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确保较低信噪比条件下的系统帧同步,是LDPC码在系统应用中的关键问题。基于最大似然的准则,提出了一种适合准循环LDPC编码系统的码辅助盲帧同步算法。该算法通过计算不同帧偏移处的信道输出软信息向量满足LDPC码校验矩阵中所有校验方程的概率与违背所有方程的概率的对数似然比值,再根据最大似然值对应的信息向量确定最终的帧同步边界。新算法可借助译码器的部分资源来实现帧同步搜索,提高了译码器的利用率,降低了实现复杂度;无需一次完整的迭代译码过程,减少了同步捕获的时间。仿真结果表明,相比已有的码辅助盲帧同步算法,新算法具有较好的帧同步性能;借助新同步算法仿真获得的系统误比特率和帧错误率接近已有的码辅助帧同步算法的译码性能。
Ensuring system frame synchronization at a low signal-to-noise ratio is a key issue for LDPC codes in system applications. Based on the criterion of maximum likelihood, a code-assisted blind frame synchronization algorithm for quasi-cyclic LDPC coding system is proposed. The algorithm calculates the log-likelihood ratio of the probabilities of all calibration equations in LDPC code parity check matrix and the probability of violating all equations by calculating the channel output soft information vector at different frame offsets. Based on the information corresponding to the maximum likelihood The vector determines the final frame sync boundary. The new algorithm can realize the frame synchronization search with part of the resources of the decoder, which improves the utilization of the decoder and reduces the implementation complexity. It does not need a complete iterative decoding process and reduces the time of synchronization acquisition. The simulation results show that the new algorithm has better frame synchronization performance than the existing code-assisted blind frame synchronization algorithm. The system bit error rate and frame error rate obtained by the new synchronization algorithm are close to the existing code-assisted frame synchronization algorithm Decoding performance.