A wide band QAM receiver based on DFE to reject ISI in wireless time varying fading channel

Abstract

Quadrature Amplitude Modulation (QAM) system with high data rate suffers from Inter-Symbol-Interference (ISI) in frequency-selective wireless channel. To reduce this ISI signal, Decision Feedback Equalizer (DFE) is used. When the channel impulse response is time varying, the channel's coefficients need to be adaptively estimated. Adaptive implementation of the forward filter on the conventional DFE can track the time variation of the channel coefficients, but its tracking capability depends on the covariance matrix of the receiver vector and the speed of channel variation. In this paper, wide band QAM receiver is proposed with new arrangement of the DFE filters. Data diversity at the receiver is achieved by using N antennas at its input. The forward filter of the DFE will be used as a Maximum-Ratio-Combiner (MRC) as well as a channel compensator. By first removing the ISI signal from the received vector, the tracking performance of the forward filter will be enhanced. The new performance of the proposed receiver will be compared with the conventional DFE receiver. The tracking performance of the forward filter using LMS and RLS algorithms in the new arrangement is compared with that of the conventional DFE receiver.