Adaptive Demodulation with Differentially Coherent Detection

Adaptive demodulation (ADM) is a new rate adaptive technique wherein the receiver demodulates only the most reliable bits and treats unreliable bits as erasures. This paper derives the optimum and simple near-optimum receivers for an ADM system operating without a coherent phase reference, where differential encoding is assumed at the transmitter (using 16-DPSK and 16-DAPSK). The new receivers offer the advantages of a rate-adaptive system, without requiring channel state information at the transmitter or a coherent phase reference at the receiver. Bit error analysis for the ADM system in both cases is presented along with numerical results of the spectral efficiency for the rate adaptive systems operating over a Rayleigh fading channel.