Fast reacquisition of a GPS signal

• US 20040220734A1
• Filed: 01/18/2004
• Published: 11/04/2004
• Est. Priority Date: 12/13/2001
• Status: Active Grant

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: SIRF Technology Incorporated (Qualcomm, Inc.)
• Inventors: Gronemeyer, Steven A.
• Granted Patent: US 7,190,307 B2
• Time in Patent Office: Days
• US Class Current: 701/214
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence
• CPC Class Codes: G01S 19/34 Power consumption
• CPC Class Codes: G01S 19/42 Determining position

Abstract

Upon reception of four GPS signals from GPS satellites and determining four pseudo ranges, along with ephemeris data previously stored in the GPS receiver, the location of the GPS receiver and real time clock time error is determined. The GPS receiver is in possession of four pseudo ranges and determines four unknown coordinate values (x, y, x, and time) identifying the location of the GPS receiver and real time clock error. The process of solving for four pseudo range formulas simultaneously with each pseudo range formula having an unknown “x”, “y” “z”, and time coordinates of the GPS receiver, results in identification of the coordinates and time of the GPS receiver. In a similar process, the GPS receiver receiving four GPS signals from four GPS satellites is able to determine four pseudo ranges. Using the four pseudo ranges, four pseudo range equations unknown values for “x”, “y”, “z” and time can be solved for simultaneously. The resulting values are then used to verify that the calculated positions of the GPS satellites are within 0.5 ms of the previous solution. If the GPS satellites are within 0.5 ms range of the prior solution then the real time clock error is estimated. Thus, using ephemeris data, the location of the GPS receiver is determined in a fraction of the time it takes to acquire the GPS satellites using conventional approaches.

Claims

1. An apparatus, comprising:

a receiver in receipt of a signal having a plurality of pseudo noise codes with each of the pseudo noise codes of the plurality of pseudo noise codes originate from a GPS transmitter;

a clock with an error of less than 0.5 ms relative to a GPS time; and

a decoder connected to the receiver and the clock that identifies four pseudo range equations for at least four GPS transmitters from the plurality of GPS transmitters, and determines a location of the receiver by simultaneously solving the four pseudo range equations.

2. The apparatus of claim 1, wherein a plurality of chips make up each pseudo noise code in the plurality of pseudo noise code and the plurality of chips is offset between 511 chips before a pseudo noise code boundary and 512 chips after the pseudo noise code boundary.

3. The apparatus of claim 2, wherein each of the pseudo range (PR) equations when the pseudo noise code boundary is less than 512 and an estimated range is R, a chip from the plurality of chips transmitted at T time C_k is received at the receiver as a chip C_j that is offset from an expected chip Ĉ

_j, and L_chip is a distance that the signal propagates in one chip time (c/1.023e6=293.0522561 m), is;

PR=R−

(C_j−

Ĉ

_j)L_chip.

4. The apparatus of claim 2, wherein each of the pseudo range (PR) equations when the pseudo noise code boundary is greater than 511 and has an estimated range R, a chip from the plurality of chips transmit at T time C_k, received at the receiver as a chip C_j that is offset from an expected chip Ĉ

_j, and L_chip being a distance that the signal propagates in one chip time (c/1.023e6=293.0522561 m), is;

PR=R+└

1023−

(C_j−

Ĉ

_j)┘

L_chip.

5. The apparatus of claim 1, wherein a time error in the clock is identified and corrected upon the determination of the location of the receiver is correct.

6. The apparatus of claim 1, further comprising:

a temperature sensor attached to a crystal in the clock to take heat measurements of the crystal and reports heat measurements to the decoder to enable the decoder to adjust the clock readings in response to heat measurements.

7. A method, comprising:

receiving at a receiver a signal generated at a plurality of GPS transmitters;

identifying at least four pseudo noise codes in the signal at the receiver;

calculating time with a clock having an error of less than 0.5 ms relative to a GPS time;

deriving at least four pseudo range equations from each of the at least four pseudo noise codes; and

locating the receiver by solving the at least four pseudo range equations simultaneously.

