Underwater acoustic communication over Doppler spread channels
Citable URI
https://hdl.handle.net/1912/5709Location
ArcticDOI
10.1575/1912/5709Keyword
Signal processing; Underwater acousticsAbstract
This work is concerned with coherent communication by means of acoustic signals
over underwater communication channels. The estimated scattering functions of real
data ranging from the Arctic environment to tropical waters show that underwater
communication channels can not be captured by a single, simple channel model.
This thesis considers mainly a subset of underwater communication channels where
the Doppler spread is more severe than the delay spread.
An appropriate representation of the linear time- variant channel is introduced,
and the wide sense stationary uncorrelated scattering (WSSUS) channel assumption
enables characterization in terms of scattering functions. The concept of Doppler
lines, which are frequency domain filters, is used in the derivation of a receiver for
Doppler spread channels.
The channel is simulated by means of a ray representation for the acoustic field
and a time-variant FIR filter. The impact of physical ocean processes on the Doppler
spread is demonstrated, and from this modeling explanations for the Doppler spread
observed in real data are obtained.
A decision feedback equalizer (DFE) adapted with recursive least squares (RLS)
is analyzed, and its limit with respect to pure Doppler spread is found. By using the
DFE with a phase locked loop (PLL) suboptimal system behavior is found, and this
is verified on real data. In the case of a simple Doppler shift the cross-ambiguity
function is used to estimate the shift, and the received signal is phase rotated to
compensate this before it enters the receiver.
A modified RLS called the time updated RLS (TU-RLS) is presented, and it is used in a new receiver. This receiver is initialized by means of the cross-ambiguity
function and the performance is characterized by probability of decoding error vs delay
spread, Doppler spread and SNR. The receiver uses Doppler lines to compensate
both discrete and continuous Doppler spread. The receiver stability depends on the
conditioning of the block diagonal correlation matrix propagated by the TU-RLS.
The receiver is used to decode both real and simulated data, and some of these data
are severely Doppler spread.
Description
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 1997
Suggested Citation
Thesis: Eggen, Trym H., "Underwater acoustic communication over Doppler spread channels", 1997-06, DOI:10.1575/1912/5709, https://hdl.handle.net/1912/5709Related items
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