Adaptive equalization of the Rician indoor radio channels

Abstract

The performance of a 4-QAM indoor wireless data communication system with with adaptive equalizer is investigated. The effectiveness of using a linear and decision-feedback equalizer for Rician frequency-selective indoor channels is evaluated, compared with results obtained for equalized Rayleigh fading time-dispersive channels and, finally, contrasted to the performance of a 4-QAM modem without equalizer. The Rician fading channel model with a small Rice factor of 2 dB is taken to describe the spatial distribution of the received signal, when terminals are moved over small distances. The temporal fading, corresponding to the case of fixed terminals and motion of personnel and machinery around the terminals, is represented by a Rician fading channel with Rice factor between 6.8 and 11 dB. The effects of some important channel and system parameters on indoor communication system performance are examined and presented. The average bit error rate is used as an index of performance. Both types of equalizer give significant performance improvement compared with the case of the unequalized channel. The decision-feedback receiver surpasses the linear equalizer in performance. Actually, the equalizer is observed to decrease the bit error rate until the approximate normalized data rate values of T/sub m/R/sub b/=2.2, 1 and 0.5 for the Rice factor of 2, 6.8 and 11 dB, respectively. Both equalizers exhibited performance improvement when the ratio of signal-to-noise power is increased, though it is observed that lower values of SNR (/spl les/ 12 dB) cause the propagation of decision errors through the backward filter of the decision-feedback equalizer. A special, modified automatic clear function is designed and inserted to the backward filter of the decision-feedback equalizer to suppress the error extension effect.