Method and apparatus for determining absolute time-of-day in a mobile-assisted satellite positioning system
A method and apparatus for determining time-of-day in a mobile receiver is described. In one example, expected pseudoranges to a plurality of satellites are obtained. The expected pseudoranges are based on an initial position of the mobile receiver and an initial time-of-day. Expected line-of-sight data to said plurality of satellites is also obtained. Pseudoranges from said mobile receiver to said plurality of satellites are measured. Update data for the initial time-of-day is computed using a mathematical model relating the pseudoranges, the expected pseudoranges, and the expected line-of-sight data. The expected pseudoranges and the expected line-of-sight data may be obtained from acquisition assistance data transmitted to the mobile receiver by a server. Alternatively, the expected pseudoranges may be obtained from acquisition assistance data, and the expected line-of-sight data may be computed by the mobile receiver using stored satellite trajectory data, such as almanac data.
1. A method of determining time-of-day in a mobile receiver, comprising:
obtaining expected pseudoranges to a plurality of satellites, said expected pseudoranges based on an initial position of said mobile receiver and an initial time-of-day at said mobile receiver;
obtaining expected line-of-sight data to said plurality of satellites at said mobile receiver;
measuring pseudoranges from said mobile receiver to said plurality of satellites at said mobile receiver; and
computing update data for said initial time-of-day using a mathematical model relating said pseudoranges, said expected pseudoranges, and said expected line-of-sight data at said mobile receiver.
2. The method of claim 1 , further comprising:
updating said initial time-of-day using said update data to compute a time-tag; and
transmitting said pseudoranges and said time-tag to a server in wireless communication with said mobile receiver.
3. The method of claim 1 , further comprising:
receiving acquisition assistance data at said mobile receiver from a server;
wherein said expected pseudoranges and said expected line-of-sight data are obtained from said acquisition assistance data.
4. The method of claim 1 , further comprising:
measuring pseudorange rates at said mobile receiver;
obtaining almanac data; and
computing an approximate position of said mobile receiver using said pseudorange rates and said almanac data;
wherein said expected line-of-sight data is obtained in response to said approximate position and said almanac data.
5. The method of claim 1 , further comprising:
obtaining almanac data;
obtaining an estimated position of said mobile receiver; and
computing an approximate position of said mobile receiver using said almanac data and said estimated position;
wherein said expected line-of-sight data is obtained in response to said approximate position and said almanac data.
6. The method of claim 1 , further comprising:
obtaining almanac data; and
obtaining an estimated position of said mobile receiver;
wherein said expected line-of-sight data is obtained in response to said estimated position and said almanac data.
7. The method of claim 1 , wherein said computing step comprises determining update data for a clock bias associated with said mobile receiver using said mathematical model.
8. The method of claim 7 , further comprising:
detecting bit transitions within satellite navigation data transmitted by at least one of said plurality of satellites;
and updating said initial time-of-day in response to said detected bit transitions and said clock bias update data.
9. The method of claim 1 , further comprising:
detecting bit transitions within satellite navigation data transmitted by at least one of said plurality of satellites;
decoding absolute time data from said satellite navigation data in response to said detected bit transitions;
and updating said initial time-of-day using said absolute time data.
10. The method of claim 9 , wherein said absolute time data comprises a time-of-week count message.
11. Apparatus for determining time-of-day in a mobile receiver, comprising:
the mobile receiver, said mobile receiver comprising:
a wireless transceiver for obtaining acquisition assistance data from a server, said acquisition assistance data comprising expected pseudoranges to a plurality of satellites based on an initial position of said mobile receiver and an initial time-of-day;
a satellite signal receiver for measuring pseudoranges from said mobile receiver to said plurality of satellites; and
a processor for obtaining expected line-of-sight data to said plurality of satellites and for computing update data for said initial time-of-day using a mathematical model relating said pseudoranges, said expected pseudoranges, and said expected line-of-sight data.
12. The apparatus of claim 11 , further comprising:
a clock circuit;
wherein said processor is further configured to calibrate said clock circuit using said update data.
13. The apparatus of claim 11 , wherein said processor is configured to obtain said expected line-of-sight data from said acquisition assistance data.
14. The apparatus of claim 11 , further comprising:
a memory for storing almanac data associated with a constellation having said plurality of satellites;
wherein said satellite signal receiver is further configured to measure pseudorange rates;
and wherein said processor is further configured to compute an approximate position of said mobile receiver using said pseudorange rates and said almanac data and to obtain said expected line-of-sight data in response to said approximate position and said almanac data.
15. The apparatus of claim 11 , further comprising:
a memory for storing almanac data associated with a constellation having said plurality of satellites;
wherein said processor is further configured to compute an approximate position of said mobile receiver using an estimated position of said mobile receiver and said almanac data and to obtain said expected line-of-sight data in response to said approximate position and said almanac data.
16. The apparatus of claim 11 , wherein said processor is further configured to compute update data from a clock bias associated with said satellite signal receiver using said mathematical model.
17. The apparatus of claim 16 , wherein said processor is further configured to detect bit transitions within satellite navigation data transmitted by at least one of said plurality of satellites and update said initial time-of-day in response to said detected bit transitions and said clock bias update data.
18. The apparatus of claim 11 , wherein said processor is further configured to decode absolute time data from satellite navigation data transmitted by at least one of said plurality of satellites and update said initial time-of-day using said absolute time data.
19. The apparatus of claim 18 , wherein said absolute time data comprises a time-of-week count message.