(Starlink)
Engineers have shown that the signals from Starlink Internet satellites can be used for geolocation using amateur radio equipment.
Having recorded the signals of six passing satellites, they calculated the position in space with an error of 33.5 meters, and when using the altimeter and positioning on the plane, the error decreased to 7.7 meters.
GPS, Galileo, GLONASS and other global satellite navigation systems work by broadcasting a signal containing data on the time of its emission.
Having received this signal, the receiver can compare it with its own time and calculate the distance to the satellite from the speed of propagation of radio waves.
And having received signals from at least three satellites, he can calculate his position.
Those sats are located at an altitude of 19-20 thousand kilometers, so the signal arrives with little power
That’s why researchers have been studying the possibility of using low-orbit vehicles located much closer to the Earth for quite some time.
In recent years, this trend has been spurred by new large constellations of Internet satellites such as Starlink, OneWeb and several planned ones.
Potentially close location to the Earth's surface and a strong received signal can improve the quality of satellite navigation
However, but in fact, existing systems are not "sharpened" for such use, therefore the classical method of receiving time signals does not work with them.
Researchers have previously proposed alternative methods that do not need to know the content of the signals, but they have not yet been applied to Starlink.
Now researchers led by Zaher Kassas of the University of California, Irvine have learned how to calculate a location using Starlink signals without knowing its contents.
They found that there are nine carrier peaks in the signal of the satellites at 11.325 GHz.
The authors decided to calculate the location using carrier phase tracking, a technique used to improve the accuracy of GPS measurements to tens of centimeters.
They supplemented it with an adaptive Kalman filter to adjust the frequency due to the Doppler shift of the signal from the satellites.
The engineers used software defined radio (SDR) and an available Ku-band antenna for experiments.
(Joe Khalife et al. / IEEE 2021)
They learned the positions of the satellites from the publicly available TLE database. The system recorded signals for 800 seconds.
After recording, they calculated the coordinates with an error of 33.5 meters when considering a three-dimensional position and 25.9 when calculating an in-plane position.
By adding altimeter data to remove the height uncertainty, they achieved an error of 7.7 meters.
The authors recorded signals from six satellites in turn, because until such a number of devices fly over their terrain at the same time
As Starlink grows, there should be more of them, which will increase the accuracy of geolocation.
In addition, they are preparing a new experiment in which they will pick up the signal from four satellites at the same time and calculate the location in real time.
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