纠正同步错误的反转级联水印码的迭代译码

摘要

为提高插入删节信道下反转级联水印码(Reverse Concatenated Watermark Code)的译码性能,本文设计了一种反转级联水印码的硬判决迭代译码方案.该方案在反转级联水印码内译码器中引入外译码器输出的硬判决估计序列,交织后的硬判决序列和水印序列的异或作为内译码器的更新后的参考序列,从而减小了码字序列对水印码的影响,改善了水印译码器的参考信息.前后向估计方法利用该参考序列和更新后的有效替代错误概率计算输出概率,进一步用于计算前向度量值和后向度量值,提高了内译码器输出的每个比特的似然信息的可靠度,改善了整体性能.仿真结果表明,当反转级联水印码方案采用硬判决迭代译码算法时,整体性能得到有效提高.%A new iterative decoding scheme was introduced for the reverse concatenated watermark code to improve the decoding performance in the presence of insertions,deletions and substitutions.The scheme fed back the hard-decision estimations into the inner decoder of the reverse concatenated watermark code and the new reference sequence chose the modulo-2 sum of the original watermark and the codeword with the hard decisions,reducing the impact of the codeword to the watermark sequence and improving the reference information of the inner decoder.The forward-backward algorithm used the new reference sequence and the updated effective substitution error probability to refine the output probability and then to update the forward and backward quantities,which improved the reliability of the likelihood for each bit in the ironer decoder and enhanced the overall performance.It is shown that the overall performance improves when using the hard-decision iterative scheme to the reverse concatenated watermark codes.