ESASTAP Meeting 12 Dec 2005

							Radio interference monitoring, spectrum protection and
                     signal security




               AFREF technical workshop
                   10-13 July 2006
                        UCT

           Ludwig Combrinck & Ruth Neilan
    Ready to install a GPS station?
You have sorted out all requirements such as:
➲   Power (UPS etc)
➲   Internet
➲   Security
➲   Multipathing etc.
All sites have the potential for RFI




                           Many sources of RFI
                           exist and each site needs
                           an independent
                           assessment of potential
                           RFI
Of course, GNSS is a RFI source
             itself!
         Not only GLONASS…..

➲   Notification of GPS L3 RFI world-wide SUBJECT: GPS
    Testing Operations. FREQUENCIE(S) AFFECTED:
    1381.05 ± 2.5 MHz DATE (UTC) TIME (UTC) Comments
    (YYYYMMDD) (HHMM) (TEXT) -----------------------------------
    ------------------------------------ 20050621 0000 - 2400
    Previously Unscheduled, late notice. 20050622 0000 -
    2400 Previously Unscheduled, late notice.
    ============================================
    ===========================
➲   We have been alerted to the following, late-notice military
    GPS-L3 Transmissions which may cause RFI to
    observations scheduled for the use of L-band (20cm) on
    the date(s) and time(s) listed below. The 1381 MHz
    frequency is within the VLA L-band 21/20cm "LL"/"21",
    "L1", and "L2", continuum default frequencies, and any L-
    band spectral line set-up that includes 1381.05 ± 2.5 MHz.
And many people are worried…

➲   Development of an L-band Spectrum Management Tool Suite.
➲   Monticone, F. Box, T. Kim, R. Snow, and M. Tran (USA) Keywords:
    distance measuring equipment (DME), tactical air navigation (TACAN),
    FAA, NAS, GPS L5, spectrum management
➲   Abstract:. Managing the use of spectrum by multiple diverse systems
    is a formidable task requiring the use of sophisticated tools. A prime
    example of a spectrum band shared by multiple Federal Aviation
    Administration (FAA) and Department of Defense (DoD) systems, that
    the research described in this paper addresses, is the 960 1215 MHz
    band, contained within the L-band. The L Band Steering Committee
    formed by the FAA and DoD and an ad hoc working group of the
    Interagency Global Positioning System (GPS) Executive Board (IGEB)
    have been independently formed to address concerns regarding the
    interference-free co-existence of L-band systems. This paper
    describes the effort that the MITRE Corporation’s Center for Advanced
    Aviation System Development (CAASD) has undertaken to develop a
    spectrum management tool suite to help address these concerns.
            The official picture


➲   GPS uses a set of rather weak radio signals
    from satellites in 20,200 kilometer high
    orbits and, as such, is susceptible to being
    overpowered by strong terrestrial
    interference. It operates in one of the
    “restricted frequency bands” of Title 47
    C.F.R. Part 15 and requires protection from
    harmful interference by international treaty.
(RTCA Paper No. 086-01/PMC-139)
Prepared by
RTCA Special Committee 159
March 27, 2001
Accuracy degrades; with rf noise
          and pulsed rf
Other techniques have far more
  serious problems though…..
       What to look out for


➲ Proximity of other radio devices
➲ Antennas, VHF, UHF, even HF could cause
  intermodulation products
➲ Other space geodesy equipment (DORIS)!
Airport areas (normally convenient)
        could be problematic

 ➲   Primary surveillance radar systems for air traffic operating in the
     frequency bands 1240 to 1350 MHz and 2700 to 2900 MHz with
     transmitter powers up to 2 MW and antenna gains up to 37 dB.
 ➲   Fortunately these services are being phased out as they are
     outdated and expensive to operate.
 ➲   Secondary surveillance radar systems for air traffic operating on
     an international standard frequency on 1030 MHz at lower power
     (1 to 2 kW transmitters) with 37 dB gain antennas.
 ➲   Distance measuring equipment (DME) transmissions for air traffic
     operating in the frequency band 960 to 1215 MHz with 1 to 2 kW
     transmitters and low gain antennas.
 ➲   Secondary Surveillance Radar (SSR) and Airborne Collision
     Avoidance System (ACAS) operating on an international standard
     Frequency on 1090 MHz.
             Other users


➲ Point-to-point links operating in the
  frequency bands 1350 to 1525 MHz
➲ The point-to-point links are usually highly
  directional and may only be troublesome if a
  transmitting beam happens to be directed at
  the GPS antenna.
➲ RFI in this case has to be combated by
  distance, topographical shielding and
  regulatory enforcement and protection.
Simple technique to locate RFI
➲   Spectrum analyzer (2 GHz)
➲   Log-periodic antenna/s
The hunt is on……..
    Quick scan may not reveal all
➲   May need a couple of days of observation to detect
    intermittent transmitters
               For AFREF




➲ We could set up a special mobile/portable
 RFI detection unit to validate/characterise
 sites.
The end