初始判决指导的DS／CDMA最大似然检测算法

本文首先给出了多径异步多用户ＤＳ／ＣＤＭＡ系统的一种数学模型，得出了恒参信道下最大似然检测（ＭＬＳＥ）算法的一种新的表示形式，然后作者具体分析了以ＲＡＫＥ接收机作为衰落信道的匹配滤波器时，最大似然检测器的算法设计问题，分析指出，在多径环境下ＭＬＳＥ算法的复杂度和计算量与多径时延的分布有关，如果有用户时延扩散在一个信息码元之内，算法复杂度和恒参信道下相同，而其实现可以用状态中变的Ｖｉｔｅｒｂｉ算法来     

带判决反馈的盲最大似然序列估计

本文提出了一种新型的带有判决反馈的减小状态最大似然序列估计ＲＳＳＤＦＰＳＰ,新算法带有两个信道估值器并且可以工作在盲环境下．使用最大似然序列估计（ＭＬＳＥ）来处理信道冲激响应的前导干扰及主径,反馈滤波器处理后尾干扰,并且用ＰｅｒＳｕｒｖｉｖｉｎｇＰｒｏｃｅｓｉｎｇ（ＰＳＰ）算法来得到ＭＬＳＥ部分的信道冲激响应,信道估值器２得到后尾干扰．计算机模拟表明,这种ＲＳＳＤＦＰＳＰ方案在减小ＭＬＳＥ的计算复杂度的同时能最大限度地得到ＭＬＳＥ的性能,是ＭＬＳＥ在计算复杂度与性能之间的较好折中．     

带判决反映的盲最大似然序列估计

本文提出了一种新型的带有判决反映的减小状态最大似然序列估计ＲＳＳＤＦ－ＰＳＰ,新算法带有两个信道估值器并且可以工作在盲环境下。使用最大似解序列估计（ＭＬＳＥ）来处理信道冲激响应的前导干扰及主径,反馈滤波器处理后尾干扰,并且用Ｐｅｒ－Ｓｕｒｖｉｖｉｎｇ Ｐｒｏｃｅｓｓｉｎｇ（ＰＳＰ）算法来得到ＭＬＳＥ部分的信道冲激响应,信道估值器２得到后尾干扰。计算机模拟表明,这种ＲＳＳＤＦ－ＰＳＰ方案在减小ＭＬＳ     

用TMS320C50实现的Viterbi译码器

用ＴＭＳ３２０Ｃ５０实现的Ｖｉｔｅｒｂｉ译码器差错控制技术是个人通信中的一大技术难点，要求信息传输误码率小于１０－５。因此，对信息序列进行卷积编码，并用最大似然Ｖｉｔｅｒｂｉ算法对接收序列进行译码成为首选的差错控制方案。工业标准的前向纠错技术（ＦＥＣ...     

码分多址数字移动通信的抗多径衰落技术

移动信道的主要特征是由于移和多径传播的多径落现象，本文首先概述了码分多址（ＣＤＭＡ）数字移动信道的数学模型，并在此基础上讨论了ＤＳ－ＦＳＨ扩频多系统在瑞利衰落信道中的多径分集接收技术的性能，推导了基于最大合并（ＭＲＣ）等增益组合（ＥＧＣ）和选择最大（ＳＭ）多径分集接收算法下，扩展系统的平均差错概率，理论分析和数值模拟表明，扩频分集技术可以明显地提高ＣＤＭＡ系统的抗衰落能力，并且指出ＭＲＣ优于ＥＧＣ     

DS－SFH扩频多址系统在瑞利衰落信道中多径分集的性能研究

本文讨论了混合ＤＳ－ＳＦＨ扩频多址ＳＳＭＡ通信系统在瑞利衰落信道中多径分集接收的性能。基于多径干扰、多址干扰和信道噪声之和为一个高斯随机变量的分析，推导了在等增益组合（ＥＧＣ）和选择最大（ＳＭ）多径分集接收算法下，扩频系统的平均差错概率。理论分析和数值模拟指出：扩频多径分集接收可以明显地改善ＤＳ－ＳＦＨＳＳＭＡ系统的性能，在提高系统性能方面，等增益组合算法优于选择最大分集算法。     

