Performance of coded OFDM in very shallow water channels and snapping shrimp noise

Abstract

-Although acoustic energy has been used effectively for point-to-point communications in deepwater channels, it has had limited success for horizontal transmissions in shallow water. Time-varying multipath propagation and non-Gaussian snapping shrimp noise are two of the major factors that limit acoustic communication performance in shallow water. Rapid time variation in the channel can limit the use of equalizers to compensate for frequency selective fading introduced due to multipath propagation. OFDM (orthogonal frequency division multiplexing), a communication technique widely used in wired and wireless systems, divides the available bandwidth across a number of smaller carriers, each of which experiences flat fading. This simplifies the equalizer structure and provides robustness against time-varying frequencyselective fading. Another source of signal degradation is impulsive noise from snapping shrimp, which affects several OFDM carriers at the same time. OFDM, when coupled with coding, can provide robustness against impulsive noise by distributing the energy for each bit over a longer period of time. We tested coded OFDM in a very shallow water channel in Singapore waters. The results show that it is a promising technique for use in very shallow, warm water channels.

Research on Improvement of Spectrum Efficiency of Spread Spectrum OFDM Communication Scheme for Cruising Sensor Network

“…Orthogonal frequency-division multiplexing (OFDM) has been drawing the attention recently, featuring its strong antimultipath and low complexity properties [5][6][7]. In OFDM modulation, a high-speed transmitted data stream is divided into a number of low rate ones which are transmitted over a certain number of subcarriers.…”

Multicarrier Communication Over Underwater Acoustic Channels With Nonuniform Doppler Shifts

“…Rescaling and phase-rotation of the received signal thus restore the orthogonality of the subcarriers of ZP-OFDM. The correlation in (12) can be performed by overlap-adding of the received signal, followed by FFT processing [2], [16].…”

“…, while experimental results are extremely scarce [8]- [12]. Recent investigations on underwater OFDM communication include [13] on non-coherent OFDM based on on-off-keying, [14] on a low-complexity adaptive OFDM receiver, and [15] on a pilot-tone based block-by-block receiver.…”

Further results on high-rate MIMO-OFDM underwater acoustic communications

“…Multicarrier modulation in the form of OFDM has been actively studied for underwater acoustic (UWA) communications [2]- [5]. Also, multi-input and multi-output (MIMO) techniques have been applied to UWA communications that can considerably increase the data rate [6], [7].…”