Capacity of orthogonal frequency division multiplexing systems over fading underwater acoustic channels.

Abstract

The channel capacity bounds of orthogonal frequency division multiplexing (OFDM) systems over the underwater (UW) acoustic fading channel as a function of the distance between the transmitter and receiver are investigated. The upper bound is obtained under perfect channel state information (CSI) assumption at the receiver. The lower bound is obtained under imperfect CSI at the receiver. The reduction from the upper bound is due to the linear minimum mean square prediction error. The UW channel deviates from the wide sense stationary and uncorrelated scattering (WSSUS) model commonly used for small bandwidths. Frequency‐selectivity is incorporated due to the acoustic propagation into each arrival path between the transmitter and receiver. This leads the UW channel to be modeled as a frequency‐dependent doubly spread fading channel characterized by the wide sense stationary and correlated scattering (WSS‐non‐US) fading assumption. Both Rayleigh and Ricean fading assumptions are investigated in the model. Results from the model show a gap between the upper and lower bounds that depends not only on the ranges and shape of the scattering function of the UW channel but also the distance between the transmitter and receiver. The model for the scattering function was confirmed from experimental data.