Research And Implementation Of ASM Baseband Signal Processing Technology

The effective and real-time communication between ships is an important guarantee for navigation safety and traffic management.A new generation of ship communication system-VHF Data Exchange System(VDES)uses a system architecture combining ships,coastal base stations,and satellites to ensure large coverage and high real-time performance of maritime communications services,and has become a current research hotspot.Application Specific Messages(ASM)is a service under VDES.However,its satellite links contain severe Doppler shifts,higher delays,and lower signal-to-noise ratios.This Thesis studies the processing technology of ASM baseband signal and implements the hardware implementation.The main works includes:(1)The modulation method and frame format of the ASM signal are analyzed.Based on the training sequences of the ASM signal under the TER and SAT links,detection algorithms are designed for them.(2)A coherent demodulation algorithm is designed for ASM baseband signals,including a symbol synchronization algorithm,a frequency offset estimation algorithm divided into two steps,and a phase estimation algorithm,which can complete the demodulation of ASM under large frequency offset conditions.(3)Channel coding and decoding technologies in ASM signal are studied,including the coding and decoding algorithm of Reed Muller code and the coding and decoding algorithm of Turbo code.Then combined with the ASM signal coherent demodulation algorithm,performance of the ASM signal processing system is simulated.(4)Based on the FPGA chip Spartan-6,a frame header detection algorithm for ASM signals are implemented.Based on the EMIF interface,a data transmission protocol between FPGA and DSP is designed.Based on the DSP chip TMS320C6748,a program is written to implement the coherent demodulation algorithm and decoding algorithm of the ASM signal.