协作分集系统中机会角色选择策略研究

Previously, the focus of opportunistic selection in cooperative diversity systems lies in scheduling system resources such as nodes, links and antennas for information transmission, while the role of each node as a source, relay or destination is generally assumed to be fixed and not to be varying regardless of the instantaneous channel conditions. Even though such as a fixed and invariable role configuration can significantly simplify the design and performance evaluation of cooperative systems, it can not choose the transmission link with the best instantaneous channel quality to convey the information, limiting therefore the potential to further improve the transmission robustness against channel fading. In this project, by formulating the distributed role decision rule and decision feedback procedure, we intend to design distributed ROle SElection (ROSE) schemes with low signaling overhead, short feedback delay and high transmission reliability for typical cooperative diversity systems such that the role of each node can be determined based on instantaneous channel conditions in a dynamic and efficient fashion. Moreover, by incorporating the information and signaling transmission failure into a comprehensive analytical framework, we attempt to make a thorough investigation into the achievable system performance and its scaling law in the high signal-to-noise ratio (SNR) regime. In addition, the optimal joint power allocation for information and signaling transmission will be solved to further improve the system transmission reliability. The most prominent feature of this study lies in that the random fluctuation of channel fading is fully exploited to configure the role for each node in a dynamic, agile, and efficient manner such that the system transmission reliability can be fully boosted. The progress of this study will be very important to construct a stable, high-efficient and reciprocal cooperative transmission framework.

协作分集系统中机会选择策略研究以往关注的大多是节点、链路、天线等资源的机会规划配置，而假定系统中各节点所担当的协作角色（如信源、中继或目的端）是固定不变的。这种固定的角色指配方式可以大大简化协作分集系统的设计与性能评估，但却不能实时选出传输质量最好的链路来承载信息，由此降低了系统传输可靠性。本项研究拟从构建分布式角色判决准则和判决反馈流程入手，为典型协作分集系统设计具有低信令开销和反馈延迟、高传输可靠性的分布式机会角色选择策略，有效解决节点协作角色的动态、高效指配问题。进而，兼顾信息和信令传输错误，完备分析角色选择协作系统的可达性能和高信噪比性能变化规律，并通过信息、信令发射功率联合优化分配全面提升系统传输可靠性。本项目的特色是充分利用无线信道的随机衰落波动来动态、灵活、高效配置各节点所担当的协作角色，本项研究的开展对于构建稳固、高效、互惠的协作传输体系具有重要的理论意义和实用价值。

协作分集系统研究以往大多假定系统中各节点所担当的协作角色是固定不变的。这种固定的角色指配方式可以极大简化协作分集系统设计，但却不能实时选出传输质量最好的链路来承载信息，降低了传输可靠性。本课题从研究具有高传输可靠性的中心化角色选择方法入手，旨在设计具有高传输可靠性和低信令开销的分布式角色选择方法。. 首先在单向和双向中继场景下设计了中心化角色选择方法。研究表明：在单向和双向中继场景下，中心化角色选择方法可获得比固定角色配置高1阶的分集增益，且系统分集复用折中性能更佳。. 进而，构建了局部信道状态信息判决反馈机制，并设计了分布式角色选择方法。在采用模拟网络编码和时分广播协议的双向中继场景下，严格证明了分布式角色选择方法与最优（中心化）角色选择方法在角色判决结果上是等价的。研究表明：（1）与固定角色配置相比，分布式角色选择方法可将系统分集增益提高1阶。（2）与最优（中心化）角色选择方法相比，分布式角色选择方法可将信令开销减少60%，同时保证最优的角色判决结果。. 为降低能耗，还研究了一种无线供电的三节点协作角色选择系统。研究表明：（1）动态角色选择方法可将系统分集增益提高至3阶，且中断曲线下降速率不再受log(SNR)和log(log(SNR))缓冲因子影响。（2）LOS路径对于提升系统性能至关重要，且基于不理想信道信息得到的角色判决结果将显著降低系统性能。. 鉴于LOS路径的重要影响，针对无线供电的协作角色选择系统，研究了LOS路径和机会规划对于两跳中继链路性能的影响机理。研究表明：（1）在LOS路径很强时，系统中断性能缓冲因子log(SNR)可被消除，系统中断性能服从1/SNR规律变化。（2）当目的端个数大于1时，机会规划第二跳链路可消除缓冲因子log(SNR)的影响。而强LOS路径和机会规划的联合作用可将系统分集增益增加至N阶（N为目的端个数）。（3）提出了无线供电和非无线供电中继系统的性能等价条件。. 本课题对于构建稳固、高效的协作传输体系具有理论指导意义。

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