Method of improving the determination of the attitude of a vehicle with the aid of satellite radionavigation signals

• US 20050043887A1
• Filed: 12/17/2002
• Published: 02/24/2005
• Est. Priority Date: 12/20/2001
• Status: Active Grant

• Current Assignee: Thales SA
• Original Assignee: T Hales
• Inventors: Revol, Marc, Chenus, Marc
• Granted Patent: US 7,454,289 B2
• Time in Patent Office: Days
• US Class Current: 701/213
• CPC Class Codes: G01S 19/22 Multipath-related issues
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence
• CPC Class Codes: G01S 19/44 Carrier phase ambiguity resolution; Floating ambiguity; LAMBDA [Least-squares AMBiguity Decorrelation Adjustment] method
• CPC Class Codes: G01S 19/53 Determining attitude

Abstract

The method in accordance with the invention, implemented with the aid of at least one pair of antennas, consists in performing: a normalized spectral analysis before intercorrelation of the demodulated signals (I, Q), by the code and the carrier, a phase coherence resetting of the signals before recombination, a phase offset measurement carried out by a true intercorrelation of the homologous satellite pathways by interferometry of the two signals arising from one and the same satellite and received respectively by a pair of antennas, then in performing a reduction of the initial ambiguity removal search domain for the determination of attitude of a vehicle by interferometric GPS measurement and implementing a statistical test for the selection of the ambiguity.

Claims

1. A method of improving the determination of the attitude of a vehicle with the aid of radionavigation signals, implemented with the aid of at least one pair of antennas (22, 23, 23A), characterized in that it consists in producing a carrier phase loop (PLL) by summing the two signals arising from a pair of antennas half a wavelength apart, these signals being rendered coherent before summation, in carrying out a measurement of phase offset with regard to the signals arising from a pair of antennas several wavelengths apart, going via the frequency domain, then in performing a reduction of the initial ambiguity removal search domain for the determination of attitude of a vehicle by interferometric GPS measurement and implementing a statistical test for the selection of the ambiguity.

2. The method as claimed in claim 1, characterized in that in order to produce a carrier phase loop, the phase offset is calculated by interferometry (normalized intercorrelation 21) between homologous signals, that is to say those that arise from one and the same satellite (S1_0 and S1b_0) and are delivered respectively by the two antennas (22, 23) of one and the same pair of antennas, these antennas being less than λ

/2 apart, and then filtered, demodulated and despread (24, 25), a coherence reset is carried out by multiplication (26) of one of the signals (S1_0) by the relative delay (27) evaluated by the above normalized intercorrelation, the two signals previously being delayed (28, 29) in such a way as to compensate for the delay introduced by the intercorrelation (20 ms in the present example), and that the phase loop PLL is slaved (30) on the basis of the vector addition (31) of the two coherence-reset antenna signals.

3. The method as claimed in claim 1 or 2, characterized in that in order to carry out a measurement of the phase offset, an intercorrelation is carried out going via the frequency domain.

4. The method as claimed in claim 3, characterized in that in order to carry out the intercorrelation processing, after Fourier transformation by FFT of the “

I” and

“

Q”

correlation outputs, a normalization of the spectrum is performed by centering and normalization of the standard deviation of the background noise, by sliding windowing, followed by a detection of the noise spikes, and identification of the carrier, followed by the suppression of the noise spikes in the frequency domain of the two signals by frequency excision by setting to zero or to the level of the background noise of the spectral amplitudes at the frequencies detected, followed by the complex multiplication of the filtered conjugate spectra (intercorrelation) and the return to temporal by inverse DFT considered at zero, so as to obtain the intercorrelation between the two signals and hence their relative phase offset.

5. The method as claimed in any one of the preceding claims, characterized in that in order to reduce the search domain, with partial aid, for the preselection of the domain of potential ambiguities, one defines a first domain of ambiguity search by two particular hypotheses regarding the aid heading, and using the other known aids, then this domain is widened with the uncertainties regarding the other aid parameters.

6. The method as claimed in claim 5, characterized in that, if no heading aid is available, the particular hypotheses are:

aid heading equal to the azimuth of the satellite, that is to say maximum of the scalar product of projection of the antenna baseline onto this direction, and aid heading equal to the azimuth of the satellite +180°

, that is to say the projection minimum.

7. The method as claimed in one of the preceding claims, characterized in that in order to improve the measurement of phase offset, simultaneous use is made of closely spaced antennas and of distantly spaced antennas making it possible to carry out accurate measurements of simple phase offset, as opposed to double differences, that are unambiguous and unaffected by RF phase biases and are initialized on the basis of the closely spaced antennas, or of any other inertial means of attitude calculation.

8. The method as claimed in one of the preceding claims, characterized in that in order to increase the robustness of the ambiguities selection test, the search domain is widened by a few extra ambiguities.

9. The method as claimed in claim 8, characterized in that the extra ambiguities are:

one or two ambiguities to compensate for the truncations due to the integer part calculations and one ambiguity for the measurement noise regarding the fractional part of the interferometric phase.

10. The method as claimed in one of the preceding claims, characterized in that in order to improve the integrity check, the test is applied over several recurrences of the attitude measurements.