System and method for compensating for scintillation and for facilitation of long-baseline RTK
The system and method facilitates Real-Time-Kinematic (RTK) GNSS with long baseline between a rover receiver and a base station receiver, even in the presence of scintillation or ionospheric disturbances that spatially fluctuate. Residual atmospheric errors can be estimated by a dual error model in a filter to promote efficient fixing or resolution of carrier phase ambiguities.
1. A system for-a estimating a position by a rover receiver in wireless communication with a base station receiver at a known location, the rover receiver and the base station receiver capable of receiving a plurality of Global Navigation Satellite System (GNSS) signals from GNSS satellites, the system comprising:
a measurement module configured to obtain initial code pseudo-range measurements and initial carrier phase measurements from the signals transmitted by GNSS satellites;
a wireless communications device associated with the rover receiver and the base station receiver, the wireless communications device configured to receive satellite orbit and clock corrections from an augmentation system;
a correction data estimator configured to generate measurement range errors and atmospheric related aiding data based on the known location of the base station receiver, with the aid of satellite orbit and clock corrections from the augmentation system;
a wireless link for sending the range errors and aiding information to the rover receiver;
the measurement module configured to use the range errors and the aiding information from base station receiver to correct the initial code pseudo-range measurements and the initial carrier phase measurements to mitigate errors in the signal, to result in corrected code pseudo-range measurements and corrected carrier phase measurements;
an atmospheric modeling module configured to estimate the residual of atmosphere delay with a dual error model that is configured to apply a preset error model before ambiguities are fixed or resolved, and to apply an adaptive error model after ambiguities are fixed or resolved; and
an ambiguity resolution module configured to conduct ambiguity resolution to fix carrier phase ambiguities for qualified or eligible ambiguities,
wherein the adaptive error model has a system or software instructions of the atmospheric modeling module to predict ionospheric activity level for each measurement epoch by epoch, and
wherein the system to predict ionosphere activity level is based on the time-differenced Geometry-Free (TDGF) for each satellite in accordance with the following equation:
Δ
L
ij
=
(
L
ij
t
-
L
ij
k
)
/
(
t
-
k
)
=
Δ
d
.
ion
f
i
2
-
d
ion
.
f
j
2
+
Δσ
ij
where the carrier phase measurements for frequency i and j at time t, L ij t , and carrier phase measurements for frequency i and j at time k, L ij k , are differenced, and where the dot above the Δ{dot over (d)} ion indicates a time derivative or a change rate in ionospheric error term between time t and k; where the dot above indicates a time derivative or change in ionospheric delay between time t and k; f i is measurement frequency i; f j is measurement frequency j; where Δσ ij is the change in measurement error for frequencies i and j at between t and at time k.
2. The system of claim 1 wherein the ambiguity resolution module is configured iteratively resolve the carrier phase ambiguities for a threshold number of satellite signals, satellite channels or satellites to provide a reliable position estimate.
3. The system of claim 1 wherein the base station receiver is configured to operate in a precise point positioning (PPP) mode with the aid of the augmentation system or single point Real-Time-Kinematic (RTK) positioning mode without the aid of the augmentation system to generate atmospheric-related aiding information.
4. The system of claim 3 wherein the atmospheric related aiding information from the base station receiver includes any of the following: tropospheric delay data, ionospheric delay data, and ambiguity resolution aiding data for carrier phase ambiguities resolution or fixing.
5. The system of claim 4 wherein the tropospheric delay data includes either zenith delay or slant delay for each carrier phase measurement of a satellite signal between the base station receiver or the rover receiver and a respective satellite.
6. The system of claim 4 wherein the ionospheric delay data includes either zenith delay or slant delay for each measurement.
7. The system of claim 1 wherein range errors associated with real-time-kinematic (RTK) processing and troposphere related aiding information are generated at the rover receiver based on the received raw measurements from base station receiver, the augmentation information and the known location in two or three dimensional coordinates.
