Global positioning system receiver

• US 20090295634A1
• Filed: 05/30/2008
• Published: 12/03/2009
• Est. Priority Date: 05/30/2008
• Status: Active Grant

• Current Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Original Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Inventors: Yu, Xiaoguang, Huang, Haiquan, Zou, Jinghua
• Granted Patent: US 8,035,559 B2
• Time in Patent Office: Days
• US Class Current: 342/357.64
• CPC Class Codes: G01S 19/27 creating, predicting or correcting ephemeris or almanac data within the receiver

Abstract

A GPS receiver includes a demodulator for obtaining ephemeris data and almanac data from a navigation message sent by satellites, and includes a calculator. The calculator is used for calculating almanac correction parameters according to coordinate differences between ephemeris-based coordinates of the satellites and almanac-based coordinates of the satellites. The GPS receiver also includes a satellite position calculator for calculating the ephemeris-based coordinates of the satellites according to the ephemeris data, for calculating the almanac-based coordinates of the satellites according to the almanac data, and for calculating positions of the satellites according to the ephemeris data, the almanac data and the almanac correction parameters.

Claims

1. A global positioning system (GPS) receiver comprising:

a demodulator for obtaining ephemeris data and almanac data from a navigation message sent by a plurality of satellites;

a calculator for calculating a plurality of almanac correction parameters according to coordinate differences between a plurality of ephemeris-based coordinates of said plurality of satellites and a plurality of almanac-based coordinates of said plurality of satellites; and

a satellite position calculator for calculating said plurality of ephemeris-based coordinates according to said ephemeris data, for calculating said plurality of almanac-based coordinates according to said almanac data, and for calculating a plurality of positions of said plurality of satellites according to said ephemeris data, said almanac data and said plurality of almanac correction parameters.

2. The GPS receiver of claim 1, wherein said calculator verifies validity of said ephemeris data, said almanac data, and said plurality of almanac correction parameters.

3. The GPS receiver of claim 1, wherein said satellite position calculator calculates said plurality of positions of said plurality of satellites according to said ephemeris data if said ephemeris data is valid, and wherein said calculator verifies validity of said almanac data and said plurality of almanac correction parameters if said ephemeris data is invalid.

4. The GPS receiver of claim 3, wherein said satellite position calculator calculates said plurality of positions of said plurality of satellites according to said almanac data and said plurality of almanac correction parameters if said almanac data and said plurality of almanac correction parameters are valid.

5. The GPS receiver of claim 1, wherein said calculator calculates said plurality of almanac correction parameters according to clock differences between a plurality of ephemeris-based clock drifts of said plurality of satellites and a plurality of almanac-based clock drifts of said plurality of satellites, and wherein said satellite position calculator calculates said plurality of ephemeris-based clock drifts and said plurality of almanac-based clock drifts according to said ephemeris data and said almanac data respectively.

6. The GPS receiver of claim 5, wherein said calculator calculates minimum values of said coordinate differences between said ephemeris-based coordinates and said almanac-based coordinates obtained at time t according to a least square approximation of said coordinate differences, and calculates minimum values of said clock differences between said plurality of ephemeris-based clock drifts and said plurality of almanac-based clock drifts obtained at said time t according to a least square approximation of said clock differences, in order to obtain said plurality of almanac correction parameters.

7. The GPS receiver of claim 6, wherein said plurality of almanac correction parameters comprise parameters a₀, a₁ . . . a_n, wherein said parameters a₀, a₁ . . . a_n are calculated according to said least square approximation by equation (1),

8. The GPS receiver of claim 5, wherein said satellite position calculator calculates said plurality of almanac-based coordinates x′

, y′

, z′

, and said plurality of almanac-based clock drifts T′

according to said almanac data at time t, wherein said satellite position calculator further calculates correction values Δ

x′

(t), Δ

y′

(t), Δ

z′

(t), and Δ

T′

(t) shown by equations (2), (3), (4), and (5) respectively,

9. The GPS receiver of claim 1, wherein said satellite position calculator calculates a plurality of correction values according to said plurality of almanac correction parameters respectively, and wherein said satellite position calculator calculates said plurality of positions by adding said plurality of correction values to said plurality of almanac-based coordinates respectively.

10. The GPS receiver of claim 1, further comprising:

a positioning device coupled to said satellite position calculator for calculating a position of said GPS receiver according to said positions of said plurality of satellites.

11. The GPS receiver of claim 1, further comprising:

a storage device for storing said plurality of almanac correction parameters.

