1. A method for vector phase tracking a plurality of global positioning satellite carrier signals (4) comprising the steps of: - determining the input phase tracking error signals by a phase extraction unit (33) depending on trackable carrier signals (4) and oscillator signals associated with the trackable carrier signals (4);
- transforming the input phase tracking error signals in a spatial domain by a transformation unit (28, 41, 91, 101, 111) for generating spatial difference signals; - filtering the spatial difference signals by a filter (27, 42, 92, 102, 112);
- performing a back transformation of the spatial difference signals into output phase tracking error signals by a back transformation unit (30, 43, 93, 103, 113) for generating control signals for the oscillators (32) that are generating the oscillator signals
- generating output phase signals depending on the output phase tracking error signals by an output phase signal accumulator (31), c h a r a c t e r i z e d i n t h a t
- for a tracked satellite (2), the phase extraction unit (33) is generating input phase tracking error signals at different frequencies associated with the various carrier signals (4) of the tracked satellite (2) , - a multi-frequency estimation of the ionospheric error is performed and that
- the output phase tracking error signals at the output of the back transformation unit (30, 43, 93, 103, 113) are determined depending on the estimated ionospheric error.
2. The method according to Claim 1, wherein:
- a trackable signal of a single satellite (2) is tracked,
- the spatial difference signal is a range difference signal including clock offset error and tropospheric delay error,
- for the tracked satellite (2), the input phase tracking error signals supplied by the extraction unit (33) at different frequencies are linearly combined by a ionospheric error estimator (34) for determining the ionospheric error and wherein
- for determining a output phase tracking error signals at different frequencies associated with the various carrier signals (4) of the satellite (2), a multi-frequency phase estimation is
performed by the transformation unit (28) depending on the input phase tracking error signals at different frequencies, after the ionospheric error has been estimated in the ionospheric error estimator (34) and after the ionospheric error has been suppressed in the input phase tracking error signals at different frequencies.
3. The method according to Claim 1, wherein:
- for each tracked satellite (2), the extraction unit (33) is generating input phase tracking error signals at different frequencies associated with the various carrier signals (4) of each tracked satellite (2);
- for each tracked satellite (2), the input phase tracking error signals supplied by the extraction unit (33) at different frequencies are linearly combined by an ionospheric error estimator (34) for determining the ionospheric error and wherein
- for determining output phase tracking error signals associated with each tracked satellite (2), a multi-frequency phase estimation is performed by the transformation unit (41) depending on the input phase tracking error signals at different frequencies after the ionospheric error has been estimated in the ionospheric error estimator (34) and after the ionospheric error has been suppressed in the input phase tracking error signals at different frequencies.
4. The method according to Claim 2 or 3, wherein the input phase tracking error signals at different frequencies are linearly combined by the ionospheric error estimator (34) at the condition that the combination is geometry-free and preserving the ionospheric term.
5. The method according to Claim 4, wherein the ionospheric error is adjusted by the ionospheric error estimator (34) based on measurements of the phase tracking error signals at subsequent periods.
6. The method according to Claim 5, wherein the adjustment of the ionospheric error is performed by the ionospheric error estimator (34) using a polynom of first order as a regression curve.
7. The method according to Claim 1, wherein:
- the spatial difference signal is a range difference signal including clock offset error and tropospheric delay error, - for a tracked satellite (2), the phase extraction unit (33) is generating input phase tracking error signals at different frequencies associated with the various carrier signals (4) of the tracked satellite (2),
- a multi-frequency estimation of the ionospheric error is performed by the transformation unit (91) depending on the input phase tracking error signals supplied by the phase extraction unit,
- the ionospheric error is filtered by the filter (92) and wherein
- the filtered ionospheric error is transformed back into output phase tracking error signals by the back transformation unit (93) for generating control signals for the oscillators that are generating the oscillator signals.
