噴泉編碼在深空通信中的應用

Abstract

深空通信的最大特點是距離遙遠、延時長，通信可靠性無法採用回饋重傳的方式來保證，主要依靠通道編碼來完成。為了進一步提高現有糾錯方案的誤包率性能，本文提出一種引入噴泉糾刪碼的差錯控制方案，利用噴泉碼在刪除通道上可近似達到通道容量的特點，通過增加少量的編碼冗餘來有效降低系統的誤包率。本文分析了噴泉碼的解碼開銷(overhead)對功率有效性的影響，給出了選擇適用噴泉碼碼型的方法。仿真結果表明，在採用CCSDS(Consultative Committee for Space Data System)標準草案中的LDPC(Low-Density Parity-Check)碼時，引入系統RU(Richardson-Urbanke)噴泉碼可獲得0.06~0.44dB的額外編碼增益。Long distance and high latency are the essential character of deep space communication, which make it hard to utilize the feedback and retransmission scheme. Therefore, reliable data delivery is guaranteed mainly by channel coding in this application. To improve the packet error performance further, a novel error control scheme is proposed by introducing certain fountain code as outer code of traditional channel code. As fountain codes are capacity achieving on erasure channel, the whole packet error rate in receiver can be reduced. However, the extra overhead brought by fountain codes also depresses the coding gain. In this paper, conditions on which the novel scheme improves the coding performance are analyzed and approaches for specific fountain code selecting are illustrated. Simulation results show that the novel scheme can achieve 0.06~0.44dB extra coding gain by concatenating a systematic RU(Richardson-Urbanke) code to the LDPC (Low-Density Parity-Check) codes suggested by CCSDS (Consultative Committee for Space Data System).