Macro-Network Location Determination, Local-Oscillator Stabilization, and Frame-Start Synchronization Based on Nearby FM Radio Signals

• US 20120201195A1
• Filed: 02/08/2011
• Published: 08/09/2012
• Est. Priority Date: 02/08/2011
• Status: Active Grant

• Current Assignee: Clearwire Ip Holdings LLC (Deutsche Telekom AG)
• Original Assignee: Clear Wireless LLC (Deutsche Telekom AG)
• Inventors: Rausch, Walter, Satapathy, Durga
• Granted Patent: US 8,503,368 B2
• Time in Patent Office: Days
• US Class Current: 370/328
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/0242 Determining the position of transmitters to be subsequently used in positioning G01S5/0289 takes precedence
• CPC Class Codes: G01S 5/08 Position of single direction-finder fixed by determining direction of a plurality of spaced sources of known location
• CPC Class Codes: H04B 17/318 Received signal strength
• CPC Class Codes: H04W 56/002 Mutual synchronization
• CPC Class Codes: H04W 56/0045 compensating for timing error by altering transmission time
• CPC Class Codes: H04W 56/005 compensating for timing error by adjustment in the receiver
• CPC Class Codes: H04W 88/08 Access point devices

Abstract

Exemplary methods and systems may generally be implemented to allow a macro-network base station without access to a GPS reference signal to provide some or all of the functionality for which existing macro-network base stations typically rely on GPS. In a first aspect, an exemplary macro-network base station may determine its location using a location-determination technique that is based upon the angles of arrival of FM radio signals from nearby FM stations. In a second aspect, an exemplary macro-network base station may stabilize its local oscillator by phase-locking its local oscillator to an FM radio signal, and periodically adjusting its local oscillator to account for phase drift of the FM radio signal. And in a third aspect, an exemplary macro-network base station may synchronize its frame-start timing with a nearby base station using a frame-start timing signal that the base station has synchronized to frame transmissions from the nearby base station during a setup routine.

Claims

1. A method carried out by a base station, wherein the base station provides service in a coverage area of a macro network, and wherein the base station is located within a given telecommunications market, the method comprising:

receiving a plurality of FM radio signals, wherein each of the FM radio signals is broadcast at a certain broadcast frequency by an FM radio station in the given telecommunications market;

for each received FM radio signal, determining an angle of arrival of the FM radio signal at the base station;

sending a location request to a network operations center, wherein the location request comprises the broadcast frequency and the determined angle of arrival for each of the FM radio signals; and

receiving a response to the location request from the network operations center, wherein the response indicates the geographic location of the first base station, and wherein the broadcast frequency and the determined angle of arrival for each of the FM radio signals are both used as a basis to determine the geographic location.

2. The method of claim 1, wherein the base station carrying out the method is a second base station, the method further comprising receiving a signal from a first base station in the macro network, wherein the signal is transmitted by the first base station at a given transmit frequency and comprises an identifier of the first base station, wherein the location request further comprises an indication of the transmit frequency and the identifier of the first base station, and wherein the indication of the transmit frequency and the identifier of the first base station are both used by the network operations center as a further basis to determine the geographic location.

3. A location-determination method carried out by at least one entity in a core network, wherein the core network supports a macro network that provides service in a coverage area, and wherein the coverage area overlaps with one or more telecommunications markets, the method comprising:

receiving a location request from a base station in the macro network, wherein the location request comprises;

(a) a plurality of FM-station identifiers, wherein each FM-station identifier corresponds to an FM radio station, and (b) for each FM-station identifier, an angle of arrival at the base station of an FM radio signal that is broadcast by the identified FM radio station;

determining a set of potential markets that comprises one or more telecommunications markets, wherein each potential market includes an FM radio station corresponding to each of the FM-station identifiers;

iteratively applying a triangulation routine to the set of potential markets until an application of the trilateration routine in one of the potential markets produces a valid crossing point, wherein the triangulation routine is based at least in part on (a) locations of FM stations that broadcast at the reported broadcast frequencies in the given potential market and (b) the reported angles of arrival; and

setting the valid crossing point as the geographic location of the base station.

4. The method of claim 3, wherein the entity in a service-provider network that carries out the method is a network operations center.

5. The method of claim 3, wherein each FM-station identifier comprises an indication of a broadcast frequency for the corresponding FM radio station.

6. The method of claim 5, wherein determining the set of potential markets comprises:

determining which telecommunication markets include FM radio stations at all of the indicated broadcast frequencies; and

identifying each market that includes FM stations at all of the indicated broadcast frequencies as a potential market.

