协作通信中的中继技术研究

随着无线信道环境的复杂多样,本文引入了协作通信,并探讨了协作通信中的中继节点选择和功率分配两个重要的技术,最后提出了基于中继节点选择和功率分配的联合优化算法。     

协作网络中基于中继选择的协作波束赋形算法

针对多中继网络中所有中继节点都参与协作的协作波束赋形方法,提出了一种基于选择的协作波束赋形算法。该方法将最小化系统中断概率作为目标,得到一个次优的中继节点选择门限,小于门限的中继节点被逐一剔除,从而保证了网络中的资源只分配给有用的中继节点,获得了分集增益。该选择方法需搜索次数和中继节点的个数相等,因此大幅降低了选择过程的复杂度。蒙特卡洛仿真表明,选择波束赋形算法可有效提高系统中断概率性能和网络能量效率。     

无线携能保密网络下的中继协作波束形成算法

本文研究了无线携能通信网络中的多窃听者场景下,基于无线能量收集放大转发中继的协作机密信息安全传输问题.提出了两种低复杂度的零空间波束形成方案.分别利用接收者或窃听者方位先验信息,将待优化的目标矢量投射到接收者或窃听者信道的零空间.与原协作波束形成方法相比,由于降低了待优化目标矢量的空间自由度,本文方法运算复杂度较低.特别的,由于第二种方法目标函数中将窃听者的交互信息迫零,将原始拟凸优化问题转化为凸问题求解,进一步降低了运算量.实验研究验证了本文方法的合理性.     

协作通信网络中的中继节点选择技术

协作通信作为一种新型的通信模式越来越受到人们的关注,而中继节点选择技术是其关键技术之一,决定了协作能否带来性能增益。文章基于协同节点选择技术的性能评价标准给出了相应的分类方法,对近年来典型的协同节点选择算法并进行分析和比较,得出结论：只有根据系统需求合理地选择、配置中继节点才能更好地优化协同通信的性能。     

多中继协作通信系统容量分析及中继选择协作分集策略

本文针对多中继辅助通信系统,将系统建模为一个两跳通信链路,并进行了系统容量分析。针对两种特殊情况:用户端接收噪声方差远小于中继端接收噪声方差和中继端接收噪声方差远小于用户端接收噪声方差的情况,本文具体给出了系统传输容量上限与协作中继个数之间的关系。基于容量的分析,本文设计了两种中继选择策略。在第一种情况下,根据中继与用户间的信道特征值对多路数据流分别选取不同的中继子信道进行传输;在第二种情况下,选择一个信道条件最好的中继完成多路数据流的并行传输。仿真分析表明,不同的信道环境需要选择不同的中继选择策略。      

多中继协作通信系统的中断概率分析

协作分集不仅能提升数据传输速率,还可以提高数据传输的稳定性。协作通信方法使用带有一根天线的移动台,在多用户环境中可以共享其他移动用户的天线,这样可产生多根虚拟发射天线,进而得到相应的分集增益,改善移动通信系统的性能。现在通过研究发现,在多中继协作通信中,非对称信道采用放大转发方式下的中继传输,在AF重复转发和机会转发2种方式下表现出了较小的链路中断概率,系统性能得到明显的提升。     

无线协作中继技术综述

无线协作中继技术具有低成本、扩大覆盖范围的作用,可以有效提高通信系统的可靠性和传输速率。对无线协作中继技术进行综述,讨论协作中继的基本协议和协作中继的选择方案,并且进行比较分析和仿真验证。     

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...     

无线协作中继技术综述

无线协作中继技术具有低成本、扩大覆盖范围的作用,可以有效提高通信系统的可靠性和传输速率。本文对无线协作中继技术进行综述,主要讨论了协作中继的基本协议,并对协作中继的选择方案进行了比较分析。     

中继卫星SMA系统反向链路多波束形成技术

对中继卫星SMA(S频段多址)反向链路多波束形成开环数字波束形成算法(DBF)、3种闭环自适应数字波束形成算法进行了分析,通过试验验证了开环波束形成算法和闭环波束自适应形成算法的可行性.试验结果表明,在飞行器捕获、跟踪的不同阶段,采用开环波束形成与自适应波束形成相结合是SMA反向链路波束形成的最优方式.     

多小区多用户无线网络下行链路协同波束成形设计

在频率复用的多小区多用户无线网络中,为了获得较好的和速率性能,研究了降低同频干扰的协同波束成形设计问题。博弈论分析结果表明,性能最优的协同波束成形矢量是自私和利他策略的线性组合。提出了一种最大化和速率的波束成形矢量迭代算法,给出了基于信道状态统计量的组合系数的估计方法。最后,仿真评估了波束成形算法的性能,表明了所提迭代算法的收敛性。     

Estimation of synchronization impairments in multi-relay DF cooperative networks

Cooperative communication systems can effectively increase channel capacity and combat fading. Effective cooperation requires synchronization impairments such as multiple timing offsets and multiple carrier frequency offsets to be accurately estimated and mitigated. This paper seeks to address the joint estimation of synchronization impairments in multi-relay decode-and-forward （DF） cooperative networks. Firstly, a simple yet effective estimation method based on the devised training signals is presented for achieving synchronization. Then, an iterative algorithm is further derived in order to improve the performance associated with the estimation of synchronization impairments. Our proposed algorithm converts the difficult multiple parameter estimation problem into more tractable sub-problems of estimating many individual impairments pairs for the independent relays. Simulations indicate that, the proposed estimator can asymptotically achieve the mean square error （MSE） for the perfectly timing or frequency synchronized case.     

