散射通信的协作分集技术研究

对协作分集进行简单介绍,提出了将协作分集应用到散射通信中的方案,分析了协作分集在散射通信中的应用可行性。并对其中的放大转发和译码转发在只有一个中继节点的情况下进行仿真,仿真结果证明在大信噪比时译码转发的性能优于放大转发。且协作分集应用到散射通信中在相同的信噪比下,误码率更低,提高了系统性能。利用协作分集技术对散射通信进行组网,较直接组网设备复杂度低,易于实现。     

固定增益的两跳OSTBC中断概率分析

研究信源和终端需要配置多根天线,而中继只有单根天线的两跳中继转发系统。为了获得空间分集,信源利用了正交空时分组编码（OSTBC）的发射策略,终端利用了选择合并方式。为了尽可能简化中继配置的复杂度,中继采用固定增益放大转发的协议。在信源和终端直接通信链路存在的情形下,首先导出总的接收信噪比的表达式,接着导出瑞利衰落条件下系统中断概率的封闭表达式,最后通过蒙特卡洛仿真和数值结果的比较,验证了理论导出表达式的精确性。     

多节点协作通信技术研究

为了解决用户节点无法安装多个天线的问题,提出了多节点协作通信技术来形成虚拟的多天线阵列。多节点协作是一种新的空间分集方法,不同节点彼此共享天线并相互转发信息来得到分集增益。通过研究多节点协作通信的关键技术,分析多节点协作的性能增益,指明了多节点协作的发展与应用方向。     

移动通信网络中的协作通信

文章介绍了一种叫做协作通信的新方法,在该方法中带有一根天线的移动台在多用户环境中可以共享它们的天线,这样就可以产生虚拟的多根发射天线从而得到相应的分集增益。     

具有天线选择与中继选择的空间调制技术

针对空间调制(SM)技术存在的缺欠,提出了具有天线选择和中继选择的空间调制系统方案。首先在多输入多输出(MIMO)信道模型下,通过对发送端天线选择,将拥有最佳信道状态的天线选出进行SM,打破SM技术对发送端天线数的限制,并提升采用高阶调制的SM分集性能。然后进一步将此思想引入协作通信网络,结合传感器网络的分级观念,提出采用中继选择和空间调制的中继传输协议,并通过仿真观察系统分集性能的改善。仿真结果表明,上述中继传输协议不仅能提升系统性能,而且使系统配置更加灵活。     

多用户SIMO-OFDM系统中的协作分集性能分析

协作分集使得在多用户环境下,具有单天线的多个终端可以共享彼此的天线,以形成一个虚拟的天线阵列结构,实现空域分集。首先介绍了多用户SIMO—OFDM系统中的两种协作方式,放大前传和译码前传。然后针对源结点和目的结点之间是否存在路径损耗,提出了一种基于信道状态信息的选择中继协作方式,并对系统性能进行了理论和仿真分析。仿真结果表明,这种基于信道状态信息的选择中继协作方式可以获得较好的系统性能。     

分布式环境中协作分集的移动中继动态选择和切换策略研究

在协作无线通信系统中,中继节点的移动会大大降低系统的性能,目前该方面的结果很少。本文探讨分布式环境中协作分集的移动中继选择算法,在放大转发（AF）协作通信模式下,给出了基于信道统计状态信息的功率分配和中继的动态选择策略。针对单中继情况提出了中继切换方案,针对多中继情况提出了动态剔除、补充中继的方案,并导出了分集增益及系统容量的计算公式。通过模拟仿真分析,该方案能有效的降低中断概率,提高系统分集增益,扩大系统容量,实现良好的整体性能。      

基于中继放大转发的多天线基站下行传输性能分析

研究基站具有多根天线、中继与用户具有单天线的中继放大转发多用户系统,利用正交空时分组编码和机会主义调度策略同时获得空间分集和多用户分集.针对自适应增益和固定增益转发策略,首先导出独立不同分布瑞利衰落下系统中断概率和误码率的闭合表达式;随后根据高信噪比下系统的渐近性能确定系统的分集阶数,分析空间分集和多用户分集对系统性能的联合影响,并与单跳多天线基站下行传输系统进行性能比较;最后利用计算机仿真验证理论分析结果的正确性.     

