REMOVING BIASES IN DUAL FREQUENCY GNSS RECEIVERS USING SBAS

• US 20100231443A1
• Filed: 03/11/2009
• Published: 09/16/2010
• Est. Priority Date: 03/11/2009
• Status: Active Grant

• Current Assignee: Hemisphere GNSS(USA) Incorporated
• Original Assignee: Hemisphere GPS LLC (Kubota Corporation)
• Inventors: Whitehead, Michael L.
• Granted Patent: US 8,085,196 B2
• Time in Patent Office: Days
• US Class Current: 342/357.230
• CPC Class Codes: G01S 19/072 Ionosphere corrections
• CPC Class Codes: G01S 19/32 Multimode operation in a single same satellite system, e.g. GPS L1/L2
• CPC Class Codes: G01S 19/40 Correcting position, velocity or attitude

Abstract

A method for removing biases in dual frequency GNSS receivers circumvents the need for ionosphere corrections by using L2(P) in combination with either L1(P) or L1(C/A) to form ionosphere-free ranges. A table of biases is stored in microprocessor controller memory and utilized for computing a location using corrected ionosphere-free pseudo ranges. A system for removing biases in dual frequency GNSS receivers includes a dual frequency GNSS receiver and a controller microprocessor adapted to store a table of bias values for correcting pseudo ranges determined using L2(P) in combination with either L1(P) or L1(C/A).

Claims

1. A method of determining the location of a global navigation satellite system (GNSS) receiver including a receiver memory, which method includes the steps of:

computing ionosphere-free pseudo ranges using code and carrier phases of GNSS signals;

correcting said ionosphere-free pseudo ranges using satellite-based augmentation system (SBAS) clock and orbit corrections;

providing a microprocessor controller connected to said GNSS receiver;

computing a table of biases to further correct said pseudo ranges;

uploading into said receiver memory biases; and

computing locations of said receiver using said corrected pseudo ranges and said biases.

2. The method of claim 1, which includes the additional step of:

carrier-smoothing said pseudo ranges at a smoothing interval of greater than one half hour.

3. The method of claim 1 wherein the troposphere is estimated as the state of a Kalman filter.

4. The method of claim 1 wherein said GNSS receiver comprises a dual frequency receiver using one of:

L2(P) and L1(P); and

L2(P) and L1(C/A).

5. The method of claim 4 wherein the SBAS-corrected L1(C/A) pseudo range =

[R−

(T_SV−

τ

_GD)−

ISC_L1/CA]+T_SV^GPS−

τ

_GD^GPS+[T_SV−

T_SV^GPS+ISC_L1/CA−

(τ

_GD−

τ

_GD^GPS)]=R

wherein;

the GPS broadcast clock model=T_SV^GPS;

the broadcast group-delay=τ

_GD^GPS;

the superscript “

GPS”

indicates that T_SV and τ

_GD^GPS are estimates provided by the GPS Control Segment rather than the true values;

the GPS navigation message, which is modulated on the GPS transmitted signals, contains coefficients of a time-based polynomial fitting T_SV^GPS;

the navigation message contains a single word providing the group-delay, τ

_GD^GPS;

each satellite sends its respective, satellite-specific values for the above quantities; and

the SBAS clock correction, T_SBAS, can be broken down into its individual constituents as follows;

T_SBAS=T_SV−

T_SV^GPS+ISC_L1/CA−

(τ

_GD−

τ

_GD^GPS).

6. The method of claim 5 wherein:

P<sub>iono—

free—

corrected</sub>^CA=K₁C₁−

K₂P₂+T_SV^GPS+T_SBAS+B<sub>ISC—

TGD</sub>.

7. The method of claim 6 wherein:

B<sub>ISC—

TGD</sub>=K₂ISC_L1/CA+(τ

_GD−

τ

_GD^GPS); and

P<sub>iono—

free—

corrected</sub>^CA=R

8. The method of claim 1, which includes the additional step of:

calibrating the biases using a Kalman filter or a least squares method to;

estimate and remove the effects of un-modeled troposphere errors and clock errors; and

to effectively time-average the data.

9. The method of claim 1, which includes the additional step of:

providing a separate B_TOTAL value for each of multiple GNSS satellites.

10. A method of determining the location of a global navigation satellite system (GNSS) receiver, which method includes the steps of:

computing ionosphere-free pseudo ranges using code and carrier phases of GNSS signals;

correcting said ionosphere-free pseudo ranges using satellite-based augmentation system (SBAS) clock and orbit corrections;

providing a microprocessor controller connected to said GNSS receiver;

storing in said microprocessor controller a table of pseudo range correction biases;

correcting said computed pseudo ranges using said biases;

carrier-smoothing said pseudo ranges at a smoothing interval of greater than one half hour;

estimating the troposphere as the state of a Kalman filter;

using either;

