空时编码OFDM与多维波束形成组合方案

针对MIMO-OFDM系统提出了一种简单灵活的空时分组码与多维特征波束形成组合方案,以充分利用MIMO信道的二阶统计信息。该方案在保证空时编码分集度的同时能最大化系统的编码增益,空时分组码的选取并不受实际发射天线数的限制,因此可以在分集度、编码增益以及系统码率之间进行灵活的折中。理论分析和仿真结果同时表明,当实际发射天线数大于空时码所需天线数时,系统的编码增益随着实际发射天线数的增加大致呈线性增长,发射天线阵列间相关性越强,增长速度越快。     

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.     

八波束STBC-BF发射方案中天线选择技术的应用

提出了大规模MIMO系统空时编码结合特征波束成形(STBC-BF)方案中的天线选择技术.发射符号空时分组编码后经天线阵列加权,形成特征波束,利用天线选择技术对发射天线和接收天线进行选择,接收端采用传统译码方法进行译码.该方案既可以获得空间分集增益和阵列增益,又能减少射频链路的数目,从而降低计算复杂度.仿真结果表明了该方案的有效性.     

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。     

高速铁路无线通信中基于正交空时码的格型正交重构算法

分析了基于正交空时码的开环和闭环MIMO系统,并着重研究了高铁场景下速度对正交空时码的影响：高速移动导致的快时变信道将会破环正交空时码的正交结构,降低由此获得的分集增益,从而引起了误码率性能的降低。提出了格型正交重构算法,通过givens变换对正交空时码进行码内正交重构;算法在恢复码内正交性的同时,也改变了发射端波束成形方向。因此,在高速移动场景下,所提算法使发射端获得了波束成形的阵列增益以及与用户静止时相同的分集增益。从系统性能仿真中看出,所提算法提升了高铁场景下基于正交空时码MIMO系统的误码性能。     

基于空时格形码的差分调制

提出了空时格形码的差分调制方案,并对空时格形码和系统模型以及差分调制技术进行了深入的研究。在发射天线和接收天线数量乘积大于3时,对QPSK和8-PSK的STTCM码和TSC码以及BBH码进行了仿真,仿真结果表明:STTCM码与相应的TSC和BBH码相比具有更低的帧误码率,而且STTCM码能够提供最大可能的分集增益和编码增益。     

可变速率预编码BLAST与特征波束形成组合方案

传统的基于迫零(ZF)和最小均方误差(MMSE)算法的分层空时码(BLAST)接收机由于其较大的复杂度不适合在移动终端使用。该文的发射方案将传输预编码BLAST与特征波束成形相结合,利用信道协方差矩阵特征值分解得到的特征波束来承载空时分层码,并在目标BER约束下自适应调整速率。在下行链路发送端使用可变速率预编码BLAST与特征波束形成组合方案,大大简化了移动终端的接收机算法。     

Rician衰落信道下空时分组码的性能分析

基于Alamouti提出的BPSK调制下空时分组码在Rayleigh衰落信道中的码性能原理,推导出高阶(M ary)调制下Rician衰落信道中空时分组码的符号差错率的最小距离球界,并进行计算机仿真分析了两信道下引入空时分组码的多天线系统中发射和接收天线的分集增益,发射天线数量的“地板效应”以及Rician因子K对符号差错性能的影响。     

无线光通信中的空时编码研究进展(三)

空时编码利用多天线阵列提供的并行信道传输信息,可以在保证通信质量的前提下进一步提高信息传输速率。介绍了笔者在正交空时码、空时网格码、酉空时码、差分空时码、混合空时码等方面的工作。采用类脉冲位置调制定义了负数、共轭、求补等运算,将编码矩阵转化为一个用脉冲位置表示的实数矩阵。分析了不同发射天线/接收天线数目、大气湍流强度与系统误码率之间的关系。讨论了差分空时码、酉空时码在不同大气湍流条件下的误码率特性;将分层空时码和空时分组码相结合,对复用增益和分集增益进行合理的折中,提出了一种适合于IM/DD式光通信的混合空时编码方案。     

低复杂度的满速率和部分分集多天线空时块码及性能

在现有几种满分集空时码的基础上,提出两种满速率和复正交的多天线空时块码方案。一种是基于时分双工(TDD)模式下最大信道增益而设计的;另一种则不再限于TDD方式,具有普遍适用性。同时利用Turbo码良好的抗衰落信道的突发错误能力,来进一步提高所提方案性能。与满分集多天线空时块码相比,该方案可实现满速率、低复杂度和部分分集,具有相对多的空间冗余信息,从而级联Turbo码后可有效弥补部分分集所带来的性能损失。仿真结果也表明在相同系统容量和级联码的情况下,所提方案比其它相应的满分集空时码有着更低的误比特率。     

Combining ideal beamforming and Alamouti space-time block codes

The simplest Alamouti space-time block code is coupled with a larger number of transmit antennas via ideal beamforming to achieve higher diversity gain. It is shown that the combined system can remain both full diversity and full code rate without orthogonality loss. Simulation results show a significant performance gain over the conventional space-time block codes.     