7. The method of claim 3, wherein the base station from which the location request is received is a second base station, and wherein the location request further comprises identification information for a first base station, and wherein the method further comprises using the identifier information for the first base station as a further basis for determining the set of potential markets.

8. The method of claim 7, wherein using the identifier information for the first base station as a further basis for determining the set of potential markets comprises:

determining one or more telecommunication markets in which a base station having the identifier information is located; and

identifying as a potential market each telecommunication market in which a base station having the identifier information is located.

9. The method of claim 7, wherein the identifier information comprises at least one of (a) an identifier of a first base station and (b) a transmission frequency of the first base station.

10. The method of claim 3, wherein the base station from which the location request is received is a second base station, and wherein the location request further comprises identification information for a first base station, and wherein the method further comprises:

using the identification information for the first base station as a basis for determining a location of the second base station in the telecommunication market in which the valid crossing point was produced; and

before setting the valid crossing point as the geographic location of the second base station, verifying that the valid crossing point is within a broadcast range from the location of the first base station.

11. The method of claim 3, further comprising sending an indication of the geographic location of the base station to the second base station.

12. A core-network component, wherein the core network supports a macro network that provides service in a coverage area, and wherein the coverage area overlaps with one or more telecommunications markets, the core-network component comprising:

a non-transitory tangible computer-readable medium;

program instructions stored on the non-transitory tangible computer-readable medium and executable by at least one processor to cause the core-network entity to;

(i) receive a location request from a base station in the macro network, wherein the location request comprises;

(a) a plurality of FM-station identifiers, wherein each FM-station identifier corresponds to an FM radio station, and (b) for each FM-station identifier, an angle of arrival at the base station of an FM radio signal that is broadcast by the identified FM radio station;

(ii) determine a set of potential markets that comprises one or more telecommunications markets, wherein each potential market includes an FM radio station corresponding to each of the FM-station identifiers;

(iii) iteratively apply a triangulation routine to the set of potential markets until an application of the trilateration routine in one of the potential markets produces a valid crossing point, wherein the triangulation routine is based at least in part on (a) locations of FM stations that broadcast at the reported broadcast frequencies in the given potential market and (b) the reported angles of arrival; and

(iv) set the valid crossing point as the geographic location of the base station.

13. The core-network component of claim 12, wherein the core-network component is a network operations center.

14. The core-network component of claim 12, wherein the program instructions stored on the non-transitory tangible computer-readable medium and executable by at least one processor to cause the core-network entity to determine the set of potential markets comprise program instructions stored on the non-transitory tangible computer-readable medium and executable by at least one processor to cause the core-network entity to:

determine which telecommunication markets include FM radio stations at all of the indicated broadcast frequencies; and

identify each market that includes FM stations at all of the indicated broadcast frequencies as a potential market.

15. The core-network component of claim 12, wherein the base station from which the location request is received is a second base station, and wherein the location request further comprises identification information for a first base station, wherein the identifier information for the first base station is used as a further basis for determining the set of potential markets.

16. The core-network component of claim 15, wherein the program instructions stored on the non-transitory tangible computer-readable medium and executable by at least one processor to cause the core-network entity to determine the set of potential markets comprise program instructions stored on the non-transitory tangible computer-readable medium and executable by at least one processor to cause the core-network entity to:

determine one or more telecommunication markets in which a base station having the identifier information is located; and

identify as a potential market each telecommunication market in which a base station having the identifier information is located.

17. The core-network component of claim 12, wherein the base station from which the location request is received is a second base station, and wherein the location request further comprises identification information for a first base station, and wherein the core-network component further comprises program instructions stored on the non-transitory tangible computer-readable medium and executable by at least one processor to cause the core-network entity to:

use the identification information for the first base station as a basis to determine a location of the first base station in the telecommunication market in which the valid crossing point was produced; and

before setting the valid crossing point as the geographic location of the second base station, verify that the valid crossing point is within a broadcast range from the location of the first base station.

18. An in-market broadcast monitoring system configured for operation in a given telecommunications market, wherein a coverage area of a macro network overlaps with the given telecommunications market, the system comprising:

at least one FM receiver configured to receive one or more FM radio signals in the given telecommunications market;

a GPS receiver configured to receive a GPS signal; and

program instructions stored in a tangible computer readable medium and executable by at least one processor to;

(a) cause the FM receiver to receive an FM radio signal that is broadcast in the given telecommunications market;

(b) cause the GPS receiver to receive a GPS signal comprising a GPS reference signal;

(c) divide down the FM radio signal to generate a comparison signal;

(d) determine a phase difference between the comparison signal and the GPS reference signal; and

(e) provide a phase-error indication for use by one or more base stations in the macro network, wherein the phase-error indication comprises an indication of the phase difference between the comparison signal and the FM radio signal.

