A Robust Underwater Acoustic Communication System using OFDM-MIMO
ABSTRACT The paper will consider the viability of exploiting the spatial diversity that exists in doubly-spread, underwater acoustic communications channels to provide enhanced capacity using an OFDM-MIMO system. The proposed method offers two forms of diversity. First, coded orthogonal frequency-division multiplexing (COFDM) provides frequency diversity by exploiting the frequency selectivity inherent in channels that suffer from multipath propagation. Second, multiple transducers are used to exploit the spatial diversity that exists in underwater acoustic channels, also due to multipath propagation. This allows the multi-transducer communication system to be viewed as a multi-input, multi-output (MIMO) system to provided potential capacity gain.
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Conference Proceeding: Pilot-tone based ZP-OFDM Demodulation for an Underwater Acoustic Channel[show abstract] [hide abstract]
ABSTRACT: Existing coherent underwater acoustic communication systems rely on single carrier transmission and adaptive decision feedback equalization to deal with time-varying and highly dispersive underwater acoustic (UWA) channels. Equalization complexity prevents any substantial rate improvement with the existing single-carrier approach, as the channel frequency selectivity increases considerably when the symbol rate increases. Multicarrier modulation in the form of orthogonal frequency division multiplexing (OFDM), on the other hand, converts a frequency selective channel into a set of parallel frequency-flat subchannels, thus greatly simplifying receiver equalization. Motivated by the success of OFDM in radio channels, we investigate its use for underwater acoustic channels. In this paper, we develop a pilot-tone based receiver design for zero-padded OFDM transmissions, and test it in a real underwater acoustic channel. Our proposed receiver performs carrier frequency offset compensation, channel estimation, and data demodulation on the basis of individual OFDM block. This approach is appealing to applications with short data bursts, or fast varying channels, as it does not rely on channel dependence across OFDM blocksOCEANS 2006; 10/2006
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ABSTRACT: Recent advances in information theory and terrestrial wireless communication show that significant performance gains are achievable with increased signaling diversity through the use of multiple transmit and receive arrays. An effective approach for increasing data rate over wireless channels is to employ coding techniques appropriate for multiple transmit antennas, namely space-time coding. This paper investigates the feasibility and effectiveness of space-time trellis and layered space-time codes for the shallow-water, acoustic, frequency-selective channel. Using data collected during a recent experiment in the Mediterranean, we show that systems using multiple transmit and receive transducers outperform more conventional single-transmit single-receiver configurations.OCEANS '04. MTTS/IEEE TECHNO-OCEAN '04; 12/2004