A VOHE System for Underwater Communications

Nonstationary System Analysis Methods for Underwater Acoustic Communications

The underwater environment can be considered a system with time-varying impulse response, causing time-dependent spectral changes to a transmitted acoustic signal. This is the result of the interaction of the signal with the water column and ocean boundaries or the presence of fast moving object scatterers in the ocean. In underwater acoustic communications using mediumto-high frequencies (0.3–...

Adaptive Doppler-shift Compensation for Ofdm Underwater Acoustic Communications System

An adaptive Doppler-shift compensation scheme for wideband orthogonal frequency division multiplexing (OFDM) is proposed in this paper. This approach accommodates a time-varying Doppler, where the time scaling factor for each OFDM symbol is frequently estimated depending on the inherent periodicity of the cyclic-prefix and its preceding neighbours' values. The proposed technique relies on a sin...

Blind equalization for underwater communications

Development of an FHMA-based Underwater Acoustic Communications System for Multiple Underwater Vehicles

This paper describes the design of an underwater acoustic communications system for multiple underwater vehicles, based on frequency-hopping multiple-access (FHMA) and tamed spreadspectrum communications. The system makes used of the tamed spread-spectrum method, frequency hopping, 4FSK, and a rake receiver. In order to make the system more practical, the underwater channel and the effect of th...

Adaptive Underwater Acoustic Communications

Underwater wireless networks consist of mobile and static nodes, which usually communicate using the acoustic channel since radio transmissions attenuate rapidly and optical communication is only suitable for short distances. The underwater acoustic channel is plagued with issues of high transmission power requirements, rapidly changing channel characteristics, multi-path echoes, possible high ...