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IUCAF SUMMER SCHOOL 2002
MITIGATION TECHNIQUES
MITIGATION FACTORS -
what is it? what is it good for?
by Klaus Ruf
IUCAF SUMMER SCHOOL 2002
INTERFERENCE
Active Services: Interference normally defined
in terms of Signal-to-Interference ratio.
The service is interrupted (interfered), when
the power ratio in dB becomes negative.
Radio Astronomy: The wanted signal is almost
always masked by noise.
IUCAF SUMMER SCHOOL 2002
Mitigation Technique used in Radio Astronomy:
Integration over time and bandwidth
Other (active) services need to restrict
bandwidth to increase signal-to-noise
(interference) ratio.
IUCAF SUMMER SCHOOL 2002
Reduce bandwidth to improve signal to noise ratio
IUCAF SUMMER SCHOOL 2002
-
=
Increase bandwidth to increase sensitivity
IUCAF SUMMER SCHOOL 2002
Mitigation Technique used in Radio Astronomy:
(cont.)
•observe large bandwidth
•intergrate for long time
•use ultra-stable receivers, e.g. switched receivers
•develop all kinds of sophisticated observing modes
•develop very high gain antennas
•go to high altitude (dessert) sites
•go to very remote sites, radio quiet zones
IUCAF SUMMER SCHOOL 2002
Conclusion:
Radio Astronomy has developed and applied
mitigation techniques long before this word
was used!
There is nothing wrong with
mitigation techniques!
IUCAF SUMMER SCHOOL 2002
What are Mitigation Factors?
Mitigation factors are the effect of the
application of mitigation techniques,
expressed in dB, which can be added to
our protection criteria.
IUCAF SUMMER SCHOOL 2002
•Which factors have been proposed?
•Who is proposing these factors?
•What will be the effect?
IUCAF SUMMER SCHOOL 2002
IRIDIUM
LEO-system, operating at 1621.35-1626.5MHz
RA-band
1610.6-1613.8MHz
Active antennas:
traffic density
dependent interference power
Intensive negotiations in WP7D, in the US, and
Europe
IUCAF SUMMER SCHOOL 2002
Proposed mitigation factors, in the absence of
filtering:
•side lobe level interference mitigation factor
•integration time interference mitigation factor
•polarisation interference mitigation factor
•and a few others
IUCAF SUMMER SCHOOL 2002
What happened to these factors?
They are meanwhile adopted, by WP7D,
plus a few more, like
•tolerable data loss to interference
•minimum elevation angle for observations
Which other factors exist, what will be the
effect of their implementation?
QUESTION ITU-R 237/7
TECHNICAL AND OPERATIONAL FACTORS RELATING TO INTERFERENCE MITIGATION
PRACTICES AT RADIO ASTRONOMY STATIONS
(2001)
The ITU Radiocommunication Assembly,
considering
a)
that radio astronomy stations are designed to detect natural emissions at extremely low power levels; their
operation may therefore be degraded by interference at levels that could be tolerated by other services;
b)
that a variety of mitigation techniques may be used to reduce the susceptibility of radio astronomy stations to the
effects of interference in observational data;
c)
that the use of mitigation techniques entails in many cases a loss of data and observing time, a loss of observational
flexibility, and a general reduction in the level of service to users of radio astronomy stations;
d)
that recent technological developments create new possibilities for mitigating interference by means of digital
techniques and operational procedures,
decides that the following Question should be studied
1
What are the technical and operational characteristics of the mitigation techniques that are being identified for use
by radio astronomy stations?
2
What are the consequences and the technical limitations for the use of identified mitigation techniques and which
of these techniques may be applied in practice?
1
2
further decides
that the results of the above studies should be included in (a) Recommendation(s);
that the above studies should be completed by 1 May 2003.
