A Maximum Likelihood Receiver for an Orthogonally Multiplexed QAM System

A maximum likelihood receiver for an orthogonally multiplexed QAM (OQAM) system has been derived based on the mathematical structure of an OQAM signal. The resulting receiver provides the minimum variance estimates of carrier and timing phases under the disturbance caused by not only Gaussian noise but also random data. It has also been proven that the carrier and timing joint control system is asymptotically stable almost everywhere in a state space. The equilibrium points are where the parallel synchronization over all subchannels in the OQAM system is established. Simulations have been carried out in order to verify the maximum likelihood receiver performances, where 9600 bit/s data are transmitted over 750-2450 Hz voiceband with 8×8 staggered QAM signal constellations. It has been shown that sufficient eye opening is obtained under 10 Hz carrier frequency offset and 10^-4timing frequency stability.