遥测系统中喷泉码的低延时改进算法

Improved Algorithm of Fountain Code with Lower Delay for Telemetry System

针对喷泉码应用于遥测系统时存在较大系统延时的问题,在对其延时特性进行分析的基础上,提出了一种改进的编译码算法。当编码器接收到部分数据符号时,按照预先制定的度选取策略和符号选取策略,选择当前编码符号的度和生成该编码符号的数据符号进行编码。该算法以减小编码延时为目标,通过分析编码符号发送速率的稳定性和可容忍的最长信号闪断时间可确定合理的编码延时。仿真得到了不同丢符号率下的编码延时、系统延时和所需的编码冗余,结果表明,与传统方案相比,改进方案的编码延时减小了一半以上。通过理论分析和仿真验证,得出了改进算法可明显减小基于喷泉码的遥测系统延时的结论。

A significant delay will be resulted when a fountain code is applied to a telemetry system. Aiming at re-ducing the system delay, an improved encoding and decoding algorithm of Luby Transform （LT） code is proposed, Before the encoder receives all data symbols belonging to one LT code block, the degree of the current encoding symbol is decided according to the predefined degree selection strategy , the related data symbols are picked according to the predefined symbol selection strategy, and the encoding symbol is then produced by the selected data symbols. Appropriate encoding delay, which is defined by the time from getting the first data symbol to transmit-ting the first encoding symbol, is deduced to guarantee the stability of encoding symbols transmission rate and the maximum tolerable fade duration of the channel. Simulation of the proposed scheme is performed to obtain the enco-ding delay, system delay and the necessary encoding redundancy at different symbol loss ratio and the results show that the encoding delay of the improved algorithm is reduced to half that of the conventional one. Theoretical analy-sis and simulation results demonstrate that the proposed scheme can significantly reduce the delay of a telemetry system based on fountain code.