基于定时模型的VSAT时隙ALOHA系统性能研究

摘要

在采用时隙ALOHA方式的VSAT卫星数据通信系统中,为数据帧分配保护时间是帧格式设计中的一项重要任务.利用系统的定时关系给出准同步时隙ALOHA系统数据帧无冲突接收的充要条件,在此基础上分析了保护时间、定时偏差对系统性能的影响,并给出了最佳保护系数的解析表达式.数值仿真结果表明:当定时偏差系数β≤0.5时,存在着一个最优的保护系数αopt,据此设定数据帧的保护时间可获得系统最大吞吐率；当定时偏差系数β＞0.5时,增加数据帧的保护时间会减小系统吞吐率.%In VSAT satellite communication system using slotted ALOHA method, assigning guard time is important for frame format design. In this paper,sufficient and necessary condition for collision-free receiving in quasi-synchronous ALOHA system was reduced from timing relation. Based on this conclusion, the joint effects of guard time and timing warp on system performance were analyzed and a scheme was proposed to calculate optimum guard coefficient Numeric simulations show that when timing warp coefficient β≤0. 5, there is a optimum guard coefficient aopt,and using it a guard time achieving maximal throughput can be obtain. When timing warp coefficient β>0. 5, increasing frame guard time will decrease system throughput