A channel preemption model for vertical handoff in a WLAN-embedded cellular network

In this paper, a channel preemption model for vertical handoff in a WLAN-embedded cellular network is presented. In a heterogeneous networking environment, since many wireless LANs may be deployed within the coverage of a cellular network, horizontal handoffs among neighboring WLANs and vertical handoffs between a WLAN and the cellular network could occur frequently. Performance in terms of blocking probability of the cellular network can be seriously degraded if the channels are not appropriately allocated. The novelty of this paper is right in that a newly initiated mobile node (MN) outside the WLAN coverage can preempt the channels occupied by an MN inside the WLAN coverage when the cellular channels are completely used up. The channel preempted MN is forced to switch its network access to a WLAN. This proposed channel preemption scheme can effectively reduce the blocking probability while not disrupting any of the existing connections within WLANs. For the purpose of performance evaluation, we build a three-dimension Markov chains to analyze the proposed channel preemption mechanism. We derive the equations of move-in and move-out mobility rates based on the node speed and residence times, respectively. The network performance in terms of the number of active WLAN users, the channel utilization and the channel blocking probability of a cellular network, the preemption probability, and the preempted probability of an MN are calculated. From the analytical results, we observe the performance improvements by varying the node speed and the ratio of WLAN coverage.