Analysis And Optimization Of The Handover Algorithm In GSM-R Network

The operation of high-speed train raised more stringent requirements on the service quality and reliability of GSM-R network. In the GSM-R mobility management technology, handoff is the key component, which ensures uninterrupted communications along the railway. The GSM-R systems are mainly characterized by the reliability and effectiveness of handoff, in other words, the handoff plays an important role to maintain the high reliability and validity in railway mobile communication.In order to ensure the normal operation of high-speed railway, in this thesis the optimization of the handoff quality of GSM-R network is the objective, for which the handoff is discussed under GSM-R wireless channel model, and through investigating the signaling process, the pretreatment process and the parameters as well as the train speed involved, the analysis and optimization of switching quality are performed. The main contents are as follows:In the GSM-R switching algorithm, the switching speed can be improved by enlarging the arithmetic average of the settings window Hreqave over an hour, while at the meantime the risk of generating ping-pong switching will be increased. The traditional method (TA, CI), fast switching right after the determination of the train direction, optimized the neighbor zone based on (TA, CI) values. Although this method solved the problem of ping-pong switching, the "false switch" rendered the high drop rate. In the first part of this thesis, with the combination of traditional (TA, CI) algorithm to determine the direction of the train, a new strategy, setting the threshold level during the process of the decision to switch, is proposed. Simulation comparison reveals that the improved algorithm greatly optimizes the handoff quality. In the high-speed environment, the handover quality of GSM-R network is affected by the speed. From the model of receiving level between the neighboring cells: As speed increases, the available switching time will decrease gradually, and when the speed reaches 500km/h, the switching time can be reduced to less than 4s. In this thesis, a strategy, dynamic adjustment as the switching threshold of the train speed, is proposed:in the high-speed cases, a relatively lower threshold is used, while in the low-speed cases, a relatively higher threshold is chosen. Under this strategy, enough time is ensured for the switching, which will reduce drop rate due to the channel switching induced poor quality. The experimental simulations show that this algorithm optimizes the handoff quality in the high-speed environment.In the environment of redundant coverage, neighbor relationship is much more complicate than the one in single-network coverage, so the fast switching algorithm suit for the environment with single network coverage is not applicable for the environment of redundant coverage. A new algorithm based on BSC learning historical record is proposed to determine the optimal target cell in this thesis. Through the pre-determination of target cell, and with the combination of the fast switching technology under a single network covering, one can increase switching speed without decreasing the switching quality. The analysis shows that this algorithm can effectively reduce the switching latency in the redundancy environment.