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在低信噪比通信环境中同步困难是任何编码系统必须解决的问题。对此,提出了基于软信息的编码辅助的迭代相位估计算法。该法采用载波相位同步、解调和译码联合处理的思想,将译码器输出的码比特的可靠量度直接反馈回估计单元以提高同步的准确度。考虑到现行系统中多采用非系统卷积码,文中利用对数似然代数原理,得到了适用于非系统码进行迭代的软输出维特比译码算法,有效降低了计算复杂度。仿真结果表明,该法仅需5次迭代,信噪比为3dB的情况下,系统误比特率可达到10-5。
Synchronization difficulties in low SNR environments are issues that any coding system must address. In this regard, a coding-assisted iterative phase estimation algorithm based on soft information is proposed. This method adopts the idea of carrier phase synchronization, demodulation and decoding joint processing, and directly feeds back the reliable measurement of the code bits output by the decoder back to the estimation unit to improve the synchronization accuracy. Considering that non-systematic convolutional codes are mostly used in current systems, the soft-output Viterbi decoding algorithm suitable for non-systematic codes is obtained by using the log-likelihood algebra principle, which reduces the computational complexity effectively. The simulation results show that this method only needs 5 iterations and the bit error rate of the system can reach 10-5 when the SNR is 3 dB.