Research On A New NAVTEX System

The old-typed NAVTEX is the system that broadcasts and automatically receives the maritime safety information by means of a Narrow Band Direct Printing telex (NBDP), which is the important part of the Global Maritime Distress and Safety System (GMDSS), too. the old-typed system has simplex function and it is also lower intellectualized which can not make it adapt to the development of modern times ship.This paper is based on the old-typed system. Modern communication technology is used to update the system and in the same time the information frequency-4209.5kHz which is appointed by the IMO to transmit native language is used to release orientation information. Because of this the wireless navigation function is added, this made it fit the need of moderness.Various kinds of technical parameters and key circuits of new-type Chinese character code for NAVTEX system have been researched. And also the systematic block diagram and preliminary technical indicators are provided. The systematic message source and encoded mode, technological form of signal, mathematics model of demodulation and despread loop, pseudo code position have been probed. The location function had been added; the simulation model had been designed and simulation experiment also had been carried on. The experimental result shows the new-type system had improved the transfer information rate and the bit error rate is lower than the previous system.This paper expatiated on the method of the groundwave field strength of non-uniformity offing. Based on this Millington method was used to calculate the groundwave field strength off seashore 400km on the frequency of 4.2MHz. The result was used to the link budget. Some budget parameters were statistical. Through receiver sensitivity of the spread spectrum digital communication, we got the maximal noise coefficient of the receiver, which meet the prescriptive,minimal receiver sensitivity. This proved the feasibility of the new-typed NAVTEX system. This paper discussed the based theory of modulation method, demodulation method, the constitution of message source, technological form of signal and pseudo code position of the new-typed system. The new system was simulated by Matlab and it result testified it reached the need of error code rate. VC was used to realize the location module , transmit and incept the information.