Design of fractionally spaced equalizers

Abstract

The main idea of equalization is simply to compensate for nonideal characteristics by additional filtering. An equalizer is, then, an adaptive filter that is capable of high-speed digital signaling over slowly varying, band limited channels whose impulse responses are unknown at the receiver. The fractionally-spaced equalizer is superior to the synchronous equalizer, and this is in its ability to be not affected by aliasing problems and independent of the sampler phase. However, for a given time span NT, a synchronous equalizer will need N tap coefficients, while (2N) tap coefficients are needed for a fractionally-spaced equalizer with tap spacing T/2. This will result in a great amount of computations needed to update the tap coefficients every symbol period, an important drawback of the fractionally-spaced equalizer. In this thesis, we introduce an idea where a compromise between performance and complexity, for both equalizers, is presented. The idea consists of setting some of the tap coefficients of a fractionally-spaced equalizer with tap spacing T/2, to zero. The zerotap coefficients are neither updated nor entered in the computational process, thus leading to simplified algorithms.