STBC和VBLAST相结合的MIMO系统

STBC编码是基于发端分集的传输方案,VBLAST是基于空间复用的传输方案;基于两种方案的MIMO 系统,在空间相关信道下系统的性能都会下降,但前者的性能会明显好于后者;该文提出一种折衷方案,将发射天线阵列分组,每组内采用STBC编码,接收端采用VBLAST算法。仿真结果表明:在空间相关信道下,该方案的误码率性能明显优于通常的VBLAST接收机。     

多径信道下基于空时分组码的发送分集技术

文章在多径信道下,提出了一种基于RAKE接收机的空时分组编码(STBC)方案.该方案将空时分组编码(STBC)与RAKE接收机的多径叠加相干检测的方法相结合,从而可以在频率选择性衰落信道下采用多发射天线实现发送分集.此方案获得的分集增益与由采用相同数量接收天线的最大比接收合并(MRRC)方案得到的接收分集增益接近,能够较大地提高传榆系统的可靠性.     

多用户STBC下行链路预处理优化算法

给出了一种基于天线选择的多用户STBC下行链路预处理优化算法.该方法对发送端天线进行组合,即从所有发送天线中选出部分天线组成多个天线集合,每个天线集合中发送天线个数为能够获得空间分集增益的最小数目,从这些天线集合中选出最大化多用户STBC系统分集增益的一个集合作为最终发送天线.对基于天线选择的算法进行了仿真分析,结果表明,该算法比未采用选择的算法可以获得更高的分集增益,还与基于特征模式选择的算法进行了比较,结果表明:该方法比基于特征模式选择的算法使系统获得了更高的性价比.     

基于空时编码的MB-OFDM超宽带通信系统

基于MB-OFDM（多带正交频分复用）超宽带通信系统上，采用了两种特殊的空时（频）编码结构来改善系统性能。仿真结果表明，在修正的S-V信道模型下，该系统增大了传输速率，基于空时分组编码（STBC）结构的超宽带系统在低信噪比情况下可以获得较好的分集增益，而基于预编码的空时频编码（STFC）的超宽带系统的BER性能比单天线系统的BER性能更加优异．     

基于特征波束形成的STBC发射天线选择

相关信道下将特征波束形成(E-BF)与空时分组码(STBC)相结合,在保持分集阶数的同时可以获得阵列增益,但需配置更多的发射天线.根据该系统特点提出了统计的发射天线选择方案,在不增加天线数情况下通过自适应子阵选择来提高系统误码率性能,并给出了平均误码率最小的天线选择准则.天线选择与E-BF共享信道信息,算法也不用频繁更新.仿真结果证明了该天线选择方案可提高系统误码率的性能.     

空间相关信道下分布式MIMO系统中的STBC-VBLAST组合方案

在空间相关信道下分布式多输入多输出(D-MIMO)系统中,提出了一种新的空时分组编码(STBC)和垂直分层空时编码(VBLAST)组合方案.为充分利用D-MIMO系统的拓扑结构和空间相关信道的特性,在下行D-MI-MO系统的每个分布式天线(DA)簇内采用STBC,而在不同DA簇之间采用VBLAST.同时,为了降低系统复杂度并节省总发射功率,采用了基于最小传播路径衰落准则的天线选择方案.仿真结果证明,对比于传统VBLAST方式,所提出的STBC-VBLAST组合方案能显著降低系统误比特率(BER)并提高空间相关信道下BER性能的鲁棒性.因此,该组合方案是实现空间相关信道下D-MIMO系统下行分集与复用的折衷的一种有效方案.     

一种基于分布式空时码的协作MIMO分集复用折衷新方案

协作MIMO通过多个单天线节点的相互协作构造多发射天线,以此形成一种虚拟MIMO多天线阵列获得空间分集增益。考虑到协作MIMO特点,天线间采用分布式空时编码进行编码协作。文章研究了协作MIMO中基于分布式空时码(DSTC)的分集复用折衷(DMT)新方案,该方案通过推导两种DSTC的中断概率与分集增益表达式,结合两类DSTC的DMT策略,根据改变复用增益阈值自适应获得最佳DMT与中断性能。数值仿真表明,所提的DMT策略可以逼近协作MIMO的DMT上限,协作节点采用该策略的中断性能仅次于上限的中断性能。在多节点构成协作MIMO网络分布式空时编码协作中,提出的DMT新方案可使系统高效地获得协作分集增益与中断性能。     

MIMO系统中分集增益和空间复用增益的折衷关系

论文导出了分集增益与空间复用增益间的最佳折衷关系式。该关系式为阶梯递减右连续函数,阶梯数等于接收天线数目。分集增益的取值与分组长度有关,只有当分组长度不小于发射天线数目时才能获得满分集增益。折衷关系表明,采用合适的空时编码可以同时获得分集增益和空间复用增益,但是两种增益不能同时达到最大。由最佳折衷关系可以推测一定空间复用增益时可得到的最大分集增益,以及一定分集增益时能获得的最大空间复用增益。     

