Resolution 606 Interference from RNSS to radars in the 1215 – 1300 MHz band Philippe GERARD Agence Nationale des Fréquences Gerard@anfr.fr 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

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 1559 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

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 1 260-1 300 MHz; b) that in the band 1 215-1 260 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 1 215-1 300 MHz,

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 1 215-1 260 MHz; 2 to recommend that WRC-03 review the results of the studies in invites ITU-R and take appropriate action,

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 1 215-1 300 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.

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)

Resolution 606 : last WP 8D : calculation of pfd for GPS and GLONASS (doc 8D/18 E) CEPT proposed : Pfd limit of -133 dBW/m2/1MHz (GALILEO : E6, 40 MHz, -155 dBW -134 dBW/ m2 /1MHz)

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

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

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

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

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 : 23600 km GPS : 24 satellites, 6 orbital plans Angles of orbital plans :55 ° Right ascension : 0 – k * 60° Anomalies : every 90° Altitude : 20 200 km

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)

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

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

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.

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

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

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

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

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 ?

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 ?

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 ?

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)