ML NDA carrier phase recovery for OFDM systems

Abstract

A maximum likelihood (ML) estimation algorithm is derived for carrier synchronization in OFDM systems with MPSK modulation. The algorithm derived is nondecision-aided (NDA) and maximizes the low SNR limit of the likelihood function averaged over the MPSK signal constellation. It is also shown that for sufficient small SNR the ML phase estimator obtained reduces to the familiar Mth order power synchronizer which belongs to the class of NDA feedforward carrier synchronizers introduced earlier in the literature. Its mean-squared performance is obtained analytically and compared with simulation results. We observe that the resulting algorithm generates very accurate estimation even when the phase offset is high, that the self noise is absent and the performance of the NDA algorithm is basically the same as the Cramer-Rao bound for moderate to high SNR. Finally we note that the error variance derived for the mean-squared performance of this NDA ML synchronizer is an extension of the approximate variance formula of Moeneclaey and de Jonghe (1994) for M-PSK constellations.