Statistical Shallow Water Acoustic Channel Modelling And BER Performance Investigation Of CI-OFDM

Underwater Acoustic(UWA)Communication uses acoustic waves to transmit and receive data under the water.Underwater radio waves suffer from high attenuation.Optical waves suffer from heavy scattering.Acoustic waves are a better communication mode for underwater environments.UWA communication is challenging due to impairments,including attenuation,multipath propagation,noise and Doppler spread.UWA channels are one of the most stimulating communication media.Time varying multipath fading,long delay spread,significant Doppler spread,and frequency-dependent path loss are the focal characteristics of such channels.Precise channel measurement is obtained through experiments which are very costly and restricted to definite settings such as water depth,transceiver distance transceiver depth,and relative speed.In order to design and analyze UWA channels,computer simulations give us enhanced degrees of freedom to efficiently simulate and analyze UWA channels.This thesis presents a statistical shallow water channel model for moving transmitter and receiver based on analytical statistics.To do so,a model of Shallow Water Acoustic(SWA)Channel Impulse Response(CIR)is derived first to capture most of the physical properties of shallow water.Then we find the Angle of Arrival(AoA)for paths with different numbers of surface and bottom reflections and the Probability Density Function(PDF)of(AoA).To find closed form expressions for the statistics of the CIR,we approximate the PDFs of AoA with half-circular Rician PDF.By mathematical controllability of this new PDF,analytical statistics including autocorrelation function and scattering function are derived.Reliable and high data rate UWA communications are hard to achieve because of multipath propagation,frequency selective fading and limited bandwidth.OFDM is an appealing technique for UWA communication with three obvious advantages: good performance against frequency multipath interference,ability to combat the frequency selective fading and high frequency efficiency.In this thesis we propose Coordinate Interleaved Orthogonal Frequency Division Multiplexing(CI-OFDM)by combing the conventional OFDM with coordinate interleaving.In this scheme,the data symbols are grouped in pairs and the real and imaginary parts of the data symbols are transmitted over different active subcarriers to achieve an additional diversity gain.The Bit Error Rate(BER)of the proposed scheme is derived,and its superiority over the conventional OFDM system is shown via computer simulation.