| 主权项 |
1. A billing server method comprising:
receiving a request for a time sync via a network interface, the request containing a unique identifier from a mobile device; transmitting the time sync to the mobile device via the network interface; receiving a plurality of messages from a plurality of ultrasonic sensors, each of the plurality of messages containing the unique identifier and a time when an ultrasound pulse is received; receiving, via the network interface and from the mobile device, a time at which the ultrasound pulse was broadcast; determining, with a processor, a fixed location nearest to the mobile device based on the plurality of messages containing the unique identifier and the time when an ultrasound pulse is received, and the time when the ultrasound pulse was broadcast; transmitting to the mobile device an invoice associated with the fixed location nearest to the mobile device. |