19. The in-market broadcast monitoring system of claim 18, wherein the FM radio signal has an identified broadcast frequency and an actual broadcast frequency, and wherein the actual broadcast frequency is variable from the identified broadcast frequency according to phase drift of the FM radio signal.

20. The in-market broadcast monitoring system of claim 19, wherein the FM radio signal is divided down such that a frequency of the comparison signal is equal to a frequency of the GPS reference signal only if the actual broadcast frequency is equal to the identified broadcast frequency.

21. The in-market broadcast monitoring system of claim 18 wherein the program instructions stored in the tangible computer-readable medium and executable by at least one processor to divide down the FM radio signal to generate a comparison signal comprise program instructions stored in the tangible computer readable medium and executable by at least one processor to:

determine a first frequency equal to the identified broadcast frequency of the FM signal divided by a frequency of the GPS reference signal; and

generate the comparison signal by dividing the FM radio signal by a signal having the determined first frequency.

22. The in-market broadcast monitoring system of claim 21, wherein the frequency of the GPS reference signal is 10.23 MHz.

23. The in-market broadcast monitoring system of claim 18, further comprising:

a divider configured to generate the comparison signal by dividing a frequency at which the FM radio signal is received by a value such that the frequency of the comparison signal should match the GPS reference signal; and

a phase comparator configured to determine the phase difference between the comparison signal and the GPS reference signal.

24. The in-market broadcast monitoring system of claim 18, wherein the phase-error indication is provided for use by one or more base stations that are using the FM radio signal for local oscillator stabilization.

25. The in-market broadcast monitoring system of claim 18, wherein the program instructions stored in a tangible computer-readable medium and executable by at least one processor to provide a phase-error indication for use by one or more base stations in the macro network comprise program instructions stored in a tangible computer readable medium and executable by at least one processor to:

send the indication of the phase drift to a network operations center that supports the macro network, wherein the network operations center is configured to send the indication of the phase drift to one or more base stations that are using the FM radio signal for local oscillator stabilization.

26. The in-market broadcast monitoring system of claim 18, wherein the program instructions stored in a tangible computer readable medium are further executable by at least one processor to periodically repeat (a)-(e).

27. The in-market broadcast monitoring system of claim 18, wherein a plurality of FM radio signals are broadcast in the given telecommunications market, and wherein the program instructions stored in a tangible computer readable medium are further executable by at least one processor to perform (a)-(e) for each of the FM radio signals that is broadcast in the given telecommunications market.

28. A method for monitoring phase error of an FM radio signal in a given telecommunications market, wherein a coverage area of a macro network overlaps with the given telecommunications market, the method comprising:

(a) receiving an FM radio signal that is broadcast in the given telecommunications market;

(b) receiving a GPS reference signal;

(c) dividing down the FM radio signal to generate a comparison signal;

(d) determining a phase difference between the comparison signal and the GPS reference signal; and

(e) providing a phase-error indication for use by one or more base stations in the macro network, wherein the phase-error indication comprises an indication of the phase difference between the comparison signal and the FM radio signal.

29. The method of claim 28, wherein the FM radio signal is divided down such that a frequency of the comparison signal is equal to a frequency of the GPS reference signal only if the actual broadcast frequency is equal to the identified broadcast frequency.

30. The method of claim 28, wherein the FM radio signal has an identified broadcast frequency and an actual broadcast frequency, and wherein the actual broadcast frequency is variable from the identified broadcast frequency according to phase drift of the FM radio signal, and wherein dividing down the FM radio signal to generate a comparison signal comprises:

determining a first frequency equal to the identified broadcast frequency of the FM signal divided by a frequency of the GPS reference signal; and

generating the comparison signal by dividing the FM radio signal by a signal having the determined first frequency.

31. The method of claim 28, wherein providing a phase-error indication for use by one or more base stations in the macro network comprises:

sending the phase-error indication to a network operations center that supports the macro network for distribution to one or more base station that are using the FM radio signal for local oscillator stabilization.

32. The method of claim 28, further comprising periodically repeating (c)-(e) for each FM radio signal in the given telecommunications market.

