On the Impact of Soft Vertical Handoff on Optimal Voice Admission Control in PCF-Based WLANs Loosely Coupled to 3G Networks

Soft vertical handoff (VHO) and admission control are usually considered as two independent mechanisms ensuring respectively packet-level QoS and call-level QoS for voice calls in loosely coupled 3G/WLAN networks. In this paper, we evaluate the impact of the soft VHO on the blocking performance of the optimal voice admission control in different mobility environments where the WLAN operates the Point Coordination Function (PCF). For this purpose, we propose an accurate analytical mobility model for the soft VHO region. Then, based on the proposed model, we derive and analyze the blocking and dropping probability expressions of the optimal voice admission control algorithm in the 3G network loosely coupled to the PCF-based WLAN. Results show us that a resource-efficient soft handoff (RESHO) performs significantly better than a static-threshold soft handoff (STSHO) particularly in WLAN mobility environments. In fact, the 3G new call blocking probability reduction gained by using RESHO compared to STSHO is largely increased when mobile station (MS) velocities have low mean and high variability which typically characterizes the WLAN mobility environment. Besides, results show us that RESHO reduces all blocking and dropping probabilities. We believe that the provided model and the presented results could help design efficient MS controlled soft VHO algorithms for emergent loosely coupled 3G/WLAN networks.