多用户异步DS/CDMA系统延迟截断解相关算法

与最大似然检测算法相比,解相关算法具有线性运算复杂度和不需要估计信道特征的优点。传统的逆矩阵滤波器在移动环境下不易实现,而滑动窗口算法对系统的定量有较严格的要求。基于信息码元之间的相关性随着时间间隔的加大而逐渐减小这个事实,本文提出了多用户异步ＤＳ／ＣＤＭＡ系统一种新的解相关算法－－延迟截断解相关算法,要判决当前时刻的信息码元,只需在延迟德行一定数量的码元之后截断,对截断后的码元按照传统的方法判决     

数字HDTV地面广播传输方法 第七讲 格状编码调制的维特比译码算法

格状编码调制（ＴＣＭ）可以在相同的频带利用率下，使信号得到２．５５～７．３７ｄＢ的编码增益，在数字通信中得到了广泛的应用。ＴＣＭ的维特比（Ｖｉｔｅｒｂｉ）译码算法是一种最大似然译码方法，它可以充分体现ＴＣＭ的优点。本文讨论了维特比译码算法的原理，并以４状态卷积码和ＨＤＴＶ地面广播中使用的ＴＣＭ－３２ＱＡＭ为例，介绍了硬判决维特比译码和软判决维特比译码算法的译码过程。     

数字流水Viterbi译码器的VLSI设计

本文介绍了高速数字流水Ｖｉｔｅｒｂｉ译码器的ＶＬＳＩ设计。在符号４值系统的基础上，给出Ｖｉｔｅｒｂｉ算法的新的功能分解公式，并介绍了用于译码器实现的两个重要的快速运算部件ＡＤＤ和ＭＡＸ的原理及其现场可编程（序）门阵列（ＦＰＧＡ）实现。文中详细讨论了译码器的ＶＬＳＩ结构、设计和性能分析。本文给出的Ｖｉｔｅｒｂｉ译码器可塑性强，并具有高度的并行性和很高的数据吞吐率。     

第七讲 格状编码调制的维特比译码算法

格状编码调制（ＴＣＭ）可以在相同的频带利用率下，使信号得到２．５５～７．３７ｄＢ的编码增益，在数字通信中得到了广泛的应用，ＴＣＭ的维特比（Ｖｉｔｅｒｂｉ）译码算法是一种最大似然译码方法，它可以充分体现了ＴＣＭ的优点，本文讨论了维特比译码算法的原理，并以４状态卷积码和ＨＤＴＶ地面广播中使用的ＴＣＭ－３２ＱＡＭ为例，介绍了硬判决维持比译码和软判决维特比译码算法的译码过程。     

基于快衰落信道的一种新型自适应MLSE接收器

在移动通信系统中,由于衰落和多普勒效应,为了实现基于Viterbi算法的极大似然序列估计(MLSE),需要不断跟踪信道参数变化.本文首先提出了一种新的基于插值的信道估计方法ICP(Interpolating channel processing),并给出了该方法的两种实现形式,同已有的一些算法的比较结果表明:新方法具有更小的计算复杂度,误码率更低.同时,本文对如何降低Viterbi算法(VA)的计算复杂度也作了探讨.通过采用自适应减小计算复杂度的算法(ATA),本文提出的ICP算法具有更优的性能.     

CDMA2000前向链路信道估计及跟踪算法的研究

对CDMA2 0 0 0移动台接收机的信道估计单元的算法和实现进行了分析 ,探讨了如何根据衰落速率对相关长度进行自适应的调整 ,研究了如何在暂态情况下跟踪信道的多径分布的变化。为了实现上述算法简要描述了一种在非理想AFC情况下的多普勒频移测量方法。以上探讨使得信道估计单元能够在准确快速选出有效径的基础上对多径系数进行精确估计     

A continuously adaptive MLSE receiver for mobile communications:algorithm and performance

The paper presents a Euclidean distance maximum likelihood sequence estimation (MLSE) receiver, based on the Viterbi algorithm (VA), suitable for fading and noisy communications channels, as that specified by the Group Special Mobiles (GSM). In a mobile cellular system, the fast varying channel characteristics, due to the fading and Doppler effects, require adaptive methods to update the channel coefficients to the MLSE receiver. The proposed technique continuously estimates the channel characteristics directly within the metric calculation of the VA. At each step of the VA, the sequence associated to the path with the best metric value (minimum-survivor method) among the survivor paths is used to update the channel estimate (employing conventional adaptive algorithms) throughout the entire informative sequence. However, the detection of the transmitted data sequence is performed by the VA only at the end of each burst. The proposed technique allows simpler receiver implementation and the simulation results show a good performance of this adaptive MLSE receiver in typical GSM environments     

