距离延时对STDMA系统网络吞吐量影响的分析

The Analysis of the Throughput Affected by the Distance Delay in the STDMA System

在船舶自动识别系统所采用的STDMA技术中 ,由于站台分布距离的不同会带来信道中时隙传播的延时 ,这种距离延时有可能会造成相邻时隙间的交叠 ,从而导致传输中的冲突 ,使系统的网络吞吐量受到影响。该文采用计算机仿真的方法 ,通过模拟站台间的不同分布状况 ,研究了STDMA系统中不同分布范围内所产生的传播延时对系统网络吞吐量的影响状况 ,并进一步分析了链路负载、站台的VHF蜂窝区半径与系统网络吞吐量之间的关系。此外 ,在仿真结果的基础上 ,该文还给出了一个定量计算系统网络吞吐量的近似公式。

In the STDMA system which adopted by the shipborne Automatic Identification System,the different distance distribution of the stations will introduce propogation delay in channels,which brings the overlapping between the current time slot and the next one.There is a probability that transmissions in adjacent slots will be in conflicts,which may reduce the overall throughput.This paper discusses how large distances,between communication stations,introduce delays and,as a result,conflict in transmissions possibly do occur due to propagation overlap.Furthermore,this paper introduces a simulation program which constructs a virtual image of a traffic situation with stations randomly spread and each slot is assigned a distance to the receiver.Based on the simulation,an analysis is performed to examine how the propagation delay affects the throughput and the cell radius of a receiving station.Finally,the equations to calculate the throughput in different areas are presented.