We present an authentication device allowing for the validation of wireless transmissions by means of a watermark signal applied at the physical layer, and demonstrate how the method may be applied to digital broadcast television signals. The novel watermarking approach presented conveys the authentication signal through explicit emulation of innocuous channel responses, further preventing Primary User Emulation attacks in Dynamic Spectrum Access theaters. The undesirable effects of the watermark signal design are removed by the receiver by traditional channel equalization practices, resulting in nearly zero impact to the bit error rate (BER) of the primary signal received. The proposed mechanism may be implemented without modification to existing Digital Television (DTV) transmission equipment using a retrofitting approach, and does not require the modification of existing receivers or protocols. A key benefit of the proposed method is that the authentication signal may be received at a BER much lower than the primary-signal, all within original transmission power and bandwidth constraints. We discuss physical layer details of the new watermarking method, and demonstrate how proven cryptographic authentication measures may be applied to the problem.
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