Committee on Radio Astronomy FrequenciesThe Committee on Radio Astronomy Frequencies (CRAF) is an Expert Committee of
the European Science Foundation (ESF).
Improvement of road safety is an important issue. Industry is contributing to this by equipping road vehicles with radar devices. Currently, two systems are considered:
The ITU-R World Radiocommunication Conference 2000, WRC-2000, re-allocated all radio frequency bands between 71 and 275 GHz and extended the frequency range footnote 5.565 to 1000 GHz. The result of this conclusion was that in the frequency range 76 - 81 GHz is now shared between inter alia the Radiolocation Service and the Radio Astronomy Service.
The issue of SRR is subject of many discussions in Europe, in the European Commission, EC, and the CEPT.
Considering the identification of the band 76 - 77.5 GHz to vehicular radar and the fact that is already in use for long range radar, the CEPT has identified the frequency range 77 - 81 GHz as the permanent frequency band not later than 1 January 2005 for SRR in Europe (see ECC Decision (04)03). This decision is an important element in the discussion on SRR and in which frequency band it should be deployed. It needs to be noted that the European Commission strongly favoured the introduction of SRR at ~24 GHz regardless the frequency regulatory difficulties since that could be more profitable for automotive industry.
In April 2004, the CEPT Working Group FM concluded on SRR that:
- the maximum penetration of SRR at ~24 GHz should not exceed 5.9%;
- the absolute reference date after which SRR at 24 GHz must no longer be placed on the market is 2012;
- SRR must be equiped from the beginning with an automatic deactivation to switch off its transmission
within a specified distance from a radio astronomy station to protect concerned radio astronomy sites;
- the centre frequency 24.125 GHz is used for the UWB as well as for the narrow band component of the system;
- a review process be carried out by the Radio Spectrum Committee in 2009 to consider actual market penetration
level and any action to be taken in order to avoid interference if the actual market penetration level is higher
than expected.
Further provisions need to be developed to provide the necessary regulatory and legal bases for this scenario.
Items 1 and 2 of this concluded scenario are important for the EESS (passive). Item 3 is essential for radio astronomy.
Considering the possible impact of this application on several radiocommunication services, the CEPT has completed a technical study on the "Compatibility of automotive collision warning short range radar operating at 24 GHz with other radiocommunication systems" (ECC Report 23).
This study concluded that the sharing study between the SRR application at ~24 GHz and the Radio Astronomy Service assuming a mean e.i.r.p. per SRR device of –90 dBm/Hz is not feasible. The CEPT agreed on a calculated negative margin in the order of 70 dB for spectral line observations and 90 dB for continuum observations, with a device density of 100 devices per km2 that are transmitting into the direction of the radio astronomy station. This conclusion depends on the aggregate impact of all SRR devices of which the emission is received at the radio astronomy station. This incompatibility scenario applies to the frequencies used by radio astronomy for spectral line observations of inter alia H2O, non-metastable ammonia line (NH3) and two lines of methyl formate and continuum observations in the frequency range between 22 and 24 GHz (footnotes 5.149 and 5.340 apply).
The CEPT also noted incompatibility between SRR and other services, such as the Fixed Services and the Earth Exploration-Satellite Service, although less severe than for the Radio Astronomy Service.
For further reading, see e.g.: Newsletter 2001-2.
CEPT has studied the the compatibility between SRR at ~79 GHz and radio astronomy. No study has yet been completed for the compatibility between long range radar operating at ~77 GHz and radio astronomy because of insufficient information to complete such a study. One should note that apart from the technical parameters of the transmitting devices also adequate ITU-R Recommendations are required. CRAF will consider this matter in due course.
As indicated above, SRR must move to ~79 GHz. The band 77 - 81 GHz is made available to this application by 1 January 2005. When SRR is deployed at ~79 GHz, the ECC Decision (04)03 states that studies have concluded that "regulatory measures could be identified enabling the coexistence between SRR in the frequency band 77-81 GHz and the Radio Astronomy Service, which is dependent on the aggregated impact of SRR devices transmitting in the direction of a radio astronomy station". The development of such regulations is very likely a matter of national Administrations only.
Spurious emissions
CRAF likes to make the following comments on the impact of spurious emissions from vehicular radar and radio astronomy:
<100 GHz
The influence of spurious emissions from vehicular radar operating below 77 GHz into bands used by radio astronomy has not yet been studied. CRAF considers that as long as this matter is not solved, it still requires attention.
>100 GHz
Spurious emission from vehicular radar operating at ~77 GHz could occur in the bands 148.5 - 151.5 GHz and 226 - 231.5 GHz. These bands fall each within one of the "windows" within which the Earth's atmosphere is relatively transparent. It is not as transparent as astronomers would like it to be. The degree of transparency varies with location, with altitude and with time, as the water vapour content varies. The most valuable observing time is obtained when the water vapour content is unusually low. At certain times it is so high that it is not worth trying to observe. In view of this it is necessary for interference calculations to assume the minimum atmospheric attenuation rather than the typical value that might be appropriate for other radio services. For this reason it would be as well to neglect the rather small, best case, contribution of atmospheric attenuation towards protecting observatories in interference calculations.
Millimetric wave radio observatories are ideally sited at high altitude where they may well be within direct line of sight of large areas of lower ground. This is true, within Europe, at the two sites of the Institut de Radio Astronomie Millimétrique, IRAM, (a joint project of France, Germany and Spain): Pico Veleta (Spain) and Plateau de Bure (France). However, it is possible to observe at sea level at Onsala (Sweden) when the atmosphere is very dry during times of hard frost in the winter. There is at present a low altitude observatory being built in the United Kingdom in the town of Bristol. There are other millimetric wave observatories in Europe and more will be built in future.
The threshold levels for harmful interference in are given in the ITU-R Recommendation RA769-2.
CRAF is seriously concerned with the effects of spurious emissions from vehicular radars on observations above 100 GHz, i.e. in the bands 148.5 - 151.5 GHz and 226 - 231.5 GHz. A preliminary study indicates that the level of the harmonic emission limits considered by the FCC indicates that a coordination zone of a few km in radius would be needed to meet harmful interference thresholds for a single radar. Most observatories are not able to regulate vehicular traffic in such a large surrounding area; at least one is located in direct line of sight to a highway less than 2 km distant, and others have direct lines of sight to roads at lower elevations.
Maintenance of spurious emission limits after the initial production of the radar units is another concern. Since many automobiles are operated with improperly functioning (or poorly maintained) headlights, tires, windshield wipers, seatbelts, and other safety items, it is reasonable to expect that many vehicles, due to minor collision damage or improper maintenance, will be operating with radar systems that do not meet spurious emission standards. While this is beyond the control of the radar manufacturers, it should be taken into account when specifying initial spurious emission limits. Besides being an interference problem, an improperly functioning millimeter wave radar system also poses a health hazard.
In order to minimize the interference potential, CRAF would like to see vehicular radar spurious emission standards set such that the harmful interference threshold is not exceeded due to the operation of motor vehicles beyond a specified distance from a radio telescope since to identify a signal as interference of vehicular radar systems is extremely difficult to impossible by radio astronomy system since radio astronomy aims to observe signals with unknown characteristics.
The radio astronomy community would like the automobile industry to consider automatic deactivation mechanisms with the different vehicular radar systems. In this fashion, radio observatories could place signs along nearby roads requesting that vehicular radars be turned off, to further protect radio astronomy observations. It seems to us that the on/off capability may be required in any event to assure safety when passing radio-controlled blasting zones.
Last modified: May 11, 2004