Research On Handoff For Air-Ground Data Link System

Data Link technology is the outcome of informational military revolution. The one who has advanced data link technique can obtain the most advantage of the war. Therefore, all countries of the whole world are developing this technique for the technique storage of the army. Because Data Link, using wireless communication to transmit many kinds of data from front to back battlefield, can obtain more time for the war, so the future army makes it one of the most important technique to study. Two most primary characteristic of Data Link are real time transmission and seamless coverage. To ensure the seamless coverage of Air-ground Data Link system and continuous transition of data, the right handoff must be made before mobile node move out from the coverage area of fixed node. Therefore, the thesis mainly research on the handoff strategy in Air-ground Data Link system.At first, this thesis systemically analyze composing and working characteristics of Air-ground Data Link system, then handoff design process of mobile communications system is deeply studied, including control strategy, judge rule, algorithm and channel assignment rule of handoff. Aimed at air-ground data link system, a whole handoff scheme is designed. First, handoff is detected and controlled by control center. Secondly, handoff is judged by ground station from communication coverage area. Thirdly, based on the flying track and the different roles in the network of the mobile platform, four different kinds of algorithms are designed, including handoff time and the choice of next ground station. Fourthly, based on the working characteristics of Data Link system, the signaling after starting the handoff process is designed. After complete every algorithm, simply validate is made to ensure the algorithm usability.At last, to analyze the feasibility of these algorithms and characteristics of parameters, OPNET Modeler is used to simulate and test. This thesis simulates several parameters, such as Speed of mobile platforms, channel error ratio, update interval of track information and direction change of mobile platforms. And it is also analyzed the influence of some results, such as reservation of handoff time, handoff time and handoff success ratio. It is found that the simulation result and theory analyses are the same. If it is allowed in the network, then handoff success ratio can be increased by mobile platform being the master node. It belongs to soft-handoff. If mobile platform flies as normal, handoff success ratio would be 100%. But if after start handoff, mobile platform accelerate suddenly, it would reduce handoff success ratio. In these handoff algorithms, update interval of track information must be less than 10ms, or it would also reduce handoff success ratio.