【作者】 杨常青；

【导师】 王文博；

【作者基本信息】 北京邮电大学 ， 信号与信息处理， 2011， 博士

【摘要】 作为一种有效的对抗无线衰落的手段,协同分集技术近年来得到了广泛而深入的研究。通过共享天线等资源,地理上分离的网络节点能够形成虚拟多输入多输出系统,充分挖掘空间分集增益来提升系统性能。而作为协同分集技术的重要组成部分,机会协同因其性能优异、实现简单和扩展性良好等特点得到了越来越多的关注,逐渐成为学术界研究的热点问题。考虑到未来通信系统的发展趋势,本论文主要针对基于译码转发的机会协同技术从分集性能方面进行理论研究,深入分析影响该协议性能的关键因素及其制约关系,为在下一代移动通信系统中应用该技术提供必要的理论支持。本论文首先研究了扩展的中继选择方案下机会协同译码转发协议的分集性能,然后评估了普适的衰落信道模型对该协议的影响,并进一步考虑了非理想信道状态信息下该协议的具体性能,最后研究在多天线技术增强之后,机会协同译码转发协议能够达到的理论分集性能。论文的主要工作和创新点在于：1.扩展的中继选择方案下机会协同分集性能研究首先研究在Rayleigh衰落信道下,基于第N佳中继这种通用选择方案来进行中继选择时,机会协同译码转发协议可以达到的性能,然后针对传统机会协同译码转发可能造成的中继节点参与协同不公平的问题,设计了一种基于归一化信道状态来进行中继选择的方案并对其性能进行分析。针对基于第N佳中继选择方案,分析得到了独立但不一定同分布Rayleigh衰落信道下机会协同译码转发的系统性能表达式,并且考虑了直传链路对于系统性能的影响,从理论上证明了系统分集度与中继选择标准之间存在线性关系。分析了基于归一化信道状态信息进行的机会协同译码转发协议性能,从分集度和公平性两个角度证明了该协议的优势,为实际系统中需要考虑中继选择公平性的场景提供了理论支撑。2.普适的衰落信道模型下机会协同分集性能研究首先研究对称网络和非对称网络在适用性较强的Nakagami-m衰落信道中采用机会协同译码转发协议可以达到的分集性能,然后结合实际系统的无线传播环境特征,考虑在混合衰落信道,即混合Rayleigh和Rician衰落信道,以及适用性更强的混合κ-μ和η-μ衰落信道下研究机会协同译码转发协议的性能,分析衰落信道参数对于机会协同性能的影响关系。从理论上得到了在Nakagami-m衰落信道下,存在直传链路时采用机会协同译码转发协议和第N佳中继选择标准的端到端中断概率表达式和分集度表达式。所得表达式相对于现有的研究结果更加简单,并且适用场景更加广泛。首次分析得到了混合衰落信道模型下机会协同译码转发时系统端到端中断概率和分集度表达式,所得结果可以直接应用于网络规划和优化,并且所采用的衰落信道模型能够更加精确地体现实际系统特征,使得结果更具推广性。3.非理想信道状态信息下机会协同分集性能研究首先研究了在接收端存在信道估计误差时机会协同译码转发协议的分集性能,评估了信道估计误差对分集度的影响,然后将非理想信道状态扩展到接收端和发送端,即联合考虑信道估计误差和反馈时延的影响,在此前提条件下得到系统可达的分集性能。从理论上给出了信道估计误差和信道反馈时延对于机会协同译码转发协议的影响,通过推导得到了此时系统端到端传输的中断概率和系统可达分集度表达式,所得结果可以针对实际系统的信道估计能力和控制信道传输能力对机会协同译码转发协议做进一步的校准。4.多天线技术增强的机会协同分集性能研究首先研究了在源端、中继端、目的端同时部署多天线并采用正交空时块码传输时,机会协同译码转发所能获得的性能提升,然后在此基础之上设计了一种增量中继传输方案,有效地利用正交空时块码和机会协同的分集增益以及直接传输的频谱效率增益来提高系统性能,并从理论上得到了此时的系统分集性能表达式。通过理论推导给出了系统中断概率和天线配置、中继配置、网络拓扑结构之间的关系,并且得到了系统可达分集度的闭式表达式,有利于在多天线场景下部署和应用机会协同传输协议。提出了一种结合正交空时块码和增量中继的机会协同译码转发协议,不仅可以保证传统机会协同译码转发协议满分集性能,而且还能够通过充分利用多天线、多中继资源维度来大幅提高系统传输效率。更多还原

