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, 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
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ABSTRACT: Frequency and time correlation of the underwater channel are exploited to obtain an adaptive channel estimation algorithm for MIMO spatial multiplexing with low complexity and low overhead. Non-uniform Doppler compensation is performed by extending the adaptive synchronization method to multiple transmitters. Algorithm 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 QPSK signals. We report in detail on an experiment where an information rate of 23 kbps (4 transmitters times 0.75 sps/Hz/transmitter times 2 bits/symbol times 10/64 times 24 kHz) is achieved using 2048 carriers in a 24 kHz bandwidth.OCEANS 2008; 10/2008
Conference Paper: MIMO-OFDM Over An Underwater Acoustic Channel[Show abstract] [Hide abstract]
ABSTRACT: Multicarrier modulation in the form of OFDM facilitates high-rate transmission over long dispersive channels, while multiple-input multiple-output (MIMO) techniques increase the system capacity. In this paper, we report on the design of a MIMO-OFDM with two transmitters and test it using experimental data recorded during the AUV Fest, Panama City, FL, June 2007. Nearly error-free performance is observed with low-density parity-check (LDPC) coding. With a 12 kHz bandwidth, the overall data rate is 12.18 kbps after rate 1/2 coding.OCEANS 2007; 11/2007