Research On Handover Strategy In Low Earth Orbit Mobile Satellite Communication Systems

LEO satellite communication systems are now becoming one of key components of personal mobile communication system due to its distinctive features such as world wide coverage, sufficient system capacity and low propagation delay. Compared to terrestrial cellular mobile network, end users are constantly handover between LEO satellites. This is because as a key node in the communication system, LEO satellites orbit around the earth in high speed. Since the handover technique involves many other techniques such as resource allocation of satellite radio, reconstruction of network topology and routing update, it has drew great attention in the aerospace research field. Existing satellite handover strategies are more concentrated on optimizing the handover performance and qualities of communication. Insufficient attention is given to how system TCP performance is affected by the handover techniques. Therefore, studying handover schemes from transmission performance of the satellite systems has practical significance.This paper provides an in-depth study of handover strategies between LEO satellites. Based on researches about how handoffs in satellite and terminal communication affect the transmission delay, it aims to propose a more reasonable scheme to compensate the difference of delay before and after handoff in a variety of scenarios, to enhance the satellite TCP protocol transmission performance while reducing the delay jitter. For this purpose, compensation handover strategy in satellite network is presented through analysis and comparison between several existing handover strategies. And then, this paper focuses on such handover mechanism and provides a specific network compensation delay optimization on problems such as unclear compensation delay. Starting from building a detection model based on Bayesian probability theory and realistic situations, a category threshold is introduced to tackle the poor sample data accuracy when applying posteriori probability estimation in determining categories. The classification process is further controlled by regulating the category weighting factor. In addition, in order to improve outliers misjudgment caused by changes in network status, this paper utilizes sliding window technique to correct category collections and model parameters, resulting in quickly identifying correct values in new state of satellite network. Simulation results show that, comparing to previous average processing delay detection method, accuracy and false positive rates of the improved version are optimized to some extent. Also the improved version yields a better performance when tested with large dataset.Besides, this paper adopts the optimized handover techniques to double-layer Satellite Communication System. Through a detailed analysis of handover scenarios under this model, to handle the diversity problem in delay compensation, an adjustment strategy is given based on multi-threshold prediction of network delay compensation. Simulation results verify the effectiveness and accuracy of the improved strategy: systems employed the improved strategy have better TCP performance over others, which only use a single fixed compensation time to tackle all handover scenarios.