12. A method for positioning a global positioning system (GPS) receiver, comprising:

obtaining ephemeris data and almanac data from a navigation message sent by a plurality of satellites;

calculating a plurality of ephemeris-based coordinates and a plurality of ephemeris-based clock drifts of said plurality of satellites according to said ephemeris data;

calculating a plurality of almanac-based coordinates and a plurality of almanac-based clock drifts of said plurality of satellites according to said almanac data;

calculating a plurality of almanac correction parameters according to coordinate differences between said plurality of ephemeris-based coordinates and said plurality of almanac-based coordinates and according to clock differences between said plurality of ephemeris-based clock drifts and said plurality of almanac-based clock drifts; and

calculating a plurality of positions of said plurality of satellites according to said ephemeris data, said almanac data and said plurality of almanac correction parameters.

13. The method of claim 12, further comprising:

calculating said plurality of positions of said plurality of satellites according to said ephemeris data if said ephemeris data is valid; and

verifying validity of said almanac data and said plurality of almanac correction parameters if said ephemeris data is invalid.

14. The method of claim 13, further comprising:

calculating said plurality of positions of said plurality of satellites according to said almanac data and said plurality of almanac correction parameters if said almanac data and said plurality of almanac correction parameters are valid.

15. The method of claim 12, wherein calculating said plurality of almanac correction parameters further comprises:

calculating minimum values of said coordinate differences between said ephemeris-based coordinates and said almanac-based coordinates obtained at time t according to a least square approximation of said coordinate differences; and

calculating minimum values of said clock differences between said plurality of ephemeris-based clock drifts and said plurality of almanac-based clock drifts obtained at said time t according to a least square approximation of said clock differences.

16. The method of claim 15, wherein said plurality of almanac correction parameters comprises parameters a₀, a₁ . . . a_n, wherein said parameters a₀, a₁ . . . a_n are calculated according to said least square approximation by equation (10),

17. The method of claim 12, wherein calculating said plurality of positions of said plurality of satellites further comprises:

calculating a plurality of correction values according to said plurality of almanac correction parameters respectively; and

adding said plurality of correction values to said plurality of almanac-based coordinates respectively to calculate said plurality of positions.

18. The method of claim 12, wherein calculating said plurality of positions of said plurality of satellites further comprises:

calculating said plurality of almanac-based coordinates x′

, y′

, z′

of said plurality of satellites, and said plurality of almanac-based clock drifts T′

according to said almanac data at time t;

calculating correction values Δ

x′

(t), Δ

y′

(t), Δ

z′

(t), and Δ

T′

(t) shown by equations (11), (12), (13), and (14) respectively,

19. The method of claim 12, further comprising:

calculating a position of said GPS receiver according to said positions of said plurality of satellites.

20. The method of claim 12, further comprising:

storing said plurality of almanac correction parameters.

21. A GPS (global positioning system) comprising:

an acquisition and track device for acquiring and tracking a plurality of satellites and obtaining a navigation message from said plurality of satellites;

a demodulator for obtaining ephemeris data and almanac data from said navigation message;

a calculator for calculating a plurality of almanac correction parameters according to coordinate differences between a plurality of ephemeris-based coordinates of said plurality of satellites and a plurality of almanac-based coordinates of said plurality of satellites and according to clock differences between a plurality of ephemeris-based clock drifts of said plurality of satellites and a plurality of almanac-based clock drifts of said plurality of satellites; and

a satellite position calculator coupled to said acquisition and track device and for calculating said plurality of ephemeris-based coordinates and said plurality of ephemeris-based clock drifts according to said ephemeris data, for calculating said plurality of almanac-based coordinates and said plurality of almanac-based clock drifts according to said almanac data, and for calculating a plurality of positions of said plurality of satellites respectively according to said ephemeris data, said almanac data and said plurality of almanac correction parameters.

22. The GPS system of claim 21, wherein said calculator calculates minimum values of said coordinate differences between said ephemeris-based coordinates and said almanac-based coordinates obtained at time t according to a least square approximation of said coordinate differences, and calculates minimum values of said clock differences between said plurality of ephemeris-based clock drifts and said plurality of almanac-based clock drifts obtained at said time t according to a least square approximation of said clock differences, in order to obtain said plurality of almanac correction parameters.

23. The GPS system of claim 22, wherein said plurality of almanac correction parameters comprise parameters a₀, a₁ . . . a_n, wherein said parameters a₀, a₁ . . . a_n are calculated according to said least square approximation by equation (19),

24. The GPS system of claim 21, wherein said satellite position calculator calculates a plurality of correction values according to said plurality of almanac correction parameters respectively, and wherein said satellite position calculator calculates said plurality of positions by adding said plurality of correction values to said plurality of almanac-based coordinates respectively.