In this paper, information-theoretic analysis of spread spectrum watermarking (SSW) is performed. The analysis is focused on deriving channel capacity of SSW system in order to determine the most embedding rate with the highest robustness. Channel capacity is calculated for three cases when the watermark channel introduces no attack, the additive noise attack and the de-synchronization attack. The analyses in this paper are based on the practical aspects and the embedding and detecting strategy of SSW. In each section, first the channel capacity of SSW is calculated and then all the effective parameters on channel capacity are examined.

In this paper, a new audio watermarking scheme is proposed that addresses the synchronization problem using an adaptive filter. To spread the watermark energy across the spectrum of the host audio signal, the scheme uses Hamming coding, convolutional encoding, and generalized PN sequence generation and for watermark recovery, the scheme utilizes Viterbi decoding. Also, the watermark cannot be detected either statistically or perceptually. To increase the watermark embedding capacity, the watermark is embedded in certain areas of the host signal, which increases the masking threshold. By using a high masking threshold, the adaptive watermark insertion, blind detection, robustness, and capacity of watermarking are enhanced in comparison to similar methods. Finally, experimental results show that in addition to guaranteeing an error bit rate (BER) of almost 0 for non-and minor-attack conditions, the BER is substantially improved in the case of low-pass filtering at a cutoff frequency as low as 3. 2 KHz.

This paper presents an innovative technique on the application of chaotic systems for secure communication. The inherent defect of shortage of chaotic bandwidths has been remedied by employing spread spectrum nonlinear functions and the information signal is masked with chaos based spread spectrum signal with high security. The designing state observer along with nonlinear output feedback control is the basis of the receiver structure. Lyapunov stability theory guarantees the synchronization of slave system with the master chaos driver. Meanwhile, duo to noisy communication channel, a stochastic ITO model for master system is supposed to design the state observer. The receiver extracts the information signal using the transmitted signal and the outputs of the observer. The results of numerical simulations based on the Chua circuit fully elaborate the proposed method.