1. Resolution 606
Interference from RNSS to radars in the 1215 – 1300 MHz band
Philippe GERARD
Agence Nationale des Fréquences
Mars 2001
AMCP WGF/6-WP/39
But de la présentation
Faire le point sur les dispositions réglementaires qui peuvent influer sur le choix des bandes à utiliser et la répartition des services dans GALILEO
Insister sur les risques

2. Resolution 606 : protection of radars in 1215 –1300 MHz band
Protection of radiolocation
resolution 606
Protection of MLS
resolution 603
Compatibility
with MSS
Sharing with
MIDS
OOB emissions
from radars
L5/E5
L5/E5 L2 L2 E6 L1 L1 C C
Compatibilité avec le service mobile par satellite autour de MHz
L ’étude de ce double brouillage devra être effectuée.
1164 MHz
1215 MHz
1260 MHz
1300 MHz
1559 MHz
1610 MHz
5010 MHz
5030 MHz
Sharing between
RNSS and ARNS
resolution 605
Protection of radiolocation
resolution 607
Protection of radioastronomy
resolution 604

3. RES 606 [COM5/20] considering
a) that this conference has decided to introduce a new allocation for the radionavigation-satellite service (space-to-Earth) in the frequency band MHz;
b) that in the band MHz radionavigation-satellite service (space-to-Earth) systems have been successfully operated for a considerable time in a band used by radars;
c) the importance of the radionavigation service authorized in certain countries in accordance with No. S5.331 and of the radiolocation service, and the need for adequate protection and continued operation of these services throughout the band MHz,

4. RES 606 [COM5/20]
resolves
1 that no additional constraints shall be placed on radionavigation-satellite service (space-to- Earth) systems operating in the band MHz;
2 to recommend that WRC-03 review the results of the studies in invites ITU-R and take appropriate action,

5. RES 606 [COM5/20]
invites ITU-R to conduct, as a matter of urgency and in time for WRC-03, the appropriate technical, operational and regulatory studies, including an assessment of the need for a power flux-density limit concerning the operation of radionavigation-satellite service (space-to-Earth) systems in the frequency band MHz in order to ensure that the radionavigation-satellite service (space-to-Earth) will not cause harmful interference to the radionavigation and the radiolocation services,
instructs the Secretary-General
to communicate the contents of this resolution to ICAO for such actions as it may consider appropriate and to invite ICAO to participate actively in the study activity identified under invites ITU-R.

6. Resolution 606 ITU-R CEPT Last WP 8D : October 2000
Next WP 8D : end of May 2001
CEPT
Last SE 28 : January 2001
Next SE 28 : 2 May 2001 (to prepare next WP 8D)

7. Resolution 606 : last WP 8D : calculation of pfd for GPS and GLONASS (doc 8D/18 E) CEPT proposed : Pfd limit of dBW/m2/1MHz (GALILEO : E6, 40 MHz, -155 dBW -134 dBW/ m2 /1MHz)

8. Calulated from rec. ITU- R M 1463
SE 28 : worst case pfd
Calulated from rec. ITU- R M 1463
Pfd limit :
-161 !!!

9. objectives of a statistical approach
- The worst case scenario uses the gain of the main beam of the radars
- Satellites are not always in the main beam
Objective of further works :
to present a statistical view of harmful interference
to propose a pfd limit acceptable for everybody

10. Resolution 606 : statistical approach
Assumptions
Radar model
Models of satellites constellations :
GPS
GALILEO
Harmful interference criteria to radars :
recommendation ITU-R M 1461
general consideration

11. Resolution 606 : statistical approach
Radar model
Rec ITU-R M 1463 does not give enough information on radiation pattern of radars
Measured radiation pattern of a civil aviation radar
- Calculated PFD for
“ no harmful interference” :
-154 dBW/m2/1MHz

12. Methodology Modelisation of a satellite constellation GALILEO GPS :
27 satellites – 3 orbital plans
Angle of orbital plans 55°
right ascension : 0 – 120 – 240°
Anomalies : every 40° from 0° – 13.33° – 26.66°
Altitude : km
GPS :
24 satellites, 6 orbital plans
Angles of orbital plans :55 °
Right ascension : 0 – k * 60°
Anomalies : every 90°
Altitude : km

13. Methodology Calculation of satellite elevation
- For one satellite
- For all satellites of an orbit
- For all satellites of the constellation
(here for a latitude of 47° N)

14. Maximal gain Gain for one satellite
Max gain for the whole constellation

15. Methodology Distribution of Gain : prob (gain<g) =
period (gain<g)/total period

16. Methodology : harmful interference criteria
Rec. ITU-R M 1461 : threshold I/N = -6 dB
From simulations :
Elevation, azimuth function of time
Several minutes per degree.
- Between several antenna rotations, the satellite azimuth and elevation can be considered as fix elements
- from the operator point of view, when there is jamming in a direction, this direction is jammed all the time and not only the percentage of tim the radar scans in this direction…
- The “harmful interference period” is the total period in which I/N superseded the threshold for at least one direction : results from the vertical radiation pattern
- The horizontal radiation pattern gives the width of the jammed area.

17. Methodology Harmful interference I/N = -6dB (rec ITU-R M 1461)
For a given PFD :
Prob (interference) = prob (Gain >PFDwc+Gmax - PFD)
With :
PFDwc = PFD worst case = -154 dBW/m2/1MHz for our radar

18. Resolution 606 : statistical approach
First results
For pfd as proposed, probability of harmful interference is above 20 % for one satellite !!!

19. Resolution 606 : statistical approach
First results
For pfd as proposed, probability of harmful interference is almost 100 % for the constellation !!!

20. Resolution 606 : statistical approach
4 periods
One orbital plan
Three orbital plans
Attempts of explanations :
Most of the time, there are one or more satellite with a low elevation
high gain of radiation pattern

21. Resolution 606 : statistical approach
But…
This approach gives similar results with GPS today
No interference seen until now…
So, WHY ???
Bad assumptions ?
Harmful interference criterias ?
Radar signal processing …
Wrong models ?

22. Resolution 606 : statistical approach
But…
This approach gives similar results with GPS today
No interference seen until now…
So, WHY ???
Bad assumptions ?
Harmful interference criteria ?
Radar signal processing …
Wrong models ?

23. Resolution 606 : Present problem
WHY are there no interference declared today between GPS and radars in L2 band ?
Wrong assumptions ?, false calculations ?
 more studies must be made
Not enough data about radars ?
Radiation patterns
Interference measurement
Interference criteria not adequate ?

24. Resolution 606 : more information from NATO
US : Same approach
Calculations with ITU-R M 1461 and M 1463 recommendations predicts interferences from current GPS, but : no interference to date
Need to examine other methodologies
Study with 8 US radars
Statistical approach, study of different criterias…
Operational tests :
To configure a GPS satellite to transmit C/A signal on L2 (1227 MHz)