Distributed Beamforming Sonar for UUVs

Distributed beamforming (DBF) has received significant attention in the Radio Frequency (RF) domain. There are also potential performance benefits in the Underwater (UW) Acoustic domain. Specifically, in this work we investigate the application of DBF to UW sonar for Unmanned Underwater Vehicles (UUVs). First, we utilize distributed coding applied across multiple UUVs to enable beamforming gain. Next, we develop a multi-vehicle UUV motion model that emulates movement of the mobile DBF UUV array. The motion model enables our simulation model to induce position errors of the DBF array that a UW DBF sonar system might experience in practice. To ensure DBF beamforming gain in the UW environment, these position errors must be estimated and corrected during DBF sonar UUV mobility. In addition, each UUV will experience unique synchronization offsets, which are also estimated and corrected. For an N-distributed UUV element array, we show that our distributed coding method provides N-2-gain in signal-to-noise ratio (SNR) on initial sonar transmission and reception, and N-3-gain thereafter. While our simulation model demonstrates these results for direct target returns, it is also theoretically possible to further increase the received SNR using multipath combining.