在无线局域网WLAN和蜂窝网组成的异构网络中,切换方案是降低切换时延和数据丢失的一个重要因素。文中设计了一个基于不同接入技术的WLAN和GPRS/UMTS系统组成的异构网络,提出了移动台在这两个网络间切换的不同方案(移动台发起的小区重选和网络发起的切换)。同时,针对WLAN的不足,为其增加了“在场检测”功能,仿真结果显示丢包率得到了明显的改善。 In a heterogeneous network consisting of a WLAN and a cellular network, a handover scheme is an important factor in reducing handover latency and data loss. In this paper, a heterogeneous network consisting of WLAN and GPRS / UMTS systems based on different access technologies is designed. Different schemes for the mobile station to switch between the two networks are proposed (cell-initiated cell reselection and network initiated handover) . At the same time, for the lack of WLAN, it adds “presence detection ” function, the simulation results show that the packet loss rate has been significantly improved.