Page 22 - ITU Journal: Volume 2, No. 1 - Special issue - Propagation modelling for advanced future radio systems - Challenges for a congested radio spectrum

ITU Journal: ICT Discoveries, Vol. 2(1), December 2019

8. THE WAY FORWARD
A formal complaint was raised in early January
2019 to ANFR, the National Frequency Agency
which manages the radio frequencies in France.
Two technicians came to OP within three days and
confirmed all the elements provided by LNE-SYRTE.
The jamming signal is under formal observation and
this is an ongoing process.
LNE-SYRTE is involved in different GPS station-
relative calibration campaigns for the first half of
2019. But the idea is to extensively test afterwards
with all available spare receivers and antennas in
order to relate more precisely the power of the
Fig. 9 – Typical spectrum observed from end of January 2019 jamming signal to the GNSS signal reception of OP
onwards. The center frequency is L1, the span is 200 MHz. stations. A multi-GNSS station based on a receiver
Marker 1 highlights the threshold where the power received from a fourth additional manufacturer is also
from the jamming signal is already surpassing the GNSS main currently being put into operation, in order to
lobe power inside the L1-band. improve our knowledge about such different units.
However, due to the unsteady nature of the
jamming signal, it is not easy to plan comprehensive
tests with all available equipment allowing the
computing of a consistent correlation function
between the jamming signal power and the GNSS
collected data.
Another prospective study is to design and to
develop a low-noise active microwave diplexer in
the 1 - 2 GHz frequency band to be inserted between
the antenna and the detection unit of a multi-GNSS
receiver (Fig. 12). The principle is to implement two
different band-pass filters; one around the L1
Fig. 10 – C/N0 of OP71 in the L1-band from 1 January to carrier, including the E1 band of the Galileo signal,
28 February 2019. Each point is a mean value of the S1
parameter in RINEX data averaged between simultaneously and the other one around the GPS L2 and L5 carriers,
tracked satellites sampled over 0.1 d. and including the E5a and E5b bands of the Galileo
signal. However, such a development will have to
take into consideration three important aspects.
First, Galileo full signals, either Open Service (OS) or
Public Regulated Service (PRS), are slightly beyond
the ITU allocated GNSS L1-band [14,15], hence
partly inside the jamming signal frequency band.
Second, the sensitivity to temperature fluctuations
of such band-pass filters should be monitored
closely. And third, the hardware delays of the low-
noise active diplexer have to be calibrated at sub-ns
level for all GNSS signals for accurate time transfer.
Finally, LNE-SYRTE has started some very
preliminary tests by using a directional antenna for
Fig. 11 – Mean power values of the detected signal in the the monitoring of the jamming signal. This might
frequency band 1515 MHz to 1561 MHz from 21 February to allow for better focus on the jamming signal
20 May 2019. Sampling period is from 20 min to 10 min.
fluctuations with time.

6 © International Telecommunication Union, 2019