An Adaptive Carrier and Symbol Synchronization Approach for QPSK Signal

Carrier and symbol synchronization are the key prerequisite for the accurate reception of the Quadrature Phase Shift Keying (QPSK) signal. The traditional synchronization methods have some intrinsic problems, such as slow speed, difficult to design the coefficients for the loop filter. In this paper, an adaptive carrier and symbol joint synchronization method is proposed, which applies the idea of segmented synchronization. The proposed approach divides the synchronization process into two stages: coarse stage and fine stage. In the coarse stage, loop filters with large bandwidth are used to fast capture the range of the carrier frequency offset (CFO) and symbol timing offset (STO). While, in the fine stage, filters with small bandwidth are adopted to accurately calculate and track the offsets. In addition, the proposed method can track the variation of the offsets dynamically, thus, it can adaptively identify the synchronization status and select the suitable structure and coefficients for different synchronization stages. Simulation results show that, compared with the traditional joint method, our proposed method can take into account the synchronization speed and stability simultaneously, and the speed and stability can be increased by 1.2 times and 21.77%, respectively, when the CFO is 1.5% of the symbol rate and STO is 0.5% of the symbol rate. Our proposed method can be used to solve the synchronization problem for the harsh environment, especially for the field of satellite communications, which has extremely large frequency and timing offsets.