认知无线电中协作中继技术的研究

在无线通信环境中,衰落、多径和节点的移动都会导致通信环境较差,这些因素严重地影响了通信质量。当系统中有协作中继参与时,主用户可以通过共享中继的多根天线来获得增益完成通信从而有效抵抗了无线环境中的不良因素影响。本文建立了一个进行双向通信的主用户需要中继协助才可以完成通信的协作模型。并且定义中继采用放大转发的方式帮助主用户传输数据。本文理论分析了各个节点的中断概率,并通过仿真结果表明,本文提出的中继传输方法不仅使得主用户有效的完成了通信而且还减小了主用户的中断概率。     

基于译码——转发的多中继协作节点选择方法

由于协作通信技术能够抵抗信道衰落的影响,提供分集增益,成为目前研究热点之一。针对传统多中继译码转发协作通信中,所有潜在中继均参与协作从而导致系统的低资源利用率问题,提出了一种基于信道容量增益的中继节点选择策略。仿真结果表明,该策略只需选择一半的中继节点数就能获得和最优中继选择方法非常相近的系统性能,同时降低了系统的功率损耗和实现复杂度。     

空时协同分集通信及其最新进展

协同通信利用通信网中其它用户的天线作为中继,实现“虚拟天线”的空间传输分集,从而提高系统性能,它在民用与军事通信应用中有广阔的应用前景。本文综述了协同通信的主要协同方法、基本性能比较、在实际应用中存在的主要问题及需解决的关键技术,以及协同通信的最新研究方向。     

编码协作MARC上全分集LDPC码的实现与性能分析

本文研究了多接入中继信道(MARC)上全分集LDPC码的实现与性能。首先,分析了MARC模型及其固有分集,然后构造了在MARC上能取得全分集的LDPC码,新构造的码字采用根校验节点把源节点传输与中继节点传输联系起来,从而获得全分集。接着,研究了所构造码字的密度演化过程,在密度演化的基础上,进一步分析了全分集LDPC码校验矩阵的结构,给出了通过提高全分集校验比特的比例,改善全分集LDPC码在MARC上编码增益的方法。仿真结果表明,本文所提算法在MARC信道上不仅能实现全分集,而且能取得较高的编码增益。     

A Survey of Distributed Relay Selection Schemes in Cooperative Wireless Ad hoc Networks

Cooperative communication aims to achieve spatial diversity gain via the cooperation of user terminals in transmission without requiring multiple transceiver antennas on the same node. It employs one or more terminals as relays in the neighbourhood of the transmitter and the receiver, which collaborate in the transmission and serve as a virtual MIMO antenna array. Allowing cooperation in wireless communication engenders new problems related to resource allocation and relay selection. Optimal relay selection is vital for reaping the performance benefit of cooperative communication. It is a challenging task to share channel information in timely and distributed manner and at the same time make optimal selection of relay in a time varying radio environment. This paper presents a comprehensive survey of distributed relay selection schemes for cooperative communication that have been proposed in the literature. We discuss various classifications of relay selection schemes and describe their characteristics and functionality. We then present a qualitative comparison of their performance against a set of representative metrics. Finally, we discuss some of their shortcomings and suggest some research directions.     

基于协作通信的TD-VAA-SCDMA系统

协作通信解决了普通单天线移动终端的空间分集问题,使单天线移动终端在多用户环境中可共享其他终端的天线,从而得到多天线分集增益,改善了移动通信系统的性能.本文从协作通信的概念和原理出发,提出了一种基于协作通信的虚拟多天线(VAA)TD-SCDMA系统,探讨了该系统中各层的实现和面临的挑战.     

