的收敛特性较好,但跟踪特性较差,几乎不具备跟踪能力.本改进算法结合了这两种自适应梯度算法的优点,在不增加算法复杂度的前提下,使其收敛性和跟踪特性较BAG算法有所提高.     

频率选择性衰落信道下长扩频序列CDMA 系统的盲波束成形

本文提出一种适用于频率选择性衰落信道下长扩频序列CDMA系统，基于DMMSE准则的盲波束成形方案。该方案反频率选择性衰落信道分解成若干个非频率选择性衰落子信道，不需要训练符号开销，回避跟踪衰落信道参数，以所需用户的扩频序列作为永久性训练序列。仿真结果验证了其抵抗远近效应、抑制多址干扰的能力。     

一种频率选择性衰落信道下的盲自适应去相关Rake接收机

多用户检测是DS－CDMA系统中的一项关键技术,而Rake接收是解决多径效应的一种有效方法,本文将基于Kalman滤波的多用户检测器与Rake接收相结合,提出了一种频率选择性衰落信道下的盲自适应去相关Rake接收机,研究结果表明,这种接收机具有较强的抑制多址干扰和克服“远－近”效应能力,并且能快速收敛。     

适用于Rayleigh衰落信道的一种新型MMSE接收机

智能天线中一般的MMSE接收机缺乏有效跟踪Rayleigh衰落信道变化的机制。在分析了MMSE接收机在Rayleigh信道中的特点之后，提出了一种新型的MMSE接收机。计算机仿真结果表明，此接收机性能较好，适用于Rayleigh衰落信道。     

瑞利衰落电离层信道的自适应盲均衡

研究通过具有加性高斯白噪声的瑞利慢衰落电离层信道的恒模盲均衡技术。著名的恒模算法(CMA)是一种重要的盲信道均衡方法。但是，普通恒模算法存在收敛速度慢和相位旋转等不足。采用一种修正恒模算法(MCMA)，该算法使修正的误差函数最小并且自适应学习率由接收序列即时调整。两种算法用8—PSK信号进行了盲均衡比较，模拟结果显示修正恒模算法比普通恒模算法的收敛速度快，符号间干扰(ISI)小，另外该算法均衡器输出具有既无相位旋转也无延迟等优点。     

DS-CDMA系统下行盲多用户接收机

本文研究多径频率选择性衰落信道下，DS－CDMA系统下行盲多用户检测技术，提出了一种新的基于恒模算法的检测方法。利用下行信号的特征构造约束条件并采用投影梯度法求解优化问题，本文方法克服了常规恒模算法无法保证收敛到期望用户的缺点。仿真结果验证了本文方法具有良好的检测性能，可以在克服信道衰落的同时抑制多址干扰。     

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。     

CDMA系统中的一种新型MMSE接收机

智能天线中一般的MMSE接收机缺乏有效跟踪Rayleigh 衰落信道变化的机制.在分析了MMSE接收机在Rayleigh信道中的特点之后,提出一种新型的 CDMA系统MMSE接收机.计算机仿真结果表明,此接收机性能较好,适用于Rayleigh衰落信道 .     

CDMA移动通信系统中的信道盲与半盲估计

介绍了应用于异步CDMA移动通信系统中的信道盲估计技术的原理,信道盲估计主要分为子空间分解、相关拟合和最大似然三种方法。分析了各自的特点,然后讨论了在部分发送数据已知条件下的半盲信道估计技术。     

高速衰落多径信道中时间/尺度分集接收机的分析

在高速衰落多径信道中,传统的Ｒａｋｅ接收机的性能会大大降低。本文基于自子波变换和时间、尺度分辨率的概念,从理论和仿真实验两方面对信道建模和时间／尺度Ｒａｋｅ接收机进行了分析,并与传统的Ｒａｋｅ接收机进行了比较,结果表明时间／尺度联合分集能有效地克服高速衰落多径信道的影响。     

Differentially Coherent Blind Adaptive Receiver for Rayleigh Fading CDMA Channels

Interest in code division multiple access (CDMA) has increased dramaticallyin boththe industry and academia. This is due to the potential increase in usercapacity andinterference, multipath fading, and jam-resistant capabilities. Differentapproaches ofmultiuser detection schemes have shown improvement over the conventionalreceiver.However, multiuser detectors require system parameters and adaptive multiuserreceivers require training sequences. These parameters are difficult toobtain inmultipath fading channels with a degradation in performance. A blind adaptivemultiuser receiver for flat fading and frequency-selective fading environments isstudied in this paper. This receiver alleviates the problem of multiuser detectors and adaptivemultiuser receivers by using a blind adaptive equalization method. The structure of the receiveris similar to that of the adaptive MMSE receiver which consists of an adaptive equalizer and an adaptivemechanism that uses a standard least mean-squared (LMS) algorithm, but uses a matched filterto generate a reference signal. The receiver is shown to be effective in different fadingchannels with perfect power control and a near-far effect. Furthermore, the simulationresults show that the blind MMSE receiver outperforms the conventional receiver and theRAKE receiver.     

