Estimating a subscriber location
View Patent ↗A method and apparatus of estimating a location of a subscriber are disclosed. One method includes receiving a request for the location of the subscriber. The subscriber's serving base station, and a plurality of neighboring base stations sensed by the subscriber, are identified. The subscriber obtains a time delay from the serving base. The subscriber estimates a distance between the subscriber and the serving base station. The subscriber receives frames and estimates a delta time for each of the selected neighboring base stations for the subscriber to synchronize to each of the selected neighboring base stations. The subscriber estimates distances between the subscriber and each of the selected neighboring base. The subscriber location is estimated by trilateration of the distance between the subscriber and the serving base station, and the distances between the subscriber and each of the selected neighboring base stations.
1. A method of estimating a location of a subscriber, comprising:
receiving a request for the location of the subscriber;
identifying a serving base station of the subscriber, and a plurality of neighboring base stations sensed by the subscriber;
obtaining a time delay from the serving base station for maintaining synchronization of the subscriber with the serving base station by comparing a time of a peak of a channel impulse response related to a downlink preamble received from the serving base station with a start time associated with the downlink preamble, the start time being estimated based on the channel impulse response exceeding a predetermined threshold value;
estimating a distance between the subscriber and the serving base station based on the time delay;
receiving frames from at least two of the plurality of neighboring base stations, and estimating a delta time for each of the at least two neighboring base stations for the subscriber to synchronize to each of the at least two neighboring base stations;
estimating distances between the subscriber and each of the at least two neighboring base stations based on the delta time for each of the at least two neighboring base stations; and
estimating the subscriber location by trilateration of the distance between the subscriber and the serving base station, and the distances between the subscriber and each of the at least two neighboring base stations.
2. The method of claim 1 , wherein the receiving frames from at least two of the plurality of neighboring base stations comprises:
receiving frames from at least two of the plurality of neighboring base stations having the largest received signal power at the subscriber.
3. The method of claim 1 , wherein the receiving frames from at least two of the plurality of neighboring base stations comprises:
analyzing a relative physical orientation of the plurality of neighboring base stations and the serving base station; and receiving frames from at least two of the plurality of neighboring base stations that along with the serving base station provide a non-collinear spatial distribution about the subscriber.
4. The method of claim 1 , further comprising:
initiating a subscriber scan of the plurality of neighboring base stations when a scan has not been initiated in greater than a threshold amount of time.
5. The method of claim 1 , wherein the identifying the plurality of neighboring base stations comprises:
scanning for potential subscriber handoff base stations, pruning sector information from the scanning, and yielding the plurality of neighboring base stations.
6. The method of claim 1 , wherein the obtaining a time delay comprises:
performing a fast fourier transform (FFT) on the downlink preamble;
correlating an output of the FFT with a predetermined pseudo random bit sequence (PRBS); and
performing an inverse fast fourier transform (IFFT) on the correlated output.
7. The method of claim 1 , wherein the obtaining a time delay comprises:
transmitting a signal to the serving base station within an unscheduled portion of an uplink sub-frame, having a time offset of zero;
receiving a time delay from the serving base station, the time delay assisting the subscriber in aligning subscriber transmissions to a start time of the unscheduled portion of the uplink sub-frame; and
estimating a transmission delay between the subscriber and the serving base station based on the time delay.
8. The method of claim 7 , wherein the receiving the time delay comprises averaging the time delay over multiple frames.
9. The method of claim 1 , wherein the estimating a delta time for each of the at least two neighboring base stations comprises:
estimating, based on preambles of wireless signal frames received from each of the at least two neighboring base stations, the delta time required to synchronize the subscriber with each of the at least two neighboring base stations; and
estimating a transmission delay between the subscriber and each of the at least two neighboring base stations based on the time delay and the delta time of each of the at least two neighboring base stations.
10. The method of claim 9 , further comprising:
averaging the delta time of each of the at least two neighboring base stations over multiple frames.
11. The method of claim 1 , wherein the subscriber comprises a host and a mobile device.
12. The method of claim 11 , wherein the host generates the request for the subscriber's location, and accesses the stored locations of the serving base station and the at least two neighboring base stations.
13. The method of claim 11 , wherein the mobile device identifies a serving base station of the subscriber and the plurality of neighboring base stations sensed by the subscriber, obtains the time delay from the serving base station for maintaining synchronization of the subscriber with the serving base station, estimates the distance between the subscriber and the serving base station based on the time delay, receives frames from at least two of the plurality of neighboring base stations, and estimates the delta time for each of the at least two neighboring base stations for the subscriber to synchronize to each of the at least two neighboring base stations, estimates distances between the subscriber and each of the at least two neighboring base stations based on the the delta time for each of the at least two neighboring base stations, and estimates the subscriber location by triangulating the distance between the subscriber and the serving base station, and the distances between the subscriber and each of the at least two neighboring base stations.
14. A method of estimating a location of a subscriber, comprising:
identifying a serving base station of the subscriber, and a plurality of neighboring base stations sensed by the subscriber;
obtaining a time delay from the serving base station for maintaining synchronization of the subscriber with the serving base station by comparing a time of a peak of a channel impulse response related to a downlink preamble received from the serving base station with a start time associated with the downlink preamble. the start time being estimated based on the channel impulse response exceeding a predetermined threshold value;
estimating a distance between the subscriber and the serving base station based on the time delay;
receiving frames from at least two of the plurality of neighboring base stations, and estimating a delta time for each of the at least two neighboring base stations for the subscriber to synchronize to each of the at least two neighboring base stations;
estimating distances between the subscriber and each of the at least two neighboring base stations based on the delta time for each of the at least two neighboring base stations; and
estimating the subscriber location by triangulating the distance between the subscriber and the serving base station, and the distances between the subscriber and each of the at least two neighboring base stations.
15. A method of a mobile device estimating a location, comprising:
identifying a serving base station, and a plurality of sensed neighboring base stations;
obtaining a time delay from the serving base station for maintaining synchronization with the serving base station by comparing a time of a peak of a channel impulse response related to a downlink preamble received from the serving base station with a start time associated with the downlink preamble. the start time being estimated based on the channel impulse response exceeding. a predetermined threshold value;
estimating a distance between the mobile device and the serving base station based on the time delay;
receiving frames from at least two of the plurality of neighboring base stations, and estimating a delta time for each of the at least two neighboring base stations for the mobile device to synchronize to each of the at least two neighboring base stations;
estimating distances between the mobile device and each of the at least two neighboring base stations based on the delta time for each of the at least two neighboring base stations; and
estimating the location by triangulating the distance between the mobile device and the serving base station, and the distances between the mobile device and each of the at least two neighboring base stations.