DA based approach for the implementation of block adaptive decision feedback equaliser

Abstract

Adaptive decision feedback equalisers (ADFEs) are used in wireless transmission systems for mitigating the InterSymbol Interference (ISI) that occurs due to multipath propagation of the transmitted signal. In case of high speed communications which involve rapid-varying channels, fast convergent and low complexity ADFEs are required. Frequency domain block processing of signals is an effective means of handling the increased complexities in such high speed systems. However, block ADFEs being inherently non-causal, the feedback filter (FBF) suffers from the lack of unknown decisions in every block computation. In this study, the authors propose an efficient approach for the computation of these unknown decisions. For this, the authors tried to minimise a cost function based on two criteria mean-absolute difference (MAD) and mean-square difference between the ADFE output and the adder that sums up the feedforward filter (FFF) and FBF. A bank of registers which store all the symbols used in the modulation scheme is also utilised for this purpose. Using the proposed solution, the authors recast block ADFE equations in the frequency domain using distributed arithmetic (DA). The algorithm has a good convergence performance and utilises only few computations compared with the existing schemes.