Multistage Spread Spectrum Watermark Detection Technique Using Fuzzy Logic

Abstract

In this letter, a new model of spread spectrum (SS) watermarking is proposed where each watermark bit is spread using a distinct code pattern over N-mutually orthogonal signal points. Decision variable for each bit of watermark decoding is formed from the weighted average of N-decision statistics. Multiple detection stages are applied where the detected bit patterns of one stage are used in the immediate subsequent stage to cancel the multiple bit interference (MBI) effect experienced by the individual bit. Fuzzy logic is used to beat the effect of such MBI through Multiple Group Combined Interference Cancelation (MGCIC) technique in the intermediate stage(s). The group is formed from the decision magnitudes corresponding to a group of code patterns and the ensemble of code patterns are classified in different groups like very strong, strong, weak and very weak based on fuzzy membership function derived from the magnitude of the decision variables. Attack channel is modeled as Rayleigh distribution followed by AWGN (additive white Gaussian noise). Simulation results show that BER (bit error rate) value is reduced more, of course, at the cost of slight increase in computational complexity if the code patterns are classified in a greater number of groups.