Optimization Of Handover Algorithms And Research On Downlink Resource Allocation For High-Speed Railway Lte Systems

Radio resource management (RRM), as one of key techniques in B3G/4G mobile communication systems, has played an important role in improving the overall performance of systems. Handover algorithms and radio resource allocation are the core functions of RRM and research hotspots in wireless communication areas. Based on high-speed railway scenarios, this dissertation mainly focuses on optimization of handover algorithms and downlink resource allocation. The main contents of this dissertation are as follows:The first part is about optimization and design of handover algorithms for high-speed railway LTE systems. Firstly, LTE protocol stacks, the basic process of handover and corresponding signaling procedure have been introduced. Meanwhile, the features of handover for high-speed environments and the basic methods for optimization have been proposed. Then, we propose two optimized handover algorithms, namely fast handover algorithm based on statistical property and seamless handover algorithm based on target cell pre-bearer. The two kinds of algorithms are proposed in order to optimize the parameter of Time-to-Trigger, eliminate handover interruption delay, reduce handover signaling overheads, and improve the successful probability of handover. Besides, LTE-SIM, a system-level simulation platform, has been described. Two indicators, ping-pong handover rate and radio link failure rate, are analysed in performance evaluation. Through the performance simulation and analysis, the two proposed algorithms can effectively improve the successful probability of handover in high-speed railway LTE systems.The second part focuses on downlink resource allocation strategies under high-speed mobile environment LTE systems. Firstly, the general modeling methods of resource allocation problems for OFDMA systems and the downlink resource allocation mechanisms for LTE systems, based on OFDMA technology, have been introduced. Meanwhile, some design specifications and common strategies have been given. Then, we propose an adaptive QoS-aware resource allocation algorithm for high-speed mobile environment. In this algorithm, we have optimized the CQI feedback mechanism and the RB allocation procedure based on QoS classification. Finally a new MCS selection method has been proposed to improve the throughput of the system. Through the performance simulation, the propsed resource allocation scheme can achieve higher system throughput, fairness performance, and better performance stability compared with some existing schemes in high-speed mobile LTE systems.