一种简单而有效的空时编码

空时编码是实现宽带无线数据通信的一种极有潜力的技术.本文研究了一种简单而有效的空时格码设计方案——广义延迟分集码.延迟分集可以认为是重复码与多发射天线之间的延迟因子的组合,而广义延迟分集码的思想是将普通的延迟分集中的重复码替换成某些简单的分组码,以提高编码增益.本文给出了广义延迟分集码达到完全分集的充要条件,进而证明了完全分集广义延迟分集码是具有最小复杂度的完全分集空时格码.对于二进制相移键控(BPSK)信号星座上的广义延迟分集码,本文证明了它们具有相同的编码增益;对于四相移键控(QPSK)信号星座上的广义延迟分集码,本文分析了它们的编码增益,并给出了最优的编码方案.所用的分析方法可以推广到其他的信号星座.     

一种新的网格空时码

本文分析了空时码在平坦准静态衰落信道下的性能,指出分集增益和编码增益并不能准确衡量空时码的性能,提出一种设计网格空时码的新思路,即通过牺牲部分分集增益来降低调制阶数以提高系统性能.依据这一思想,本文给出一种传输速率为3bits/s/Hz,4-PSK调制,8状态的新的非满秩网格空时码.仿真结果表明,这种码虽然没有获得最大分集增益,但相比同速率的满秩网格空时码性能更好,实现更简单.     

结合信道编码的两用户协作分集方案及其性能研究

基于一种分布式空时码的非正交协作分集（DSTC-NOCD）系统,并且结合信道编码,在译码转发（DF）中继信道模型下对两用户协作分集的方案性能进行了研究。通过将turbo码和空时码引入到协作分集中,在准静态的瑞利衰落信道下对此方案的误比特率进行了系统仿真。仿真结果表明：即使协作用户间的信道存在噪声,该文所采用的方案仍优于未加信道编码的分布式空时码的非正交协作分集系统,使得误比特率进一步降低。     

无线通信领域中空时编码技术

多天线系统是第三代甚至未来的第四代无线移动通信中极具前途的一种技术，本文在论述了无线移动通信中分集尤其发射分集技术必要性的基础上，详细论述了将发射分集与编码相结合而产生的空时编码技术，空时码分为空时格码和空时块码，然后就其性能准则和译码准则进行论述；并讨论一种属于空时块码且不需要信道信息的酉空时码及其编译码准则。文章最后给出空时码研究的最新动态及目前需要解决的问题。     

一种基于OFDM的空频码的设计

提出了一种基于OFDM达到最大可达分集增益的空频码设计方案。该编码利用正交频分复用把频率选择性衰落信道变换成平衰落信道的特性，同时引入了基于多天线的空间分集和基于时延扩展的频率分集，比空时编码具有更高的分集增益。     

协同通信中一种基于期望SNR最大的功率分配方案

协同通信是一种新的空间分集技术,而功率分配技术直接影响了协同通信的有效性和可靠性。针对这个问题,给出了一种AF中继转发模式下分布式空时码协同通信系统,讨论了基于期望信噪比最大情况下的功率分配方案,并且基于该框架分析了通信系统的性能,并得出其性能与采用满分集分布式空时码时的性能一致。     

发射分集技术及在WCDMA系统中的应用

发射分集是近年来才发展起来的一种技术，在第三代移动通信系统中已经开始普遍采用。本文简单介绍了几种发射分集技术，并分析了各自的优缺点。特别针对发射信号设计的新技术－空时码进行了详细讨论，然后论述了WCDMA中发射分集技术的应用，并进行了性能仿真比较。     

一种降低码构造复杂度的QSTBC设计

本文采用分圆格方法,设计了一种简化型具全分集、满速率特性的四发四收准正交空时分组码。该准正交空时分组码不仅比传统的基于星座调制技术的四发四收准正交空时码具有更大的分集增益上界,而且比已有的八发一收分圆准正交空时码在误码率和信道容量、以及中断概率等方面皆具有显著的优越性。     

