Research And Implementation On Modulation And Demodulation Algorithm In VDES

VDES (VHF Data Exchange System) is a new type of digital communication system from the development of the AIS (automatic identification system). As a new kind of digital communication system, VDES attracts wide attention in many countries, but VDES research is still in the early stage. Some countries are testing their systems. Following the advanced technology, this paper mainly research the GMSK modulation and demodulation algorithm in AIS. Based on this, we research the OFDM, QAM modulation and demodulation algorithm which may be used in the VDES. And also we analyze their performance.This article mainly researches the key technology of QAM modulation and demodulation, including the baseband shaping filter design and implementation in modulation, the research and implementation of bit synchronization algorithm and carrier synchronization algorithm in demodulation. The Gradner algorithm is adopted to Bit synchronous technology. In this paper, the Decision-Directed algorithm, Reduction-Constellation algorithm and polarity decision algorithm was researched, and the Reduction-Constellation algorithm was implemented.Using the FPGA (Field Programmable Gate Array), this research implements the system. In this paper, the Verilog HDL language was used to implement the QAM modulation and demodulation in the ISE environment of the XILINX company, the system was simulated with the MODELSIM, and the NEXYS4 development board was used to verify the system.The content of this thesis is a part of research of National Support Program "key technology and system development of AIS/GNSS ship borne navigational equipment (2012BAH36B02) under taken by the Institute of Navigation".