8. The method of claim 7, further comprises:

solving each of the at least four pseudo range equations when the pseudo noise code boundary is less than 512 and an estimated range is R, a chip from the plurality of chips transmitted at T time C_k is received at the receiver as a chip C_j that is offset from an expected chip Ĉ

_j, and L_chip is a distance that the signal propagates in one chip time (c/1.023e6=293.0522561 m), is;

PR=R−

(C_j−

Ĉ

_j)L_chip.

9. The method of claim 7, further comprising:

solving each of the pseudo range (PR) equations when the pseudo noise code boundary is greater than 511 and has an estimated range R, a chip from the plurality of chips transmit at T time C_k, received at the receiver as a chip C_j that is offset from an expected chip Ĉ

_j and L_chip being a distance that the signal propagates in one chip time (c/1.023e6=293.0522561 m), is;

PR=R+└

1023−

(C_j−

Ĉ

_j)┘

L_chip.

10. An apparatus, comprising:

means for receiving at a receiver a signal generated at a plurality of GPS transmitters;

means for identifying at least four pseudo noise codes in the signal at the receiver;

means for calculating time with a clock having an error of less than 0.5 ms relative to a GPS time;

means for deriving at least four pseudo range equations from each of the at least four pseudo noise codes; and

means for locating the receiver by solving the at least four pseudo range equations simultaneously.

11. The apparatus of claim 10, further comprises:

means for solving each of the at least four pseudo range equations when the pseudo noise code boundary is less than 512 and an estimated range is R, a chip from the plurality of chips transmitted at T time C_k is received at the receiver as a chip C_j that is offset from an expected chip Ĉ

_j, and L_chip is a distance that the signal propagates in one chip time (c/1.023e6=293.0522561 m), is;

PR=R−

(C_j−

Ĉ

_j)L_chip.

12. The apparatus of claim 10, further comprising:

means for solving each of the pseudo range (PR) equations when the pseudo noise code boundary is greater than 511 and has an estimated range R, a chip from the plurality of chips transmit at T time C_k, received at the receiver as a chip C_j that is offset from an expected chip Ĉ

_j, and L_chip being a distance that the signal propagates in one chip time (c/1.023e6=293.0522561 m), is;

PR=R+└

1023−

(C_j−

Ĉ

_j)┘

L_chip.

13. A machine-readable signal bearing medium containing instructions that cause a controller to perform a method for fast satellite acquisition, the method comprising:

receiving at a receiver a signal generated at a plurality of GPS transmitters;

identifying at least four pseudo noise codes in the signal at the receiver;

calculating time with a clock having an error of less than 0.5 ms relative to a GPS time;

deriving at least four pseudo range equations from each of the at least four pseudo noise codes; and

locating the receiver by solving the at least four pseudo range equations simultaneously.

14. The method of claim 13, further comprises:

solving each of the at least four pseudo range equations when the pseudo noise code boundary is less than 512 and an estimated range is R, a chip from the plurality of chips transmitted at T time C_k is received at the receiver as a chip C_j that is offset from an expected chip Ĉ

_j, and L_chip is a distance that the signal propagates in one chip time (c/1.023e6=293.0522561 m), is;

PR=R−

(C_j−

Ĉ

_j)L_chip.

15. The method of claim 13, further comprising:

solving each of the pseudo range (PR) equations when the pseudo noise code boundary is greater than 511 and has an estimated range R, a chip from the plurality of chips transmit at T time C_k, received at the receiver as a chip C_j that is offset from an expected chip Ĉ

_j, and L_chip being a distance that the signal propagates in one chip time (c/1.023e6=293.0522561 m), is;

PR=R+└

1023−

(C_j−

Ĉ

_j)┘

L_chip.