Liaison Statement from CEPT WG SE to TC SES (copy to CRAF and ERM/RM)

Liaison Statement from CEPT WG SE to TC SES (copy to CRAF and ERM/RM)

The European Science Foundation is an association of its 67 member research councils and academies in 23 countries. The ESF brings European scientists together to work on topics of common concern, to co-ordinate the use of expensive facilities, and to discover and define new endeavors that will benefit from a co-operative approach
The scientific work sponsored by ESF includes basic research in the natural sciences, the medical and biosciences, the humanities and the social sciences.
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On behalf of European radio astronomers, the ESF Committee on Radio Astronomy Frequencies, CRAF, coordinates activities to keep the frequency bands used by radio astronomers free from interference.

Subject: AES unwanted emission in 1610.6-1613.8 MHz

This Liaison Statement is also forwarded to CRAF for consideration, so that CRAF might submit some comments on this proposal directly to TC SES. TC SES is requested to take into account these possible comments at the Resolution Meeting.

The CEPT WG SE, which met on 12th-16th, June, want to bring the following elements to TC SES, after carefully examination of the liaison statement received from TC SES:

  • the time which is necessary to complete a full study for the determination of a correct value to protect the radio astronomy in the 1610 MHz is long (in the order of one or two years), and so probably not compatible with the on-going procedure of the Resolution Meeting(s) concerning the finalisation of AES standard (Draft pr EN 301 473).
  • it is understandable that TC SES was surprised by the discrepancy between the results concerning the two RAS frequency bands (1610 and 1660 MHz), this is due to two different approaches. In the 1610 MHz a worst case scenario has been taken into account whereas the 1660 MHz value is based on a statistical model, with parameters which have never been studied by SE, because the result is based on a statistical model agreed between Inmarsat and CRAF, satisfying both parties, including the relevant assumptions, so that WG SE did not undertake the review of the model
  • Nevertheless, during the last SE meeting, WG SE set up a drafting group in order to examine the differences in terms of assumption, that apply to the two frequency bands. The calculation is detailed in annex. The SE proposal is that :

  • 1) TC SES include in the Draft pr EN 301 473 the limit of -65 dBW/20 kHz for unwanted emission of AES in the frequency band 1610.6-1613.8 MHz.
  • 2) WG SE will carry out the full studies mentioned above, in order to confirm or revise this value.
  • 3) If the studies are demonstrating that there is a need to revise this value, CEPT will then request a revision of this standard.

    Annex

    The basis of the comparison is the interference caused to spectrum-line observation (no continuum observation at 1610 MHz) where CRAF and Inmarsat agreed that an out-of-band emission level of -49.5 dBW in 20 kHz would be sufficient to protect radio astronomy.

    ParameterAdditional interference effect from CDMA system compared to InmarsatComment
    Detrimental interference level of the RAS measurement0 dBITU-R Rec.769 specifies -194 dBW/m2 in 20 kHz for both bands for spectrum line observations
    Dynamic power control0 dBConservative value : power control for a CDMA system is expected to be better than for a FDMA system
    Difference in traffic10 dBWhile there is no real background to expect more AES traffic from a CDMA system compared to Inmarsat, it is assumed that AES traffic from a CDMA system could be 10 times higher than Inmarsat.
    Antenna discrimination0 dBSame aircraft-mounted antennas

    As a result, a value of -59.5 dBW in 20 kHz would be expected to be sufficient to protect radio astronomy at 1610 MHz. Given that this analysis might not have taken into account all differences between the 2 situations, an additional 5.5 dB margin is proposed, so that the out-of-band emission level in the band 1610.6-1613.8 MHz is proposed to be :

    Frequency bandunwanted emission level
    1610.6-1613.8 MHz-65 dBW in 20 kHz

    Concerning Intermodulation, the conclusion that the probability of 2 simultaneous transmission for an aircraft with intermodulation product falling into the radioastronomy band is extremely low is even more valid for the case of a CDMA system and an observation limited to spectrum line.

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    Last modified: October 5, 2005