频率选择性衰落信道中一种低复杂度的正交空时分组码译码算法

针对正交空时分组码在频率选择性衰落信道中正交性被破坏的问题,该文提出了一种基于干扰对消的译码方案。该方案借鉴D-BLAST系统的检测方法,采用干扰抵消和干扰置零方法消除多径干扰,从而有效地检测出期望信号。理论分析和系统仿真表明,与迭代干扰抵消算法相比,该译码方案在有效地改善系统误码性能的同时,降低了译码复杂度,尤其适用于信道阶数较小的环境。     

一种改进的基于多用户检测的独立分量分析算法

为了降低FastICA算法的计算复杂度,提出了一种基于多用户检测串行干扰抵消的新型独立分量分析算法MUD_FastICA。该算法结合了盲信号分离和多用户检测串行干扰抵消两种信号处理技术,利用减法和低维特征值分解来保证每次分离出不同独立分量和达到降低算法复杂度的目的。通过分析和仿真可以看出,所提算法在不影响分离性能的前提下,显著降低了算法的迭代次数和每次迭代的计算复杂度。在信噪比0 dB和4个源信号混合情况下,分离第二个信号的迭代次数和所需计算单元分别下降了14%和37%,分离第三个信号的迭代次数和所需计算单元分别下降了22%和58%,因此更加适合对实时性要求高的通信系统。     

频率选择性衰落下一种基于迭代干扰抵消的空时分组码译码算法

针对频率选择性衰落下空时分组码的正交性由于多径干扰而遭到严重破坏,提出一种基于迭代干扰抵消的最大似然序列估计(MLSE)译码方案;并结合最大比合并方法对所提方案进行改进和提高,以进一步降低计算复杂度。这些方案能很好地弥补通常空时分组码在频率选择性衰落下译码时的不足,它们不仅能抵消正交性没有破坏的在偶次项上的多径干扰,还能抵消正交性受到破坏的在奇次项上的多径干扰;有着非常好的性能。而且与直接对长序列信号进行MLSE译码相比,有着非常低的译码复杂度;从而以低复杂度实现了较好的空时分组码译码性能。     

一种适用于TD-SCDMA系统的多用户检测算法

利用逐次干扰抵消多用户检测结构,结合空时RAKE接收机,提出一种空时逐次干扰抵消多用户检测算法.仿真结果表明,该算法相比传统空时RAKE接收机有近5 dB的增益,误码率有了相当的改进.     

不完全信道状态信息条件下多用户Turbo-BLAST迭代检测算法

该文将空时多用户检测技术和Turbo-BLAST方案相结合,构造了基于CDMA技术的多用户Turbo- BLAST系统模型,提出了不完全信道状态信息条件下的解相关算法和迭代检测算法。在发送端将V-BLAST结构与CDMA技术相结合实现多路复用,在接收端利用空时多用户检测算法去除用户间干扰,得到期望用户的接收信号,然后采用考虑信道估计误差的软干扰抵消迭代检测算法,对期望用户的接收信号进行检测以去除天线间干扰。仿真结果说明,所提算法对于多用户Turbo-BLAST系统是有效的,可在不增加复杂度的条件下达到良好的迭代效果。     

频率选择性快衰落信道中的MIMO—OFDM系统检测算法研究

当MIMO—OFDM（Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing）系统工作于频率选择性快衰落信道时，子载波正交性会受到破坏从而引入子载波间干扰（Inter-Cartier Interference：ICI）．ICI的存在将严重降低那些传统的用于检测准静止频率选择性衰落信道下MIMO—OFDM的检测算法的性能．本文将Schniter针对SISO（Sinsle Inputsingle Output）OFDM系统提出的最优线性预处理扩展到MIMO—OFDM系统，基于这个信号模型推广了基于最小均方误差滤波的迭代软判决干扰抵消（Minimum Mean Square Errorfiltering based Iterative Soft Decision Interference Cancellation：MMSE—ISDIC）逐符号检测算法，同时提出一种基于准最大后验概率准则的迭代软判决干扰抵消（quasi—maximum A postefiofi probability based ISDIC：quasi—MAP-ISDIC）联合检测算法．仿真结果表明在本文考虑的系统参数设定下这两种检测算法的性能均优于文献[8]中算法的性能，其中quasi．MAP-ISDIC检测算法能够获得接近基于理想ICI抵消的MAP检测算法的性能。     

