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:
receiving a broadcast of an estimate of time from a server at the satellite signal receiver;
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. A method of receiving an estimate of time in a satellite signal receiver comprising:
receiving a broadcast of an estimate of time from a server at the satellite signal receiver;
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.
4. The method of claim 3 , further comprising:
operating the clock in a low-power state while the satellite signal receiver is inactive.
5. A method of receiving an estimate of time in a satellite signal receiver comprising:
determining a time of last compensation of the clock;
comparing the time of last compensation with a threshold;
requesting the estimate of time from the server in response to the time of last compensation exceeding the threshold;
receiving a broadcast of an estimate of time from a server at the satellite signal receiver;
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.
6. The method of claim 5 , wherein receiving an estimate of time from a server and compensating for error of a clock in the satellite signal receiver are performed periodically.
7. The method of claim 5 , wherein requesting and receiving an estimate of time is performed in response to the unavailability of absolute time.
8. 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 a broadcast of an estimate of time from a server;
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 updates the a-priori estimate of absolute time to determine the position of the satellite signal receiver and an absolute time.
9. The method of claim 8 , 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.
10. 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 a broadcast of 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.
11. The method of claim 10 , wherein the estimate of time from the server is in error by more than ten milliseconds.
12. A system for determining a position of a mobile device comprising:
a mobile device having a satellite signal receiver and a wireless transceiver; and
a server being in wireless communication with the mobile device, for broadcasting an estimate of time;
wherein said satellite signal receiver compensates for error of a clock in the satellite signal receiver using the estimate of time, designates the output of the compensated clock as an a-priori estimate of absolute time, and employs 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.
13. The system of claim 12 , wherein the wireless transceiver transmits pseudoranges and the output of the local clock to the server; and
wherein the server receives ephemeris data and computes a position of the mobile device using the pseudoranges, the ephemeris data, and the output of the local clock.