Channel Capacity Analysis of Spread Spectrum Watermarking in Radio Frequency Signals

The carrier of the digital watermark expands from audio signals to radio frequency (RF) signals. Unlike audio signals, RF signals, such as the watermark transmission carrier, must be correctly demodulated with the watermark signals so that the distortion of the digital carrier embedded with the watermark is associated with the change in bit error rate. Based on the spread spectrum watermarking scheme, the distortion of the digital carrier signal is redefined, and the channel capacity expression of the watermarking scheme is derived. In addition, the optimal parameters to achieve the maximal channel capacity are discussed, and the constraint relation between the channel capacity and the allowable distortion is investigated.