The Research Of Handover Mechanism Optimization In High Speed Long Term Evolution System

With the rapid development of high-speed railway and public growing demand on datacommunication, people pay much more attention to provide a high data rate and highreliable wireless communication in the high-speed mobile scenarios. Due to LTE system hashigher data transmission rate and smaller system time delay, so the International Union ofRailways has selected it to be standard of the next generation railway wirelesscommunication. However, LTE system applied in high speed environment still has manyproblems to be solved, especially the frequent handover causing high handover failure rateand the dynamic time-varying channel fading model causing high communication interruptprobability, these are great challenges of wireless access technology. Therefore, representedby high-speed railway scene, using the unique characteristics of high-speed private networkand the LTE system’s flat structure, multi-antenna and cooperative communication, thispaper research a handover algorithm that it can adapt to the mobile terminal speed greaterthan300km/h. The research results have certain guiding significance for the construction ofhigh speed environment network.For the above problems, this paper make a corresponding improvement for handovermechanism that puts forward by the3GPP LTE working group, so the optimizationalgorithms are proposed, and the superiority of the algorithms are validated by Matlabsimulation. The main work is as follows:(1) The architecture of LTE system and handover technology are introduced, and thecause of handover and handover measurement process are analyzed in detail. At the sametime, High-speed mobile scenarios wireless communication system solutions, the solutionsbased LTE system, the negative impact of high speed mobile to handover and the existingsolutions for optimization of handover these four aspects were reviewed in detail(2) The A3event trigger handover rule that puts forward by the3GPP LTE workinggroup has been difficult to adapt to running speed and complex geomorphic environment ofhigh speed railway. To improve it, we proposed a joint optimization algorithm based on backpropagation fuzzy neural network that it can dynamically adjust the handover parameter K,Hyst and TTT in LTE system. This algorithm has the advantages of artificial intelligence,without human intervention and it can automatically select the most matching triggerhandover parameters. Mathematical theory derivation of parameter optimization is given inthis paper and we design an on-train equipment based on this algorithm. Building LTE linklevel simulation by Matlab, we simulate handover process and prove that the optimizationalgorithm reduces the number of ping-pong handover and he number of radio link failureeffectively.(3) Because high-speed private network wireless has abundant resources and extremelynetwork reliability requirement, so we briefly analyzed the possibility and economy of the soft handover scheme similar to CDMA system under the environment of high-speedrailway,on the other hand, we propose a base station coordination transmission soft handoverscheme based on joint transmission.We compare the two mechanisms of hard handover andsoft handover in average SINR, communication interrupt probability, handover failure ratethree indicators through mathematical analysis, and then through the simulation results weconfirme that soft handover mechanism in the above three indicators are better than hardhandover mechanism, at the same time using signal improvement factor reflect how muchthe signal improves.