Maximum likelihood open loop carrier synchronizer for digital radio

The problem of carrier synchronization frequency offset is considered. New frequency estimation algorithms for the data-aided (DA), the decision directed (DD), and the nondata-aided (NDA) mode are derived from the maximum likelihood principle. Their performance is assessed by both analysis and simulation, and the error variance is compared to the Cramer-Rao bound. The resulting open-loop system for estimating and correcting frequency and carrier phase for a coherent M-ary phase shift keying (MPSK) transmission system is presented and verified. Implementation issues like filter functions and nonlinearities are addressed. It is found that the proposed structures provide optimal synchronization at high SNR and robust synchronization even at low SNR