Accession Number:

ADA230171

Title:

Digital, One Way, Acoustic Communication in the Ocean

Descriptive Note:

Doctoral thesis

Corporate Author:

SCRIPPS INSTITUTION OF OCEANOGRAPHY LA JOLLA CA MARINE PHYSICAL LAB

Personal Author(s):

Report Date:

1990-09-01

Pagination or Media Count:

165.0

Abstract:

This dissertation summarizes the work done on developing methods for underwater telemetry, between two freely drifting stations, in the presence of a slowly time-varying, frequency-selective fading channel and strong multipath. At sea experiments conducted during 1989-90 show that the acoustic communication channel suffers from strong frequency-selective fading and strong multipath on the order of seconds. Moreover, most of the time, the intensity of the received signal due to the first multipath is much stronger than the received direct signal. In order to establish a reliable communication channel in the presence of strong fading, diversity must be used. DPSK chirp modulation proved to be superior over all other frequency diversity methods. Moreover, it is shown that a chirp QDPSK with bandwidth expansion of 5 has better performance than a combination of an error correcting code and frequency diversity method with similar bandwidth expansion. The achieved bit error rate when a chirp DPSK is used in the presence of frequency selective fading is the same as that of a conventional DPSK modulation in the presence of AWGN. Both bit synchronization and equalization methods which take into consideration the multipath and fading effects, are proposed. The major problem with bit synchronization is the destructive effect of the micromultipath that causes large time jitter.

Subject Categories:

  • Acoustics
  • Telemetry

Distribution Statement:

APPROVED FOR PUBLIC RELEASE