Systematic search for multi-phase codes and design of mismatched filters for multi-user underwater sonar ranging system

Summary form only given. A technique is introduced to select poly-phase codes and design mismatched filters of a pulse compression system to have specific temporal and frequency response characteristics. In the particular problem under study, multiple sonar vehicles, up to eleven, need to be assigned codes and receiver filters that have nearly orthogonal signatures. Also, narrowband users that act as interference are present within the system. A code selection procedure based on global optimization technique called simulated annealing is used that selects codes which have low auto-correlation sidelobes and low cross-correlation peaks. Mismatched filters are designed for these codes which minimize the peak values in the auto-correlation and the cross-correlation. Also, a slight adjustment to the mismatched filter design technique produces mismatched filters with nulls in their frequency response in addition to having low correlation peaks. These two separate procedures, code selection and mismatched filter design, taken together, provide a unique approach to solving the problems of multi-user system corrupted by narrowband interference. The mismatched filter design also allows the design frequency nulls at any frequency with arbitrary null attenuation, null width, and sidelobe level, at the cost of processing gain.<
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