中文摘要：

低密度奇偶校验码级联水印码的编译码方案可纠正非二进制同步错误。为了提高上述系统中水印码识别同步错误的能力,提出了扩展多个符号子集的改进水印调制方案。具体而言,该改进方案将每个传输符号携带的水印信息扩展至两位,对应地将传输信号的子集扩展为四个。扩展后的系统星座图的划分更为精细,提高了借助更多水印比特码识别同步错误的能力。仿真结果表明,与传统方案相比,在加性噪声较小情况下如信噪比为10 d B,当误帧率为10~（-3）时,改进方案可以纠正的同步错误概率达13%,且适用于非线性信道。

英文摘要：

A concatenated coding scheme of a low-density parity-check code and a watermark code is capable of correcting non-binary synchronization errors. In order to improve the capability of the watermark code identifying these errors, an im-proved scheme is proposed using not two but multiple signal subsets. Specifically, in the proposed scheme, each transmit-ted symbol includes have two watermark bits and thus separate the constellation into four subsets. In this way, the expanded constellation can be classified into four more distinguishing subsets and thus the synchronization identification is improved using more watermark bits. Simulation results reveal that when the additive noise is small, for example, the signal- to-noise ratio is 10 dB and the frame error rate is 10 3, the synchronization error probability that the proposed scheme can correct is as much as 13% . Also, the proposed scheme is more suitable for non-linear channels.