An efficient method for prefilter computation for reduced-state equalization

In advanced TDMA mobile communications systems, reduced-state equalization algorithms have to be employed because a high-level modulation is used in order to improve the spectral efficiency. Such equalizers only have a high performance, if the overall discrete-time system to be equalized is minimum-phase. Therefore, in general, a discrete-time prefilter has to be inserted in front of equalization. In the literature, several approaches have been proposed for computation of a suitable FIR or IIR prefilter. We present an approach for FIR prefilter computation, which is quite robust and requires an only moderate computational complexity. The prefilter consists of the cascade of a channel-matched filter and a prediction-error filter, which can be calculated via the Levinson-Durbin algorithm. Simulation results are given, which demonstrate that the performance of the proposed approach is essentially equivalent to the case of reduced-state equalization combined with ideal allpass prefiltering