基于天线波束成形的OFDMA系统的自适应资源分配

对正交频分复用接入系统在多用户多天线传输情况下的自适应资源分配策略进行了研究,提出了一种基于天线波束成形的,包括动态子载波分配、自适应调制、比特加载的无线资源分配方案.算法的优化设计目标是在满足总的恒定传输比特数和误比特率性能要求的情况下,使得系统总的发射功率最小.仿真结果表明,由于多天线阵列增益和多用户分集增益,系统整体性能得到了明显的优化.     

基于阿拉莫提模型的BLAST与STBC结合算法

提出了一种基于2×2天线阵列的BLAST与STBC的结合算法,在初始传输的时候使用BLAST来提高系统容量,如果出错则重传的信号和初始信号结合为STBC来获得高的分集增益.该算法相对于BALST算法有更低的误码率,相对于STBC算法有更高的传输速率,因此具有良好的性能和优越的鲁棒性.仿真结果证明,通过少量的额外带宽为代价换取了性能的很大提升.     

Robust Transmit Antenna Selection with Phase Feedback Over Correlated Fading Channels

A new transmit antenna selection (TAS) scheme with phase feedback for multiple-input multiple-output systems is proposed in this paper. This scheme allows two or more transmit antennas to simultaneously use one radio frequency chain. By grouping the transmit antennas according to their similarities in instantaneous channel coefficients into two subsets and treating each subset as a single antenna, both hardware complexity reduction and antenna array gain can be achieved. Compared with the transmit antenna selection combined with space-time block code (TAS/STBC) scheme, the proposed TAS scheme provides excellent robustness, in terms of symbol error rate performance, against spatially correlated fading channels. Moreover, the proposed TAS scheme need not use STBC encoder and decoder which used in the TAS/STBC schemes. Therefore, the proposed TAS scheme is simpler than the TAS/STBC schemes in practical hardware implementation.     

短波单载波空时分组码的频域均衡研究

短波通信受多径衰落、干扰复杂等影响严重。空时分组码(Space Time Block Code,STBC)技术在无需增加频谱资源和天线发射功率的前提下,可以利用多输入多输出(Multiple-Input Multiple-Output,MIMO)信道提供的分集增益提升传输可靠性。分析短波MIMO研究现状,提出短波单载波STBC频域均衡(Frequency-Domain Equalization,FDE)系统架构,针对短波信道引入的码间干扰研究MIMO MMSE-FDE均衡技术,并将单载波STBC频域均衡与时域均衡及短波现有波形进行仿真对比。仿真结果表明,相较于短波现有波形,单载波STBC频域均衡系统的可靠性有较大幅度提升,且性能与STBC时域均衡接近,但计算复杂度远低于STBC时域均衡。     

Performance of selective space‐time coding and selection diversity under perfect and imperfect CSI

Selective space‐time coding and selection diversity can be viewed as practical means to reduce the implementation complexity of multiple‐input multiple‐output (MIMO) systems while still taking benefit of the use of multiple antennas. In this paper, we evaluate the performance of selective space‐time block coding (selective‐STBC) and antenna selection diversity, and analyze the performance of both techniques under perfect and imperfect channel state information (CSI) available at both ends of the transmission link. Our performance analysis reveals that, under perfect or imperfect CSI and ideal feedback channel, selective‐STBC yields a loss in selection diversity gains and that selecting just a single antenna at the transmitter side is the best transmission strategy. We also show that selective‐STBC and antenna selection diversity have different behaviors when the feedback channel is imperfect. Indeed, it is shown that selection diversity outperforms selective‐STBC when the feedback channel is of high quality, while selective‐STBC yields better performance when the feedback channel is of low quality. Copyright © 2008 John Wiley & Sons, Ltd.     

Impact of space-time block codes on 802.11 network throughput

By employing more than one antenna at the transmitter and by properly coding data across the transmit antennas, physical layers (PHYs) with space-time block codes (STBCs) promise increased data rates with minimal decoding complexity at the receiver. This paper presents a comprehensive study of how the STBC gains at the PHY translate to significant network performance improvement in 802.11a wireless local area networks. We base our study on a detailed, across-all-layers, simulation of an 802.11a system. We have extended the network simulator with an implementation of the 802.11a PHY, which allows us to assess the impact of STBC not only at the PHY layer, but at the higher layers as well. An extensive set of simulations illustrates the merits of transmit diversity (in the form of STBC) and sheds light on how performance can be improved for transmission control protocol (TCP) traffic. Essentially, STBC presents to TCP a "smoother" wireless channel; this is corroborated by a brief theoretical analysis as well.     

