利用边信息嵌入的CDMA水印信道性能研究

稳健性是数字水印的重要指标之一.为了改善水印稳健性,CDMA技术已被引入到数字水印中.但是,目前基于CDMA扩频技术的水印算法基本都是通过实验方式来确定嵌入强度以及相关参数.本文分析了把载体作为边信息情况下CDMA水印信道的性能.研究了PSNR值,嵌入强度参数 β ,正交码码长N以及用户数K之间的关系,给出了 PSNR关于这三者的显式表达式.根据PSNR值,给出了水印嵌入强度参数 β 的估计算法,仿真实验结果表明估计的有效性.并指出CDMA水印信道中,用户数不影响PSNR值的大小,实验结果有力地支持了这个结论.通过分析CDMA水印信道的误码形成过程,给出了信道误码率表达式,并得出,在给定PSNR值的情况下,CDMA正交扩频码码长 N 的选择不影响信道误码率值.

Performance Analysis of CDMA-Based Watermarking Channel with Side-Information Embedding

Robustness is one of the important requirements of digital watermarking.To improve robustness,CDMA (Code Division Multiple Access) technologies have been introduced into digital watermarking.However,most existing CDMA-based watermarking parameters are usually determined via experience.With the side-information embedding scheme,we have analyzed the relationship between PSNR,embedding strength,orthogonal codes length,and number of users,in the case of CDMA additive embedding.The expression for estimating the embedding strength is derived in terms of PSNR.Experimental results show the estimating is effective.Furthermore,while keeping the PSNR constant,the relationship between spread code length and watermark bit error rate is analyzed.As a conclusion,when keeping the length of watermark bits and PSNR constant,the choice of orthogonal spreading code does not influence watermark bit error rate.The conclusion can be used to guide the actual watermarking system to choose the correct embedding parameters.