33. A method for stabilizing a local oscillator of a first base station in a macro network, the method comprising:

a first base station in a macro network receiving an FM radio signal from an FM station, wherein the first base station and the FM station are both located in a given telecommunications market, and wherein the first base station comprises a local oscillator;

the first base station phase-locking the local oscillator to the FM radio signal;

the first base station periodically receiving a phase-error indication, wherein each received phase-error indication indicates phase drift of the FM radio signal; and

the first base station using each received phase-error indication to adjust the phase of the local oscillator in order to account for phase drift of the FM radio signal.

34. The method of claim 33, further comprising the first base station initially determining that the FM radio signal is the strongest FM radio signal out of a plurality of FM radio signals that are each broadcast by another FM station in the telecommunications market.

35. The method of claim 33, further comprising the first base station initially determining that a signal strength of the FM radio signal is above a predetermined threshold.

36. The method of claim 33, further comprising the first base station sending an identifier of the FM radio signal or the FM station to a network operations center in order that the first base station can periodically receive the phase-error indications from the network operations center.

37. The method of claim 33, further comprising:

the first base station initially receiving a signal from a second base station in the macro network and phase-locking the local oscillator to the signal from the second base station; and

the first base station transferring phase-lock of the local oscillator from the signal from the second base station to the FM radio signal by carrying out the steps of receiving the FM radio signal and phase-locking the local oscillator to the FM radio signal.

38. The method of claim 33, wherein the steps of receiving the signal from a second base station, phase-locking the local oscillator to the signal from the second base station, and transferring phase-lock of the local oscillator from the signal from the second base station to the FM radio signal are carried out during a setup routine, the method further comprising:

after carrying out the setup routine, the first base station switching to an operating mode in which the first base station provides wireless service in the macro network, wherein the steps of periodically receiving a phase-error indication and using each received phase-error indication to adjust the phase of the local oscillator are carried out while the first base station is in the operating mode.

39. A base station in a macro network, wherein the base station comprises:

a macro-network communication interface;

an FM receiver configured to receive one or more FM radio signals;

a local oscillator; and

program instructions stored in a tangible computer readable medium and executable by at least one processor to;

(a) tune the FM receiver to an FM radio signal that is broadcast by an FM station, wherein the base station and the FM station are both located in a given telecommunications market;

(b) phase-lock the local oscillator to the FM radio signal;

(c) periodically receive phase-error indications, wherein each received phase-error indication indicates phase drift of the FM radio signal; and

(d) use each received phase-error indication to adjust the phase of the local oscillator in order to account for phase drift of the FM radio signal.

40. The base station of claim 39, further comprising program instructions stored in a tangible computer readable medium and executable by at least one processor initially determine that the FM radio signal is the strongest FM radio signal out of a plurality of FM radio signals in the given telecommunications market.

41. The base station of claim 39, further comprising program instructions stored in a tangible computer readable medium and executable by at least one processor to initially determine that a signal strength of the FM radio signal is above a predetermined threshold.

42. The base station of claim 39, further comprising program instructions stored in a tangible computer readable medium and executable by at least one processor to send an indication of the FM radio signal to a network operations center in order that the first base station can periodically receive the phase-error indications from the network operations center.

43. The base station of claim 39, further comprising program instructions stored in a tangible computer readable medium and executable by at least one processor to:

initially receive a broadcast signal from a nearby base station in the macro network;

phase-lock the local oscillator to the broadcast signal from the second base station; and

transfer phase-lock of the local oscillator from the broadcast signal to the FM radio signal by carrying out the steps of receiving the FM radio signal and phase-locking the local oscillator to the FM radio signal.

44. The base station of claim 43:

wherein a setup routine comprises the program instructions stored in a tangible computer readable medium and executable by at least one processor to receive the broadcast signal from the second base station, phase-lock the local oscillator to the broadcast signal, and transfer phase-lock of the local oscillator from the broadcast signal to the FM radio signal;

wherein the base station further comprises program instructions stored in a tangible computer readable medium and executable by at least one processor to, after carrying out the setup routine, switch to an operating mode to provide wireless service in the macro network, and while in the operating mode, to periodically receive the phase-error indications and use each received phase-error indication to adjust the phase of the local oscillator.

45. A method for facilitating local-oscillator stabilization for a first base station in a macro network, the method comprising:

(i) a core-network entity receiving a phase-error indication for each of one or more FM radio signals in a given telecommunications market; and

(ii) for each of the one or more FM radio signals the core-network entity;

(a) identifying one or more base stations that are using the FM radio signal as a reference signal for local-oscillator stabilization; and

(b) sending the phase-error indication for the FM radio signal to each identified base station.

