As described in Sect. 1, many telecom and/or broadband operators have deployed Wi-Fi APs extensively in urban areas. This effort not only facilities Internet access of their subscribers, but also alleviates the burden of the increasing data traffic over 3G cellular networks. Take Taiwan’s largest telecom operator—Chunghwa Telecom (CHT) as an example, it has deployed more than 36 thousands Wi-Fi hotspots around the island [24]. Subscribers of CHT can use the ‘‘CHT Wi-Fi’’ Android application [25] (snapshot shown in Fig. 10) to search the CHT-operated Wi-Fi hotspots (the red pins) around them (the blue pin). In this operating model, these telecom-operated APs play a crucial role for indoor locationing. Specifically, telecom operators not only own these Wi-Fi APs, but also have the knowledge of the MAC address associated with each Wi-Fi interface and the location information at which every AP is deployed. That is, this database with all the Wi-Fi MAC addresses and the associated location information is exactly the asset that telecom operators can take full advantage of. In other words, various location-based services can be supported by the telecom-assisted locationing service. Therefore, as long as telecom operators establish the Wi-Fi AP database, within which each entry is a pair of a MAC address and a location, smartphones can follow the flow of operations to do locationing (shown in Fig. 11):
1. User’s smartphone receives the beacon frames of a specific Wi-Fi AP
2. The smartphone queries the database with the sensed MAC address
3. The database returns the location information associated with the Wi-Fi AP