Research On Handover Algorithm For Air-Ground Broadband Communication

The air-ground broadband communication system can support various aviation communication services such as Air Traffic Services(ATS),while meeting the increasingly strong demand of Aeronautical Passenger Communications(APC)at the same time.So it requires higher system stability than traditional ground communication networks which provide internet service only.However,the air-ground broadband communication system cannot but face the problems of handover frequently because of high-speed mobility characteristics of airplane users which are different from ground communications and the cell coverage radius of air-ground broadband communication system is relatively limited.In addition,the traditional handover algorithms judge the received signal strength(RSS)simply which will further deteriorate the performance of air-ground broadband communication,such as lower handover accuracy,redundant handover,Ping-Pong effect and other problems,and cannot meet the requirements of air-ground communication.Therefore,it is necessary to establish a handoff algorithm suitable for air-ground broadband communication.The paper is supported by the project of “Development and Testing of Air-ground Broadband Data Link Communication System Prototype”,which focuses on the efficient handover problem of air-ground broadband communication system,and proposes an efficient handover algorithm suitable for air-ground broadband communication,and provides reference for actual deployment.The main works are as follows:(1)The current handover algorithms of mobile communication do not consider and make use of the user's mobile directionality,resulting in low handover accuracy,redundant handover and other problems.Aiming at efficient handover of the air-ground broadband communication system,this paper uses the particularity of the air-ground broadband communication that the trajectory of aircraft is linear and can be known in advance to construct a joint handover algorithm combine signal strength threshold and angle threshold.Joint handover algorithm regards the base station closest to the aircraft course as an effective base station with the help of aircraft course information,can greatly improve the handover accuracy.The simulation results and analysis show that the joint handover algorithm can greatly reduce the numbers of handover and improve the accuracy of handover at the cost of increasing small handover delay distance compared with the traditional handover algorithm.(2)Aiming at the problem that joint handover algorithm reduces the numbers of handover at the cost of increasing the handover delay distance when the hysteresis threshold is fixed,an adaptive hysteresis threshold adjustment algorithm is proposed.The algorithm adaptively adjusts the hysteresis threshold with the moving distance as a function,and maintains a large hysteresis threshold near the base station to reduce the numbers of handover,a small hysteresis threshold at the edge of the cell to reduce the handover delay distance,which could avoid the problem that fixed hysteresis threshold cannot effectively improve system performance.The simulation results show that adjusting the coefficient ? and ? of the adaptive function can further reduce the handover delay distance and numbers.(3)Aiming at the problem that the adaptive hysteresis threshold adjustment algorithm may cause the probability of handover trigger to slow down with the increase of ?,an improved algorithm is proposed.By adjusting the adaptive adjustment function,the simulation results show that the improved algorithm avoids the problem of the probability of handover trigger to slow down,and can further reduce the handover delay distance and handover numbers.