Liaison statement from WG SE to ETSI/TC-SES
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.
The ESF links scholarship and research
supported by its members and adds value by cooperation across national
frontiers. Through its function as coordinator, and also by holding
workshops and conferences and by enabling researchers to visit and
study in laboratories throughout Europe, the ESF works for the
advancement of European science.
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.
During its last meeting (14-18 February), WG SE addressed the issue of the unwanted emission
limits of AES (DEN/SES-00023) in the radio astronomy band 1610.6-1613.8 MHz and 1660-1670 MHz.
WG SE noted the liaison statement sent by SE28 to ETSI TC SES and particularly the discrepancy
identified between the approach for determining limits :
In the band 1660-1670 MHz, CRAF and Inmarsat have agreed unwanted emission values
(-39.5 dBW/MHz for wideband emission, -49.5 dBW/20 kHz for narrowband emission) considered
to be sufficient to protect the radio-astronomy, based on statistical analysis taking into
account real traffic data.
In the band 1610.6-1613.8 MHz, the unwanted emission which had been proposed earlier by
SE28 (-80 dBW/MHz), was based on a worst case analysis (such as aircraft route in the
vicinity - 3 km - of a radio astronomy observatory and 7 channels continuously operational).
As a consequence, the limit for the band 1612 MHz is more stringent by about 40 dB compared
to the band 1660 MHz. This is even more surprising when considering that the Rec.769 protection
level for radio astronomy is 14 dB more stringent at 1660 MHz, due to continuum observations in
this band.
WG SE noted that the analysis made by CRAF and Inmarsat might rely only on the existing
traffic, without taking into consideration likely development of AMS(R)S and the potential
outcome of a new operator. However, WG SE does not wish to undermine the agreement between
CRAF and Inmarsat and is therefore accepting the proposed limits.
As stressed in the liaison statement from SE28, WG SE is considering that similar methodology
and operational factors should be applied in the analysis for the 2 bands, otherwise the
difference between the 2 limits will be unequal. The gap between the two limits demonstrates
that the previous proposed limit of -80 dBW/MHz in the band 1610.6-1613.8 MHz is probably
unduly stringent. WG SE is therefore advising ETSI TC SES to replace the value of -80 dBW/MHz
with a statement that this limit is "under consideration", without delaying the approval of the
standard.
WG SE is aware that the development of limits for the band 1610.6-1613.8 MHz on the same basis
as the CRAF/Inmarsat analysis will be difficult since it needs assumptions on traffic data
which is, for a new operator, only an expectation and which is commercially sensitive.
Therefore, WG SE will aim to develop a generic and transparent methodology applicable to
any operator and which will fully take into account the statistical nature of the AES traffic.
This task will require significant time before completion (e.g. 2 years). CRAF and MSS
operators are encouraged to participate actively in this work.
Last modified: July 3, 2000