Joint sonar-watermark detection using pulse compression filter

Sonar watermarking is defined by the secure embedding of a low power authentication code in selected components of a cover signal. The components to be watermarked are the selected time-frequency cells of the sonar pulse. In the past, watermark detection has been implemented as a step separate from sonar detection. From a practical standpoint, sonar detection must precede watermark detection. In this work, we present an integrated framework which brings together sonar and watermark detection in one step. The idea is that watermark detection should be attempted only after a sonar echo has been detected. For an LFM signal, a pulse compression filter is the most commonly used receiver. We propose an approach where watermark and signal detection takes place concurrently at the output of the filter. Implementation of both sonar detection and watermark detection is complicated by the fact that the sonar return time is unknown. We have incorporated a parameter estimation approach in the loop whereby sonar echo time of arrival is first estimated using a generalized likelihood function. This estimate is used in setting up a proper matched filter. Shallow water simulations are carried out and Receiver Operating Characteristics (ROC) curves are produced to quantify watermark detection performance under different signal-to-watermark ratios.