Abstract: In this paper, the problem of symbol detection in the presence of unknown carrier phase is studied. A joint symbol detection and phase estimation algorithm based on the EM algorithm is developed, which is difference from the traditional optimum receive algorithm. The algorithm does not need to estimate the carrier phase, and obtain symbol information directly. After the algorithm convergence, obtain signal information, at the same time can estimate the unknown carrier phase, and consequently realized the joint symbol detection and phase estimation. Because the algorithm does not require synchronization parameters estimation, can reduce the loss of performance which bring about by hierarchical processing of the traditional method. Simulation results show that the algorithm compared with the traditional optimum receive algorithm that to estimate the phase by non-data-aided first, then to detect symbol information，the performance was improved significantly.

Key words: Communication technology, Expectation-maximization algorithm, Symbol detection, Phase estimation, SER