System and method for multiple range estimation location
A system and method of determining the location of a mobile station by determining the time of transmission of a signal by a mobile station and determining range rings at a plurality of reference stations receiving the transmitted signal, where the range rings represent the distance f the mobile station from the plurality of reference stations.
1. A method of estimating the geographic location of a mobile device, wherein the mobile device communicates with a base station using a communication protocol, comprising the steps of:
(a) observing at a first reference station, the time of transmission of a first signal from a base station to a mobile device;
(b) receiving at the first reference station, a timing parameter transmitted in the first signal;
(c) receiving at the first reference station, a second signal transmitted by the mobile device;
(d) determining the range of the mobile to the first reference station as a function of the received first signal, the timing parameter and the received second signal.
2. The method of claim 1 wherein the step of determining the range includes determining the time of transmission of the second signal at the mobile device.
3. The method of claim 1 further comprising the steps:
(e) receiving the second signal at a plurality of reference stations;
(f) determining the range of the mobile device to the plurality of reference stations as a function of the time of transmission of the second signal and the time of receipt of the second signal at each of the plurality of reference stations; and
(g) determining the geographic location of the mobile device as a function of the determined ranges to the plurality of reference stations.
4. The method of claim 3 wherein the step of determining the range of the mobile device to the plurality of reference stations is performed at one of the plurality of reference stations.
5. The method of claim 4 wherein the step of determining the range of the mobile device to the plurality of reference stations is performed at the first reference station.
6. The method of claim 3 wherein the step of determining the range of the mobile device to the plurality of reference stations is performed at a centralized site remote to the plurality of reference stations.
7. The method of claim 1 wherein the bases station and the mobile device are synchronized.
8. The method of claim 1 wherein the first reference station is co-located with the base station serving the mobile device.
9. The method of claim 1 wherein the first reference station is a receiver at a known location.
10. The method of claim 3 wherein the step of determining the geographic location of the mobile includes adjusting each of the determined ranges to determine the geographic location of the mobile device.
11. The method of claim 2 wherein the mobile device uses the timing parameter transmitted in the first signal to determine a time of transmission of the second signal.
12. The method of claim 1 wherein the timing parameter is timing advance (TA).
13. The method of claim 12 wherein the communication protocol used by the mobile device and the base station is GSM.
14. The method of claim 10 wherein the step of adjusting includes adjusting each of the range rings approximately the same amount.
15. The method of claim 14 wherein each of the range rings is adjusted iteratively.
16. The method of claim 10 wherein the step of adjusting includes adjusting each of the range rings as a function of the presence of multipath.
17. The method of claim 10 wherein the step of adjusting is achieved by minimizing the quantity [R−A−D]H*C−1*[R−A−D];
wherein,
R is the set of range rings for each of the plurality of reference stations to the mobile device,
D is set of distances for each possible location of the mobile device to the plurality of reference stations,
A is a vector of equal values of α for each possible location, and
C is the covariance matrix for the set of Range Rings.
18. The method of claim 1 wherein the time of transmission of the first signal is determined as a function of the time at which a marker on the downlink is observed and the propagation time for the first signal to traverse the distance from the base station to the first reference station.
19. A method of estimating the geographic location of a mobile device, wherein the mobile device communicates with a base station using a communication protocol, comprising the steps of
(a) observing at a first reference station, the time of transmission of a first signal from a base station to a mobile device;
(b) receiving at the first reference station, a timing parameter;
(c) receiving at the first reference station, a second signal transmitted by the mobile device;
(d) determining the time of transmission of the second signal at the mobile device;
(e) transmitting the determined time of transmission of the second signal from the first reference station to a plurality reference stations;
(f) receiving at the plurality of reference stations the second signal;
(g) determining the range of the mobile device to the plurality of reference stations as a function of the time of transmission of the second signal and the time of receipt of the second signal; and
(h) determining the geographic location of the mobile device as a function of the determined ranges to the plurality reference stations.
20. The method of claim 19 wherein the time of transmission of the first signal is determined form the time of transmission of a marker in the first signal.
21. The method of claim 19 wherein the step of determining the time of transmission of the second signal is given by the equation
tM= ½( tR+tF−f ( P ))
where tM is time of transmission of a marker of the second signal;
tR is time of arrival of the marker of the second signal at the first reference station;
tF is the time of transmission of the first signal;
P is a timing parameter; and
f(P) is a function of the timing parameter.
22. The method of claim 19 wherein the timing parameter is timing advance (TA), the communication protocol is GSM and f(P)=3.6928×TA.
23. The method of claim 19 wherein the timing parameter is the position of physical channel frame makers, the communication protocol is UMTS and f(P)=−(1024+P)×26.042 wherein P is in the range 0-148.
24. The method of claim 19 , wherein the range between the each of the plurality of reference stations and the mobile device is given by the equation
τ pi=tRi− ½( tR−tF+f ( P )
where τpi=is the distance between the mobile device and the ith reference station;
tRi is the time of receipt of the second signal at the ith reference station;
tR is the time of receipt of the second signal at the first reference station;
tF is the time of transmission of the first signal;
P is a timing parameter; and
f(P) is a function of the timing parameter.
25. The method of claim 19 wherein the first reference station is co-located with the base station.
26. The method of claim 19 wherein the first reference station is the serving base station for the mobile.
27. A system for estimating the geographic location of a mobile device, wherein the mobile device communicates with a base station using a communication protocol, comprising:
a first monitoring unit at a known location for receiving transmissions from the mobile device and the base station, having a processor programmed:
(i) to determine the time of transmission of a first signal from a base station to a mobile device;
(ii) to identify a timing parameter transmitted in the first signal;
(iii) to determine the time of receipt of a second signal transmitted from the mobile device; and
(iv) to determine the range of the mobile device to the first monitoring unit as a function of the received first signal, the timing parameter and the received second signal.
28. The system of claim 27 , further comprising;
a second and third monitoring unit of known location, each having a processor programmed to determine the time of receipt of the second signal, and to determine the range of the mobile device to the respective monitoring unit, wherein the first monitoring unit communicates the timing parameter to the second and third monitoring units; and
a locating processor programmed to determine the estimated location of the mobile as a function of the determined ranges.
29. The system of claim 28 wherein the first, second and third monitoring units are co-located at separate base stations.
30. The system of claim 29 wherein the locating processor is co-located with one of the monitoring units.
31. A computer program product for estimating the geographic location of a mobile device, wherein the mobile device communicates with a base station using a communication protocol, said computer program product comprising:
a non-transitory computer usable medium having computer readable program code modules embodied in said medium for estimating the geolocation of the mobile device;
computer readable first program code module for causing a processor to determine the time of transmission of a first signal from a base station to a mobile device;
computer readable second program code module for causing a processor to identify a timing parameter transmitted in the first signal;
computer readable third program code module for causing a processor to determine the time of receipt of a second signal transmitted from the mobile device; and
computer readable fourth program code module for causing a processor to determine the range of the mobile device to the first monitoring unit as a function of the received first signal, the timing parameter and the received second signal.
32. The computer program of claim 31 further comprising computer readable fifth program code module for causing a processor to receive a determined range to the mobile device from a plurality of computer readable fourth program code modules and for causing said processor to determine the estimated location of the mobile as a function of the determined ranges.
33. The computer program of claim 32 wherein first, second, third and fourth program code modules control a first processor and the fifth program module controls a second processor distributed from the first processor.
34. The computer program of claim 33 wherein the first processor is co-located at as base station.