Using preliminary decisions to reduce complexity in adaptive equalizers

An alternative structure for full digital implementations of high-speed adaptive equalizers, as in digital microwave radio (DMR) systems, is presented. The proposed structure consists of a modified intersymbol interference canceller, which makes use of preliminary decisions on the transmitted symbols. In comparison with conventional equalizer structures, a better complexity/performance trade-off is achieved, mainly as a result of the short wordlength required to code the preliminary decisions. For equalizers typically employed in 140 Mbit/s DMR systems, the reduction in complexity can exceed 50%. A numerical method of calculating symbol error probability for conventional equalizers and modified intersymbol interference cancellers is briefly presented