低复杂度迭代干扰消除的OFDMA初始测距算法

针对现有正交频分多址(OFDMA)系统初始测距算法检测性能不佳以及复杂度过高的问题,该文提出一种低复杂度迭代干扰消除的多用户初始测距算法。该算法采用迭代并行干扰消除方法,在接收端按照最大功率准则并行检测活动测距用户的有效径,利用估计出的有效径参数信息来减小信道估计中的干扰,再通过重构和并行消除多用户测距信号。计算机仿真结果表明,与连续多用户检测(SMUD)干扰抵消算法相比,当信噪比为9 dB,且一个测距时隙内测距用户数为8时,所提算法的复杂度大约是SMUD的25%,检测性能大约提高了5%。     

一种高速率单载波空时分组码系统的分层及迭代检测

针对一种应用于频率选择性信道的两路复用的空时分组码系统，基于最小均方误差均衡，提出了根据均衡后的均方误差的大小进行排序的分层检测算法，在保持低复杂度的同时提高了系统整体性能。在此基础上给出了一种基于干扰抵消的迭代算法，增加了每一路信号的分集增益。仿真结果表明本文给出的分层检测及迭代检测算法对信道估计误差具有鲁棒性。     

双迭代级联译码的Turbo V-BLAST结构

垂直贝尔实验室分层空时(V-BLAST)方案能有效提高系统的信道容量而成为研究的热点。但多发送天线造成了接收信号的空间干扰,这严重造成了误比特(误帧)系统性能的下降。在接收端,采用了迫零(Zero-forcing)排序的迭代混合干扰消除(Hybird Interference Cancellation,HIC)算法,相比迫零排序的串行干扰消除(Serial Interference Cancellation,SIC)算法,在降低复杂度的同时提高系统性能。干扰消除后的软信息经过Turbo迭代译码,得到的硬判决信息可以反馈回到V-BLAST的迭代ZF-HIC干扰检测,进行系统级联迭代。因此,文中的Turbo V-BLAST结构具有双迭代级联的多迭代环特征。仿真证明能很大程度上改进系统的BER和FER,是一种理想的系统结构。     

一种适用于空分复用MIMO系统的迭代检测器

本文在比特交织turbo编码调制的空分复用M IMO系统发送框架下,研究了一类与Turbo码的迭代译码联合进行的软干扰抵消迭代检测算法。在首次检测中,使用了基于匹配滤波(M F)的多级串行软干扰抵消方法,在后续的检测中使用了单级并行软干扰抵消方法。本文又把迭代检测同turbo码的迭代译码联合,大大降低了每次联合检测turbo译码需要的迭代译码次数。     

一种满速率空时分组编码CDMA系统及多用户接收方案

通过引入满速率空时分组码方案, 该文给出一种满速率空时分组编码CDMA系统模型, 并针对现有空时编码CDMA系统过高的译码复杂度, 提出一种低复杂度的多用户接收方案。该方案在通过类似多用户检测方法有效抑制多用户干扰后, 充分利用空时分组码的复正交性来简化原有方案高译码复杂度。与原有指数性译码复杂度相比, 该方案有着线性复杂度, 而且与满分集空时分组编码CDMA系统相比, 可实现满速率、低复杂度和部分分集, 有着相对多的空间冗余信息, 从而级联信道编码后可有效弥补部分分集所带来的性能损失。仿真结果表明在相同系统容量和级联码的情况下, 所给系统比相应的满分集空时编码CDMA系统有着低的误比特率。     

