一种基站可靠组播动态重传控制算法

A Dynamic Retransmission Control Algorithm for Reliable Mobile Multicast in MSS

在移动环境下 ,组播的重传方式是影响系统性能的重要问题 ,如采用静态多播重传方式 ,将使许多终端收到重复数据包 ,由于移动终端带宽、电力资源紧缺 ,重复传输将可能造成终端链路利用率过高 ,严重浪费终端资源 ;如采用静态单播重传方式 ,在丢包接受者数量很多时 ,又将导致较大网络负荷 .该文提出了一种在基站进行动态重传的控制算法NLPAM(NetworkLoadPriorityAlgorithminMSS) ,动态选择单播或组播进行重传 ,从而既可避免网络出现过高的负荷 。

This paper separates the mobile multicast network into fixed and mobile parts. It focuses on the mobile part. Firstly authors deduce the expressions of the expected value of link utilization under static unicast and multicast retransmission mode (E and E), and find E is always smaller than E, which means unicast retransmission mode is in favor of avoiding congestion in the wireless interfaces. Secondly authors deduce the expressions of the expected value of network load under static unicast and multicast retransmission mode (Eand E), and find multicast retransmission mode works better than unicast mode with the increasing of the number of MHs and the loss probability, which means multicast retransmission mode may save network bandwidth in some cases. Consequently, it is contradictive to optimize both link utilization and network load and we have to establish a trade-off between the optimization of link utilization and the optimization of network load. Then authors present a new algorithm called NLPAM(Network load Priority Algorithm)to dynamically alternate between unicast and multicast retransmission mode. When it is the time to make retransmission decisions, NLPAM will check whether the network load exceeds the predefined threshold. If the network load doesn't exceed the predefined threshold, NLPAM will choose unicast mode to lower link utilization, otherwise NLPAM will optimize network load according to E[β m|K m]and E[β u|K m]. Finally Analysis and simulation results show NLPAM can avoid both congestion in the receivers' wireless interfaces and great network load, and make network bandwidth and terminal computing and power resources under better control.