8. The system of claim 1 wherein the measurement module is configured to correct pseudo-range or code phase measurements and carrier phase measurements by applying the range errors and slant atmospheric delay of base station receiver to adjust or correct code phase measurements and carrier phase measurements of the rover receiver.
9. The system of claim 8 wherein the atmospheric modeling module is configured to obtain the slant atmospheric delay from an estimated slant delay of the base station receiver for each code phase or carrier phase measurement in the aiding information.
10. The system of claim 8 wherein the atmospheric modeling module is configured to obtain slant atmospheric delay by multiplying base zenith atmospheric delay received from aiding information and the mapping function of each carrier phase and code phase measurement.
11. The system of claim 1 wherein the dual error model comprises a tropospheric delay estimation that applies the mapping function of rover receiver and rover troposphere zenith delay in accordance with the following equation:
Δ d trop =M R d tropR Z
where Δd trop is a change in tropospheric delay, M R is the rover mapping function, and d tropR Z is the rover tropospheric delay in the Zenith direction above the rover receiver.
12. The system of claim 1 wherein the dual error model comprises the prefixed error model for ionospheric delay that is configured to depend on the distance or baseline distance between the base station receiver and the rover receiver and the elevation angle of each code phase or carrier phase measurement.
13. The system of claim 1 wherein the system or the software instructions to predict ionosphere activity level is based on the averaged, time-differenced Geometry-Free (TDGF) over the carrier phase measurements in accordance with the following equation:
Δ
L
ij
_
=
(
∑
n
Δ
L
ij
)
/
n
where ΔL ij is the time-averaged (TA), time-differenced geometry-free (TDGF) carrier phase measurements at frequencies i and j (or frequency indexes i and j) for carrier phase measurements 1 through n, where n is positive integer value greater than 1.
14. The system of claim 1 wherein the system or the software instructions to predict ionosphere activity level is based on the weighted averaged time-differenced Geometry-Free (TDGF) over the carrier phase measurements in accordance with the following equations:
j
=
(
∑
n
w
n
×
Δ
L
ij
)
/
n
where Δ{tilde over (L)} ij is the time-averaged (TA), a time-differenced geometry-free (TDGF) carrier phase measurements at frequencies i and j (or frequency indexes i and j) for carrier phase measurements 1 through n, where n is a positive integer value greater than 1, and where w n is weight for the TDGF carrier phase measurements 1 through n.
15. The system of claim 14 wherein calculation of the TDGF is based on the corrected measurements or based on base measurements and rover measurements.
16. The system of claim 1 wherein a value to predict ionospheric activity level is based on converting the respective time-differenced Geometry-Free (TDGF) to a specific measurement frequency.
17. The system of claim 1 wherein the atmospheric modeling module is adapted to apply only an adaptive error model component, instead of both error models of the dual error model.
18. The system of claim 1 wherein the ambiguity resolution module is configured to include a quality control technique to minimize wrong fixes or resolutions of ambiguities for carrier phase of one or more carrier signals or channels.
19. The system of claim 18 wherein:
the ambiguity resolution module is configured to qualify or verify eligibility of an ambiguity candidate for an ambiguity search, and
the fixing carrier phase ambiguities is based on a value of time-differenced Geometry-Free (TDGF) for that measurement.
20. The system of claim 18 wherein:
the ambiguity resolution module is configured to qualify or verify eligibility of an ambiguity candidate for an ambiguity search, and
the fixing carrier phase ambiguities is based on the baseline length dependent cut off angle and the elevation of each measurement.
21. The system of claim 18 wherein:
the ambiguity resolution module is configured to qualify or verify eligibility of an ambiguity candidate for an ambiguity search, and
the fixing carrier phase ambiguities is based on time-differenced Geometry-Free (TDGF) testing or augmented baseline testing.
22. The system of claim 1 wherein the base station receiver is configured to send, via a wireless communications channel, raw phase measurements, raw code measurements and known location coordinates instead of range errors to the rover receiver along with aiding information.