Variable-rate space-time block codes in M-ary PSK systems

We consider a multiple antenna system when combined array processing with space-time coding is used. We present variable rate space-time block codes for two, three, and four transmit antennas and optimize the transmit power so that the average bit-error rate (BER) is minimized. Numerical results show that this optimum power allocation scheme provides significant gain over the equal power allocation scheme. We then classify all the variable rate space-time block codes having the same code rates and identify the unique code that achieves the lowest BER. We explicitly compute the performance of the variable rate codes over a Rayleigh-fading channel. The proposed variable rate space-time block codes are useful for unequal error protection in multiple transmit antenna systems.     

Application of quasi-orthogonal space-time block codes in beamforming

It is well known that when channel information is available at the transmitter, transmit beamforming scheme can be employed to enhance the performance of a multiple-antenna system. Recently, Jongren et al. and Zhou-Giannakis proposed a new performance criterion based on partial channel side information at the transmitter. With this criterion, an optimal beamforming matrix was constructed for the orthogonal space-time block codes. However, the same method has not been applied to the recently proposed quasi-orthogonal space-time block codes (QSTBCs) due to the nonorthogonal nature of the quasi-orthogonal designs. In this paper, the issue of combining beamforming with QSTBCs is addressed. Based on our asymptotic analysis, we extend the beamforming scheme from Jongren et al. and construct the beamforming matrices for the quasi-orthogonal designs. The proposed beamforming scheme accomplishes high transmission rate as well as high-order spatial diversity. The new QSTBC beamformer can be presented as a novel four-directional or eight-directional eigen-beamformer that works for systems with four or more transmit antennas. Simulations for systems with multiple transmit antennas demonstrate significant performance improvement over several other widely used beamforming methods at various SNRs and for channels with different quality of feedback.     

一族满分集度酉空时分组码

对于接收端和发送端均不具备信道状态信息的MIMO系统,本文将Cayley变换与对角块正交空时分组码结合,提出了一种新的酉空时分组码构造方法。新构造的空时分组码适用于任意发送天线数为偶数的MIMO系统,能提供满发送分集度和1.5符号/信道利用的信息传输率,并可采用球检测法等低计算复杂度检测算法得到准最优的检测结果。     

Super-quasi-orthogonal space-time trellis codes for four transmit antennas

We introduce a new family of space-time trellis codes that extends the powerful characteristics of super-orthogonal space-time trellis codes to four transmit antennas. We consider a family of quasi-orthogonal space-time block codes as building blocks in our new trellis codes. These codes combine set partitioning and a super set of quasi-orthogonal space-time block codes in a systematic way to provide full diversity and improved coding gain. The result is a powerful code that provides full rate, full diversity, and high coding gain. It is also possible to maintain a tradeoff between coding gain and rate. Simulation results demonstrate the good performance of our new super-quasi-orthogonal space-time trellis codes.     

On the probability of error of antenna-subset selection with space-time block codes

Orthogonal space-time block codes (OSTBCs) can obtain full diversity advantage with a simple, but optimal, receiver. Unfortunately, OSTBCs lack in array gain compared with beamforming techniques and suffer a rate loss for more than two transmit antennas. One simple method for improving the array gain and adapting OSTBCs to any number of transmit antennas is antenna-subset selection, where the OSTBC is transmitted on a subset of the transmit antennas. In this letter, we analyze the symbol-error rate performance of antenna-subset selection combined with OSTBCs.     

Diagonal block space-time code design for diversity and coding advantage over flat fading channels

The potential promised by multiple transmit antennas has raised considerable interest in space-time coding for wireless communications. In this paper, we propose a systematic approach for designing space-time trellis codes over flat fading channels with full antenna diversity and good coding advantage. It is suitable for an arbitrary number of transmit antennas with arbitrary signal constellations. The key to this approach is to separate the traditional space-time trellis code design into two parts. It first encodes the information symbols using a one-dimensional (M,1) nonbinary block code, with M being the number of transmit antennas, and then transmits the coded symbols diagonally across the space-time grid. We show that regardless of channel time-selectivity, this new class of space-time codes always achieves a transmit diversity of order M with a minimum number of trellis states and a coding advantage equal to the minimum product distance of the employed block code. Traditional delay diversity codes can be viewed as a special case of this coding scheme in which the repetition block code is employed. To maximize the coding advantage, we introduce an optimal construction of the nonbinary block code for a given modulation scheme. In particular, an efficient suboptimal solution for multilevel phase-shift-keying (PSK) modulation is proposed. Some code examples with 2-6 bits/s/Hz and two to six transmit antennas are provided, and they demonstrate excellent performance via computer simulations. Although it is proposed for flat fading channels, this coding scheme can be easily extended to frequency-selective fading channels.     

MIMO系统中简单的扩展空时块编码分集技术研究

本文提出一种多输入多输出（MIMO）天线系统中简单的扩展空时块编码（SSTBC）分集技术，采用沃尔什码来区分各天线发送数据子流。采用这种方法，在系统带宽一定时，不降低发送信息速率，同时接收机简单。不同天线的发送信息经过了所有收一发天线对之间的空间子信道，获得了所有路径的部分空间分集增益，仿真结果表明，这种增益的获得不受限于接收分集阶数，并且随发射天线的增加以一定的线性关系增加。     

Space-time block codes from cyclic design

It has been proved that full-rate complex orthogonal space-time block codes do not exist for systems with more than two transmit antennas. In this paper, we present a space-time block coding scheme based on cyclic design. The proposed codes provide full rate and full diversity for quaternary phase shift keying (QPSK) symbols in systems with three or four transmit antennas.