Capacity Analysis Of The Covert Channel Based On The Generalized Spread Spectrum Watermarking Technology

The digital watermarking technology considered to be the imperceptible, robust, secure communication of information by embedding it into other digital data is applied widely. The researches mainly focus on the imperceptibility and robustness of the watermark, but there is still a key problem to be studied for the application of digital watermarking technology in the field of information hiding, that is the information hiding capacity. Research shows that, if the hidden watermarking information is embedded in the same public carrier in a different way, it means that the transmission channel and channel capacity differ for the watermarking, so the research of covert channel capacity under different watermarking schemes is of great significance. At present the theoretical analysis framework of watermarking channel capacity is not perfect, and the channel capacity of the spread spectrum watermarking has rarely been investigated in detail.This paper mainly analyses the capacity of the covert channel based on the generalized spread spectrum watermarking technology. The core idea is to establish the research model of covert channel capacity for the practical application scene of generalized spread spectrum watermarking communication, then present the complete derivation and analysis procedure of the channel capacity. There are two original carriers in our research, i.e. audio signals and digital communication signals. The two kinds of carriers have different characteristics and their needs for imperceptible also differ, so the capacity analysis models and methods are not the same. Then the theoretical capacity expressions of watermarking channel in two different carriers are derived respectively. And the capacity performance is analyzed, the effects to the capacity caused by the statistical properties of carrier and the selected values of embedding parameters are investigated for a certain distortion factor. The optimum parameter values for channel capacity are obtained, and the relationship between distortion and covert channel capacity is analyzed to help get a compromise solution in practical application.Finally, a series of simulation results is given. Results show that the embedding parameter of the watermarking scheme has great influence on the covert channel capacity, the optimum parameter values we analyzed can always ensure the capacity upper reaching the theoretical limit of 1 bits/symbol. And simulation results also show that the distortion and the watermarking channel capacity performance are interchangeable. Especially when the distortion is limited in a small level, its change has a huge influence on channel capacity, it means that the adjustment effect will be obvious in this case.