DS/CDMA系统中的一种自适应单用户接收机

本文提出了一种在异步多径DS/CDMA系统中基于独立分量分析算法的单用户接收机,这种接收机仅需要已知期望用户的定时和特征波形,计算量小、结构简单.它不但能用于在基站进行多用户信号的上行接收,而且适合于用在移动台进行下行接收.其性能较之匹配滤波器和盲MMSE多用户检测器有很大提高.     

Blind Channel Estimation for Multi-Rate Multicarrier DS/CDMA Communications

Multi-rate multicarrier DS/CDMA is a potentially attractive multiple access method for future wireless communications networks that must support multimedia, and thus multi-rate, traffic. Several receiver structures exist for single-rate multicarrier systems, but little has been reported on multi-rate multicarrier systems. Considering that high-performance detection such as coherent demodulation needs the explicit knowledge of the channel, based on the finite-length chip waveform truncation, this paper proposes a subspace-based scheme for timing and channel estimation in multi-rate multicarrier DS/CDMA systems, which is applicable to both multicode and variable spreading factor systems. The performance of the proposed scheme for these two multi-rate systems is validated via numerical simulations. The effects of the finite-length chip waveform truncation on the performance of the proposed scheme is also analyzed theoretically.     

一种新的用于DS/CDMA系统的多级盲空时多用户接收机

本文讨论的接收机是用于DS/CDMA系统的多级自适应阵列和串行干扰消除联合接收机(AA-SIC),介绍的接收机同时使用了空域和时域处理以及多用户联合检测技术.一般的联合接收机要使用RAKE单元,本文所讨论的接收机没有使用RAKE单元,而利用智能天线的自适应算法能起到分集接收的功能,不仅能抑制多址干扰信号,而且构成简便,计算时间较短,有利于实际应用.     

MMSE RAKE Reception for Asynchronous DS/CDMA Overlay Systems and Frequency-Selective Fading Channels

In this work the authors introduce and analyze a detection scheme for simultaneous suppression ofmultiaccess and digital narrowband interference (NBI) for an asynchronousDS/CDMA system operatingover a frequency-selective fading channel. The proposed detector may possibly consider a processing interval greater than the bit-interval, andamounts to a RAKE structure, wherein each branch is designed under an MMSE optimization strategy, followedby a propercombining rule. It is shown that narrowband interference rejection entails ingeneral a time-varyingdetection structure. As to the performance assessment, we give closed-form formulas for the systemBit Error Rate (BER),Near-Far Resistance and Signal-to-Interference Ratio (SIR).Numerical results show that the proposed receiver proves effective in suppressing interference, and that itlargely outperforms conventional multiuser detectors which do not account forthe presence of theNBI, at the price of little complexity increase.Finally, we provide a blind adaptive implementation of the proposedreceiver, based on the exponentially weighted Recursive-Least-Squares (RLS)algorithm, andrequiring knowledge of the relevant parameters of the desired user only, andof the NBI signaling time.     

Adaptive Detection and Channel Estimation for Dual-Rate DS/CDMA Networks in Frequency-Selective Fading

In a Dual-Rate DS/CDMA system, a primary, ``high rate' network coexists witha secondary one with a slower rate. Demultiplexinghigh-rate users typically entails, at the receiverend, a time-varying processing ifVariable Spreading Length (VSL), Variable Chip Rate (VCR), or Variable ChipRate with Frequency Shift (VCRFS) modulation formats are used, and Rake-Typedemodulation schemes if the chip rate exceeds the channel coherence bandwidth.The realization of fully adaptive receivers thus requires the joint estimationof(a) the interference to be suppressed, whether from other users ofthe high-ratenetwork or from the secondary network, and (b) the channel tap weights.The solutionthat we consider here assumes that,for each user, a pilot signal is transmitted alongwith the information-bearing signal, whether in a time-multiplexed orin a parallel-channel format. We consider both the uplink and the downlink channel and, based on a Minimum-Mean-Square-Error(MMSE) optimality criterion, we have come up with a fully adaptive system,capable on the one handof tracking, through a cyclic Recursive-Least-Squares typealgorithm, the periodically time-varying variations of theinterference subspace andon the other of updating the channel tap weights estimates.A thorough performance assessment is presented, and the convergence dynamicsof the system are derived through computer simulations in order to assessthe impact of the prior uncertainty with regard to the other-users signaturesand thechannel tap weights realizations.     

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…     

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。     

O<Superscript>3</Superscript>BPSK-based Linear Decorrelating Detector for Asynchronous DS/CDMA Systems over Frequency-Selective Rayleigh Fading Channels

In this paper, a convenient signaling scheme, called orthogonal on–off BPSK (O³BPSK), along with a simple one-shot linear decorrelating detector (LDD) and a whitening Rake bank, is proposed for near–far resistant detection in asynchronous DS/CDMA systems. Based on the maximum multi-path spreading delay, a minimum duration of “off” is suggested, during which the temporally adjacent bits (TABs) that contain multi-user interference (MUI) and inter-symbol interference (ISI) from different users at the receiver are decoupled. The O³BPSK signaling scheme is combined with the whitening Rake receiver to preserve multi-path diversity gain in multi-path fading CDMA channels. The scheme offers low complexity, no detection delay, near–far resistance, and compensation for fading channels.