Time synchronization of a satellite positioning system enabled mobile receiver and base station

• US 6,452,541 B1
• Filed: 02/20/2001
• Issued: 09/17/2002
• Est. Priority Date: 02/20/2001
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Wang, Hugh, Zhao, Yilin
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US09/788,753
• Publication Number:
  US 20020135511A1
• Time in Patent Office: 574 Days
• Field of Search: 342/357.06, 455/456, 370/519, 370/508, 375/356
• US Class Current: 342/357.62
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• CPC Class Codes: H04W 56/0015 one node acting as a reference for the others

Abstract

Satellite positioning system enabled mobile receivers (310) and cellular communication network base stations (330) synchronized with satellite positioning system clocks and method therefore. In a network-assisted embodiment, a variable propagation delay for transmission of an assistance message (232) from the base station to the mobile receiver is determined for correcting the handset clock (318). In others embodiments, local clock drift of mobile receivers (310) and/or base stations (330) are determined by a ratio of local and satellite time differences, based on sequential time snapshots, for use in correcting the local clocks.

Claims

1. A method for synchronizing a satellite positioning system enabled mobile receiver having a local clock with a satellite positioning system, comprising:

sampling first and second satellite signals at the mobile receiver;

sampling first and second local clock signals at the mobile receiver, the first local clock signal having the same relationship to the first satellite signal as the second local clock signal has to the second satellite signal;

determining a local clock drift proportional to a difference between the first and second sampled satellite signals divided by a difference between the first and second local clock signals;

correcting the local clock based upon the local clock drift.

2. The method of claim 1, sampling the first satellite signal and the first local clock signal at substantially the same time, sampling the second satellite signal and the second local clock signal at substantially the same time.

3. The method of claim 1, the mobile receiver is a cellular handset for use in a cellular communication network, periodically correcting the local clock, updating the local clock drift less frequently than the local clock is corrected.

4. The method of claim 3, sampling the first satellite signal and the first local clock signal at substantially the same time, sampling the second satellite signal and the second local clock signal at substantially the same time.

5. A method for synchronizing a cellular communications network base station local clock with a satellite positioning system clock, comprising:

sampling first and second satellite signals having satellite time at the base station;

sampling first and second base station local clock signals, the first local clock signal having the same relationship to the first satellite signal as the second local clock signal has to the second satellite signal;

determining a local clock drift proportional to a difference between satellite times of the first and second satellite signals divided by a difference between the first and second local clock signals;

correcting the local clock based upon the local clock drift.

6. The method of claim 5, re-correcting the local clock.

7. The method of claim 5, sampling the first satellite signal and the first local clock signal at substantially the same time, sampling the second satellite signal and the second local clock signal at substantially the same time.

8. A satellite positioning system enabled mobile receiver, comprising:

a satellite positioning system interface for receiving satellite signals having satellite time from a satellite positioning system;

a local clock;

means for determining a local clock drift (T_DRIFTMOBILE) proportional to [T_MS1−

T_MS2]/[T_GPS1−

T_GPS2],

where T_MS1 and T_MS2 are first and second sampled local clock times and T_GPS1 and T_GPS2 are first and second sampled satellite times,

the first satellite time having the same relationship to the first local clock time as the second satellite time having to the second local clock time.

9. The mobile receiver of claim 8, means for correcting the local clock based on the local clock drift.

10. The mobile receiver of claim 8 is a satellite positioning system enabled cellular handset comprising a wireless communications interface for communicating in a cellular communication network.

11. A cellular communication network base station, comprising:

a satellite positioning system interface for receiving satellite signals having satellite time from a satellite positioning system;

a local clock;

means for determining a local clock drift (T_DRIFTBS) proportional to [T_BS1−

T_BS2]/[T_GPS1−

T_GPS2],

where T_BS1 and T_BS2 are first and second sampled local clock times and T_GPS1 and T_GPS2 are first and second sampled satellite times,

the first satellite time having the same relationship to the first local clock time as the second satellite time having to the second local clock time.

12. The base station of claim 11, means for correcting the local clock based on the local clock drift.

13. A method for synchronizing a satellite positioning system enabled mobile receiver in a network having a base station that periodically determines a round trip delay (RTD) between the mobile receiver and a base station based on a known bit duration (BD) and that transmits an assistance message with satellite time between synchronization signals transmitted at a known synchronization interval, comprising:

determining a time factor that compensates for movement of the mobile receiver relative to the base station;

determining an estimated round trip delay (eRTD) based on the RTD and the time factor that compensates for movement of the mobile receiver;

determining an estimated propagation delay between the base station and the mobile receiver proportional to a product of the eRTD and the BD;

setting a clock in the mobile receiver based on the estimated propagation delay.