Genetic algorithm assisted joint multiuser symbol detection andfading channel estimation for synchronous CDMA systems

A novel multiuser code division multiple access (CDMA) receiver based on genetic algorithms is considered, which jointly estimates the transmitted symbols and fading channel coefficients of all the users. Using exhaustive search, the maximum likelihood (ML) receiver in synchronous CDMA systems has a computational complexity that is exponentially increasing with the number of users and, hence, is not a viable detection solution. Genetic algorithms (GAs) are well known for their robustness in solving complex optimization problems. Based on the ML rule, GAs are developed in order to jointly estimate the users' channel impulse response coefficients as well as the differentially encoded transmitted bit sequences on the basis of the statistics provided by a bank of matched filters at the receiver. Using computer simulations, we showed that the proposed receiver can achieve a near-optimum bit-error-rate (BER) performance upon assuming perfect channel estimation at a significantly lower computational complexity than that required by the ML optimum multiuser detector. Furthermore, channel estimation can be performed jointly with symbol detection without incurring any additional computational complexity and without requiring training symbols. Hence, our proposed joint channel estimator and symbol detector is capable of offering a higher throughput and a shorter detection delay than that of explicitly trained CDMA multiuser detectors     

An MLSE receiver using channel classification for Rayleigh fadingchannels

We propose a channel classification method that identifies the delay path profile of Rayleigh fading channels, which can be used in conjunction with conventional maximum-likelihood sequence estimation (MLSE) receivers. The proposed method determines the appropriate number of delay taps for the MLSE trellis, based on a decision variable obtained from multiple traffic bursts. By formulating the decision variable using the F-distribution, we derive exact expressions for misclassification probability. A new MLSE receiver structure that utilizes the channel classification method is described, and bit error rate (BER) simulation results are presented to demonstrate the performance improvement. The particular application which is discussed is the IS-136 TDMA standard     

Performance of adaptive linear interference suppression in thepresence of dynamic fading

Adaptive linear interference suppression for direct-sequence (DS) code-division multiple access (CDMA) is studied in the presence of time- and frequency-selective fading. Interference suppression is achieved with an adaptive digital filter which spans a single symbol interval. Both decision-directed and blind adaptive algorithms, which do not require a training sequence, are considered. Modifications to least squares adaptive algorithms are presented which are compatible with differential coding and detection. For frequency-selective fading, adaptive algorithms are presented based upon different assumptions concerning knowledge of the desired user's channel. Specifically, the cases considered are as follows: (1) perfect knowledge of the desired channel; (2) knowledge of only the relative path delays; and (3) knowledge of only one delay corresponding to the strongest path. Computer simulation results are presented which compare the performance of these algorithms with the analogous RAKE receivers. These results show that for case (3), even slow fading can cause a significant degradation in performance. Effective use of channel parameters in the adaptive algorithm reduces the sensitivity to fade rate, although moderate to fast fading can significantly compromise the associated performance gain relative to the RAKE receiver     

适用于慢衰落信道的联合最大似然序列估计

为了克服移动通信中存在的多径衰落效应,基于Viterbi算法的最大似然序列估计需要不断跟踪信道参数的变化.在建立有限带宽信号的多径衰落信道传输模型的基础上,提出了一种适合于慢衰落信道特性的降阶联合信道跟踪与最大似然均衡算法D-PSP.该方法根据信道特性选择不同的降阶维数N,在保证数据正确接收率的条件下,不同程度的有效减小PSP算法的计算时间和存储空间.     

相关衰落下多天线 LS-CDMA信道容量

对相关多径信道下不同扩频地址码的多天线CDMA系统的信道容量进行了研究,在研究中分别采用了在多码检测和多用户检测联合检测算法.在多码检测的情况下,李道本教授发明的LS码多天线CDMA系统比Walsh码和Gold码的多天线系统有更大的系统容量,后两者在大的信噪比(20dB)时候均有平台效应;在采用多用户检测时它们的容量几乎相同.由于具有零相关窗特性,对于LS码而言这两种方法是等效的.当发射天线数目等于接收天线数目时,系统的容量和天线数目呈线性关系.