Method of detecting interference in a satellite radio-navigation signal by detecting a deformation of the correlation function
A method of detecting interference in a satellite radio-navigation signal, calculates an item of information representative of the slope of the correlation function correlating the said signal with a local spreading code. The correlation function has substantially the theoretical form of an isosceles triangle, with the slope being estimated on any one of the equal-length sides of the isosceles triangle. The method further includes comparing the item of information with a detection threshold configured at least as a function of a target signal-to-noise ratio.
1. Method, implemented by a radio-navigation signals receiver comprising a correlator and an interference detector, for detecting interference in a received satellite radio-navigation signal, comprising the steps of:
calculating, at the correlator, a correlation function correlating the received satellite radio-navigation signal with a local spreading code, the said correlation function having substantially a theoretical form of an isosceles triangle,
calculating, at the interference detector, an item of information representative of a slope of the correlation function, the said slope being estimated on any one of the equal-length sides of the said isosceles triangle; and
comparing, at the interference detector, the said item of information with a detection threshold configured at least as a function of a target signal-to-noise ratio and producing, from said comparison, an information on the presence or absence of interference in the received satellite radio-navigation signal to thereby improve performance of the receiver.
2. Method for detecting interference according to claim 1 , in which the said item of information representative of the slope is calculated at least on a basis of a first measurement of the maximum of the correlation function at a first temporal position, of a second measurement of the correlation function at a second temporal position advanced relative to the first temporal position by a smaller duration than a duration of a slot of the spreading code and of a third measurement of the correlation function at a third temporal position delayed relative to the first temporal position by a smaller duration than the duration of a slot of the spreading code.
3. Method for detecting interference according to claim 2 , in which a time offset between the first measurement and the second measurement and a time offset between the first measurement and the third measurement are substantially equal in absolute value.
4. Method for detecting interference according to claim 3 , in which the said item of information representative of the slope is calculated on a basis of a ratio of the energy of the first measurement to a sum of the respective energies of the second and third measurements.
5. Method for detecting interference according to claim 2 , in which the said item of information representative of the slope is calculated on a basis of a number greater than three of measurements of the correlation function, taken according to various time abscissae, by performing a linear regression.
6. Method for detecting interference according to claim 1 , in which the said item of information representative of the slope is calculated at least on a basis of a time offset and of a length of a slot of the spreading code.
7. Method for detecting interference according to claim 1 , in which the said detection threshold is configured as a function of a ratio of the powers of the signal and of the interference.
8. Method for detecting interference according to claim 1 comprising a step of receiving, at the radio-navigation signals receiver, a satellite radio-navigation signal.
9. Method for detecting interference according to claim 1 comprising a step of undertaking corrective processing to the satellite radio-navigation signal when a presence of interference in the received satellite radio-navigation signal is detected.
10. Method for detecting interference according to claim 1 comprising a step of excluding a measurement performed on a received satellite radio-navigation signal when a presence of interference in the received satellite radio-navigation signal is detected.
11. Device for receiving satellite radio-navigation signals comprising:
a correlator for calculating a correlation function correlating the received satellite radio-navigation signal with a local spreading code, the said correlation function having substantially a theoretical form of an isosceles triangle,
an interference detector for calculating an item of information representative of a slope of a correlation, the said slope being estimated on any one of the equal-length sides of the said isosceles triangle; and
the interference detector being further configured to compare the said item of information with a detection threshold configured at least as a function of a target signal-to-noise ratio and for producing, from said comparison, an information on the presence or absence of interference in the received satellite radio-navigation signal to thereby improve performance of the device.
12. Device for receiving satellite radio-navigation signals according to claim 11 , in which the said item of information representative of the slope is calculated at least on a basis of a first measurement of the maximum of the correlation function at a first temporal position, of a second measurement of the correlation function at a second temporal position advanced relative to the first temporal position by a smaller duration than a duration of a slot of the spreading code and of a third measurement of the correlation function at a third temporal position delayed relative to the first temporal position by a smaller duration than the duration of a slot of the spreading code.
13. Device for receiving satellite radio-navigation signals according to claim 12 , in which a time offset between the first measurement and the second measurement and a time offset between the first measurement and the third measurement are substantially equal in absolute value.
14. Device for receiving satellite radio-navigation signals according to claim 13 , in which the said item of information representative of the slope is calculated on a basis of a ratio of the energy of the first measurement to a sum of the respective energies of the second and third measurements.
15. Device for receiving satellite radio-navigation signals according to claim 12 , in which the said item of information representative of the slope is calculated on a basis of a number greater than three of measurements of the correlation function, taken according to various time abscissae, by performing a linear regression.
16. Device for receiving satellite radio-navigation signals according to claim 11 , in which the said item of information representative of the slope is calculated at least on a basis of a time offset and of a length of a slot of the spreading code.
17. Device for receiving satellite radio-navigation signals according to claim 11 , in which the said detection threshold is configured as a function of a ratio of the powers of the signal and of the interference.
18. Device for receiving satellite radio-navigation signals according to claim 11 , said device being configured to undertake corrective processing to the satellite radio navigation signal when a presence of interference in the received satellite radio-navigation signal is detected.
19. Device for receiving satellite radio-navigation signals according to claim 11 , said device being configured to exclude a measurement performed on a received satellite radio-navigation signal when a presence of interference in the received satellite radio-navigation signal is detected.