We focus on device-to-device (D2D) enhanced multicast transmission in cellular systems,formulate the relationship between the number of retransmitters and the efficiency of D2D retransmission,and derive a closed-form expression to search the optimal number of D2D retransmitters and the optimal sub-cluster partition.Based on the analysis,we propose an adaptive D2D cooperative retransmission scheme with limited channel feedback,which adaptively selects the number of retransmitters and the optimal routing.Exploiting the multicast gain and multi-channel diversity jointly,the proposed scheme achieves a significant gain in terms of spectrum efficiency compared to its counterparts with a fixed number of retransmitters.%针对蜂窝系统中的D2D增强型多播传输,分析了D2D重传效率与重传发射者数目之间的函数关系,推导了求解最优重传发射者的数目及子集划分的闭合表达式.以此为理论基础,提出了一种基于有限反馈的D2D自适应协作重传方案.该方案根据D2D链路质量自适应地选择重传发射者数目及最优重传路由,实现了多播增益与多信道分集增益的联合优化.仿真表明,该方案可显著提高D2D重传的频谱效率,逼近理论最优解,提升蜂窝系统多播的吞吐量.
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