8. The method according to Claim 1, wherein:
- for each tracked satellite (2), the extraction unit is generating input phase tracking error signals at different frequencies associated with the various carrier signals of each tracked satellite (2);
- a multi-frequency estimation of the position error of the actual position of the receiving device (5, 14), the receiver clock offset error, the tropospheric error and the ionospheric error is performed by the transformation unit (101, 111) depending on the input phase tracking error signal supplied by the extraction unit (33); - the position error, the receiver clock offset error, the tropospheric error and the ionospheric error are filtered by the filter (102, 112);
- the position error, the receiver clock offset error, the tropospheric error and the ionospheric error are transformed back into output phase tracking error by the back transformation unit (103, 113) for generating control signals for the oscillators (32) that are generat- ing the oscillator signals.
9. The method according to Claim 7 or 8, wherein the multi-frequency phase estimation is performed by the transformation unit (91,
101) with a weighted least-square estimation process that minimizes the quadratic norm of the differences of the measured phase tracking errors and the mapped unknown parameters wherein the unknown parameters are mapped into the space of the measured tracking errors by a mapping matrix.
10. The method according to Claim 7 or 8, wherein at least one projection unit (111) determines at least one of the unknown parameters including the position error, the receiver clock offset error, the tropospheric error and the ionospheric error by: - performing a projection operation that projects the measured phase tracking errors and a mapping matrix, which maps the unknown parameters into the measured phase tracking errors, on the subspace of the at least one unknown parameter chosen from the list comprising the position error, the receiver clock offset error, the tropospheric error and the ionospheric error; and by - performing the multi-frequency phase estimation with a weighted least-square estimation process that minimizes the quadratic norm of the differences of the projected phase tracking errors and the at least one mapped unknown parameter.
11. The method according to Claim 9 or 10, wherein the mapping matrix contains the unit vectors pointing from the tracked satellites to the receiver, the ratio between the frequencies of the carrier and a reference frequency and mapping coefficients for the tropospheric errors.
12. The method according to any one of Claims 1 to 11, wherein the ionospheric error is determined for each satellite individually and the tropospheric error is estimated in the direction of the zenith and projected into the actual slant direction of the tracked satellite.
13. The method according to any one of Claims 1 to 12, wherein the phase tracking errors supplied by the phase extractors are verified by a weighted sum of squared error test statistics that is computed from the range residuals and the inverse weighting matrix and wherein a subset of all measurements is selected whose
associated weighted sum of squared error test statistics is below a predefined threshold value.
14. The method according to any one of Claims 1 to 13, wherein upon initialization the phases of the carrier signals (4) are tracked individually and wherein the operation is switched into vector phase tracking once the number of locked phases is sufficient for vector phase tracking.
15. The method according to any one of Claims 1 to 14, wherein the ionospheric dispersion within the frequency band of a particular carrier signal (4) is corrected before the vector phase tracking is performed.
16. The method according to Claim 15, wherein the ionospheric dispersion within the frequency band of a particular carrier signal is corrected using a compensation unit (220) by:
- estimating the total electron content by combining code measurement from at least two frequencies,
- determining the ionospheric delays for a number of frequencies within the frequency band, - transforming the ionospheric delay into phase shifts in the frequency domain,
- applying the conjugate of the phase shifts to associated frequency components of the received signal.
17. The method according to Claim 15, wherein the ionospheric dispersion within the frequency band of a particular carrier signal is corrected by:
- estimating the total electron content by combining code measurement from at least two frequencies,
- retrieving the phase shift from a look-up table containing the phase shift dependent on the total electron content.
18. The method according any one of the Claims 1 to 17, wherein:
- the clock difference signal is filtered with filter parameters optimized to the oscillator characteristics and/or that
- the tropospheric error signal is filtered with filter parameters optimized to atmospheric conditions and/or that - the ionospheric error signal is filtered with filter parameters optimized to ionospheric activity, and/or that
- the position difference or range difference signal is filtered with filter parameters optimized to receiver dynamics.
19. A device for global satellite navigation adapted for tracking a plurality of global positioning satellite signals c h a r a c t e r i z e d i n t h a t the device (5, 14) is arranged for executing a method according to any one of the Claims 1 to 18.
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