| DVB-S2 is one of the most popular wireless digital video broadcasting standards in the world.It supports adaptive coding modulation and variable coding modulation,and has many advantages such as high spectral efficiency,strong correction capability and long transmission distance.However,the DVB-S2 system requires four modulation signals to be flexible and variable,and its complex channel environment is very vulnerable to clock drift,carrier drift and channel fading.This puts higher requirements on the synchronization performance of DVB-S2 receivers.Therefore,this paper focuses on the multi-modulation mode timing synchronization technology and carrier synchronization technology for DVB-S2 system.According to the characteristics and application requirements of DVB-S2 standard,the research direction is firstly determined as non-data-aided synchronization algorithm.After comparing the advantages and disadvantages of various classical non-data-aided synchronization algorithms,Gardner’s algorithm and decision feedback loop are selected as the implementation schemes for timing synchronization and carrier synchronization,respectively,and the main work is as follows.(1)To address the shortcoming that the traditional Gardner timing synchronization algorithm is only applicable to BPSK and QPSK signals,this paper derives a modified multi-level Gardner timing error detection algorithm,which makes the algorithm support all four modulation methods of DVB-S2.Simulation results show that the modified multi-level Gardner timing synchronization algorithm synchronizes the four modulated signals of DVBS2 system well,and the maximum BER performance loss of timing synchronization is only1.2d B.(2)In this paper,we propose a hybrid phase and frequency discrimination(HPFD)algorithm based on the phase and frequency discrimination(PFD)algorithm to replace the direct discriminative(DD)discriminative algorithm in the traditional feedback loop.Tests show that the HPFD algorithm not only inherits the advantages of the PFD algorithm’s large capture range,but also improves the synchronization speed by 33%.At the same time,because the HPFD algorithm is not suitable for high-order APSK signals,this paper proposes an optimized M-squared downscaling algorithm for APSK signals,so that the APSK signals can be downscaled to QPSK signals and thus be suitable for the HPFD algorithm.(3)The numerical control oscillator(NCO)is also one of the important modules that affects the performance of the feedback loop of the verdict,and its common look-up table-based direct digital frequency synthesis(LUT-DDFS)method has truncation errors and other spurious that are difficult to suppress.To this end,this paper proposes a direct digital frequency synthesis(RDP-CORDIC-DDFS)method based on the rotation direction prediction CORDIC algorithm.Compared with the current superior BBR-CORDIC-DDFS in frequency stability is improved by 26%,the signal-to-noise ratio is improved by about 1.54 d B,and the improved judgment feedback loop BER performance loss is less than 1.3 d B.Based on the implementation architecture of timing synchronization and carrier synchronization algorithm proposed in this paper,the whole synchronization algorithm is implemented on FPGA platform.The hardware test results show that the overall synchronization algorithm can synchronize all the four signals of DVB-S2 standard stably.The speed of the overall synchronization algorithm is 34% higher than the target requirement,and the sampling frequency bias capture range and carrier frequency bias capture range also exceed the required target;the maximum BER performance loss is 1.8d B,which is less than the target requirement of 2d B. |
