Why the SIM Card is Becoming Important for Wi-Fi
With the continuously growing smartphone penetration and the popularity of social media, music, and video streaming, the data consumption is exponentially increasing. Mobile network operators (MNOs) as well as wireless infrastructure vendors are working hard on solutions and possibilities to prepare for the coming data demand.
Many users are accustomed to use Wi-Fi. In fact, several studies e.g. by Mobidia show that up to 80 % of smartphone originated data traffic goes over Wi-Fi. The used spectrum lies in the 2.4 GHz and 5 GHz band. The latter offering several hundred MHz of unlicensed bandwidth, Wi-Fi Traffic Offload obviously not interfering with the cellular network frequencies. With the new IEEE 802.11ac WLAN standard supporting up to 8x8 MIMO, multiple Gbit/s can be transmitted. All that makes Wi-Fi a cost-efficient small cell for hotspots and indoor deployments.
In order to provide a fully automated and truly seamless handover from the cellular network (e.g. LTE) to Wi-Fi, standardization bodies are adding features for the interworking. 3GPP has defined new network elements and interfaces. They differentiate between trusted (S2a) and untrusted (S2b) access. MNOs with their own Wi-Fi access points such as Swisscom tend to use the S2a based access, while MNOs integrating also other Wi-Fi access points e.g. from coffee shops, are using S2b based access. The IEEE and the Wi-Fi Alliance® also worked on a standard amendment to automatically establish secure Wi-Fi connections in a controlled way (Hotspot 2.0). All these functions allow the MNO or Internet Service Provider to control where, when, under what conditions (signal levels, traffic load, etc.), and for what IP flows Wi-Fi or LTE is used.
Finally, it can only become seamless if no user interaction is required. Nobody wants to constantly search for Wi-Fi SSIDs and enter passwords in order to establish a secure connection. Smartphones use SIM cards for the authentication on the cellular network. Thanks to protocols like EAP-SIM or EAP-AKA, the same (U)SIM can also be used for authentication on Wi-Fi. Many smartphones, or more precisely their operating systems, already support these. Swisscom implemented EAP-SIM authentication in their public Wi-Fi networks already in 2004.
As the integration and interworking of the popular and widely used radio access technologies progresses, the smartphones evolve more and more into cognitive radio devices, using or even combining the best available radio links.
Author: Adrian Schumacher, Innovation Engineer Wireless Access, Swisscom (Switzerland) Ltd.
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