The current LTE-R handover algorithm uses fixed handover hysteresis when switching, or grades train speeds to adjust the dynamic hysteresis,fulfilling only"local dynamic",which highlights the importance of determining a more accurate switching trigger point. First of all, to put forward the switching scheme, the distance between the transition zone and the switching section of the LTE-R network overlay coverage area is deduced based on actual channel model. In order to improve the handover success rate and optimize the performance of the system in the high-speed environment, a handoff optimization algorithm is proposed based on real-time dynamic hysteresis. The handover hysteresis values at different speeds are obtained by using the ping-pong handover rate and wireless link failure rate. Then,the least squares method is used to obtain the best function match between the train speed and the switching hysteresis. Simulation results show that the improved algorithm has higher handover success rate than the current handover algorithm,which proves that the proposed scheme can trigger the switch more effectively than the current scheme.%现行的的LTE-R切换算法在进行切换时采用固定的切换迟滞,或者对列车速度进行分级,进而调节动态迟滞,只做到了"局部动态",这意味着确定更准确的切换触发点是一个关键问题.首先,为了切换方案的顺利提出,根据实际信道模型对LTE-R网络重叠覆盖区的过渡区段、切换区段的距离作了理论的推导;然后,为了提高高速环境下的切换成功率,优化系统性能,提出基于实时动态迟滞的越区切换优化算法,先利用乒乓切换率和链路失效率等指标得到不同速度下的切换迟滞值,之后利用最小二乘法得到列车速度与切换迟滞的最佳函数匹配.仿真结果表明,相比于现行的切换算法,改进算法具有更高的切换成功率,佐证了所提出的方案比现行方案能更有效地触发切换.
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