Improved Baton Handover Algorithm In TD-SCDMA System

TD-SCDMA is the first international standard of communication system, with independent intellectual property rights proposed by China. The TD-SCDMA network has been laid in 10 cities of China, and now it is in the trial commercial stage. Baton handover is a key technology of TD-SCDMA system which affects the performance of TD-SCDMA system directly. At present, the interruption existing in the trail network is serious, and the investigation shows that 60% of the communication interruption is caused by unsuccessful handover. To improve the performance of TD-SCDMA network significantly, the optimization on baton handover is necessary, and the research on optimization can provide technical support for its impelling in the commercial stage.In this paper, the processes and the algorithms of baton handover are introduced and the parameters which affect the handover performance are analyzed (such as filter coefficient, the hysteresis of baton handover, cell individual offset) in detail firstly. Then based on the test experience of TD-SCDMA trial network, the problems on baton handover in TD-SCDMA system are analyzed, such as the effect of the corner, the communication interruption for high-speed users. Thirdly, according to the technical characteristics of TD-SCDMA system (such as smart antenna and uplink synchronization), the processes and algorithms of baton handover are optimized, including the candidate list improvement based on DOA calculated by smart antenna, measurement improvement, and admission control improvement for different services. Fourthly, a new handover algorithm is proposed to deal with the problems existing in the trial network. This new algorithm is based on the pilot signal strength and takes user equipment's speed, direction of movement, distance between the base station and user equipment as the adaptive factors of handover parameters. This algorithm can solve handover issues for the high-speed users and can also improve the performance of TD-SCDMA system. Finally, a simulation system on baton handover is set up. Using this simulation system, the influence of parameters on handover performance is analyzed, and the new algorithm for baton handover is simulated and verified. The simulation results show that the new algorithm can decrease the probability of unsuccessful handover, reduce the delay of handover, and improve the system performance. It will be of great importance for network optimization and development of TD-SCDMA system.