Method and system for determining time in a satellite positioning system
View Patent ↗Method and apparatus for receiving an estimate of time in a satellite signal receiver receives an estimate of time from a server and compensates for error of a clock in the satellite signal receiver using the estimate of time. The output of the compensated clock is used when computing a position of the satellite signal receiver. The estimate of time is received using a network time protocol (NTP), a simple network time protocol (SNTP), or by one-way broadcast from the server.
1. A method of receiving an estimate of time in a satellite signal receiver comprising:
requesting and receiving an estimate of time from a server using a time transfer protocol;
compensating for error of a clock in the satellite signal receiver using the estimate of time;
designating the output of the compensated clock as an a-priori estimate of absolute time; and
employing the a-priori estimate of absolute time in a mathematical model that updates the a-priori estimate of absolute time to compute a position of the satellite signal receiver and an absolute time.
2. The method of claim 1 , further comprising
employing the absolute time when computing a position of the satellite signal receiver.
3. The method of claim 2 , wherein the time transfer protocol comprises a network time protocol (NTP).
4. The method of claim 2 , wherein the time transfer protocol comprises a simple network time protocol (SNTP).
5. The method of claim 1 , wherein the time transfer protocol comprises a network time protocol (NTP).
6. The method of claim 1 , wherein the time transfer protocol comprises a simple network time protocol (SNTP).
7. The method of claim 1 , wherein requesting and receiving an estimate of time comprises:
transmitting a packet from the satellite signal receiver to the server with an originate time stamp derived from the clock;
returning the packet to the satellite signal receiver from the server with receive and transmit time stamps derived from a server clock; and
receiving the packet at the satellite signal receiver with a destination time stamp.
8. The method of claim 7 , wherein compensating for error of the clock comprises:
processing the originate, receive, transmit, and destination time stamps to determine an offset for the clock.
9. The method of claim 1 , further comprising: operating the clock in a low-power state while the satellite signal receiver is inactive.
10. The method of claim 1 , wherein receiving an estimate of time from a server and compensating for error of a clock in the satellite signal receiver are performed periodically.
11. The method of claim 1 , wherein requesting and receiving an estimate of time is performed in response to the unavailability of absolute time.
12. A method of receiving an estimate of time in a satellite signal receiver comprising:
requesting and receiving an estimate of time from a server using a time transfer protocol;
compensating for error of a clock in the satellite signal receiver using the estimate of time;
designating the output of the compensated clock as an a-priori estimate of absolute time;
employing the a-priori estimate of absolute time in a mathematical model that updates the a-priori estimate of absolute time to compute a position of the satellite signal receiver and an absolute time;
providing an a-priori estimate of absolute time from a time source;
computing a position of the satellite signal receiver and an absolute time using a mathematical model that updates the a-priori estimate of absolute time; and
comparing the computed absolute time with the output of the compensated clock.
13. The method of claim 12 , wherein the time transfer protocol comprises a network time protocol (NTP).
14. The method of claim 12 , wherein the time transfer protocol comprises a simple network time protocol (SNTP).
15. A method of receiving an estimate of time in a satellite signal receiver comprising:
requesting and receiving an estimate of time from a server using a time transfer protocol; which comprises:
determining a time of last compensation of the clock;
comparing the time of last compensation with a threshold; and
requesting the estimate of time from the server in response to the time of last compensation exceeding the threshold; and
compensating for error of a clock in the satellite signal receiver using the estimate of time;
designating the output of the compensated clock as an a-priori estimate of absolute time; and employing the a-priori estimate of absolute time in a mathematical model that updates the a-priori estimate of absolute time to compute a position of the satellite signal receiver and an absolute time.
16. A method for determining a position of a satellite signal receiver comprising:
computing pseudoranges that estimate the range of the satellite signal receiver to a plurality of satellites in a satellite constellation;
requesting and receiving an estimate of time from a server using a time transfer protocol;
receiving ephemeris data relating to the satellite constellation;
designating the estimate of time as an a-priori estimate of absolute time; and
employing the designated a-priori estimate of absolute time in a mathematical model that update the a-priori estimate of absolute time to determine the position of the satellite signal receiver and an absolute time.
17. The method of claim 16 , wherein determining position comprises:
designating the estimate of time as an absolute time; and
employing the designated absolute time when determining the position of the satellite signal receiver.
18. The method of claim 17 , wherein the time transfer protocol comprises a network time protocol (NTP).
19. The method of claim 17 , wherein the time transfer protocol comprises a simple network time protocol (SNTP).
20. The method of claim 16 , wherein the time transfer protocol comprises a network time protocol (NTP).
21. The method of claim 16 , wherein the time transfer protocol comprises a simple network time protocol (SNTP).
22. The method of claim 16 wherein the estimate of time from the server is in error by more than ten milliseconds.
23. A method for determining a position of a satellite signal receiver comprising:
computing pseudoranges that estimate the range of the satellite signal receiver to a plurality of satellites in a satellite constellation;
requesting and receiving an estimate of time from a server using a time transfer protocol;
receiving ephemeris data relating to the satellite constellation;
providing an a-priori estimate of absolute time from a time source;
computing a position of the satellite signal receiver and an absolute time using a mathematical model that updates the a-priori estimate of absolute time; and
comparing the computed absolute time with the estimate of time.