一、引言卫星通信系统通常由空间分系统、通信地球站群、跟踪遥测及指令分系统和监控管理分系统四大部分组成。仅就传输部分而言,一条卫星通信链路包括发端地球站、上行链路、卫星转发器、下行链路、收端地球站。衡量卫星通信链路传输质量的最主要指标是:接收系统输入端的载波功率与噪声功率之比值,即载噪比。在模拟制卫星通信系统中,接收 I. INTRODUCTION Satellite communication system usually consists of four parts: space subsystem, communication earth station group, tracking telemetry and command subsystem and monitoring management subsystem. For the transmission part alone, a satellite communication link includes the originating earth station, the uplink, the satellite transponder, the downlink, the terminating earth station. The most important indicator to measure the transmission quality of the satellite communication link is the ratio of the carrier power to the noise power at the input of the receiving system, that is, the carrier-to-noise ratio. In the analog satellite communications system, to receive