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1、西南交通大学硕士学位论文基于分集复用折中分析的协作分集技术研究姓名：孙伟申请学位级别：硕士专业：通信与信息系统指导教师：陈庆春20090501西南交通大学硕士研究生学位论文 第l页摘 要多径传播是移动无线信道的主要特征，其引起的信号幅度衰落和时延扩展是影响信号质量的主要因素。分集技术作为一种常用抗衰落技术得到了广泛应用，根据分集信号的产生原理可分为时间分集、空间分集、频率分集、极化分集等多种方式。其中空间分集可以与其他多种分集方式结合，因此应用更加广泛。近年来提出的多输入多输出(MultipleInput Multiple-Output，MIMO)技术，通过多天线形成MIMO信道结构，从而充分
2、利用了空间资源，大幅度提高了信道容量。但是移动终端由于物理条件限制很难满足传统MIMO要求，于是出现了一种利用用户间协作传输来模拟多天线结构的新技术协作分集。由于多天线技术可以同时提供分集增益和复用增益，而研究又发现提高其中一种增益会导致另一种增益的下降，所以分集增益和复用增益的合理折中渐渐成为了评价分集技术的新标准。本文在现有的研究和分析基础上，分别对同步和异步条件下的几种常用协作分集技术进行了分析，主要采用误码率和分集复用折中两种指标评估协作分集技术性能。对于同步条件下的协作分集方案，本文首先对基于Alamouti发射分集的协作分集方案的误码率性能分别进行了分析。研究结果表明，基于Alam
3、outi发射分集的协作方案误码率性能随着接收天线数的增加而逐渐改善，随着信号调制阶数的增加而逐渐变差。接着本文对基于正交信号的协作分集方案进行了分析，在原模型基础上考虑了当两用户到接收端信道条件不同时系统的误码率性能，并通过引入链路自适应功率控制对协作方案进行了改进，分析结果说明，链路自适应可以有效缓解“门限效应”。其次本文分别分析了两种方案的分集复用增益折中关系，得到基于Alamouti发射分集的协作分集方案的分集复用折中曲线。分析表明随着接收天线数m的增加，协作系统的分集增益逐渐提高，而复用增益无变化。对基于正交信号协作分集方案的分集复用折中关系的分析结果说明链路自适应只能改善系统的误码率
4、性能，而不能改善分集复用折中性能。对于异步条件下的协作分集方案。本文首先对延迟分集方案的误码率性能和分集复用折中性能进行了理论分析，得出了用中继节点等效的分布式延西南交通大学硕士研究生学位论文 第1I页迟分集的误码率性能，并进行了仿真验证。接着分析了这种分布式延迟分集的分集复用折中关系，结果表明当各路延迟信号间的延时满足一定条件时，延迟分集方案能实现与同等信道传输条件的同步重复编码的协作分集相同的分集复用增益折中。其次论文对基于分布式延迟分集的异步协作分集方案的误码率性能和分集复用折中进行了分析，并对方案的延时选择和中继转发策略做了改进。分析结果表明对方案的改进可以带来一定的性能提升。针对异步
5、协作分集的分集复用折中关系的分析表明，当分集信号的相对延时满足一定条件时，异步协作分集方案可以实现与基于中继传输的同步协作分集方案相同或更好的分集复用折中性能。论文的相关分析从误码率以及分集增益和复用增益折中关系的角度来对协作分集方案进行了评估，为协作分集方案的设计和评价提供了参考。关键词：协作分集；Alamouti；正交信号；延迟分集；异步协作分集；分集复用折中 、西南交通大学硕士研究生学位论文 第ll l页Abst ractThe mobile wireless channels could be characterized by its multipathpropagation，from
6、 which the signal fading and delay spread ariseAs an effectiveantifading technology,diversity,has been widely used in wirelesscommunicationAccording to the way to achieve the diversity,there are timediversity,space diversity,frequency diversity and their combinationsAmongdifferent implementations，sp
7、ace diversity is widely utilized due to itseffectiveness and impressive performance improvement without additional timeand frequency resourceMulti-Input MultiOutput(MIMO)systems Cansignificantly increase the channel capacity by exploiting the multi。pathtransmission characteristic in wireless systemH
8、owever，the MIMO techniquemay be hard to be implemented directly in some cases duo to the physicalconstraints of mobile unitThus，the idea of cooperative diversity is proposed tosolve this problem by using a virtual multiantenna structure generated by pairs ofuser with single antennaIt is known that m
9、ultiantenna deployment can offerboth diversity gain and multiplexing gainMoreover,its unveiled that，theincrease in one of two gains will definitely result in the decrease in another gainTherefore，a rational tradeoff between diversity gain and multiplexing gainbecomes a new design criterion for multi
10、ple antenna diversityIn this thesis，fourdifferent types of synchronized and asynchronous diversity schemes will beanalyzed in terms of BER performance and the diversity-multiplexing(DM)tradeoffThe thesis begins with the analysis of synchronous cooperative diversityschemesThe Alamouti-type of coopera
11、tive diversity scheme is firstly analyzedon its BER performanceIt is shown through simulation results that，the BERperformance increases with the number of receive antennas and decreases withthe modulation orderThen the thesis analyzes the BER performance of thescheme based on orthogonal signaling wh
12、en the channel conditions between users西南交通大学硕士研究生学位论文 第1 V页and the receiver are dissimilarThen a linkadaptive power control is used tomodify the orthogonal signaling diversity schemeIt is validated that，thelinkadaptive power control can effectively alleviate the threshold phenomenaSecondly,the DM t
13、radeoffs of the previous two types of cooperative diversityschemes are derivedThe tradeoff curves of the Alamouti type of cooperativediversity scheme show that，with the increase of the number of receiver antennas，the diversity gain increases while the multiplexing gain remains unchangedAnalysis of t
14、he orthogonal signaling cooperative diversity scheme indicates thatlink-adaptive technology Can only improve the BER performance，but call notbring an enhancement on the DM tradeoffThe thesis continues with the analysis of asynchronous cooperative diversityschemesThe BER performance and DM tradeoff a
15、nalysis of the delay diversityscheme demonstrates that，the delay diversity can achieve the same DM tradeoffas the repetition coded diversity as long as the relative delay between relays meetcertain conditionsThe thesis then investigates the BER performance and the DMtradeoff for a kind of asynchrono
16、us cooperative diversity based on the distributeddelay diversitySome modifications are made to the scheme by improving thedelay selection and the forward scheme of relay nodesResults indicate that，withcertain delays between relays，the asynchronous cooperative diversity Call achievethe same，or even better,DM tradeoff as the synchronous cooperative diversityThe BER and DM tradeoff analysis in this thesis could be used as a referencein both th
