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Publication
OFDM demodulation in underwater time-reversed shortned channels
Authors
Advisor(s)
Abstract(s)
This work addresses the problem of OFDM transmission
in dispersive underwater channels where impulse responses
lasting tens of miliseconds cannot be reliably handled
by recently proposed methods due to limitations of channel
estimation algorithms. The proposed approach relies on passive
time reversal for multichannel combining of observed waveforms
at an array of sensors prior to OFDM processing, which produces
an equivalent channel with a shorter impulse response that
can be handled much more easily. A method for tracking
the narrowband residual phase variations of the channel after
Doppler preprocessing is proposed. This is a variation of an
existing technique that can improve the spectral efficiency of
OFDM by reducing the need for pilot symbols. This work also
examines techniques to handle sparse impulse responses and
proposes a channel estimation method where an l1 norm is
added to the standard least-squares cost function to transparently
induce sparseness in the vector of channel coefficients. Algorithms
are assessed using data collected during the UAB’07 experiment,
which was conducted in Trondheim fjord, Norway, in September
2007. Data were transmitted with bandwidths of 1.5 and 4.5 kHz,
and recorded at a range of about 800 m in a 16-hydrophone array.
Significant multipath was observed over a period of at least 30
ms.
Description
Keywords
Bandwidth Channel estimation Cost function Demodulation Dispersion Narrowband OFDM modulation Quadrature phase shift keying Sensor arrays Underwater communication
Citation
J.P. GOMES, A. SILVA and S.M. JESUS, ''OFDM Demodulation in Underwater Time-Reversed Shortned Channels'' in OCEANS'08, Quebec, Canada, pp. 1-8, September.
Publisher
IEEE Explore