【作者】 郭艳艳；

【导师】 张平； 康桂霞；

【作者基本信息】 北京邮电大学 ， 电路与系统， 2010， 博士

【摘要】 在无线移动通信系统中,信道的衰落会降低信号传输的可靠性。空间或多天线协作分集技术通过用户之间共享天线,实现虚拟多天线传输以获得空域分集,从而减小无线信道衰落影响,提高通信性能,是一种具有较大实用价值的新型空间分集技术。协作分集技术在无线传感器网络(WSN)、无线自组织(Ad-Hoc)网、无线Mesh网、以及蜂窝网等系统中有着广泛的应用前景,并将成为以多种异构融合网络为特征的下一代无线通信系统的关键技术之一。另一方面,随着无线通信技术的飞速发展,频谱资源变得越来越紧张,认知无线电(Cognitive Radio, CR)技术已经被公认为是提高网络频谱资源利用率问题的有效解决方法。尽管协作通信技术能够提高系统的抗衰落能力,认知无线电技术可以提高无线频谱的使用效率,但这还不足以解决无线通信中存在的上述两个问题。协作通信技术和认知无线电技术结合已经成为近年来的研究热点。两种技术结合将为同时提高系统的抗衰落性能、信道容量、频谱利用率提供一种可能的解决方案。为此,论文开展了对协作中继通信关键技术的研究,研究提高协作分集性能或效率的方法。进一步,论文将研究协作通信和认知无线电结合技术,对认知网络协作分集进行优化设计。论文的主要研究内容和研究成果如下：首先,研究在授权网络中用户固定分配信道资源情况下的协作策略,内容涵盖于第三章。考虑能量受限的网络,如传感器网络,研究最小化网络传输能量消耗,延长网络生命周期的协作MIMO传输策略。在此基础上,提出了基于协作MIMO的节点选择及优化算法。和以前的研究不同的是：算法不考虑源节点到目的节点一次传输中一跳或多跳能耗最小化问题,而是考虑整网为执行整个应用的能量消耗,从而最大化网络生命周期。其次,研究共存式(underlay)频谱共享模式下认知网络协作分集技术,将研究CR系统在峰值传输功率限制条件下的协作策略及性能分析,内容涵盖于第四、五、六章。具体如下：1、第四章针对能量受限的认知网络,如传感器网络,研究频谱共享模式下提高网络能效的认知网络协作技术,提出了一种基于认知网络协作功率分配策略,该策略在保证授权用户服务质量的前提下最小化认知系统的能量消耗。仿真结果表明,和直接传输相比,所提出的算法提高了认知网络的能效性。2、第五章针对多个中继与源节点协作通信的认知无线电协作场景,提出了一种基于放大转发(Amplify and Forward, AF)模式下的功率分配优化算法,算法不需要中心节点控制,中继节点根据目的节点广播的很少信息进行传输功率调整,算法实现简单。仿真结果表明和直接传输及等功率传输方案相比,提出的分布式协作功率分配方案获得了进一步的性能增益,中断概率显著下降。3、现有的对协作分集容量、中断概率及误码率(BER)等的分析主要是针对固定频谱分配情况。第六章对共存式频谱共享环境下的认知无线电单节点协作系统性能进行了分析,并给出了基于译码转发模式的认知系统协作中断概率近似表达式。仿真结果验证了理论分析的正确性。通过全文的研究可以看出：在无线协作通信系统中,针对特定的传输策略选取合适的协作策略以及功率分配算法,就能够有效利用不同用户节点的天线以获取协作分集,从而显著改善系统性能或降低系统能量消耗。更多还原

【Abstract】 In wireless communication system, channel fading can decrease the reliability of communications. Cooperative diversity, in which users share their antennas to obtain space diversity, becomes a new valuable diversity technique. To date, cooperative diversity has been widely used in wireless sensor networks, wireless Ad-hoc networks, wireless Mesh networks and wireless celllar networks. Obviously, cooperative communication will be the key technology for convergence of various heterogeneous networks.On the other hand, as wireless technologies continue to expand, more and more spectrum resources will be needed. Cognitive radio (CR) is an exciting emerging technology that has the potential of dealing with the stringent requirement and scarcity of the radio spectrum. Although cooperative diversity can increase the ability of combating channel fading and the cognitive radio can enhance the untization of licensed spectrum in the wireless communication systems, it is not enough to solve above two problems. The cooperative relay and cognitive radio techniques based convergence mechanism which is a potential solution to increase the performance of combating the detrimental effects of fading channels, channel capacity and frequency ustilization for wireless system has attracted more attentions in recent researches.This dissertation considers the special issues of cooperative relay communication and investigates optimized design of cooperative diversity. Furthermore, how to cooperative diversity works in the cognitive radio (CR) networks is investigated.First, the cooperative and power allocation strategies based on energy-constrained licensed wireless networks, in which the frequency bands are exclusively allocated to the users, is provided in Chaper 3. For energy-constrained wireless networks, such as wireless sensor networks (WSN), MIMO (Multi-input-multi-output) cooperative energy efficient protocols to prolong the network lifetime are investigated. Then, a new partner choice algorithm based on cooperative MIMO transmission is proposed. Compared with existing work, cooperative nodes choice in every transmission is not based on minimizing energy consumption but balancing residual energy among participant nodes including source node and relays for one special application so as to maximize network lifetime.Second, cooperative diversity which works in the underlay sharing-spectrum environment, in which peak transmit-power of CR system must be below the interference temperature constraint of primary user, is investigated in the Chaper 4,5 and 6 of this thesis. The main content includes the following aspects:1) For energy-constrained CR networks, such as wireless sensor networks (WSNs), the user cooperative strategy in the spectrum sharing environment is investigated in Chaper 4. Optimal power allocation strategy in order to minimize the energy consumption of CR system and meanwhile guarantee the quality of service (QoS) of the primary system is proposed. Simulation results showed that the proposed method obtains higher energy efficiency in CR system and better performance of primary link than those of the direct transmission.2) For multi-relays spectrum sharing cooperative CR system, Chaper 5 proposes a distributed transmit power allocation algorithm based on Amplify and Forward (AF) cooperative model. By this algorithm, the relays adjust their transmit-power based on broadcast information from destination without central node to control. The simulations validate the efficiency of proposed algorithm by comparing it with the direct transmission and the scheme where equal weights are assigned to the relays.3) The performance of capacity, outage probability and bit errors rate (BER) has recently been investigated only in licensed cooperative wireless networks. The outage performance of wireless cognitive radio relay networks based on decoding and forward (DF) mode in a spectrum sharing environment is investigated in Chaper 6. In particular, the relation between the outage performance of the secondary relay link and the interference inflicted on the primary user is quantified. Numerical results are provided to validate this anlysis.From the dissertation, it can be found that, in cooperative communications system, selecting suitable cooperative schemes and power allocation algorithms for special transmission strategies can achieve cooperative diversity, which can significantly improve the performance and reduce the energy cost of systems.更多还原