基于合作分集的无线网络的研究

在发送端采用多根天线实现发送分集技术可以有效抑制多径干扰引起的信号衰落。但在很多实际应用中由于硬件复杂性和成本等方面的限制,不允许终端用户配置多根天线。针对此情况在物理层提出一种合作通信方式,利用网络中多个用户共享天线形成虚拟多天线,达到天线分集作用, 有效降低无线网络成本,提高网络的覆盖范围。研究了基于合作分集技术系统结构和合作方法,提出实现中涉及的若干关键技术。     

Nakagami衰落信道下合作分集的无线家庭网络性能分析

提出在未来无线家庭网中采用合作分集的思想,通信时利用处于空闲状态的终端用户对所发送信息进行中继发送,保证整个网络误码率性能、中断概率以及发送功率达到最佳折衷.在Nakagami平衰落信道条件下研究了再生中继和非再生中继两种合作方式下的中断概率和误码率性能,给出误码率和中断概率的解析表达式,并用matlaab进行仿真,仿真结果表明,在低信噪比条件下再生中继大大优于非再生中继方式,但高信噪比条件下两者性能接近.     

基于选择性分集技术的无线中继系统性能

采用中继传输能够抵抗无线信道的多径衰落,克服阴影效应,从而增强通信质量,提高频谱效率。该文首先给出了两跳中继系统模型,针对非再生及再生两类中继方式,简要介绍了采用非分集接收及最大比合并时的链路性能。考虑到接收机复杂度和系统实现的性能代价比,该文引入了处理相对简单但又具备分集优势的选择性合并方式,并根据中继节点不同的位置分布,分析了两类中继方式下系统的通信中断概率和误码率。数值结果表明,非再生中继传输具有较好的性能,同时中继系统若采用选择性分集接收,则既能降低收端复杂度,又能获得较大的性能增益。     

Nakagami衰落信道下多跳合作分集系统的中断率

该文在Nakagami衰落信道下研究了多跳无线网络中合作分集系统的中断性能。根据单节点和多节点中继的情况导出了合作系统再生中继时中断率的数学闭式解,并在高平均信噪比下给出了系统的分集度。理论分析和仿真研究的结果表明多跳合作系统在一定条件下可实现全路由分集,其分集度为所有路由的分集度之和,不是所有合作节点的和,但每支路由的分集度取决于该路由两跳中较小的值。     

连续重传协议和选择重传协议的性能分析

连续重传(gobackn)协议和选择重传(selectiverepeat)协议都属于滑动窗口协议范畴。数据链路层的许多协议(如HDLC,PPP)都是在此基础上发展起来的。本文利用Linux系统下的管道概念模拟实际通信中的物理媒质,对连续重传协议和选择重传协议进行了仿真,并将两者的性能进行对比分析。     

基于无线电波广播特性的多用户自动请求重传

提出了一种多用户自动请求重传的方法。采用网络编码基站将多个用户的重传数据包线性组合在一起后广播;用户利用置信传播算法从中检测出基站发给本用户的重传数据包,并和以前传输的数据包软合并后译码。分析表明：多用户自动请求重传能够将无线通信系统的频谱效率提高10%左右,并且复杂度和单用户自动请求重传相近。另外,该方法适用于所有类型的自动请求重传机制。     

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。     

通用选择合作分集及其阈值选择改进方案的性能分析

提出了适用于多跳无线网络的通用选择合作分集及其基于阈值选择的改进方案。在瑞利衰落下研究了所提方案再生中继的容量性能,并推导了中断率的闭式解。数值分析和仿真研究表明通用选择合作方案实现了全路由分集增益,而阈值选择合作不仅提供了一个有效的合作节点的选择方案,也实现了系统性能与目的节点的处理代价的良好折中,对降低目的节点接收机的信号处理功耗和复杂度很有好处。     

基于发射分集的多点中继合作通信系统性能研究

为了降低合作通信系统中的误码率和中断概率,本文研究了多点中继合作通信系统.采用矩母函数(Moment Generating Function)分析方法,通过引入超几何函数,详尽推导出Rayleigh衰落信道下的平均符号错误率和中断率的精确表达式.通过蒙特卡洛仿真,验证了表达式的正确性,其性能优于单点中继合作通信系统.     

一种机会协作重传协议及其性能分析模型研究

 本文基于机会中继协作通信系统的优良特性,改进了传统的多中继ARQ(Automatic Repeat Request)协作分集机制,联合物理层与数据链路层优化了无线频谱与能量的利用率,并且首次提出了采用Markov(马尔可夫)吸收链方法的端到端性能分析模型.在此分析模型的基础上,对本文改进的机会协作重传协议进行了端到端成功传输概率、丢包率、时延、吞吐量等性能参数的数值分析,最后用仿真实验对此模型进行了验证,详细讨论了最大重传次数、信道衰落参数、总发送功率等对性能的影响.结果表明,本文改进的机会协作重传协议在节能、抗信道衰落方面,表现出了比直接重传协议和传统的多中继协作重传协议具有更优越的性能.     

ARQ strategies for relay cooperative systems

We propose two novel automatic repeat request (ARQ) strategies for relay cooperative systems over Rayleigh fading channel one uses relay ARQ and the other destination ARQ. The BER performance of these two strategies is derived in fast block fading. Numerical analysis and simulation show the systems can get more performance gain when the inter-channel (the source to the relay) quality is bad in the relay ARQ strategy. In the destination ARQ strategy, when the uplink qualities of the source and relay to the destination are poor, the average received SNR of the destination is much low, the systems performance can be improved efficiently.     