Iterative receivers for multiuser space-time coding systems

Space-time coding (STC) techniques, which combine antenna array signal processing and channel coding techniques, are very promising approaches to substantial capacity increase in wireless channels. Multiuser detection techniques are powerful signal processing methodologies for interference suppression in CDMA systems. In this paper, by drawing analogies between a synchronous CDMA system and an STC multiuser system, we study the applications of some multiuser detection methods to STC multiuser systems. Specifically, we show that the so-called “turbo multiuser detection” technique, which performs soft interference cancellation and decoding iteratively, can be applied to STC multiuser systems in flat-fading channels. An iterative multiuser receiver and its projection-based variants are developed for both the space-time block coding (STBC) system and the space-time trellis coding (STTC) system. During iterations, extrinsic information is computed and exchanged between a soft multiuser demodulator and a bank of MAP decoders, to achieve successively refined estimates of the users' signals. Computer simulations demonstrate that the proposed iterative receiver techniques provide significant performance improvement over conventional noniterative methods in both single-user and multiuser STC systems. Furthermore, the performance of the proposed iterative multiuser receiver approaches that of the iterative single-user receiver in both STBC and STTC systems     

On channel parameter estimation in a space-time bit-interleaved-coded modulation system for multipath DS-CDMA uplink with receive diversity

In this paper, we consider iterative space-time multiuser detection and channel parameter estimation in a bit-interleaved coded modulation scheme for asynchronous direct-sequence code division multiple access (DS-CDMA) transmission over frequency selective, slowly fading channels. Accurate estimation of the channel parameters is critical as it has great impact on the overall BER performance. We present an iterative space-time multiuser (STMU) turbo detection and estimation scheme, based on space alternating generalized expectation maximization (SAGE) algorithm. This algorithm operates on the coded symbols by exchanging soft information between the detector and the estimator. We show through computer simulations that the proposed low complexity STMU receiver considerably outperforms conventional estimation schemes and achieves excellent performance, both in terms of BER and estimation error variance. Finally, we will consider different mapping strategies and investigate their impact on the performance and complexity of the estimator.     

Iterative space-time processing for multiuser detection in multipath CDMA channels

Space-time processing and multiuser detection are two promising techniques for combating multipath distortion and multiple-access interference in code division multiple access (CDMA) systems. To overcome the computational burden that rises very quickly with increasing numbers of users and receive antennas in applying such techniques, iterative implementations of several space-time multiuser detection algorithms are considered here. These algorithms include iterative linear space-time multiuser detection, Cholesky iterative decorrelating decision-feedback space-time multiuser detection, multistage interference canceling space-time multiuser detection, and expectation-maximization (EM)-based iterative space-time multiuser detection. A new space-time multiuser receiver structure that allows for efficient implementation of iterative processing is also introduced. Fully exploiting various types of diversity through joint space-time processing and multiuser detection brings substantial gain over single-receiver-antenna or single-user-based methods. It is shown that iterative implementation of linear and nonlinear space-time multiuser detection schemes discussed in this paper realizes this substantial gain and approaches the optimum performance with reasonable complexity. Among the iterative space-time multiuser receivers considered in this paper, the EM-based (SAGE) iterative space-time multiuser receiver introduced here achieves the best performance with excellent convergence properties.     

A RAKE-based iterative receiver for space-time block-coded multipath CDMA

A turbo multiuser receiver is proposed for space-time block and channel-coded code division multiple access (CDMA) systems in multipath channels. The proposed receiver consists of a first stage that performs detection, space-time decoding, and multipath combining followed by a second stage that performs the channel decoding. A reduced complexity receiver suitable for systems with large numbers of transmitter antennas is obtained by performing the space-time decoding along each resolvable multipath component and then diversity combining the set of space-time decoded outputs. By exchanging the soft information between the first and second stages, the receiver performance is improved via iteration. Simulation results show that while in some cases a noniterative space-time coded system may have inferior performance compared with a system without space-time coding in a multipath channel, proposed iterative schemes significantly outperform systems without space-time coding, even with only two iterations. Furthermore, the performance loss in the reduced-complexity receiver due to decoupling of interference suppression, space-time decoding, and multipath combining is very small for error rates of practical interest.     

