Hardware for time delay beamforming, demodulation, and processing

Abstract

A digital time delay beamformer/demodulator/processor was designed and built as part of the U of M's involvement in ocean acoustic tomography measurements. This paper describes the overall system design, the criteria on which design decisions were made, and how well the resulting equipment performs. The beamformer can form up to eight simultaneous beams using up to 24 hydrophone inputs per beam. The beam outputs are coherently shifted from any center frequency in the range from 10 Hz to over 500 Hz down to baseband. Center frequencies can be set in steps of 1 mHz. Special hardware was included in the system to speed up commonly performed processing operations. The fast arithmetic device uses serial multipliers and adders to aid in performing double precision complex additions and various multiplication operations. The sequence removal hardware speeds up the computations involved in pulse compressing the linear maximal sequence coded transmissions commonly used in making ocean acoustic multipath measurements. The speed‐up factor is about 100. [Work supported by ONR.]