| 摘要 |
The position of a mobile device, e.g smartphone, is determined by GPS or by signals from multiple wireless access points (WAPs), e.g. Wi-Fi. When determining position by reference to WAPs, the mobile device needs to be in wireless communication, e.g. GSM, with a positioning system controller associated with a base station. The positioning controller has access to a database of WAP locations, and either transmits the AP locations to the mobile device for onboard calculation of position or performs the calculation itself before transmitting position to the mobile device. When the mobile device is near or is about to enter an offline region where wireless communication between mobile device and positioning controller is unreliable, e.g. a tunnel, the positioning controller transmits local positioning data concerning WAPs in the offline region to the mobile device. The mobile device estimates its own position within the offline region without needing to communicate with the positioning controller. The positioning controller may determine that the mobile device is about to enter an offline region by reference to position data or in response to a signal generated by the mobile device, e.g. signal strength of a bearer service. The position of the mobile device within the offline region can be logged and transmitted to the positioning controller on leaving the offline region. |
