University of Connecticut

Massachusetts Institute of Technology

Woods Hole Oceanographic' Institution

Baosheng Li

Shengli Zhou

Peter K Willett

Milica Stojanovic

Lee Freitag

Advantageous OFDM-based underwater acoustic (UWA) apparatus, systems and methods are provided according to the present disclosure. In general, OFDM transmissions over UWA channels encounter frequency-dependent Doppler drifts that destroy the orthogonality among OFDM subcarriers. The disclosed apparatus, systems, and methods use a two-step approach to mitigate frequency-dependent Doppler drifts for zero-padded OFDM transmissions over fast-varying channels: (1) non-uniform Doppler compensation via resampling to convert a 'wideband' problem into a 'narrowband' problem; and (2) high-resolution uniform compensation on the residual Doppler. The disclosed apparatus, systems and methods are based on block-by-block processing and do not rely on channel dependence across OFDM blocks. Thus, the disclosed apparatus, systems and methods are advantageously applicable for fast-varying UWA channels.

Apparatus, systems and methods for enhanced multi-carrier based underwater acoustic communications

Trellis-based methods for reducing feedback while maintaining performance in a Multiple Input, Multiple Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system. The methods involve: receiving a plurality of symbols from a plurality of sub-carriers at a receiver; selecting a plurality of indices of codewords corresponding to a codebook of pre-coding weighting matrices for the sub-carriers based on vector quantization compression of the codewords, including selecting a plurality of indices based on trellis-based feedback encoding; and transmitting the selected indices over a wireless channel to a transmitter. Optimal precoding matrices are selected at the same time for all subcarriers by searching for the optimum choice of matrices along a trellis. Selecting a plurality of indices based on trellis-based feedback encoding includes constructing a trellis by specifying a state transition table.

Trellis-based feedback reduction for multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) with rate-limited feedback

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Willington, CT, United States of America

Baosheng Li