title: High-rate synthetic aperture communications in shallow water.
abstract: Time reversal communication exploits spatial diversity to achieve spatial and temporal focusing in complex ocean environments. Spatial diversity can be provided easily 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. This paper presents coherent synthetic aperture communication results from at-sea experiments conducted in two different frequency bands: (1) 2-4 kHz and (2) 8-20 kHz. Case (1) employs binary-phase shift-keying modulation, while case (2) involves up to eight-phase shift keying modulation with a data rate of 30 kbits/s divided by the number of transmissions (diversity) to be accumulated. The receiver utilizes time reversal diversity combining followed by a single channel equalizer, with frequent channel updates to accommodate the time-varying channel due to coupling of space and time in the presence of motion. Two to five consecutive transmissions from a source moving at 4 kts over 3-6 km range in shallow water are combined successfully after Doppler compensation, confirming the feasibility of coherent synthetic aperture communications using time reversal.
authors.affiliation: Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093-0238, USA.
authors.forename: H C
authors.initials: HC
authors.lastname: Song
authors.forename: W S
authors.initials: WS
authors.lastname: Hodgkiss
authors.forename: W A
authors.initials: WA
authors.lastname: Kuperman
authors.forename: T
authors.initials: T
authors.lastname: Akal
authors.forename: M
authors.initials: M
authors.lastname: Stevenson