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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ABSTRACT: In this paper, frequency and time correlation of the underwater channel are exploited to obtain a low-complexity adaptive channel estimation algorithm for multiple-input-multiple-output (MIMO) spatial multiplexing of independent data streams. The algorithm is coupled with nonuniform Doppler prediction and tracking, which enable decision-directed operation and reduces the overhead. Performance is demonstrated on experimental data recorded in several shallow-water channels over distances on the order of 1 km. Nearly error-free performance is observed for two and four transmitters with BCH(64,10) encoded quadrature phase-shift keying (QPSK) signals. With a 24-kHz bandwidth, overall data rates of up to 23 kb/s after coding were achieved with 2048 carriers. Good results have also been observed in two other experiments with varying MIMO-OFDM (orthogonal frequency-division multiplexing) configurations.IEEE Journal of Oceanic Engineering 08/2010; · 1.16 Impact Factor
Conference Paper: Capacity of underwater acoustic OFDM cellular networks[Show abstract] [Hide abstract]
ABSTRACT: We analyze the capacity of underwater acoustic cellular networks that utilize Orthogonal Frequency Division Multiplexing (OFDM) modulation. The capacity analysis is presented based on a model of the average path loss and frequency-dependent absorption, both of which are distance-dependent. We show that capacity-achieving systems utilize multiple architectural layers, each of which uses a different subband with its own frequency reuse number. We solve the problems of data rate maximization per mobile user, and the transmit power minimization under an average target data rate constraint per cell, for both the single- and multiple-layer architectural solutions. We discuss the practical issues in the implementation of such capacity-achieving underwater acoustic OFDM cellular systems.OCEANS 2010 IEEE - Sydney; 06/2010
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ABSTRACT: In this paper, we propose UW-OFDMAC, a distributed Medium Access Control (MAC) protocol tuned for Under-Water Acoustic Sensor Networks (UW-ASNs). It is a transmitter based Orthogonal Frequency Division Multiple Access (OFDMA)scheme that integrates an original power and OFDMA parameters self-assignment algorithm to set the optimal transmit power, subcarrier spacing and guard interval duration. UW-OFDMAC aims at achieving two objectives, namely, guarantee high bandwidth efficiency and low energy consumption. Simulation results show that UW-OFDMAC outperforms the basic OFDMA protocol tuned for the underwater environment.Communications (ICC), 2011 IEEE International Conference on; 07/2011