INTERNATIONAL TELECOMMUNICATION UNION
RADIOCOMMUNICATION
STUDY GROUPS
Document 1/37(Rev.1)-E
15 November 2000
Original: English
Source:
Task Group
1/5
DRAFT NEW RECOMMENDATION ITU-R SM.[PS]
THE PROTECTION OF PASSIVE* SERVICES FROM UNWANTED EMISSIONS
(Question ITU-R 211/1)
The ITU Radiocommunication Assembly,
considering
a)
that it is desirable that unwanted emissions of new stations in any radio service should not
b)
that, in some cases, passive services and services employing high-power transmitters have
c)
that in many cases passive services and space services (space-to-Earth) have been allocated
d)
that in some cases space-based passive services and services using uplink earth stations or
e)
that, in making these allocations, transmitter and receiver compatibility may not have been
f)
that the radio astronomy service, the earth exploration satellite service (passive) and space
g)
that, due to these low received power levels, these passive services are generally more
h)
that several footnotes to the Radio Regulations (such as S5.149, S5.340, S5.372 and
i)
that there are various operational practices and mitigation techniques that can be used by
j)
that there may be practical and economic limitations on the applicability of these mitigation
k)
that general limits for spurious emissions may not protect to the desired extent the passive
m)
that Recommendation 66 (Rev.WRC-2000) requests in recommends 5 that ITU-R "study
n)
that Recommendation 66 (Rev.WRC-2000) requests in recommends 6 that ITU-R "study
o)
that the Radio Regulations state (S29.5) that the locations of the radio astronomy stations to
noting
a)
that explanations of why passive services are more vulnerable to interference from
b)
that ITU-R Recommendation [SM.OAB] provides guidance with regard to unwanted
c)
that an expeditious conclusion of band-by-band studies and the identification of other
d)
that appropriate levels for those situations need to be established and the impact be
recommends
1
that when allocating frequency bands to the satellite services, their proximity to
frequency bands allocated to the radio astronomy service, the Earth exploration-satellite (passive)
service, and the space research (passive) service should be taken into account;
2
that when designating frequency bands for specific terrestrial applications such as HAPS or
HDFS, their proximity to frequency bands allocated to the radio astronomy service or the earth
exploration-satellite (passive) service, and the space research (passive) service be taken into
account;
3
that where possible allocations adjacent to existing passive services should be such as to
minimize the potential for interference;
4
that the use of zones around stations used for radio astronomy observations where active
services are excluded or restricted should be considered as a means of minimizing interference
due to unwanted emissions from terrestrial transmitters;
5
that mitigation techniques such as those described in Annex 2 and Annex 3 should be
considered as appropriate means and employed as much as practicable by active services and
passive services, to minimize the interference generated by unwanted emissions to passive
services, bearing in mind the constraints placed on system design and operational effectiveness;
6
that the passive service frequency bands identified in Annex 4 are bands for which more
stringent spurious emission limits than the general limits in Appendix S3 may be used to protect
passive services;
7
that the active service frequency bands identified in Annex 4 are bands for which out-ofband limits may be used to protect adjacent or nearby passive service bands;
8
that the following measures should be taken to minimize the potential of interference to
passive services:
a)
consultation and exchange of technical and operational information between the relevant
parties,
b)
co-operation on the selection and implementation of the most suitable measures between
operators of passive systems and active systems, and
c)
appropriate spectrum management techniques.
ANNEX 3
Mitigation techniques that may be used by passive services
1
Spaceborne passive sensors
.................
2
Radio astronomy receivers
2.1
Site shielding and site selection
2.2
Quiet zones and coordination zones
2.3
Receiver architecture
2.4
Antenna patterns
2.5
Analogue filtering at either RF or IF stages
2.6
Interference excision techniques
2.7
Digital adaptive interference cancellation
2.8
Adjustment of sensitivity levels
2.9
Cooperative solutions
c)
Guardbands
IUCAF SUMMER SCHOOL 2002
Some practical examples
•good ones
•bad ones
IUCAF SUMMER SCHOOL 2002
The beam pattern at 10.6 GHz of the Effelsberg 100 m radio telescope,
towards 3C84. field size: 30’ x 12’, flux 20.5 Jy (~ -247 dB(W m-2 Hz-1)),
before the TV satellite was switched on.
A field of the sky, 30’ x 12’, 10 degrees away from the satellite. The
strong source 3C84 is barely visible.
IUCAF SUMMER SCHOOL 2002
Passband of the filter used to suppress the
satellite emissions.
IUCAF SUMMER SCHOOL 2002
21cm continuum
observation with
interference
(diagonal stripe
in lower left
corner) resulting
from a strong
source.
IUCAF SUMMER SCHOOL 2002
The interference was caused by DAB satellite
AfriStar.
After filtering, AfriStar is invisible in the 21cm band.
Field: 2x2 deg.
Maximum pfd:
9.3 Jy/beam
In the 18 cm band, AfriStar remains visible with moderate pfd level.
Field: 2x2 deg
Maximum pfd:
43.8 Jy/beam
IUCAF SUMMER SCHOOL 2002
The 1.3-1.7 GHz system is a prime focus receiver with cooled HEMT .......
To suppress strong radio transmitter signals above 1450 MHz the filter at 1.345 to 1.435 GHz is
recommended for sensitive continuum measurements.
IUCAF SUMMER SCHOOL 2002
Further 21 cm
continuum
measurements.
IUCAF SUMMER SCHOOL 2002
Colour scale:
LHC/RHC 1.6 - -0.16 K
U/Q
0.12 - -0.16 K
elongated feature in
RHC: 0.25 Jy/beam
integration time:
1 sec/pixel
duration of interference:
35 sec
IUCAF SUMMER SCHOOL 2002
Dear Gerry.
one of our observers has experienced interference in the 1400 - 1427 MHz band yesterday,
and we wonder, if this illegal transmitter on ISS is switched on already, or was switched
on yesterday. IF so, one chance of identification would be the polarisation. The observer was looking into two
frequency bands, on below the passive band, the other within the passive band, and at both circular polarisations
in each band. The interference showed up in one channel only, within the passive
band and in one circular polarisation.
Do you have a chance to find out such operational details,
or, if not, do you know a better source to contact?
