System and method for GPS navigation before signal bit synchronization

• US 7,064,709 B1
• Filed: 03/17/2005
• Issued: 06/20/2006
• Est. Priority Date: 03/17/2005
• Status: Expired due to Fees

• Current Assignee: Qualcomm, Inc.
• Original Assignee: RF Micro Devices Incorporated (Qorvo, Inc.)
• Inventors: Norman, Charles, Weisenburger, Shawn
• Primary Examiner(s): PHAN, DAO LINDA
• Application Number:
  US11/082,276
• Time in Patent Office: 460 Days
• Field of Search: 342/357.01, 342/357.06, 342/357.12, 342/357.15, 701/207, 701/213, 701/215
• US Class Current: 342/357.62
• CPC Class Codes: G01S 19/24 Acquisition or tracking or demodulation of signals transmitted by the system synchronisation aspects of direct sequence spread spectrum modulation H04B1/7073
• CPC Class Codes: G01S 19/42 Determining position

Abstract

A system and method are provided for determining a position of a Global Positioning System (GPS) receiver prior to bit and frame synchronization. As such, the time-to-first-fix is substantially reduced. More specifically, pseudoranges to five GPS satellites are measured by correlating locally generated Pseudo-Random Number (PRN) codes with signals received from the GPS satellites. After correlation, the pseudorange measurements are correct with an unknown integer number of milliseconds error, which is different for each of the pseudorange measurements. Using the measurements of the pseudoranges and a mathematical model where each of the pseudorange measurements is forced to have a common channel time error, the user position and the common channel time error are determined prior to bit and frame synchronization.

Claims

1. A method for computing a user parameter of a Global Positioning System (GPS) receiver comprising:

providing a mathematical model of pseudoranges from a number of GPS satellites, wherein each of the pseudoranges is forced to have a common channel time error, the common channel time error being an integer number of milliseconds; and

computing a user parameter based on the mathematical model of the pseudoranges, measurements of the pseudoranges, a known estimate of user position, and known positions of the number of GPS satellites.

2. The method of claim 1 wherein the user parameter is the user position.

3. The method of claim 1 wherein the user parameter is a user clock error of the GPS receiver.

4. The method of claim 1 further comprising:

measuring the pseudoranges from the number of GPS satellites by correlating locally generated Pseudo-Random Number (PRN) codes corresponding to each of the number of GPS satellites with signals received by the GPS receiver to provide the measurements of the pseudoranges.

5. The method of claim 1 wherein the number of GPS satellites is at least five GPS satellites.

6. The method of claim 1 wherein computing the user parameter comprises computing the user parameter prior to bit and frame synchronization.

7. The method of claim 1 wherein providing the mathematical model of the pseudoranges comprises providing an offset term for each of the pseudoranges in order to force each of the pseudoranges to have the common channel time error.

8. The method of claim 7 further comprising computing the offset term for each of the pseudoranges based on the known positions of the number of GPS satellites, the known estimate of the user position, and the measurements of the pseudoranges.

9. The method of claim 7 wherein providing the mathematical model comprises providing a mathematical model for each of the pseudoranges according to the following equation:

R_i(t)=√

{square root over (((X_Si−

X_U)²+(Y_Si−

Y_U)²+(Z_Si−

Z_U)²))}{square root over (((X_Si−

X_U)²+(Y_Si−

Y_U)²+(Z_Si−

Z_U)²))}{square root over (((X_Si−

X_U)²+(Y_Si−

Y_U)²+(Z_Si−

Z_U)²))}+dT+m_c(c−

{dot over (φ

)}₁)+K_i,

wherein R_i is the pseudorange;

X_Si, Y_Si, and Z_Si define a known position of a corresponding one of the number GPS satellites;

X_U, Y_U, and Z_U define the user position;

dT is an error of a clock of the GPS receiver;

m_c is the common channel time error;

c is the speed of light;

{dot over (φ

)}_i is a known doppler error; and

K_i is an offset term used to mathematically force the pseudorange R_i to have the common channel time error (m_c).

