基于跨层机制的最佳协作中继选择及其系统实现

为了获得最佳的协作中继用户,通过推导协作中继传输系统的误符号率,提出了基于放大重传和解码重传下最佳协作中继的选择准则,并结合跨层协作的思想给出了基于MAC层来实现最佳协作中继选择的分布式协议.与此同时,提出了协作分集系统的物理层传输方案,分析了瑞利衰落信道环境下所提方案的系统性能,得到了系统误比特率的闭式解.此外,针对协作中继选择准则和协作分集传输方案的误码性能进行了系统仿真和性能比较,结果表明,所提出的协作中继选择准则明显优于传统中继选择准则,且协作传输方案可以获得明显的分集增益,系统平均误比特率显著下降.     

编码协作通信技术的研究

协作分集技术是目前移动通信技术的研究热点。文中首先介绍了协作分集技术的研究现状，然后分剐阐述了目前已经提出的三种协作通信中继协议——放大前传、译码前传以及编码协作，最后重点研究了性能最佳的编码协作分集技术．     

编码协作分集研究与展望

用户协作方案是协作分集研究的一个重要方面。在慢衰落和快衰落信道条件下,均能带来传输性能改善的编码协作分集方案,是目前协作分集方案中备受关注的一种。尤其在将空时编码的思想引入该方案后,更带来了编码协作分集在快衰落信道条件下的良好性能。用户要想从协作中受益,协作伙伴/中继节点的选取是编码协作分集中一个重点。     

基于分布式中继选择的自适应协作传输方案

协作分集通过使网络用户共享彼此天线以形成虚拟多天线阵列,可以显著提高网络容量,然而针对网络拓扑的动态变化与无线传输的时变特性,仅靠协作分集并不能十分有效地解决这些问题,必须结合考虑相应的自适应传输策略.本文提出动态网络环境中协作中继的最佳选择准则,在此基础上给出最佳协作中继的分布式选择协议.根据协作中继与源节点间的无线信道质量,进一步提出一种自适应协作传输方案,以有效抵抗多用户网络环境中的无线衰落.此外,对自适应协作传输方案的误码性能,在瑞利衰落信道下进行相应的理论分析,得到了系统误比特率的解析表达式,据此给出数值仿真实验以进行性能比较.结果表明:相对于传统协作分集而言,本文提出的自适应协作传输方案获得了进一步的性能增益,误比特率显著下降.     

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。      

协作分集中中继选择算法的研究

协作分集是近几年无线通信技术的研究热点.在协作通信中合理地选择中继能给系统带来更大的增益.本文介绍了协作时机的选择和协作关系的形成,重点讨论了3种主要的中继选择方法:基于位置信息、基于平均接收信噪比和基于瞬时信道状态的中继选择算法,并对这些方法进行了分析和比较.     

协作通信中一种改进的最佳中继选择算法

已有研究结果表明,机会中继可以获得与更为复杂的空时编码协作通信相同的分集增益。但是,随着可选中继节点数的增多,发生冲突从而导致选择失败的概率也明显变大。本文提出了一种改进的最佳中继选择算法,源站收到最佳中继发出的标志分组后发送选择确认消息,中继节点在冲突发生后进行退避。分析结果证明,采用新算法可以大大降低选择失败的概率,而增加的开销却很小。     

AF协同通信系统最优多跳中继位置

协作中继能够提供分集增益以提高链路成功发送分组的概率,除传输功率外,中继位置也是影响端到端性能的一个重要参数。为了降低多个协作节点对系统容量的影响,多跳中继是当前协作中继发展的一种新趋势。通过中断概率,得出了吞吐量的理论近似表达式,并进一步研究多跳中继位置对吞吐量的影响。仿真结果表明,多跳中继处于源节点和目的节点的中点...     

