Parallel feedforward equalization-a new nonlinear adaptive algorithm

Adaptive equalization can be used to improve digital data transmission on wireless links with time-varying multipath distortion. It was proved by Zhou, Proakis and Ling (see IEEE Transactions on Communications, vol.38, p.8-24, no.1, 1990) that feedforward schemes are universally capable of approximating any measurable function to any desired degree of accuracy. We propose a new realization of such feedforward scheme to the channel equalization problem, parallel feedforward equalization (PFE). An important feature of the new approach is the decomposition of any equalization into linear and nonlinear components. The new approach chooses F_j(·) (j=1, ...) from a family of nonlinear functions to approximate the nonlinear component decomposed from the desired mapping f(·). The other new idea proposed in this paper is a measure called nonlinearity distribution which characterizes the nonlinearity in multipath fading channels. The architecture of the new equalization consists of parallel feedforward nonlinear filters, each of them has a specifically tailored nonlinear function F_j(·)