Page 23 - ITU Journal: Volume 2, No. 1 - Special issue - Propagation modelling for advanced future radio systems - Challenges for a congested radio spectrum
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ITU Journal: ICT Discoveries, Vol. 2(1), December 2019



                                                               the  L1-band  was  severely  affected,  depending  on
                              Antenna                          the  receiver’s  type  and  on  the  bandwidth  of  the
                                                               antenna used. GPS-only stations were not affected,
                                                               because  the  related  antenna  bandwidth  is  sharp
                                                               enough around L1 carrier frequency to reject the
                         Low Noise Amplifier                   jamming signal.
                                                               Changes  in  the  jamming  signal  power  were
                                                               observed over time, according to some provisional
                            Power Divider                      monitoring. The potential implementation of a low-
                                                               noise active microwave diplexer is under study. In
                                                               addition,  future  plans  are  to  implement  a  more
                  Band-pass Filter                             consistent  dedicated  observation  of  the  jamming
                   L2/L5/E5a/E5b                               signal,  and  more  generally  of  the  frequency
                                                               spectrum around all the GNSS frequency bands. To
                                   Band-pass Filter            develop  our  knowledge  in  this  field  appears
                                        L1/E1                  mandatory  today  for  all  future  GNSS  activities
                                                               according  to  the  laboratory  time  metrology
                                                               missions.
                          Power Combiner
                                                               ACKNOWLEDGEMENT

                                                               We  acknowledge  the  Agence  Nationale  des
                             Attenuator                        Fréquences (ANFR) for the help in trying to solve
                                                               the issue.

                                                               REFERENCES
                           Receiver Main Unit
              Indoor                                           [1]   M. Abgrall, B. Chupin, L. De Sarlo, J. Guéna, Ph.
                                                                     Laurent, Y. Le Coq, R. Le Targat, J. Lodewyck,
                                                                     M. Lours, P. Rosenbusch, G.D. Rovera, S. Bize
           Fig. 12 – Block diagram of the low-noise active microwave   (2015). Atomic Fountains and optical clocks
              diplexer aiming at filtering out the jamming signal
                                                                     at SYRTE: Status and perspectives, Comptes
                                                                     Rendus Physique, Vol.16, Issue 5, June 2015,
          9.   CONCLUSION
                                                                     461-470.
          For  fulfilling  its  time  and  frequency  metrology   [2]   G.D.  Rovera,  S.  Bize,  B.  Chupin,  J.  Guéna,
          missions, LNE-SYRTE is operating an ensemble of            Ph. Laurent,  P.  Rosenbusch,  P.  Uhrich  and
          calibrated GNSS stations in OP aiming at accurate          M. Abgrall  (2016).  UTC(OP)  based  on
          time  transfer  between  remote  atomic  standards.        LNE-SYRTE     atomic    fountain   primary
          But  since  November  2018,  a  powerful  signal           frequency standards, Metrologia 53 S81.
          occupying  a  frequency  band  just  below  the  L1
          frequency  band  allocated  to  GNSS  signals  has   [3]   BIPM (2019). 2018 Group 1 GPS calibration
          appeared.  Its  signal  power  level  is  indicating  a    trip (Cal_Id 1001-2018), v1.4 / 20190327.
          ground source near to OP. This is apparently not in        https://www.bipm.org/utils/common/Time
          line  with  ITU  frequency  tables,  where  this           Calibrations/Current/1001-
          frequency  band  is  allocated  to  space  to  Earth       2018_GPSP3C1_Group1-trip_V1-4.pdf
          satellite telecommunications. The signal is jamming   [4]   IGS Central Bureau (2019).
          OP stations’ reception when using large bandwidth          http://www.igs.org/igsnetwork/network_by
          multi-GNSS  antennas  and  receivers.  A  formal           _site.php?site=opmt00fra
          complaint was raised to ANFR in early 2019.
                                                               [5]   IGS Central Bureau (2019).
          The impact of this jamming signal was observed in          http://www.igs.org/igsnetwork/network_by
          different ways. First, a sudden loss of  some GNSS         _site.php?site=op7100fra
          data,  together  with  an  increase  of  noise,  was
          detected,  leading  to  unexpected  large  offsets
          between calibrated OP stations. Second, the C/N0 in




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