无线光通信中的空时编码研究进展（二）

无线光MIMO技术结合了天线发射分集、接收分集与信道编码分集,可以显著提高信道容量。介绍了笔者在分层空时编码方面的若干研究进展,分析了误码率特性与发射/接收天线数目、检测算法之间的关系,比较了水平分层空时码、螺旋分层空时码、对角分层空时码和垂直分层空时码不同的编码方案,以及不同检测算法对不同的湍流强度的抑制作用。经分析得出:三种分层空时编码性能最好的是对角分层空时编码,其次是螺旋分层空时编码,最后是水平分层空时编码。     

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。     

Using Orthogonal and Quasi-Orthogonal Designs in Wireless Relay Networks

Distributed space-time coding was proposed to achieve cooperative diversity in wireless relay networks without channel information at the relays. Using this scheme, antennas of the distributive relays work as transmit antennas of the sender and generate a space-time code at the receiver. It achieves the maximal diversity when the transmit power is infinitely large. This paper is on the design of practical distributed space-time codes (DSTCs). We use orthogonal and quasi-orthogonal designs which are originally used in the design of space-time codes for multiple-antenna systems. It is well known that orthogonal space-time codes have full diversity and linear decoding complexity. They are particularly suitable for transmissions in the network setting using distributed space-time coding since their ldquoscale-freerdquo property leads to good performance. Our simulations show that they achieve lower error rates than the random code. We also compare distributed space-time coding to selection decode-and-forward using the same orthogonal designs. Simulations show that distributed space-time coding achieves higher diversity than selection decode-and-forward (DF) when there is more than one relay. We also generalize the distributed space-time coding scheme to wireless relay networks with channel information at the relays. Although our analysis and simulations show that there is no improvement in the diversity, in some networks, having channel information at the relays saves both the transmission power and the transmission time.     

分层空时编码及应用研究

分层空时编码是应用于多输入多输出系统中的一种空时编码,具有结构简单、易于实现且频带利用率随着发射天线数目的增加而线性增加等优点。针对分层空时编码传输速率高、无法获得最大分集增益以及系统抗衰落性能差等缺点,提出了一种结合空时分组码的混合结构模型——分层空时混合码。同时,介绍了分层空时编码检测算法的最新进展以及分层空时编码在自由空间光通信、OFDM系统中的研究成果及应用。     

Distributed differential space-time coding for wireless relay networks

Distributed space-time coding is a cooperative transmission scheme for wireless relay networks. With this scheme, antennas of the distributive relays work as transmit antennas of the sender and generate a space-time code at the receiver. It achieves the maximum diversity. Although the scheme needs no channel information at relays, it does require full channel information, both the channels from the transmitter to relays and the channels from relays to the receiver, at the receiver. In this paper, we propose a differential transmission scheme, which requires channel information at neither relays nor the receiver, for wireless relay networks. As distributed space-time coding can be seen as the counterpart of space-time coding in the network setting, this scheme is the counterpart of differential space-time coding. Compared to coherent distributed space-time coding, the differential scheme is 3dB worse. In addition, we show that Alamouti, square real orthogonal, and Sp(2) codes can be used differentially in networks with corresponding numbers of relays. We also propose distributed differential space-time codes that work for networks with any number of relays using circulant matrices.     

一种新的两用户协作分集方案及其性能研究

该文提出了一种基于信道编码和分布式空时分组码级联下的两用户协作分集方案,并且在准静态的瑞利衰落信道下对此方案的系统容量,中断概率以及误比特率进行了理论推导和系统仿真,分别给出了解析表达式和数值结果。通过将信道编码和空时码引入到协作分集中,系统容量得到显著改善,同时中断概率也明显降低。在协作用户间信道存在噪声的情况下,对卷积码与分布式空时分组码级联下的发射方案进行了性能分析和仿真。仿真结果表明:即使协作用户间的信道存在噪声,该文所提方案在各方面都优于传统协作分集,系统容量明显增大,中断概率及误比特率大大降低。     