无线传感器网络中能量有效的波束成形机制

针对无线传感器网络中单个节点能量和通信距离均受限,以及传统波束成形机制中由于忽略能耗均衡而造成单个节点过早死亡的特点,提出了一种能量有效的波束成形机制。首先分析了节点个数、发射系数、功率受限、相位等因素对网络能耗的影响,给出了对应的设计原则。然后,基于此原则来选择参与发射的节点,并结合节点的剩余能量和相位来调整各自的发射系数。理论分析和仿真结果表明,该机制有效地增加了数据成功传输的次数,均衡了节点间的能耗,延长了网络寿命。     

无线传感器网络中协作波束形成的能量有效性分析

分析了无线传感器网络中端到端误码率给定情况下协作波束形成的能量效率,给出了不同路径损耗因子和传输距离下的最优协作发射节点个数.首先,综合考虑发射能耗和电路能耗,给出了接近实际情况的系统能耗模型,并推导出系统能耗与误码率之间的近似闭式关系.然后,基于该近似模型,给出了不同路径损耗因子和传输距离下使系统能耗最小的优化协作发射节点个数.理论分析和仿真结果表明:在系统调制方式和误码率给定的情况下,存在着一个临界距离使协作波束形成比非协作传输和协作空时编码都更节能;而且在不同路径损耗因子和传输距离下,存在不同的最优协作发射节点个数使系统能耗最小.     

基于非对称信道状态信息的协作通信：一种契约理论建模方法

In relay-assisted cooperative com-munication, relay nodes help forwarding the information of a source node in case of link failure between the source and a destination. Although user cooperation improves the over-all efficiency of the network, it requires incen-tive to stimulate potential relay nodes to assist the source by forwarding its data to the desti-nation. Moreover, the potential relays are bet-ter informed than the source about their chan-nel conditions to destination, which results in asymmetric information between the source and the relays. In this paper, we study the problem of lack of forwarding incentive in cooperative communication when channel state information of relays is private infor-mation and not known by the source. To tackle this problem, we apply the principle of contract theory to a cooperative wireless system. Source first designs incentive compatible and individually rational contract, consisting of a set of power-credit pairs. Then it broadcasts contract items to nearby nodes. Once the source node receives reply messages from the volunteer relays, it chooses one or more relays based on its re-quirements and communication starts. Simulation results show how credit assignment works in order to stimulate relays to cooperate and prevents relays from cheating behavior.     

Green multi-hop cooperative wireless communication with signal space diversity

The cooperative communication in wireless multi-hop networks is a reliable energy efficient mechanism that mitigates the effects of channel fading and improves the performance and throughput of the systems. In this paper, green cooperative multi-hop scheme is proposed by employing signal space diversity (SSD). The proposed scheme offers a significant improvement in performance of the regenerative multi-hop networks without the requirement of extra bandwidth or power. The expressions for the average end to end bit error probability of the multi-hop networks employing the SSD scheme is derived. The optimal relay location for a better performance and the total energy consumption of the scheme is also probed. The simulation results show that the proposed scheme provides better quality of service and is more energy efficient compared to the conventional decode and forward scheme in single-hop as well as multi-hop situations.     

协作通信系统的中继选择算法研究

协作通信作为一种新颖的无线通信技术,它的主要思想是通过中继节点参与协作传输,在目的端获得两个或者多个在空间上独立的信号样本,实现空间分集,获得分集增益.因此如何合理选择中继节点成为协作通信的关键问题之一.本文在协作通信模型及原理的基础上,对基于信道状态信息的中继选择算法进行了介绍,并对具体的选择算法的性能进行了仿真.     

Capacity of FH wireless multi-hop networks

In this article, the capacity of wireless multi-hop networks with the frequency hopping (FH) technique is derived. Different from the previous work based on non- spread spectrum (SS) system, this study is based on frequency hopping spread spectrum (FHSS) and the retransmission mechanism. The analysis results show that the normalized transport capacity decreases as 1/(Mλ) , when the total available frequency band is divided into M sub-bands for frequency hopping and the nodes are randomly distributed in space according to a Poisson point process with intensity λ . In this work, the best transmission range per hop to get the maximum capacity is also derived. Besides, the results summarize how the capacity of FH wireless multihop networks is affected by the outage probability, target signal to interference plus noise ratio (SINR) and other system parameters.     

多跳无线传感器网络吞吐量分析

针对无线传感器网络这种典型多跳网络的吞吐量进行了理论分析,提出了在线性网络路由的情况下的网络吞吐量的计算模型,并通过NS-2仿真模拟进行了验证。发现吞吐量随着网络节点数目的增加而呈现出一种类似于简谐振动的变化,并且最终收敛到一个稳定值。这一规律揭示了无线传感器网络的节点行为特征与网络吞吐量之间的内在联系,对网络性能的优化具有指导性的帮助。