Access to multimedia data has become much easier due to the rapid growth of the Internet. While this is usually considered an improvement of everyday life, it also makes unauthorized copying and distributing of multimedia data much easier, therefore presenting a challenge in the field of copyright protection. Digital watermarking, which is inserting copyright information into the data, has been proposed to solve the problem. In this paper, we first discuss the features that a practical digital watermarking system for ownership verification requires. Besides perceptual invisibility and robustness, we claim that the private control of the watermark is also very important. Second, we present a novel wavelet-based watermarking algorithm. Experimental results and analysis are then given to demonstrate that the proposed algorithm is effective and can be used in a practical system.

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A noncoherent limiter-discriminator receiver is often considered for the Bluetooth system because of its simplicity and low cost. While its performance is more than adequate for some channels, the results are significantly degraded in either an interference-limited environment or a frequency selective channel. In this paper, we compare the performance of the traditional limiter-discriminator with integrate and dump filter to a more sophisticated Viterbi receiver. We find that the Bluetooth access code is sufficient to be used for channel estimation in the Viterbi receiver. A comparison is carried out in a Rayleigh fading channel and in the presence of interference either from another Bluetooth piconet or an IEEE 802.11b wireless local area network. Performance metrics include bit error rate and packet loss rate.

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