节点在某时刻的切换概率取决于该时刻之前所有时间内的状态，而考虑这些状态是十分困难的，因此传统分析方法只考虑前一时刻的状态，通常具有较大的误差. 本文针对无线局域网和蜂窝网组成的异构网络，提出了一种基于信号强度与距离的迟滞门限垂直切换算法；针对该算法的特点，提出了一种两步追踪的分析方法，解决了传统分析方法的不足. 最后从切换次数和阻塞概率两个方面，利用仿真对本方法的效果能进行了验证. 结果表明分析结果与仿真结果相当吻合.

 The handoff probability of a node depends on all the states before current moment, and considering all the states is impossible. So traditional analysis method only take the states of the previous moment into consideration, which results in large errors. A vertical handoff algorithm based on hysteretic levels of received signal strength and distance is proposed in heterogeneous networks which are composed of cellular network and wireless local area network. A two-tracking method is also proposed for analyzing the algorithm performance, which resolves the deficiencies in tradition methods. We justify the analysis effects of the new method from the number of handoffs and the block probability. Simulation results show that they are coincided with the analysis results.