14. The method of claim 13, the assistance message transmitted at a known assistance message time offset relative to the transmission of a synchronization signal,

determining a time interval between sequential synchronization bursts received at the mobile receiver;

determining a time difference between the time interval and the known synchronization interval;

determining the time factor proportional to a product between the time difference and a ratio of the assistance message offset divided by the known synchronization interval.

15. The method of claim 13, generating the assistance message at a reference node, transmitting the assistance message from the reference node to the base station, determining a total propagation delay between the reference node and the mobile receiver by adding the estimated propagation delay to a propagation delay between the reference node and the base station, setting the clock in the mobile receiver based on the total propagation delay.

16. The method of claim 13,

determining the estimated round trip delay (eRTD) by calculating eRTD=RTD+[T′

_SCH/T_SCH−

1]*[T_OFFSET],

where T_SCH is the synchronization interval and T′

_SCH is an interval between sequential synchronization signal received at the mobile receiver, and where T_OFFSET is a time interval between a synchronization signal and the assistance message;

determining the estimated propagation delay (T_PROP) between the base station and the mobile receiver by calculating T_PROP=[1/2]*[eRTD]*[BD].

17. A satellite positioning system enabled mobile receiver in a network having a base station that periodically determines a round trip delay (RTD) between the mobile receiver and a base station based on a known bit duration (BD) and that transmits an assistance message with satellite time between synchronization signals transmitted at a known synchronization interval (T_SCH), comprising:

means for determining an estimated round trip delay, eRTD=RTD+[T′

_SCH/T_SCH−

1]*[T_OFFSET], between the mobile receiver and the base station,

where T_OFFSET is a time interval between a synchronization signal and the assistance message, and T′

_SCH is a time interval between sequential synchronization bursts received at the mobile receiver;

means for determining an estimated propagation delay, T_PROP=[1/2]*[eRTD]*[BD], between the base station and the mobile receiver;

means for synchronizing a clock in the mobile receiver based on the estimated propagation delay.

18. A method for synchronizing a satellite positioning system enabled mobile receiver in a network having a base station that periodically determines a round trip delay (RTD) between the mobile receiver and a base station based on a known bit duration (BD) and that transmits an assistance message with satellite time between synchronization signals transmitted at a known synchronization interval, comprising:

determining a time correction component proportional to a product of a resolution of the bit duration and an average of two or more time intervals between sequential synchronization signals received at the mobile receiver;

determining an estimated propagation delay between the base station and the mobile receiver proportional to a summation of RTD and the time correction component;

setting a clock in the mobile receiver based on the estimated propagation delay.

19. The method of claim 18,

determining a time correction, T_CORRECTION, component by calculating: $T_{\mathrm{CORRECTION}}=\left[\left[\underset{i=1}{\overset{n}{\sum <br><br>}}<br><br>T_{\mathrm{SCH}}^{\mathrm{\prime <br><br>}}\right]/n\right]<br><br>\left[\mathrm{BDR}\right],$

 

where T′

_SCH is an average of an interval between two or more synchronization signals T_SCH received at the mobile receiver and n is the number of intervals;

determining the estimated propagation delay, T_DELAY, by calculating;

T_DELAY=[1/2]*[RTD]*[BD]+[T_CORRECTION], where BD is the bit duration, and where BDR is bit duration resolution of the bit duration.

20. A satellite positioning system enabled mobile receiver in a network having a base station that periodically determines a round trip delay (RTD) between the mobile receiver and a base station based on a known bit duration (BD) having a bit duration resolution (BDR) and that transmits an assistance message with satellite time between synchronization signals, T_SCH, transmitted at a known synchronization interval, comprising:

means for determining a time correction component, $T_{\mathrm{CORRECTION}}=\left[\left[\underset{i=1}{\overset{n}{\sum <br><br>}}<br><br>T_{\mathrm{SCH}}^{\mathrm{\prime <br><br>}}\right]/n\right]<br><br>\left[\mathrm{BDR}\right],$

where T′

_SCH is an average of an interval between two or more synchronization signals T_SCH received at the mobile receiver;

means for determining an estimated propagation delay, T_DELAY=[1/2]*[RTD]*[BD]+[T_CORRECTION], between the base station and the mobile receiver;

means for synchronizing a dock in the mobile receiver based on the estimated propagation delay.