Receiver structures for time-varying frequency-selective fading channels

Several receiver structures for linearly modulated signals are proposed for time-varying frequency-selective channels. Their channel estimators explic itly model the time variation of the channel taps via polynomials. These st ructures are constructed from the following building blocks: i) sliding or fixed block channel estimators; ii) maximum likelihood sequence detectors ( MLSD's) or decision feedback equalizers (DFE's); and iii) single or multipl e passes. A sliding window channel estimator uses a window of received samp les to estimate the channel taps within or at the end of the window, Every symbol period, the window of samples is slid along another symbol period, a nd a new estimate is calculated. A fixed block channel estimator uses all r eceived samples to estimate the channel taps throughout the packet, all at once. A single pass receiver estimates the channel and detects data once on ly. A multipass receiver performs channel estimation and data detection rep etitively, The effect of the training symbol positions on the performance o f the block multipass approach is studied. The bit error rate (BER) perform ance of the MLSD structures is characterized through simulation and analysi s. The proposed receivers offer a range of performance/complexity tradeoffs , but all are well suited to time-varying channels. In fast fading channels , as the signal-to-noise ratio (SNR) increases, they begin to significantly outperform the per-survivor processing-based MLSD receivers which employ t he least mean-squares (LMS) algorithm for channel estimation.