Method and device method for detecting frequency jumps of a navigation satellite's master clock
A method for detecting frequency jumps of a navigation satellite's master clock, comprising the steps of i) monitoring the master clock signal that is generated by a master clock onboard of the satellite for a frequency jump, and ii) signaling a detected frequency jump of the master clock signal.
1. A method for enhancing integrity performance of a global navigation satellite system that includes a plurality of navigation satellites, each of which has a master clock, said method comprising:
on board at least one of said satellites, monitoring a master clock signal generated by the master clock onboard said at least one of the satellites using a clock monitoring and control unit, to detect a frequency jump, wherein the monitoring comprises comparing a frequency of an untransmitted master clock signal with a frequency of an untransmitted backup clock signal; and
said at least one of the satellites signaling a detected frequency jump of said master clock signal.
2. The method of claim 1 , wherein the backup clock signal is generated by a backup clock onboard said at least one of the satellites, and wherein said monitoring comprises:
comparing a detected frequency jump with a threshold; and
if the detected frequency jump exceeds the threshold, generating a frequency jump detection event.
3. A method for enhancing integrity performance of a global navigation satellite system that includes a plurality of navigation satellites, each of which has a master clock, said method comprising:
on board at least one of said satellites, monitoring a master clock signal generated by the master clock onboard said at least one of the satellites, to detect a frequency jump; and
said at least one of the satellites signaling a detected frequency jump of said master clock signal,
wherein said monitoring comprises
comparing the frequency of an untransmitted master clock signal with the frequency of an untransmitted backup clock signal, which is generated by a backup clock, onboard said at least one of the satellites, for detecting a frequency jump of a clock signal;
comparing a detected frequency jump with a threshold; and
if the detected frequency jump exceeds the threshold, generating a frequency jump detection event,
wherein the comparing step comprises
estimating the frequency of each of said clock signals based on phase measurement values of the respective clock signal; and
comparing the estimated frequencies of both clock signals;
wherein the comparing of a detected frequency jump with a threshold comprises,
detecting a difference between the estimated frequencies;
comparing the detected difference with the threshold; and
generating the frequency jump detection event if the detected difference exceeds the threshold.
4. The method of claim 2 , wherein the threshold is a remotely configurable parameter.
5. The method of claim 1 , wherein the monitoring step comprises estimating the frequency of the master clock signal using a reference clock signal that is generated onboard of the satellite by a reference clock.
6. The method of claim 1 , wherein the step of signaling of a detected frequency jump of the master clock signal comprises setting a flag in a navigation message broadcast by the satellite.
7. The method of claim 6 , wherein a Data Validity Status —DVS—Flag is used as the flag for signaling a detected frequency jump.
8. The method of claim 1 , wherein the signaling of a detected frequency jump of the master clock signal further comprises signaling of at least one of a used master clock type and a threshold that is implemented onboard the satellite for monitoring the frequency jump of the master clock signal, at a user level of a global navigation satellite system.
9. Apparatus for detecting frequency jumps of a navigation satellite's master clock, said apparatus comprising:
a clock monitoring and control unit that monitors a master clock signal generated by the master clock onboard the satellite, for a frequency jump by comparing a frequency of an untransmitted master clock signal with a frequency of an untransmitted backup clock signal; and
a frequency jump signaling unit which signals a detected frequency jump of the master clock signal.
10. A navigation satellite comprising the apparatus of claim 9 .
11. A receiver for receiving navigation messages from the navigation satellite of claim 10 , and being adapted for processing a received navigation message by:
detecting a signal indicative of a detected frequency jump of the master clock signal of the satellite in a navigation message from a particular satellite; and
a step comprising one of i) excluding navigation messages from the particular satellite, and ii) inflating a relevant signal in space accuracy information (SISA) for said particular satellite.
12. The receiver of claim 11 , wherein said step of inflating the relevant SISA is performed according to the following equation:
S
I
S
A
i
=
σ
·
ⅇ
b
2
2
·
σ
2
,
wherein b is a bias in meters and σ is a standard deviation of an underlying Gaussian distribution.
13. The receiver of claim 12 , wherein:
the SISA received with a navigation message from the satellite is used as the standard deviation σ; and
the threshold applicable for frequency jumps of the satellite's master clock is used as bias b.
14. The receiver of claim 11 , wherein the receiver is further adapted to consider age of the navigation data received with a navigation message, for inflating the relevant SISA information.
15. The method of claim 1 , wherein the comparing step comprises:
estimating the frequency of each of said clock signals based on phase measurement values of the respective clock signal; and
comparing the estimated frequencies of both clock signals;
wherein the comparing of a detected frequency jump with a threshold comprises,
detecting a difference between the estimated frequencies;
comparing the detected difference with the threshold; and
generating the frequency jump detection event if the detected difference exceeds the threshold.