EXTENDED MLSE DIVERSITY RECEIVER FOR THE TIME-SELECTIVE AND FREQUENCY-SELECTIVE CHANNEL

This paper develops a maximum-likelihood sequence estimation (MLSE) di versity receiver for the time- and frequency-selective channel corrupt ed by additive Gaussian noise when linear constellations (M-ASK, M-PSK , M-QAM) are employed, The paper extends Ungerboeck's derivation of th e extended MLSE receiver for the purely frequency-selective channel to the more general channel, Although the new receiver structure and met ric assume ideal channel-state information (CSI), the receiver can be used wherever high-quality CSI is available, such as a comb of pilot t ones or time-isolated symbols, The major contributions of this paper a re as follows: 1) the derivation of a finite-complexity diversity rece iver that is maximum likelihood (ML) for all linear channel models and sources of diversity, as long as ideal CSI is available; 2) a benchma rk, in that the new receiver's performance is a lower bound on the per formance of practical systems, which either lack ideal CSI or are not ML; 3) insight into matched filtering and ML diversity receiver profes sing for the time- and frequency-selective channels; and 4) bounds on the new receiver's bit-error rate (BER) for ideal CSI and pilot tone C SI, in a fast Rayleigh-fading channel with multiple independently fade d paths. The new receiver can seamlessly tolerate square-root Nyquist pulses without a fading-induced ISI error floor.