Multipath identification by comparing two different GNSS signals
A method for detecting a multipath effect in a GNSS receiver which is designed to receive different signals from a GNSS satellite and includes a parameter which is determined from directly received signals and has a substantially constant target value, including the steps receiving at least two mutually independent signals; determining a current parameter value from at least the first and the second signal; evaluating the parameter value in relation to the target value, and detecting a multipath effect when the parameter value has a deviation (ΔK) which deviates from the already known target value.
1. A method for detecting a multipath effect in a GNSS receiver which is designed to receive different signals from a GNSS satellite, comprising:
receiving at least two mutually independent signals, the signals including a first signal having a first frequency and a second signal having a second frequency different than the first frequency,
determining a phase shift between at least the first signal and the second signal,
evaluating the phase shift in relation to a target phase shift determined from an expected phase shift between the first signal and the second signal when directly received by the GNSS receiver, and
detecting a multipath effect when the evaluation indicates that the phase shift:
is less than a lower phase shift threshold that is less than the target phase shift, or
is greater than an upper phase shift threshold that is greater than the target phase shift.
2. The method according to claim 1 , wherein the phase shift is caused in part by atmospherically induced error in the signals.
3. The method according to claim 2 , wherein the target shift is newly determined after expiry of a predefined period, upon the occurrence of a predefined event or upon environmental changes.
4. The method according to claim 1 , further comprising:
detecting the multipath effect when the evaluation indicates that the phase shift is less than the lower phase shift threshold or greater than the upper phase shift threshold within a predefined time period.
5. The method according to claim 4 , wherein a change in the phase shift over time indicates a trend.
6. The method according to claim 4 , wherein the lower phase shift threshold is set in relation to a measured value from the first and/or second signal.
7. The method according to claim 4 , wherein the upper phase shift threshold is set in relation to the signal strength of the first and/or the second signal.
8. The method according to claim 1 , wherein the signals differ in terms of their carrier frequency.
9. The method according to claim 1 , wherein a GNSS L 1 signal and an L 2 or L 5 signal or other combinations of the carrier frequencies are compared with one another.
10. The method according to claim 1 , wherein the signals differ in terms of their modulation frequency.
11. The method according to claim 1 , wherein a C/A signal and P/Y signal are compared with one another.
12. The method according to claim 1 , wherein, after detecting a multipath effect, the received GNSS signals are marked as erroneous.
13. A system for a motor vehicle, having a receiver for receiving satellite signals for determining an actual position and for implementing a method according to claim 1 , wherein the receiver is designed to receive and to process signals of different frequencies.
14. The method according to claim 5 , wherein the lower phase shift threshold is set in relation to a measured value from the first and/or second signal.