Adaptive MLSE receiver over rapidly fading channels

This paper develops an adaptive maximum likelihood sequence estimator (MLSE ) for rapidly fading channels corrupted by additive white Gaussian noise. T his estimator is based on an explicit incorporation of the time-varying cha racteristics in channel modelling. When the multipath is caused by a few st rong reflectors, the channel is shown to be poly-periodically time varying. The channel impulse response is then approximated by a linear combination of a finite set of complex exponential functions whose frequencies are term ed Doppler frequencies. This modelling is well motivated in aeronautical ra dio communications and cellular telephony. During the training period, a cy clic statistics-based approach is developed to estimate the Doppler frequen cies. An eigenvector approach as well as a maximum likelihood method are pr oposed to estimate the coefficients of linear expansion. After this initial ization, the channel parameters are updated using a modified version of the LMS algorithm. Computer simulations are carried out to evaluate the propos ed receiver performance. The new approach exhibits a large saving in comput ational complexity and offers superior performance over conventional adapti ve MLSE in rapidly fading environment. (C) 2000 Published by Elsevier Scien ce B.V. All rights reserved.