الفهرس 
CHAPTER 2 FUNDAMENTAL OF UNDERWATER ACOUSTIC COMMUNICATION SYSTEMOnly 14 pages are availabe for public view
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Abstract
Communicating underwater has been an area of
interest of researchers, engineers, and practitioners alike. One
of the main reasons for the slow rate of progress in this area is
that the underwater acoustic channel is in general much
more hostile-in terms of multipath effect, frequency
selectivity, noise effect, and Doppler effect. The Underwater
Acoustic Orthogonal Frequency Division Multiplexing (UWAOFDM)
system is a well-known system that has recently
became a preferred choice for underwater wireless
communications.
This thesis is presented to find a good solution to
underwater communication problem. First, the thesis
investigates a proposed implementation of Zero forcing (ZF)
pre-equalization in UWA channels. It is known that the preequalization
is highly effective in wireless communications. It
mitigates the channel effects in an efficient manner. Due to the
varying channel nature in UWA communications, it is expected
that pre- equalization will be feasible in UWA channels. It will
also mitigate the complicated nature of UWA channels. This
channel suffers from channel variations, Doppler shift,
attenuation, and multipath propagation. The implementation of
the proposed pre-equalization and comparison with normal ZF
equalization reveal a large degree of success of the proposed
scheme.
In fact, the frequency synchronization has a great
importance in preserving the performance of the UWA-OFDM
systems. The Carrier Frequency Offset (CFO) estimation can be
blind or data aided. In this thesis, the Zadoff-Chu (ZC)
sequences are used for OFDM synchronization in UWA
communications, and they are compared with different data-
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aided algorithms. We propose a low-complexity algorithm for
CFO estimation based on ZC sequences. Also, a joint
equalization and CFO compensation scheme for UWA-OFDM
communication systems is presented. Simulation results
demonstrate that the proposed CFO estimation algorithm allows
estimation of the CFO accurately with a simple implementation
in comparison with the traditional schemes. Moreover, the
performance of the UWA-OFDM system can be preserved in
the presence of frequency offset.