46. The method of claim 45, wherein the core-network entity is a network operations center.

47. A method for frame-start synchronization with nearby base stations in the macro network, the method comprising:

(a) a second base station receiving a first signal from a first base station in the macro network, wherein the first signal comprises frames, and wherein the first signal further comprises an identifier of the first base station;

(b) the second base station synchronizing a frame-start timing signal with the frames in the first signal;

(c) the second base station determining a time-of-flight delay between the first base station and the second base station;

(d) the second base station adjusting timing of the frame-start signal to account for the time-of-flight delay between the first base station and the second base station; and

(e) the second base station transmitting a second signal that is formatted into frames, wherein the second base station uses the frame-start timing signal to control the timing of the frames in the second signal.

48. The method of claim 47, wherein the second base station carries out steps (a)-(d) during a setup routine, and wherein the second base station carries out step (e) after finishing the setup routine and switching to an operating mode.

49. The method of claim 47, wherein the second base station switches out of the operating mode, repeats the setup routine, and then switches back to the operating mode.

50. The method of claim 47, wherein the second base station determining a time-of-flight delay between the first base station and the second base station comprises:

the second base station determining its geographic location;

the second base station sending (i) the identifier of the first base station and (ii) the geographic location of the second base station to a network operations center for use in a determination of a distance between the first base station and the second base station; and

the second base station receiving an indication of the time-of-flight delay from the network operations center, wherein the time-of-flight delay is based at least in part on the distance between the first base station and the second base station.

51. The method of claim 47, wherein synchronizing the frame-start timing signal with the frames in the first signal comprises creating periodic frame-start triggers in the frame-start timing signal, wherein the frame-start triggers occur in the timing signal at a frequency that is matched to a frequency of frame transmissions by the first base station.

53. The method of claim 47, wherein the program instructions stored in a tangible computer readable medium and executable by at least one processor to determine the time-of-flight delay experienced by the first broadcast signal comprise program instructions stored in a tangible computer readable medium and executable by at least one processor to:

determining a geographic location of the macro-network base station;

send (i) an identifier of the nearby base station and (ii) the geographic location of the macro-network base station to a network operations center for use in a determination of a distance between the nearby base station and the macro-network base station; and

the first base station receiving an indication of the time-of-flight delay from the network operations center, wherein the time-of-flight delay is based at least in part on the distance between the first base station and the second base station.

54. The method of claim 47, wherein the program instructions stored in a tangible computer readable medium and executable by at least one processor to synchronize a frame-start timing signal with receipt of the frames in the first broadcast signal comprise:

program instructions stored in a tangible computer readable medium and executable by at least one processor to synchronize periodic frame-start triggers in the frame-start timing signal with the receipt of frames in the first broadcast signal such that a frequency at which the frame-start triggers occur is equal to a frequency at which the frames are received.

52. A macro-network base station configured to provide wireless service in a coverage area of a macro network, wherein the base station is configured to communicate with client devices in the coverage area via a broadcast signal comprising frames, the base station comprising:

a macro-network communication interface;

a backhaul communication interface; and

program instructions stored in a tangible computer readable medium and executable by at least one processor to;

(a) cause the macro-network communication interface to receive a first broadcast signal from a nearby base station in the macro network, wherein the first broadcast signal comprises a plurality of frames, and wherein the first signal further comprises an identifier of the first base station;

(b) synchronize a frame-start timing signal with receipt of the frames in the first broadcast signal;

(c) determine a time-of-flight delay experienced by the first broadcast signal between transmission of the first broadcast signal from the nearby base station and receipt of the first broadcast signal;

(d) adjust timing of the frame-start signal to account for the determined time-of-flight delay; and

(e) cause the macro-network base station to transmit a second broadcast signal that comprises frames, wherein the frame-start timing signal is used to control the timing of the frames in the second signal.

55. A method for facilitating frame-start synchronization of a base station, the method comprising:

a core-network component receiving a request from a second base station for a time-of-flight delay between a first base station and the second base station, wherein the request includes (i) an identifier of a first base station and (ii) a the geographic location of the second base station, and wherein the second base station is configured to use the time-of-flight delay to synchronize a frame-start timing signal with frames in a broadcast signal of the first base station;

the core-network component using the identifier of the first base station as a basis to determine the geographic location of the first base station;

based at least in part on (i) the received geographic location of the second base station and (ii) the determined geographic location of the first base station, the core-network component determining a distance between the first base station and the second base station;

the core-network component using the distance between the first base station and the second base station as a basis to determine the time-of-flight delay experienced by a broadcast signal between the first base station and the second base station; and

the core-network component sending an indication of the time-of-flight delay to the second base station.