基于解码重传的最佳协作中继选择策略

近年来提出的协作分集技术通过使网络中各单天线用户共享彼此天线以形成虚拟多天线阵列,从而可以显著提高网络容量,也使得其备受科研工作者的关注。提出了基于解码重传（DaF）下的被动式最佳协作中继选择准则,该准则是通过推导协作中继传输系统的误符号率而得出的。在总功率限制下,可以证明基于解码重传下的机会中继在中断性能上考虑是最佳的,更确切地说,它的中断性能和利用全部候选中继传输的最佳解码重传策略是一样的。     

空时编码协作中的中继选择与功率分配联合方案

提出了一种空时编码协作中的中继选择与功率分配联合方案,称为DD(Destination Decision)方案.该方案由目的终端根据协作终端的信道状态信息进行中继选择与功率分配,并决定各中继发送STBC编码矩阵的哪一列,从而避免了通过中继之间的信息交互进行中继选择的冲突.理论分析和仿真结果表明,此方案在保证分集阶数和误码率性能的同时,提高了系统容量.     

Joint resource allocation,routing and CAC for uplink OFDMA networks with cooperative relaying

In this paper, we propose a joint resource allocation, routing, and connection admission control (CAC) scheme for uplink transmission in orthogonal frequency division multiple access (OFDMA) relay networks with cooperative relaying. For cooperative relaying, relay station can relay uplink data from mobile station (MS) to base station with cooperation of the MS using transmit diversity. Transmit diversity can be achieved by virtual MISO via distributed space–time coding. The proposed scheme jointly allocates OFDMA resources and selects path for each user with CAC to maximize the upink throughput of cooperative OFDMA relay networks. The basic OFDMA resource unit is considered as a resource element which is one subcarrier over one OFDMA symbol. An efficient multi-choice multi-dimensional knapsack (MMKP) algorithm is presented for the proposed scheme. The proposed MMKP algorithm provides a unified framework which is applicable to OFDMA networks with and without cooperative relaying. We evaluate the performance of the proposed scheme with and without cooperative relaying in a hilly terrain with heavy tree density by using OPNET-based simulation. We show that the cooperative relaying improve the uplink system throughput compared with non-cooperative relaying, and the proposed scheme outperforms the conventional link quality-based scheme in both cooperative and non-cooperative relay networks.     

Cooperative communications with relay selection for wireless networks: design issues and applications

Relay selection schemes for cooperative communications to achieve full cooperative diversity gains while maintaining spectral and energy efficiency have been extensively studied in a recent research. These schemes select only the best relay from multiple relaying candidates to cooperate with a communication link. In the present paper, we reviewed recently proposed cooperative communication protocols that integrate with relay selection mechanisms. The key design issues for relay selection mechanisms, for example, relaying candidate selection, optimal relay assignment, and cooperative transmission, were identified. We further discussed the challenges of optimal relay assignment in multi‐hop wireless sensor networks and presented the potential applications of cooperative communications with a relay selection in such networks. Future research directions were outlined, for example, the issues of service differentiation and system fairness in cooperative communication systems and the joint use of game theory and adaptive learning techniques in relaying candidate selection and optimal‐relay assignment mechanisms for efficient allocation of network resources. Copyright © 2011 John Wiley & Sons, Ltd.     

一种基于自适应网络卷积编码的协作中继方法

在无线衰落信道环境中,协作中继是一种增加额外分集增益的有效方法,而网络编码可以用来提高网络吞吐量。网络编码采用XOR(异或)来混合两个源端的信息包,其稳健性差并且每个中继只能服务两个源端。该文提出一种自适应网络卷积编码协作中继方法,在中继端采用卷积编码方法代替XOR来混合两个或多个源端的信息包,混合后的信息可以看作是卷积编码器的一路输出,然后将其转发给目的端。当信道处于深度衰落时,该文提出了一种宽松自适应网络卷积编码协作中继方法,放松了中继参与转发的条件。该文提出的中继方法稳健性好,可以自适应匹配变化的无线网络拓扑结构,并且减少了网络编码协作中继方法所需要的中继个数。理论分析和仿真结果表明所提出的中继方法相比网络编码协作中继方法在性能上有大幅提高,尤其是随着协作节点数目增加,可保证系统获得稳定的额外满分集增益。     

Adaptive Path Selection Scheme with Combining for Multiple Relaying Cooperative Communications Networks

In future communications, cooperative communications with relay networks will be one of the most effective schemes to enlarge the coverage area and to boost the data rate. In the recent research results, the path selection, power allocation, and relay protocols on relay networks are the most important factors to improve the system performance. However, the channel quality of the direct transmission path and the relaying path has an influential effect on the performance of relay networks. Therefore, in this paper, we propose a best relaying path selection (BRPS) scheme to obtain the path diversity to improve the system capacity and data rate for cooperative networks (CNs). Simulation results show that the more the relay nodes are selected, the lower the bit error rate (BER) is. The proposed BRPS scheme obtains a high concession between both BER and system capacity for CNs.     

