A Study Of Software Modulation And Demodulation Technology In Maritime Communication Service

Based on the study of GMDSS concepts, GMDSS modernization trends and software radio technology, the study analyzes the mechanism and algorithm of signal modulation and demodulation, and proposes a new method which is used in the field of maritime communications signal processing:software modulation and demodulation technology. It makes to reduce the impact constraints of distance between coast stations control systems and radio equipments, and improving the business agility. The technology brings out a method of networked control and digital signals transmission, and reduces the cost of maritime communications hardware investment, daily operation and maintenance for coast stations.In the existing maritime telex communication services, FSK modulation technique is used in DSC, NBDP and NAVTEX, by adjusting the parameters it could be used for different services’applications. NAVDAT, which is the future high-speed data services that using OFDM modulation technology, makes the high-speed serial data streams into low-speed parallel data streams, and uses the signal multiplexing by orthogonal frequency division.Through the study of modulation and demodulation principle within the existing and future maritime communication services, adopts the digitized audio waveform to achieve the modulation of FSK signal and the OFDM signal, and according to the specific requirements of NBDP, NAVTEX and NAVDAT services, gives the basic theory and algorithm. At demodulation side, in order to meet engineering applications, for the FSK signal and OFDM signals, adopts methods of "software filter +zero-crossing detection" and Fast Fourier Transform separately, and achieves a good demodulation effect. Then, based on the software radio idea which is made the application and the antenna separation, proposes an architecture of maritime communication services platform, to make the baseband signal processing, the protocols of coding and decoding more simplified and generic. Finally, the simulation results verify that the software modem technology is feasible in this architecture.The results of this study has been applied to the maritime safety information broadcast system and DSC system, and to generalize the use of the future maritime digital communication system, to meet the project requirement.