中文摘要：

在采用LDPC编码的再生转发卫星通信中,取消星上编译码可降低转发器的负载,但地面接收终端的标准MP算法难以精确估计比特后验概率,从而影响LDPC译码器的性能。本文研究地面接收终端精确估计比特后验概率的算法。首先建立再生转发卫星通信模型,分析并给出比特后验概率估计问题产生的原因,然后采用概率论的方法进行理论推导,给出精确估计比特后验概率的算法。Matlab仿真结果表明,在上下行链路载噪比相等、误比特率为10-5时,改进算法可获得0.7 dB的增益。在星上无编译码的再生转发卫星通信中,改进算法可用来提高地面接收机的译码性能。

英文摘要：

In on-board regeneration satellite communications,the burden of satellite transponder is light when on-board processor works without channel decoding and recoding,but LDPC performance degradation will occur because the bit posteriori probability can not estimated precisely in LDPC classic MP algorithm.This paper researches on the algorithm of estimating the posteriori probability precisely in the downlink.Firstly a satellite communication model is constructed and the kernel of posteriori probability estimation puzzles is analyzed,then an advanced posteriori probability estimation algorithm is derived by means of probability theory.The matlab simulation displays 0.7 dB gain of the enhanced algorithm when the SNR in the uplink and that in the downlink are equivalent,and the bit error probability is 10-5）.In the regeneration satellite communication system without on-board decoding and recoding,the advanced algorithm can be used to improve the performance of the receiver.