中继节点随机均匀分布的机会中继

本文研究了中继节点空间随机均匀分布时,采用机会中继进行协作通信。在路径损耗及块衰落独立信道条件下,推导和分析了两节点间采用传统中继结合机会中继以及增量中继结合机会中继两种方式下的中断概率。数值仿真结果表明,虽然中继节点的空间随机分布破坏了高信噪比条件下中继节点能够提高的分集阶数,但机会中继仍比直接通信有更好的抗信道衰落能力。      

Joint power allocation and relay selection for decode-and-forward cooperative relay in secure communication

In this paper, we investigate the cooperative strategy with total power constraint in decode-and-forward (DF) relaying scenario, in the presence of an eavesdropper. Due to the difference of channel for each source-relay link, not all relay nodes have constructive impacts on the achievable secrecy rate. Besides, the final achieved secrecy rate depends on both source-relay and relay-destination links in DF relaying scenario. Therefore, the principal question here is how to select cooperative strategy among relays with proper power allocation to maximize the secrecy rate. Three strategies are considered in this paper. First, we investigate the cooperative jamming (CJ) strategy, where one relay with achieved target transmission rate is selected as a conventional relay forwarding signal, and remaining relays generate artificial noise via CJ strategy to disrupt the eavesdropper. Two CJ schemes with closed-form solutions, optimal cooperative jamming (OCJ) and null space cooperative jamming (NSCJ), are proposed. With these solutions, the corresponding power allocation is formulated as a geometric programming (GP) problem and solved efficiently by convex programming technique. Then, to exploit the cooperative diversity, we investigate the cooperative relaying (CR) strategy. An iterative algorithm using semi-definite programming (SDP) and GP together with bisection search method is proposed to optimize the cooperative relaying weight and power allocated to the source and relays. Furthermore, to exploit the advantages of both CR and CJ, we propose an adaptive strategy to enhance the security. Simulation results demonstrate that the efficiency of the proposed cooperative strategies in terms of secrecy rate.     

基于协作通信的最佳中继选择方案

协作通信中的机会中继是一种基于即时信道状态选择的中继选择算法,可以获得与传统协作分集技术相同的分集增益,而不需要使用复杂的空时编码技术。但是多个节点同时竞争最佳中继时,可能出现冲突而导致选择失败。提出一种新的方案,通过引入候选节点限制策略以及控制信道对算法进行改进,仿真表明,该算法特别适用于候选中继较多的情况,可以在实现快速选择节点的同时降低选择失败概率。     

Asymptotic analysis of amplify-and-forward relaying in Nakagami-fading environments

Amplify-and-forward (AF) relaying strategies are studied for Nakagami-fading channels in an (N + 2)-terminal wireless cooperative system where a source terminal transmits information to a destination terminal with the assistance of N relay terminals. The asymptotic outage behavior is investigated in terms of coding and diversity gains for channel-state information (CSI)-assisted AF relaying and semi-blind AF relaying in various channel profiles. It is shown that semi-blind AF relaying system achieves strictly higher average SNRs. Further, when there exists fading severity difference between the source-to-relay and relay-to-destination links, both AF strategies achieve the same diversity gain whereas semi-blind AF achieves strictly lower coding.     

认知合作中继网络中的最优中继选择策略

认知合作中继通信可以有效提升无线通信网络的性能和频谱效率。在中继节点较多的情况下,最优中继选择是一个有待解决的问题,它是中继探测成本与合作通信的分集增益之间的一个折中。基于有限情形的最优停时理论给出了最优中继选择策略,进一步得到一个纯SNR（signal-to-noise ratio,信噪比）阈值结构的策略。数字仿真结果验证了其有效性,在待探测中继较多和每个中继探测成本较高情况下,该最优中继选择策略以最少的探测次数获得最大的收益增益。