Performance analysis of distributed Alamouti space-time codes in full-duplex cooperative communication system

The error performance of distributed Alamouti space-time code (DASTC) was investigated in a 3-node full-duplex (FD) cooperative communication system with the presence of residual self-interference (RSI).Based on the asymptotic expression of the pairwise error probability in the high transmit power region,the diversity and coding gain were derived.The impact of residual self-interference on the construction of space-time code was analyzed and the achievable condition of diversity gain was obtained.Analytical results show that DASTC achieves full rate and full diversity in the FD cooperative communication system with high transmit power and low RSI.The error performance of the FD system is superior to which of the half-duplex system under the same spectral efficiency constraint.The diversity and coding gain can be increased by sufficiently suppressing the self-interference,and the spectral efficiency and power efficiency can be improved as well.     

Diversity–Multiplexing Tradeoff of Asynchronous Cooperative Diversity in Wireless Networks

Synchronization of relay nodes is an important and critical issue in exploiting cooperative diversity in wireless networks. In this paper, two asynchronous cooperative diversity schemes are proposed, namely, distributed delay diversity and asynchronous space-time coded cooperative diversity schemes. In terms of the overall diversity-multiplexing (DM) tradeoff function, we show that the proposed independent coding based distributed delay diversity and asynchronous space-time coded cooperative diversity schemes achieve the same performance as the synchronous space-time coded approach which requires an accurate symbol-level timing synchronization to ensure signals arriving at the destination from different relay nodes are perfectly synchronized. This demonstrates diversity order is maintained even at the presence of asynchronism between relay node. Moreover, when all relay nodes succeed in decoding the source information, the asynchronous space-time coded approach is capable of achieving better DM tradeoff than synchronous schemes and performs equivalently to transmitting information through a parallel fading channel as far as the DM tradeoff is concerned. Our results suggest the benefits of fully exploiting the space-time degrees of freedom in multiple antenna systems by employing asynchronous space-time codes even in a frequency-flat-fading channel. In addition, it is shown asynchronous space-time coded systems are able to achieve higher mutual information than synchronous space-time coded systems for any finite signal-to-noise ratio (SNR) when properly selected baseband waveforms are employed.     

Some analytical tools for the design of space-time convolutional codes

Space-time convolutional codes have shown considerable promise for providing improved performance for wireless communication through combined diversity and coding gain. An efficient design procedure is presented for optimizing the coding and diversity gain measures proposed in the first papers on space-time codes. The procedure is based on some simple lower and upper bounds on coding gain. The same calculations needed to compute these bounds can be used to check either necessary or sufficient conditions on space-time codes which achieve maximum diversity gain. A new simple, but useful, measure of code performance is also suggested which augments existing measures. The use of the design procedure is illustrated and new codes are provided. These codes are shown to outperform the space-time convolutional codes provided in the initial papers introducing space-time codes.     

MIMO系统中线性弥散空时码的优化设计

MIMO系统的大部分空时编码方法在设计时单一强调对传输分集性能或传输复用性能的提高,为了联合提高分集性能和复用性能,在LDC编码基础上提出了线性正交弥散空时码(OLDC),LDC编码的优化中利用遗传算法来构造OLDC的空时正交调制基矩阵.优化的编码方法设计简单,便于调制解调.仿真结果表明,OLDC码比传统的LDC编码在误码性能、分集性能、复用性能等方面均有大幅度提高.     

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。     

满速率串行级联空时分组MTCM编码方法研究

该文研究了级联空时编码系统在编码增益,分集增益和传输能量效率的限定下最大化传输速率的问题,提出了一种在保留TCM编码方法校验位冗余的同时,还可获得满速率串行级联空时分组TCM编码方法。新方法通过引入具有不同功率分集因子的正交发射码字矩阵,并给出新的译码算法,从而使得新的编码方法在获得满速率的同时还可以获得满分集增益。分析和MATLAB仿真结果表明,在相同的编码状态数下,新方法在编码增益上比现有的满速率超正交空时分组编码方法提高1dB左右。