The Emulation Of EPIRB Positioning Algorithm

As a very important simulator in training sailor,GMDSS(global maritime distress and safety system) is widely used in marine capability training。 This simulator is mainly used in teaching sailors how to send distress signal to the terrestrial station or to the satellite with GMDSS when they are in danger in the sea. It simulates all the complexed equipments in GMDSS with pure software with many virtues such as true appearance、living manipulation and low price. Because of the high price and difficult maintenance, recently GMSSS facility is replaced by GMDSS simulator in tuitions in order to economize the money and human resource. EPRIB(Satellite-Emergency Position Indicating Radio Beacon) is a module in this simulator. Nowadays manipulation emulation is achieved in EPIRB module but positioning emulation is not achieved.In this article, the algorithm of satellite positioning is obtained considering the basic principle and the EPIRB module is improved. According to the positioning theory of GPS, in the course of positioning, if the clock in the satellite is synchronous to that in the users’receivers, the coordinates of the object in the space reference frame can be worked out by virtue of the three formats between the three satellites and the objects on the earth. And after transferring the coordinates, the longitude and the latitude will be obtained and the course of positioning will be finished. In the course of positioning, the satellites will rotate around the earth all the time. So considering the satellites height and running period and consulting the true data, after calculation, three different orbits will be needed with nine satellites in each orbits in order to making sure that each point on the each can be covered. As a result of this, each point can be positioned. In the algorithm many physical factors do not need to be considered such as the gravitation of the earth and the sun pressure. The algorithm is obtained in ideal state. After getting the algorithm, the interface of the software is designed out through VC++. In the interface, the world map and the coordinates of each satellite at any time is displayed. And then the algorithm is worked out by programming and the course of achieving the algorithm is detailed introduced. Finally the result is tested. In the test, when a point in the map is double clicked by the user, the longitude and the altitude of the point is displayed in a dialog. Next the result is compared with the true result. For example, when the point of Beijing is double clicked, the result in the dialog is nearly the same to the true result. So the result is highly accurate. And the algorithm is accurate and feasible.