10. The method of claim 9 further comprising computing the offset term (K_i) for each of the pseudoranges based on the known estimate of the user position, the known positions of the number of GPS satellites, and the measurements of the pseudoranges.

11. The method of claim 10 wherein computing the offset term (K_i) comprises computing a difference of an actual channel time error for the pseudoranges and the common channel time error (m_c), wherein the common channel time error (m_c) is the actual channel time error for one of the pseudoranges.

12. The method of claim 11 wherein computing the difference of the actual channel time error for the pseudoranges and the common channel time error (m_c) comprises computing the difference based on the following equation:

13. A Global Positioning System (GPS) receiver that computes a user parameter, the GPS receiver comprising:

a processor adapted to compute a user parameter based on measurements of pseudoranges for a number of GPS satellites, known positions of the number of GPS satellites, a known estimate of user position, and a mathematical model of the pseudoranges that forces each of the pseudoranges to have a common channel time error, the common channel time error being an integer number of milliseconds.

14. The GPS receiver of claim 13 wherein the user parameter is the user position.

15. The OPS receiver of claim 13 wherein the user parameter is a user clock error of the GPS receiver.

16. The GPS receiver of claim 13 further comprising:

a correlator adapted to provide the measurements of the pseudoranges from the number of GPS satellites by correlating locally generated Pseudo-Random Number (PRN) codes corresponding to the number of GPS satellites with signals received by the GPS receiver.

17. The GPS receiver of claim 13 wherein the number of GPS satellites is at least five GPS satellites.

18. The GPS receiver of claim 13 wherein the processor is further adapted to compute the user parameter prior to bit and frame synchronization.

19. The GPS receiver of claim 13 wherein the mathematical model of the pseudoranges comprises an offset term for each of the pseudoranges in order to force each of the pseudoranges to have the common channel time error.

20. The GPS receiver of claim 19 wherein the processor is further adapted to compute the offset term for each of the pseudoranges based on the known positions of the number GPS satellites, the known estimate of the user position, and the measurements of the pseudoranges.

21. The GPS receiver of claim 19 wherein the mathematical model comprises a mathematical model for each of the pseudoranges defined by the following equation:

R_i(t)=√

{square root over (((X_Si−

X_U)²+(Y_Si−

Y_U)²+(Z_Si−

Z_U)²))}{square root over (((X_Si−

X_U)²+(Y_Si−

Y_U)²+(Z_Si−

Z_U)²))}{square root over (((X_Si−

X_U)²+(Y_Si−

Y_U)²+(Z_Si−

Z_U)²))}+dT+m_c(c−

{dot over (φ

)}₁)+K_i,

wherein R_i is the pseudorange;

X_Si, Y_Si, and Z_Si define a known position of a corresponding one of the number of GPS satellites;

X_U, Y_U, and Z_U define the user position;

dT is an error of a clock of the GPS receiver;

m_c is the common channel time error, c is the speed of light;

{dot over (φ

)}_i is a known doppler error; and

K_i is an offset term used to mathematically force the pseudorange R_i to have the common channel time error (m_c).

22. The GPS receiver of claim 21 wherein the processor is further adapted to compute the offset term (K_i) for each of the pseudoranges based on the known estimate of the user position, the known positions of the number of GPS satellites, and the measurements of the pseudoranges.

23. The GPS receiver of claim 22 wherein the processor is further adapted to compute the offset term (K_i) based on a difference of an actual channel time error for the pseudoranges and the common channel time error (m_c), wherein the common channel time error (m_c) is the actual channel time error for one of the pseudoranges.

24. The GPS receiver of claim 23 wherein the processor is further adapted to compute the offset term (K_i) based on computing the difference of the actual channel time error for the pseudoranges and the common channel time error (m_c) based on the following equation: