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.