协作通信系统中基于频谱效率优化的跨层设计

为改善协作分集系统的频谱效率，提出一种改进的跨层设计方案,对协作通信系统物理层的自适应调制编码（AMC）技术和链路层的混合自动重传(HARQ)协议进行联合优化设计。该方案利用少量比特的反馈，使得仅当目的节点通过直接信道不能正确译码分组时或者当直接信道处于深度衰落时触发中继节点转发协作伙伴数据。给出了所提方案基于瑞利衰落信道、解码转发（DF）条件下频谱效率的表达式，然后搜索在任意信噪比条件下使频谱效率最大化的调制与编码方案。通过计算机仿真对理论分析进行了验证。理论分析和仿真表明该跨层设计在中低信噪比(SNR)可进一步提升协作通信系统的频谱效率。 

Closs-layer design based on optimal spectral efficiency in cooperative communication system

This paper presents an improved cross-layer design which combines adaptive modulation and coding (AMC), cooperative diversity(CD) at physical layer (PHY) and the hybrid automatic repeat request (HARQ) protocol at data link layer (LL) to enhance the spectral efficiency in cooperative communication system. Only when the destination node (D) is unable to decode a packet directly from the source node (S) correctly, or the source destination channel is suffering deep fading, the relay node (R) forwards the data from the source to the destination on receiving a feedback signal of a little bits. We first derive a closed form expression for the spectral efficiency of the joint cooperative HARQ-AMC under Rayleigh fading channel and decode-and-forward (DF) scenarios, then, aiming at maximizing the spectral efficiency, we search for the optimum AMC scheme by a computer algorithm. Simulations are done to verify the method. Numerical and simulation results show that the proposed scheme can further improve the spectral efficiency at medium to low signal-to-noise ratio (SNR) scenarios.