A New Scheme for Efficiently Managing Call Admissions in 3G/WLAN Mixed Cells

Design interest for an efficient call admission control (CAC) scheme for a mixed cell (i.e., a 3G cell with embedded WLAN hotspots) is proliferating for the traffic load sharing between 3G and WLAN to improve system capacity and performance as well. Some article proposes CAC schemes to increase 3G system capacity and to reduce dropping probabilities of handoff calls by using WLAN hotspots. Most of the schemes do not consider the vertical handoffs from WLAN to UMTS which is also necessary to fulfill ubiquitous connectivity for some services. In some schemes, the WLAN is not used best way i.e., leaving scenario(s) where a user does not access WLAN under the circumstance in which WLAN can give access to the user(s). We propose a CAC scheme which considers all possible vertical handoff scenarios and provides the fullest usage of WLAN i.e., all users necessarily access WLAN as long as they reside in WLAN coverage. A blocked request (i.e., call) in WLAN is always taken back by overlay 3G system, therefore a request is dropped when all the channels of both 3G and WLAN are busy. We develop an analytical model of proposed CAC scheme and validate it by simulation results. We provide extensive numerical results which show that the model improves not only the 3G performance but also the handoff performance in an entire mixed cell.