【Abstract】 As an effective method to combat wireless fading, cooperative diversity technique has been researched extensively and intensively recently. Through sharing the resources such as antennas, geographically isolated network nodes can exploit spatial diversity gain to improve system performance by forming a virtual multiple input multiple output (MIMO) system. As an important aspect of cooperative diversity techniques, opportunistic cooperation has attracted more and more attention due to its features including excellent performance, simple implementation, good scalability et al., and has gradually become a hot issue in academic circles. In consideration of the development tendency of future communication systems, we theoretically study the diversity performance of decode-and-forward based opportunistic cooperation technique in this dissertation, deeply analyze the key factors that impact the performance of the protocol and their relations, provide necessary theoretical support to apply this technique in next generation mobile communication systems. In this dissertation, we firstly study the diversity performance of decode-and-forward opportunistic cooperative protocol with extended relay selection schemes, then evaluate the impact of different universal fading channel models on the protocol, and furthermore take the specific performance of this protocol with imperfect channel state information (CSI) into consideration, and finally we research on the achievable theoretical diversity performance of decode-and-forward opportunistic cooperative protocol enhanced by MIMO techniques. The major work and contributions of this dissertation consist in:1. Research on diversity performance of opportunistic cooperation with extended relay selection schemesFirstly the performance of decode-and-forward opportunistic cooperation with a general relay selection scheme, i.e., the Nth best relay selection, is studied under Rayleigh fading channels, where the impact of the direct link is taken into consideration. Then considering the unfair problem that might happen when traditional decode-and-forward opportunistic cooperation is implemented, we propose a relay selection scheme based on the normalized channel state and analyze its performance. Based on the Nth best relay selection, we analyze and obtain the expressions of system performance when decode-and-forward opportunistic cooperation is utilized under independent but not necessary identical Rayleigh fading channels, and take the impact of the direct link on system performance into consideration, and prove in theory that the system diversity order varies linearly with the relay selection criterion N. We also analyze the performance of decode-and-forward opportunistic cooperative protocol with normalized channel state, and prove its advantages in terms of both diversity order and fairness, which provides theoretical support when fairness of relay selection is needed in practical systems.2. Research on diversity performance of opportunistic cooperation under universal fading channel modelsThe achievable diversity performance of decode-and-forward opportunistic cooperation under universal applicable Nakagami-m fading channel model is first analyzed, where both symmetric and asymmetric network topologies are taken into consideration. Then combined with the feature of wireless propagation environment in real systems, the performance of decode-and-forward opportunistic cooperation under mixed fading channel models,ⅰ.e., mixed Rayleigh and Rician fading channel models, and more general mixedκ-μandη-μfading channel models, are studied, and the impact of fading channel parameters on performance is analyzed. Theoretically we derive and obtain the expressions of end-to-end outage probability and diversity order of decode-and-forward opportunistic cooperation under Nakagami-m fading channels, where the availability of the direct link is considered and the Nth best relay selection scheme is implemented. The obtained expressions are simpler than existing ones, and they can be applied in more scenarios. Under mixed fading channel models, the expressions of end-to-end outage probability and diversity order of decode-and-forward opportunistic cooperation are derived for the first time, and the results can be utilized directly in network planning and optimization. Furthermore, the used universal fading models can describe the features of practical systems more accurately, which makes the results more appropriate be used in real networks.3. Research on diversity performance of opportunistic cooperation with imperfect CSIWe first study the diversity performance of decode-and-forward opportunistic cooperative protocol when channel estimation errors exist at receivers, and evaluate the impact of channel estimation errors on diversity order. Then we extend the imperfect CSI to both transmitters and receivers,ⅰ.e., jointly considering the impact of channel estimation errors and feedback delay, and obtain the achievable diversity performance of the system under such conditions. Theoretically, we prove the impact of channel estimation errors and channel feedback delay on performance of decode-and-forward opportunistic cooperative protocol, and derive and obtain the expressions of end-to-end outage probability and the achievable diversity order. The related results can be utilized to calibrate the performance of decode-and-forward opportunistic cooperative protocol in practical systems when the capability of channel estimation and control channels should be taken into consideration.4. Research on diversity performance of opportunistic cooperation enhanced by MIMO techniquesFirstly we study the performance improvement of decode-and-forward opportunistic cooperation when multiple antennas are implemented at source node, relay nodes, and destination node and enhanced with orthogonal space-time block code (OSTBC) transmission. Then based on the results we design a new incremental relaying transmission scheme, which can effectively improve the system performance by harvesting the diversity gain of OSTBC and opportunistic cooperation together with the spectral efficiency gain of direct transmission, and also we obtain the expressions of diversity performance in theory. Theoretically, we derive and obtain the relation among system outage probability, antenna configuration, relay deployment and network topology, and also obtain the closed-form expressions of system diversity order, which facilitates the implementation and application of decode-and-forward opportunistic cooperative protocol under multiple antenna scenarios. We propose a novel decode-and-forward opportunistic cooperative protocol by combining OSTBC and incremental relaying, and prove that this protocol not only obtains the full diversity order gain, but also improves the system transmission efficiency through making full use of resource dimension including multiple antennas and multiple relays, et al.更多还原