分组协同中继系统性能研究以及分组长度性能影响分析

针对AF(amplify-and-forward)和DF(decode-and-forward)2种转发模式,分析了分组协同中继通信系统在高信噪比下的误帧率性能,并研究了帧长对误帧率的影响。研究表明,以误帧率为准则,AF和DF模式都取得了相同的分集增益,但是编码增益不一样,并且编码增益与帧长有关。与现有的研究结论不一样,考虑到实际的分组长度,DF总是能够获得较AF更好的性能,帧越短DF的优势越明显;当帧长足够大时AF能够获得和DF相近的性能。还研究了最优的中继位置,对于AF系统,最优的中继位置总是位于源和目的节点中点处;而对于DF系统,当帧长增大时最优的中继位置将从靠近源处逐渐移至中点处。     

Space-time cooperative diversity scheme using full feedback

This article proposes a new space-time cooperative diversity scheme called full feedback-based cooperative diversity scheme (FFBCD). In contrast to the conventional adaptive space-time cooperative diversity schemes that utilize the feedback from only the destination node, the new scheme utilizes the feedback from both the destination node and the cooperation node. With the feedback from the destination node, the occasional successful reception of the destination node in the information distribution stage can be detected, thus avoiding unnecessary retransmissions in the information delivery stage. The feedback from the cooperation node indicates the receiving state of the cooperation node in the information distribution stage, and the source node and the cooperation node will not perform cooperative retransmission during the information delivery stage unless the cooperation node is received successfully in the information distribution stage. In this way the new scheme can reduce the number of transmission attempt and improve the channel utilization. The expressions of the average number of transmission attempt are given. Numerical approximations and simulation results both show that the new scheme performs better than the non-cooperative scheme and the conventional adaptive space-time cooperative diversity scheme.     

基于节点选择的Turbo编码协同ARQ协议

文中给出了一种基于节点选择的Turbo编码协同ARQ(TC-ARQ)协议方案,并从理论上证明了采用基于节点选择的TC-ARQ协议相比传统的Turbo ARQ协议(T-ARQ)能获得更高的分集增益以及比非节点选择的协同ARQ协议更低的误帧率.仿真结果证实了该方案相对T-ARQ的优异性能,并仿真分析了节点数对节点选择性能增益的影响.     

Performance analysis of cooperative diversity for two-way multi-relay system with channel estimation error

In this work, we consider an amplify-and-forward two-way multi-relay system for wireless communication and investigate the effect of channel estimation error on the error rate performance. With the derivation of effective signal-to-noise ratio at the transceiver and its probability density function, we can get approximate expression for average bit error rate. Simulation results are performed to verify the analytical results.     

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.     

无线数据传输中的混合ARQ

本文针对无线数据传输中的混合ARQ,介绍了混合ARQ的基本概念和技术,重点分析评述了用于混合ARQ系统中的各种包合并方案和相关的纠错编码技术,并对混合ARQ的相关研究工作进行了展望.     

慢瑞利衰落信道下一种变分组长度的自适应ARQ协议

信道的慢瑞利衰落特性导致通信系统的性能——吞吐量的下降。本文基于选择重传(SRARQ)与返回-n(GBN ARQ)相结合的混合ARQ协议(SR GBN ARQ),依据发送方连续收到的确认(ACK)/非确认(NACK)消息的次数,正确评估慢瑞利衰落信道的状况以改变分组长度的一种自适应ARQ协议。仿真结果表明对于慢瑞利衰落、长往返旅程延迟(T)信道,该协议能取得较优的吞吐性能。     

Outage analysis of blind cooperative diversity

Mobile users with single antennas can still take advantage of spatial diversity through cooperative space–time‐encoded transmission. In this paper, we considered a scheme in which a relay chooses to cooperate only if its source–relay channel is of an acceptable quality, and we evaluate the usefulness of relaying when the source acts blindly and ignores the decision of the relays whether they may cooperate or not. In our study, we consider the regenerative relays in which the decisions to cooperate are based on a targeted end‐to‐end data rate R. We derived the end‐to‐end outage probability for a transmission rate R and a code rate ρ and look at a power allocation strategy between the source and the relays in order to minimize the end‐to‐end outage probability at the destination for high signal‐to‐noise ratio, by using the golden section search method. Performance results show that the computer simulations‐based results coincide with our analytical results. Copyright © 2011 John Wiley & Sons, Ltd.     

无线传感器网络中协作ARQ协议能量效率分析及优化

文章研究了无线传感器网络中协作自动请求重传（Cooperative Automatic Repeat Request, CARQ）协议的能量效率及其优化问题。定义协议的能量效率为单位能耗所支持的分组成功传输的个数,导出了CARQ协议和传统ARQ协议的能量效率表达式以及CARQ协议相对ARQ协议的能效增益表达式,依此对两协议的能量效率进行了仿真研究,发现协作节点的位置对协议的能量效率有重要影响,当通信距离大于“门限距离”时,CARQ协议的能量效率才高于传统ARQ协议能效;进而提出了一种离散优化算法,通过优化调制水平,大大提高了CARQ协议的能效及能效增益。