Mobile Intelligence

22.3 LOCATION-BASED SERVICE ENVIRONMENT

Since our location-based service environment aims for a campus-wide environment, it is essential to build an intelligent testbed that various services can be operated. Figure 22.2 illustrates the architecture of our testbed. Three important components of the target testbed are a communication infrastructure, a location-tracking infrastructure, and a middleware.

Communication infrastructure lays the groundwork for ubiquitous computing. Two well-known standards are used to support anytime and anywhere wireless communication services; IEEE 802.11 (WLAN) [24] and IEEE 802.15.4 (ZigBee) [25] We installed an enough number of ZigBee sensor nodes and WLAN access points in a wide mesh manner. In this environment, communication could be done via multihop sensor nodes for low-speed data transmission and WLAN for high-speed data transmission.

Location-tracking infrastructure is necessary for location-based services. The ZigBee sensor nodes are also used for location tracking. Every nodes periodically broadcast beacon signals, which uses 2.4 GHz band as a physical channel. A moving user receives beacon signals from the ZigBee communication interface. When the user receives multiple beacons from the multiple sensor nodes, the users who have received the beacons can identify his location by calculating each Received Signal Strength Indicator (RSSI) value from each sensor node [15].

During the measurement, however, we found that the resolution of location ...