A low-complexity iterative multiuser receiver for turbo-codedDS-CDMA systems

Optimal joint multiuser detection and decoding for direct-sequence code-division multiple-access (DS-CDMA) systems with forward error correction normally requires prohibitively high computational complexity. A suboptimal solution with low complexity is therefore appealing for use in practical applications. We propose a low-complexity iterative multiuser receiver for turbo-coded DS-CDMA systems. The proposed approach consists of a modified decorrelating decision-feedback detector (MDDFD) and K single-user turbo decoders, where K is the number of users in the DS-CDMA system. The MDDFD is derived on the basis of maximizing a likelihood probability and has a feature that it can use the reliability information from the turbo decoders' output. In addition, the MDDFD can deliver interference-cancelled soft outputs to the turbo decoders where the calculation of transition metrics is modified appropriately. Both performance analysis and computer simulation results have indicated that the reliability information from the turbo decoders' output can enhance the multiuser detection capability of the MDDFD. Computer simulations have also shown that the proposed iterative multiuser receiver outperforms the conventional DDFD-based multiuser receiver in terms of the bit-error probability     

Layered space-time multiuser detection over wireless uplink systems

In this paper, we investigate the use of layered space-time (also known as the vertical Bell Laboratories layered space-time (V-BLAST) scheme) for multiuser detection in fading channels. The multiple transmit antennas in V-BLAST are treated as individual mobile station transmitters, while the base station consists of multiple receive antennas. In the proposed system, users are organized in groups and allocated a unique spreading code within the same group. Using these codes, we are able to separate the different groups, and layered space-time algorithm is then invoked to further remove the remaining interference between users. A decorrelator-type receiver-based layered space-time detection is proposed for both complex and real constellations. For the latter case, we derive our receiver after evaluating and comparing the performance of two decorrelators based on the V-BLAST scheme. It is demonstrated that a significant performance improvement and increase in system capacity is obtained with very low spreading factors. Further results are also introduced by considering reduced complexity receivers based on serial layered space-time group multiuser detection, and parallel layered space-time group multiuser detection.     

一种低复杂度空-时选择性干扰消除方法

提出了一种行之有效的将智能天线技术同多用户检测技术结合的空-时接收方法,并对其参数进行了优化。它根据误码率信息有选择地实施干扰消除,先并行消除低误码率用户信号的影响,再检测高误码率用户信号。它复杂度低,计算效率高,易于实时实现,具有很好的应用价值。蒙特卡洛仿真实验表明,该方法可以显著改善码分多址移动通信系统的性能。     

Iterative semiblind multiuser receivers for a space-time block-coded MC-CDMA uplink system

Iterative multiuser detection and space-time coding are two promising techniques to improve the capacity and performance of coded multiuser systems in wireless channels. In this paper, we present iterative multiuser detection schemes for a space-time block-coded multicarrier code-division multiple-access system with multiple transmit and receive antennas. We consider a more general case of an uplink system in the presence of both intra- and intercell interferences. We propose two types of iterative semiblind space-time receivers for such an uplink environment. The first is based on the minimum mean-square error criterion and the second is a hybrid scheme based on a combination of parallel interference cancellation and linear multiuser detection. These iterative receivers are derived, using a subspace approach, which utilizes known users' information for the computation of log-likelihood ratios (LLRs) while blindly suppressing the unknown interference. The LLRs are refined successively during the iterative process by using the extrinsic information available through decoding of all known users. A turbo code is used for channel coding. Simulation results in a frequency-selective Rayleigh-fading environment are presented to verify the performance of the proposed schemes.