L2(P) and L1(P);

or L2(P) and L1(C/A);

said GNSS receiver comprising a dual frequency receiver;

correcting the L1(C/A) pseudo range according to the formula

[R−

(T_SV−

τ

_GD)−

ISC_L1/CA]+T_SV^GPS+[T_SV−

T_SV^GPS+ISC_L1/CA−

(τ

_GD−

τ

_GD^GPS)]=R

wherein;

the GPS broadcast clock model=T_SV^GPS;

the broadcast group-delay=τ

_GD^GPS;

the superscript “

GPS”

indicates that T_SV^GPS and τ

_GD^GPS are estimates provided by the GPS Control Segment rather than the true values;

the GPS navigation message, which is modulated on the GPS transmitted signals, contains coefficients of a time-based polynomial fitting T_SV^GPS;

the navigation message contains a single word providing the group-delay, τ

_GD^GPS;

each satellite sends its respective, satellite-specific values for the above quantities; and

the SBAS clock correction, T_SBAS, can be broken down into its individual constituents as follows;

T_SBAS=T_SV−

T_SV^GPS+ISC_L1/CA−

(τ

_GD−

τ

_GD^GPS)

P<sub>iono—

free—

corrected</sub>^CA=K₁C₁−

K₂P₂+T_SV^GPS+T_SBASB<sub>ISC—

TGD</sub>

B<sub>ISC—

TGD</sub>K₂ISC_L1/CA+(τ

_GD−

τ

_GD^GPS); and

P<sub>iono—

free—

corrected</sub>=R

calibrating the biases using a Kalman filter or a least squares method to;

estimate and remove the effects of un-modeled troposphere errors and clock errors; and

to effectively time-average the data; and

providing a separate B_TOTAL value for each of multiple GNSS satellites.

11. A GNSS receiver system for receiving signals from GNSS satellites, including at least one SBAS satellite, which receiver system includes:

a receiver including a nonvolatile memory adapted for storing a table of bias corrections for at least one GNSS satellite;

each bias correction including at least one of a group delay correction component and an inter-signal bias correction component; and

means to compute an ionosphere-free pseudo range using data broadcast in the SBAS signal as well as data in the bias correction table.

12. The GNSS receiver system of claim 11, which includes:

a Kalman filter adapted for estimating the troposphere as its state.

13. The system of claim 11, which includes:

said GNSS receiver comprising a dual frequency receiver using one of;

L2(P) and L1(P); and

L2(P) and L1(C/A).

14. The system of claim 11 wherein the L1(C/A) pseudo range is SBAS—

corrected according to the formula;

[R−

(T_SV−

τ

_GD)−

ISC_L1/CA]+T_SV^GPS−

τ

_GD^GPS+[T_SV−

T_SV^GPS+ISC_L1/CA−

(τ

_GD−

τ

_GD^GPS)]=R

wherein;

the GPS broadcast clock model=T_SV^GPS;

the broadcast group-delay=τ

_GD^GPS;

the superscript “

GPS”

indicates that T_SV^GPS and τ

_GD^GPS are estimates provided by the GPS Control Segment rather than the true values;

the GPS navigation message, which is modulated on the GPS transmitted signals, contains coefficients of a time-based polynomial fitting T_SV^GPS;

the navigation message contains a single word providing the group-delay, τ

_GD^GPS;

each satellite sends its respective, satellite-specific values for the above quantities; and

the SBAS clock correction, T_SBAS, can be broken down into its individual constituents as follows;

T_SBAS=T_SV−

T_SV^GPS+ISC_L1/CA−

(τ

_GD−

τ

_GD^GPS)

P<sub>iono—

free—

corrected</sub>^CA=K₁C₁−

K₂P₂+T_SV^GPS+T_SBAS+B<sub>ISC—

TGD</sub>

B<sub>ISC—

TGD</sub>=K₂ISC_L1/CA+(τ

_GD−

τ

_GD^GPS); and

P<sub>iono—

free—

corrected</sub>^CA=R

15. The system of claim 11, which includes means for calibrating the biases using either:

a Kalman filter or a least squares method to;

estimate and remove the effects of un-modeled troposphere errors and clock errors; and

to effectively time-average the data.

16. The method of claim 11, which includes means for providing a separate B_TOTAL value for each of multiple GNSS satellites.

17. A storage medium encoded with a machine-readable computer program code, the code including instructions for determining the location of a GNSS receiver, which method comprises the steps of:

computing ionosphere-free pseudo ranges using code and carrier phases of GNSS signals;

correcting said ionosphere-free pseudo ranges using satellite-based augmentation system (SBAS) clock and orbit corrections;

providing a microprocessor controller connected to said GNSS receiver;

storing in said microprocessor controller a table of pseudo range correction biases; and

correcting said computed pseudo ranges using said biases.

18. A computer data signal comprising code configured to cause a processor to implement a method for determining the location of a GNSS receiver, which method comprises the steps of:

computing ionosphere-free pseudo ranges using code and carrier phases of GNSS signals;

correcting said ionosphere-free pseudo ranges using satellite-based augmentation system (SBAS) clock and orbit corrections;

providing a microprocessor controller connected to said GNSS receiver;

storing in said microprocessor controller a table of pseudo range correction biases; and

correcting said computed pseudo ranges using said biases.