Extended MLSE receiver for the frequency-flat, fast fading channel and linear modulations

This paper develops an MLSE receiver for the frequency-flat, fast fading channel corrupted by additive Gaussian noise, when linear modulations (M-ASK, M-PSK, M-QAM) are employed. The paper extends Ungerboeck's derivation of the extended MLSE receiver for the purely frequency-selective channel to the time-selective channel. Although the new receiver's structure and metric assume ideal channel state information (CSI), the receiver can be used wherever high-quality CSI is available. The receiver is maximum likelihood for a variety of channels, including Rician, Rayleigh, log-normal and AWGN channels. Bounds on the receiver's BER are deduced for ideal CSI and fast Rayleigh fading. The paper offers insight into matched filtering and receiver processing for the fast fading channel. The new receiver can seamlessly tolerate square-root Nyquist pulses without a fading-induced ISI error floor.