关键词: 异构分层无线网络，切换，服务质量，保护信道，信道侵占

Abstract: A handoff strategy was proposed to guarantee the traffic QoS in heterogeneous hierarchical wireless networks. Based on the bidirectional call-overflow between different networks, guard channels were set for real-time traffic handoffs and buffer queues were set for non-real-time traffic handoffs. In order to further decrease the dropping probability of real-time traffic handoffs, preemption scheme was also used, which principle is that real-time traffic handoffs can preempt the channels used by the ongoing non-real-time traffic. Simulation results show that the proposed handoff control scheme can evidently decrease the dropping probability of each type of traffic, the channel utilization of overall heterogeneous system is slightly increased simultaneous.

Key words: Heterogeneous hierarchical wireless networks, Handoff, Quality of service ( QoS),Guard channels, Channel preemption