Demodulation structure for fast fading cellular channels

Abstract

A demodulator and demodulating technique is provided which automatically switches modes according to the flat-fading or multipath channel status of an incoming signal. If an incoming signal has delay spread in addition to fading a standard Maximum Likelihood Sequence Estimator (MLSE) equalization is selected as an optimum demodulation mode. If the incoming signal is only flat-fading a symbol-based demodulation mode is selected. The Maximum Likelihood Sequence Estimator (MLSE) equalizer mode is thus integrated with the symbol based mode. Channel status is first identified in order to do mode selection in the demodulator. A dual-mode receiver for demodulating both flat-fading and multipath signals in a communications system (FIG. 1) comprises a Baseband Digital Signal (DSP) Processor further comprising a Channel Identification Processor, the Channel Identification Processor computing a Maximum Likelihood Sequence Estimate x=(x.sub.0 x.sub.1).sup.t of a first ray channel response and a second ray channel response x.sub.0 and x.sub.1, t denoting a transpose, and determining a demodulation mode based upon a squared magnitude ratio .GAMMA. of x.sub.1 and x.sub.0 relative to a predetermined threshold.

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