Novel WLAN Coverage Area Estimation Leveraging Transition of Cellular Signal Using Multi-Mode Mobile Terminal for Heterogeneous Networks

It is necessary to select an appropriate access network out of the several available as well as perform vertical handover, which can be considered to be one of the key features of IMT-advanced. We now have a dual-mode mobile terminal (MT) which can connect to both wireless LAN (WLAN) and cellular NWs, featuring a high transmission rate and wide coverage area, respectively. Before selecting and switching access NWs, it must detect the coverage areas of the access NWs that are candidates for connection. Since the MT is generally battery powered, it is a mandatory requirement to detect NWs without consuming too much power. Thus, the authors consider the possibility of controlling WLAN interface (I/F) activation solely by monitoring the transition of the signal quality of a cellular system. From some preliminary experiments and based on previous literature, it has been shown that the signal quality tends to rapidly degrade and then become more stable when moving into an indoor space, which is a different signal transition than that under fading circumstances. From the findings, in this paper, the authors introduce a radically new WLAN area estimation approach for such dual-mode MT leveraging the transition. The transition is used for the estimation of the movement from an outdoor cellular area into an indoor space, where the WLAN areas are expected. The MT activates the WLAN I/F only when it is deduced that the user is about to walk indoors. Furthermore, the authors introduce a method of ascertaining the deduction by leveraging the GPS signal. Thus, the proposed approach adopts a completely different concept from existing ones which require changes to existing NWs or keeping the WLAN I/F active for WLAN area detection. Experimental results and analysis show that the proposed approach has huge potential for reducing the amount of power consumed in detecting the coverage area compared to continuous or periodic search of the WLAN area while keeping the I/F active.