Stochastic Channel Models for Wireless Communications

A mathematical model has been elaborated which provides a small-scale characterization of direction dispersion or equivalently space selectivity jointly at both transmitter (Tx) and receiver (Rx) sites in propagation environments. Space selectivity and direction dispersion considered jointly at both sites are referred to as bi-space selectivity and bi-direction dispersion respectively. The central functions in this characterization are the bi-direction spread function and the bi-direction power spectrum. The former function describes the manner the Tx signal is spread jointly in the launching direction and the incidence direction at the Rx. The latter function describes the manner the averaged transmitted power is spread with respect to the above two directions. Using an analogy, the bidirection spread function and the bidirection power spectrum describe bidirection dispersion in the same way as the impulse response and the so-called delay power spectrum (or power delay profile) characterise dispersion in delay. The bi-direction spread function and the bidirection power spectrum are the appropriate objects for a general investigation of the potential of deploying multiple-element antennas at both Tx and Rx sites as these functions characterize the propagation channel regardless of any assumption on the characteristics (geometrical layout, element field patterns, element coupling) of the arrays. It was shown that the transfer matrix, the covariance matrix, and the capacity of a multiple-input, multiple-output (MIMO) system can be expressed as a function of one of these functions as well as the responses of the Tx and Rx antenna arrays. This project was performed in collaboration with Elektrobit Ltd., Finland. (Bernard H. Fleury, A. Kocian, X. Yin)