Research And Implementation Of 8PSK And 16QAM Signal Demodulation Technology In VDE

The VHF Data Exchange System(VDES)is a new generation of maritime communication system developed on the basis of the traditional maritime Automatic Identification System(AIS).It is an important guarantee for the safety of future international maritime navigation and traffic management.VDES integrates AIS,Application Specific Messages(ASM),and VHF Data Exchange(VDE)service channels.VDE is the core business of VDES.For the problems of Doppler frequency shift,higher time delay and lower signal-to-noise ratio in the process of receiving VDE signals,this paper studies 8PSK and 16 QAM signal demodulation techniques in VDE signals and makes the hardware realization.The main research contents include:(1)The message frame and message format of the VDE signal are analyzed,and the modulation method of the VDES signal is introduced.For the frame header training sequence under the two links of VDE-TER and VDE-SAT,a coherent detection algorithm and a differential frame header detection algorithm are designed respectively.(2)The 8PSK baseband signal demodulation algorithm is designed,including two-step frequency offset estimation algorithm,matched filtering,symbol synchronization algorithm and phase estimation algorithm.The simulation results show that the performance loss is controlled in about 1.5d B when the working condition is about.(3)According to the characteristics of the frame structure,using Reed Muller code's good error correction performance and phase tracking ideas,a 16 QAM baseband signal demodulation algorithm is designed,and the improved accurate frequency offset estimation algorithm and phase tracking algorithm are studied to solve the problem of low estimation accuracy,the simulation results show that the performance loss is controlled in about 0.5d B when the working condition is about.(4)Based on FPGA chip Spartan-6,the frame header detection algorithm of VDE signal is designed and implemented.Based on the EMIF interface,the data transmission protocol between FPGA and DSP is designed.Based on the DSP chip TMS320C6748,the program is written to realize the demodulation algorithm of 8PSK and 16 QAM baseband signals.