Adaptive watermark power control for capacity optimized MC-CDMA system

Increase in watermark power, for a given noise variance, increases watermark-to-noise ratio (WNR). This in turn improves data hiding capacity according to Shannon's channel capacity theorem. On the other hand, with the increase of embedding power/strength for multiple bits hiding on a set of host samples, both the watermark and interference power increase. Consequently, watermark-to-(interference plus noise) power ratio (WINR) and therefore the data hiding rates saturate at a constant value. As a matter of fact, adaptive watermark power allocation in distortion constrained scenario becomes important to improve overall data hiding capacity. This paper proposes an adaptive power allocation algorithm for multicarrier code division multiple access (MC-CDMA) watermarking system that simultaneously supports variable embedding rate. Implementation is done by allocating all host samples to high priority watermark bits and alternate odd and even host samples are assigned to the low priority hidden bits. The use of alternate host samples suggests to split spreading codes in odd and even parts that lead to an increase in watermark payload. An optimal watermark power allocation algorithm then maximizes the sum capacity that not only improves overall data hiding rate but also assures that each host sample can achieve a required data hiding rate.