深空通信系统中高阶LDPC码的软定时同步算法

深空通信具有信号衰减严重,接收机信噪比低的特点,针对深空通信系统中高阶LDPC码定时同步实现困难的问题,提出一种码辅助定时同步算法．首先使用高阶LDPC码的译码软信息构造一种代价函数,进行大定时偏移的粗同步,其次基于最大似然准则,使用EM算法进行定时偏移的细同步．该算法将定时同步器、解调器与译码器联合迭代,利用高阶LDPC译码器输出的软信息辅助定时同步,并通过数字插值方式对过采样信号进行补偿,从而得到接近修正克拉美罗限的定时估计．仿真结果表明,在低信噪比条件下,算法能够在较大定时偏移范围内实现有效的定时同步,并以较低的复杂度获得近似理想的系统误码率性能．

Soft timing synchronization algorithm for LDPC codes on GF(q) in deep space communication

Aiming at the timing synchronization difficulty of LDPC-coded system on GF(q) in deep space communication, a new soft timing synchronization algorithm is proposed. Firstly one cost function using the soft decoding information of LDPC on GF(q) is introduced for coarse timing synchronization, then the Expectation-Maximum algorithm is used for fine timing synchronization based on the maximum likelihood criterion. Conducting the joint iteration of timing synchronizer, demodulator and decoder, the soft information provided by LDPC decoder is used to aid the timing estimation, and the timing estimation close to the modified Cramer-Rao bound can be obtained by interpolation of the over-sampled data. Simulation results show that, at low SNRs, the efficient timing synchronization can be achieved with large timing offset, and almost ideal performance is obtained with low system complexity.