MIMO CDMA系统中一种新的循环空时分组编译码方法

该文提出了MIMO CDMA系统中一种新的空时分组编译码方法,称为循环空时分组码(Cyclic Space-Time Block Code,C-STBC),它是将输入信息进行分组循环编码,然后对循环编码后的码字通过不同的天线分别采用不同的扩频码扩频后发射出去。这种CDMA系统下的循环空时分组码对任意的发射天线数都能达到满编码速率和满分集度,且其译码与传统的空时分组码一样简单。仿真结果验证了这种循环空时分组码优于传统的空时分组码。     

On the performance of multi‐hop wireless relay networks

User cooperation has evolved as a popular coding technique in wireless relay networks (WRNs). Using the neighboring nodes as relays to establish a communication between a source and a destination achieves an increase of the diversity order. The relay nodes can be seen as a distributed multi‐antenna system, which can be exploited for transmit diversity by using distributed space–time block coding (STBC). In this paper, we investigate the bit error rate (BER) of multi‐hop WRNs employing distributed STBC at the relay nodes. We develop the general model of WRNs using distributed STBC, and we derive the pairwise error probability and an approximation of the BER. We examine the impact of several parameters, such as distributed STBC at the relays, the number of relays, the distances between the nodes, and the channel state information available at the receivers, on the BER performance of the multi‐hop WRN. The obtained results provide guidelines about the expected error performance and the design of channel estimation for these networks. Copyright © 2011 John Wiley & Sons, Ltd.     

A Unified Capacity Analysis for Wireless Systems With Joint Multiuser Scheduling and Antenna Diversity in Nakagami Fading Channels

A Unified Capacity Analysis for Wireless Systems With Joint Multiuser Scheduling and Antenna Diversity in Nakagami Fading Channels In this paper, we present a cross-layer analytical framework to jointly investigate antenna diversity and multiuser scheduling under the generalized Nakagami fading channels. We derive a unified capacity formula for the multiuser scheduling system with different multiple-input multiple-output antenna schemes, including: 1) selective transmission/selective combining (ST/SC); (2) maximum ratio transmission/maximum ratio combining (MRT/MRC); 3) ST/MRC; and 4) space–time block codes (STBC). Our analytical results lead to the following four observations regarding the interplay of multiuser scheduling and antenna diversity. First, the higher the Nakagami fading parameter, the lower the multiuser diversity gain for all the considered antenna schemes. Second, from the standpoint of multiuser scheduling, the multiple antennas with the ST/SC method can be viewed as virtual users to amplify multiuser diversity order. Third, the boosted array gain of the MRT/MRC scheme can compensate the detrimental impact of the reduced amount of fading gain on multiuser scheduling, thereby resulting in greater capacity than the ST/SC method. Last, employing the STBC scheme together with multiuser diversity may cause capacity loss due to the reduced amount of fading gain, but without the supplement of array gain.     

LSTBC+OFDM分层方法的一种改进

基于OFDMA(Orthogonal Frequency-Division Multiple Access)中不同用户的子载波选择矩阵相互正交,提出了频率选择性衰落信道下分层结构的空时分组编码LSTBC(Layered Space-Time Block Code)的一种改进的分层方法.发射端采用分层结构的空时分组编码结合OFDM技术,在接收端提出了利用OFDM中子载波选择矩阵进行分组干扰抑制,然后对LSTBC的每层进行空时分组码的传统解码.相对于基于奇异值分解的分组干扰抑制方法,该方法只需要一根接收天线,降低了系统接收机设计的复杂度.仿真结果验证该方法的有效性.     

Performance Comparison of MIMO-STBC Systems with Adaptive Semiblind Channel Estimation Scheme

Wireless communication is now a part of everyday life in the urban areas. Wireless LAN is mostly utilized communication system as an example. These wireless devices are data rate and range limited, for which the scientists are spending great efforts on finding ways to overcome these limitations. Multi input multi output (MIMO) antenna systems are the example through which these limitations have been reduced upto great extent which provides multilayer beamforming, diversity, and spatial multiplexing. Analysis of adaptive semiblind channel estimation scheme for MIMO antenna array systems with different code rate space time block coding (STBC) has been performed using the adaptive pilot assisted modulation scheme proposed earlier. Semi blind channel estimation method provides the best trade-off in terms of bandwidth overhead, computational complexity and latency. The result after using MIMO systems shows higher data rate and longer transmit range without any requirement of additional bandwidth or transmit power. This paper presents the detailed analysis of diversity coding techniques using MIMO antenna systems. Different STBC schemes have been explored and analyzed with the different code rate STBC using MATLAB environment and the simulated results have been compared in the semiblind environment which shows the improvement even in highly correlated antenna arrays, and is found close to the condition when channel state information is known to the channel.