Nonlinear channel estimation using correlation properties of PN sequences

Abstract

Nonlinear distortion of the radio-over-fiber (ROF) link and, multipath dispersion of the wireless link are the two major factors that limit the performance of a fiber based wireless system. This is especially true when the radio frequency is only a few GHz. The fact that both of these impairing factors are generally unknown, makes any equalization effort very difficult. In this paper, an algorithm that estimates both the nonlinear transfer function of the ROF link plus the impulse response of the wireless channel is described. Correlation properties of pseudonoise (PN) sequences are used for this estimation. This eases the implementation because, PN sequences are widely used in spread spectrum systems and their properties are well understood. An efficient, Vandermonde matrix approach is used to separate the Volterra kernels of the fiber-wireless channel which, eliminates the computation of higher order correlation functions.