Underwater acoustic communication is limited to very low rates without the use of techniques that mitigate the influence of the acoustic channel. A new multichannel spatial diversity communication scheme has been developed at Florida Atlantic University (FAU). This technique combines a novel synchronization method with a maximum-likelihood symbol estimation. The technique is tested with the FAU Dual Purpose Acoustic Modem (DPAM) which uses one transducer for data transmission and 4 hydrophones for data reception. The DPAM transmits messages using 4 types of Frequency-Hoped Multiple-Frequency-Shift-Keying (FH-MFSK) modulation: 4 hops at 221 coded bits per second (cps), 2 hops at 442 cps, or no hoping at 886 cps, or 1182 cps. The bit sequence modulated can be encoded using 3 different Error Coding Codes (ECC): a convolutional code Viterbi 7/sup 1/2/, a Reed Solomon block code, or a combination of both codes. These types of modulation and encoding techniques allow for robust data transmission in adverse environment. The DPAM operates at ranges from 1 to 3 km in 50 feet of water using all 4 transducers. Such a performance can be confirmed using the model of Crepeau.
[1]
Lee Freitag,et al.
Analysis of channel effects on direct-sequence and frequency-hopped spread-spectrum acoustic communication
,
2001
.
[2]
J. A. Catipovic,et al.
Performance limitations in underwater acoustic telemetry
,
1990
.
[3]
Robert J. Urick,et al.
Principles of underwater sound
,
1975
.
[4]
Bernard Sklar,et al.
Digital communications
,
1987
.
[5]
Oliver R. Hinton,et al.
Analysis of experimental shallow water network channel and theoretical channel model
,
2000,
OCEANS 2000 MTS/IEEE Conference and Exhibition. Conference Proceedings (Cat. No.00CH37158).
[6]
Roger L. Peterson,et al.
Introduction to Spread Spectrum Communications
,
1995
.