Abstract: Effective link-layer trigger mechanisms and timely firing of Link_Going_Down（LGD） triggers are critical to handover performance and are significant in determining whether the handover completes successfully.The predictive scheme doesn’t consider the moving condition of the Mobile Terminal（MT）.It would increase unnecessary handover times when MT moves in low speed or changes moving direction.In this paper，an improved LGD trigger scheme is proposed.It constructs two timescales，and the LGD trigger time can be dynamically determined by comparing and mapping the two different timescales.Simulation results show that the proposed method significantly decreases the unnecessary handover probability.

Key words: Link Going Down（LGD） trigger, predictive timescale, theoretic timescale, unnecessary handover

摘要： 接收信号强度对比理论和LMS预测理论的链路触发机制没有考虑到终端的移动情况，当终端的移动速度较低或者移动方向改变时，会造成无效的网络切换。综合考虑了预估计的网络切换时间，以及采用无线传播模型与移动速度计算出的理论时间，提出了基于时间表映射的链路触发机制。通过映射对比这两个时间表，设置静默时钟的时长，动态确定LGD触发时刻。仿真结果表明，算法不仅降低了无效网络切换率，而且可以节约系统资源。

关键词: 链路即将中断（LGD）触发, 预测时间, 理论时间, 无效切换