| Since the radio spectrum is limited and the high demand for data rate incommunication network, it is desirable to use spectrally efficient modulation methodssuch as quadrature amplitude modulation (QAM) for high data rate channels. In acommunication system, due to the frequency inconsistency of the local oscillator betweenthe transmitting end and the receiving end, the Doppler frequency shift and thetime-varying characteristics of the channel and other reasons, there will be a carrierfrequency offset and phase deviation between the transmitting end and the receiving end,reflected in the QAM constellation diagram is the rotation of the constellation, which willgreatly reduce the performance of the receiver.This paper studies the carrier synchronization algorithm under lager frequency offsetand low SNR. First of all, non-data-aided and data-aided algorithms are described in detail,and their scope are analyzed, followed by comparative analysis of the two carriersynchronization structure, feedback and feed-forward. Then pilot structure designing isanalyzed with the reference standard of DVB-S2, and gives an overall block diagram ofpilot-aided carrier synchronization. The entire carrier synchronization is divided into threemodules: coarse frequency synchronizing module, the fine frequency synchronizationmodule and phase synchronization module, all feedforward structure. Matlab simulationsfor each module are done, under conditions which the initial normalized carrier frequencyoffset is set to0.2, and the SNR range is set to0~10dB. Related parameters aredetermined and laid the foundation for a hardware implementation. The hardwaredesigning gives the realization diagram of each module, some of the sub-module has beenoptimized, the hardware simulation results are analyzed, and gives the resourcesoccupation.Matlab and hardware simulation results show the selected carrier synchronizationalgorithm is able to work in the low signal-to-noise ratio and the initial frequency. |
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