Optimal Voice Admission Control Performance under Soft Vertical Handoff in Loosely Coupled 3G/WLAN Networks

Low cost WLAN networks are very likely to be loosely coupled to high cost 3G networks in order to provide the 3G subscribers with an extended WLAN capacity and the WLAN subscribers with the 3G ubiquitous coverage. Considering the high signaling latency when handing off critical voice calls between the two loosely coupled networks, soft vertical handoff (VHO) has already been introduced to ensure packet-level QoS however its resource efficiency is not evaluated yet. Therefore, in this paper we study the impact of mobility and soft VHO on the performance of the optimal voice admission control in terms of blocking probabilities. First, we propose an accurate analytical model for our system. Then we show that a resource-efficient soft handoff (RESHO) algorithm provides much better performance than a static-threshold soft handoff (STSHO) algorithm in WLAN mobility environments. In fact, we observe that the 3G new call blocking probability reduction gained by using a RESHO algorithm compared to a STSHO algorithm is largely increased when multi-mode mobile station velocities have low mean and high variability. This velocity profile typically characterizes the WLAN mobility environment. We believe that the provided model and the presented results could push and help the design of highly efficient soft VHO algorithms for loosely coupled 3G/WLAN networks.