A Closed-Loop Carrier Synchronization Method for GMSK Signals with Small BT Values

This paper introduces a closed-loop carrier synchronization method for GMSK signals with small BT values. The BT parameter determines two indexes, spectral utilization and intersymbol interference of GMSK signals. The BT values of currently applied GMSK communication systems are mainly in the range of 0.3 to 0.5. In order to further improve the spectral efficiency and concentrate the spectral energy, the BT value can be lowered, but it is accompanied by the increase of the intersymbol interference of GMSK signals and the increase of the proportion of higher-order memory components. The traditional carrier synchronization method uses only the first-order components after Laurent decomposition, which leads to low carrier synchronization accuracy at small BT values. In order to solve this problem, based on the Laurent decomposition of the GMSK signal, this paper introduces the second-order memory component after the phase lock loop's phase discriminator to add phase tracking value to the phase discrimination result of the first-order component, so as to realize more accurate carrier phase tracking. In this paper the feasibility of this method is verified by MATLAB simulation. This method not only improves the accuracy of the carrier synchronization results of GMSK signals at small BT values, but also shows a wider applicability at very small BT values which is not available in traditional method.