Shallow Water Fluctuations and Communications

Abstract

LONG TERM GOALSThe central effort of this research will be the development of robust algorithms for reliable, high data rate, acoustic communications in a dynamic ocean environment and demonstration of their use with data collected in a shallow water environment. OBJECTIVEWe will study shallow water fluctuation physics and the enhancement of performance of broad area acoustic communications in shallow water by building on developments in adaptive channel equalizers in conjunction with the time reversal approach. APPROACHTime reversal communications exploits spatial diversity to achieve spatial and temporal focusing in complex ocean environments. Spatial diversity easily can be provided by a vertical array in a waveguide. Alternatively, spatial diversity can be obtained from a virtual horizontal array generated by two elements, a transmitter and a receiver, due to relative motion between them, referred to as a synthetic aperture. In this case, the same data is transmitted periodically. The cost is a reduction in the overall data rate by the number of transmissions accumulated in generation of synthetic aperture. In addition, Doppler compensation is required involving Doppler shift estimation and re-sampling of the broadband communication signal.Recently we have investigated the feasibility of synthetic aperture communications (SAC) in shallow water [1]. In that work, simple on/off keying modulation was employed to minimize the complexity and not require coherent demodulation. Furthermore, the motion was almost transversal resulting in a small Doppler shift. In this case diversity appears to come from the data being collected in an azimuthally inhomogeneous environment coupled with temporal channel variation between transmissions.