Optimization of time-to-trigger parameter on handover performance in LTE high-speed railway networks

Handover (HO) is one of the key procedures ensuring that user equipments (UE) can move through the network freely in long term evolution (LTE) systems. The basic idea is to use the handover control parameters, such as HO hysteresis and time-to-trigger (TTT), to enhance the HO success rate. Although TTT can mitigate the ping-pong handover (PPHO) effect, it also causes radio link failure (RLF) due to delayed HO. In this paper, we propose a HO parameter optimization algorithm where TTT is replaced by a statistical threshold value - S_threshold, which can reduce the RLF rate. Both HO hysteresis and S_threshold have been designed and implemented in a dynamic system level simulator and have been discussed for adaptive parameter combinations depending on different UE speed ranges in a high-speed railway scenario. Simulation results show that the optimized algorithm performs better than the traditional A3 event-based HO algorithm in high-speed railway networks.