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Doppler distortion causes inter-carrier interference which prevents the use of differentially coherent detection in OFDM systems. To recover this efficient detection method, we propose to use several FFT demodulators operating in parallel over non-overlapping time segments, and to combine their outputs prior to detection. This technique aims for efficient implementation of front-end matched filtering,...
The purpose of this paper is to show that convexity of the underwater acoustic channel and that near-convexity of an approximate closed-form model for that channel holds, in order to use network optimization techniques. We obtain a lower bound on transmission power using subgraph selection to establish minimum-cost multicast connections in underwater acoustic networks with network coding. We solve...
The underwater acoustic channel is characterized by a path loss that depends not only on the transmission distance, but also on the signal frequency. Signals transmitted from one user to another over a distance l are subject to a power loss of l-alphaa(f)-l. Although a terrestrial radio channel can be modeled similarly, the underwater acoustic channel has different characteristics. The spreading factor...
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...
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...
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...
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