分布式协同传输协议设计与系统实现

协同传输作为一种可靠通信技术,通过利用空间分集,能够克服无线通信收发双方经历的信道衰落、噪声干扰、路径损耗等,有效提升系统传输性能。目前有关协同通信技术的基础理论研究较多,但大多数理论研究并没有应用到实际的原理样机中,因此缺少实测数据作为支撑。本文首先设计实现了一种自适应分布式协同传输协议,该协议通过信道感知技术实时获取信道质量信息,自适应地选择协同节点和协同传输方式。通过将所设计的传输协议实现在自主研发的原理样机上,本文从误码率、丢包率和吞吐量三个性能指标上,分别测试了系统在室内、室外、地面、空中等应用场景下的实际传输性能。测试结果表明,相比于传统点对点直传方式,本文所提的自适应分布式协同传输技术能够显著提升节点间的可靠传输性能,实现分布式多节点的自主协同组网通信。      

Predictive relay‐selection cooperative diversity in land mobile satellite systems

Cooperative diversity protocols promise a new dimension of diversity that provides better communication by engaging nearby relays in forming a ‘virtual’ array of antennas for combined signal transmission. The current incremental cooperative diversity algorithms incrementally select best relay(s) to cooperate based on the channel quality reported by the relays. However, the algorithms do not take into consideration the fact that the chosen best relay(s) at estimation may not always be the best at the time of communication. This is due to the time delay between the relay selection and its transmission of signal (problem of outdated channel quality information (CQI)). To solve this problem, the concept of channel prediction is introduced and employed whereby each relay determines a predicted value of its CQI based on its past measurements. The paper therefore develops a novel predictive relay‐selection (PRS) cooperative diversity model that seeks to improve land mobile satellite communication through prediction protocols. In the model, the chosen best relay is the one with the best predicted CQI value instead of the traditional outdated one. Performance analysis of outage probability and average bit error probability for the newly developed PRS cooperation shows that the PRS cooperation is better than direct and outdated CQI relay communication. Copyright © 2015 John Wiley & Sons, Ltd.     

Cooperative diversity performance for OFDM transmission over partially jammed channels

Cooperative diversity is a transmission technique, where multiple terminals share their resources to form a virtual antenna array that realizes spatial diversity gain in a distributed fashion. In this paper, we focus on a performance evaluation for orthogonal frequency division multiplexing (OFDM) transmission in cooperative networks under partial-band jamming (PBJ) environments. We present a bit error rate (BER) analysis for a cooperative diversity system with amplifying-and-forward (AF) relays over partially jammed Rayleigh fading channels. In addition, a simple jamming mitigation technique, called relay-based sub-band shifting method, is proposed. Through this approach, each sub-band of the amplified OFDM symbol at the relay can be changed by the predefined shifting rule of each relay, and the jamming effects at the destination are partially removed. Simulation results show that the proposed method improves significantly the BER performance at a low signal-to-jamming ratio.     

具有大规模天线选择与功率分配的协作通信

在瑞利衰落信道下研究了采用前向译码转发协议的三节点协作模型,分析了中继分布大规模天线阵列时系统的可靠性能。为了有效地降低系统复杂度,同时又能获得大规模天线带来的分集增益,给出了中继选择合并(SC)与天线选择空间调制(SM)相结合的组合传输方案。为了进一步提高可靠性能,研究了SC/SM组合方案如何通过功率分配优化其误比特率性能。仿真分析表明,大规模中继SC/SM方案的功率分配能够有效改善系统的误比特率性能。     

Performance Analysis of Maximum SNR Scheduling with an Infrastructure Relay Link

We consider infrastructure-based amplify-and-forward (AF) relaying for extending downlink and uplink coverage areas of a cellular base station. The base station serves multiple mobile users via a multi-hop backhaul relay link by sharing out access link channel resources with maximum signal-to-noise ratio (SNR) scheduling. We analyze the performance of the system by deriving closed-form expressions for outage probability, outage capacity, ergodic capacity, average end-to-end SNR and amount of fading (AoF). These measures show that maximum SNR scheduling of multiple users in a cellular relay link offers significant diversity, capacity and SNR improvement over single-user transmission and round robin scheduling. We also relate performance of the relay link to that of a distributed antenna system (DAS), and show that the noisy wireless backhaul relay link induces tolerable performance deterioration compared to deploying a cable-connected distributed antenna.