Cheers,
Klaus
IUCAF SUMMER SCHOOL 2002
To: Klaus Ruf <[email protected]>
Date: Thu, 14 Feb 2002 11:03:37 +0100
Subject: Re: ISS
Klaus,
The GTS has right hand circular polarisation. I heard during the last days in
Geneva that GTS may be switched on occasionally for testing purposes , but people
seem rather tight lipped. Keep watching!
There should be an evaluation report available rather soon, in which the
potential of rfi to the RA band is also investigated.
Best regards,
Gerri
IUCAF SUMMER SCHOOL 2002
Dear Gerri,
>The GTS has right hand circular polarisation.
Volltreffer!!
I'll talk to the observer, and keep you informed.
Klaus
IUCAF SUMMER SCHOOL 2002
IUCAF SUMMER SCHOOL 2002
IUCAF SUMMER SCHOOL 2002
Proposed mitigation factors!
IUCAF SUMMER SCHOOL 2002
2.1. The provisions listed below relating either to frequencies or bands to be used for
safety and distress communications or allocated for passive usage prohibit any other use:
a) Provisions relating to safety and distress communications:
aa) Appendix S13 (Part A2) ....;
ab) Appendix S15 (GMDSS), .... .
b) Provisions relating to passive usage: Nos. S5.267 and S5.340.
2.2. The Board considers that, in view of this prohibition, a notification concerning any
other use than those authorized in the band or on the frequencies concerned cannot be
accepted even with a reference to No. S4.4; furthermore the administration submitting
such a notice is urged to abstain from such usage.
In the case of assigning frequencies in a band to which S5.340 applies to radio stations
the notes Nos. 2.1b and 2.2 shall apply."
From: The “Rules of Procedure” of the RRB.
Spectral emissions
ATTEN
1 0 dB
RL 0 dBm
17.5
M KR
1 0 dB
/
-1 4 . 3 3 dBm
2 4 . 0 2 4 GH z
7.5
- 2.5
REF LV L
0 dBm
Proposed broadband automotive radar
across a passive band at 24 GHz.
Residual carrier due to
limited AM index
Abs. Bandwidth 3GHz @-10dB
fractional BW appr. 12.5%
( per definition WB or UWB ? )
-12.5
-22.5
-32.5
-36.5
-42.5
-52.5
10dB
Comb lines of unsmoothed spectrum
placed -6dB below power limit
for spurious emissions (-30dBm)
-50.5
-62.5
-72.5
CEN TER
2 4 . 0 2 4 GH z
* RBW 1 0 0 kH z
* V BW
ATTEN
RL 0dBm
SPAN
50.00
10dB
10dB/
1 kH z
MKR
SPAN
5 GH z
SWP 1 3 0 sec
-68.33dBm
23.50000GHz
MHz
Power density of smoothed spectrum
(appr. -100dBm/Hz)
Emissions drop below thermal noise
(kT= -174dBm/Hz) at distance of 5m
for isotropic receivers
-36.5dBm
-54
-50.5dBm
-68
CENTER
23.50GHz
*RBW
100kHz
*VBW
1kHz
SPAN
50.00MHz
SWP
1.30s ec
No emissions below 20 GHz
Traditional VHF/UHF bands
are not affected
IUCAF SUMMER SCHOOL 2002
Audi, BMW, DaimlerChrysler, Fiat, Ford, Jaguar, Opel / GM, Porsche, PSA Peugeot Citroën, Renault, Saab, Seat,
Volkswagen, Volvo, A.D.C., Bosch, Delphi, InnoSent, Megamos, Siemens VDO, TRW, Tyco Electronics, Valeo, Visteon.
24 GHz Short Range Radar
UWB Workshop Apr.11th, 2002
Estimation of Occurence Probability for elevation ? < 15°
Boundary conditions of worst case TX-PSD calculation:
•Best case weather condition without water vapour attenuation (e.g. cold winter
night,oxygen attenuation only, 0.04dB/km) ==> Sensitivity = -247dBm/Hz @10°
elevation
•otherwise (e.g. normal dry summer day with typically 0.16dB/km, 7.5mm H2O)
==> Sensitivity = -241dBm/Hz @10° elevation ==> 6dB RA sensitivity
degradation
==> p bestcase. weather 10days/a = 2.7%
•RA dish has to point towards the SRR transmitter in azimuth and elevation
(e.g. between 8..20°, span 12°), otherwise high spatial separation
==> p bestcase. spatial 12°/90° * 12°/360° = 0.44%
•The SRR has to point towards the RA dish. p Tx azimuth 90° / 360° = 25%
==> p entire = (pi)= 3E-5 and last but not least the vehicle is moving
There is no evidence for aggregation due to the high spatial RA separation
IUCAF SUMMER SCHOOL 2002
Final Conclusions:
• Mitigation techniques have been invented by radio
astronomers, have always been applied, and still
have a great potential for future improvement.
•Mitigation techniques may be costly and
constraining. Need to take the initiative to study and
to define, what is achievable and at which price.
•Mitigation factors are being used to replace the RR!