Retransmission Diversity in Large CDMA Random Access Systems
Retransmission Diversity in Large CDMA Random Access Systems
复制标题
DOI：
10.1109/tsp.2007.894393
复制
发表时间：
2007-07
影响因子：
5.4
通讯作者：
Yi Sun;Junmin Shi
中科院分区：
文献类型：
--
作者：
Yi Sun;Junmin Shi
本文研究了一个大型CDMA随机接入系统，其中用户通过一个公共CDMA信道随机接入一个基站。用户数量和扩频增益趋于无穷大，它们的比值收敛于一个常数。提出了一种利用重传分集（RD）的方法，该方法首先消除先前成功检测到的数据包引起的干扰信号，然后共同利用所有接收到的信号进行数据包检测。分析了两种方案的性能：(1)利用RD随机扩展方案和(2)利用RD随机选择但每个数据包固定扩展方案，并与不利用RD的常规方案进行了比较。得到了两种方案的极限信干扰比的下界。得到了限制系统的吞吐量、分组延迟、传输时间和等待时间以及频谱效率作为介质访问控制的函数。仿真结果证实了分析结果。还讨论了通过改变传输分组的顺序来提高RD的其他方案。研究了媒体访问控制（MAC）的优化问题。在频谱效率最大化和MAC简化方面，方案(i)是所有方案中最有利的。
This paper considers a large CDMA random access system where users randomly access a base station through a common CDMA channel. The number of users and spreading gain tend to infinity with their ratio converging to a constant. An approach to exploitation of retransmission diversity (RD) is proposed that first eliminates the interference signals caused by the previously successfully detected packets and then jointly utilizes all received signals in packet detection. Performance of two schemes is analyzed: (i) random spreading with RD exploitation and (ii) randomly selected but fixed spreading for each packet with RD exploitation, and compared with the conventional scheme that RD is not exploited. Lower bounds on the limit signal-to-interference ratios (SIRs) of the two schemes are obtained. Throughput, packet delay, transmission time, and waiting time as well as spectral efficiency in the limit system are obtained as a function of medium access control. The analytical results are confirmed by simulations. Other schemes that increase RD by changing order of transmitted packets are also discussed. Optimization of media access control (MAC) is studied. In terms of maximization of spectral efficiency and simplicity of MAC, scheme (i) is the most favorable out of all the schemes.