1、 Recommendation ITU-R RA.1513-2 (03/2015) Levels of data loss to radio astronomy observations and percentage-of-time criteria resulting from degradation by interference for frequency bands allocated to the radio astronomy service on a primary basis RA Series Radio astronomy ii Rec. ITU-R RA.1513-2 F
2、oreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequency spectrum by all radiocommunication services, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommen
3、dations are adopted. The regulatory and policy functions of the Radiocommunication Sector are performed by World and Regional Radiocommunication Conferences and Radiocommunication Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in th
4、e Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms to be used for the submission of patent statements and licensing declarations by patent holders are available from http:/www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Co
5、mmon Patent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information database can also be found. Series of ITU-R Recommendations (Also available online at http:/www.itu.int/publ/R-REC/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for televisio
6、n BS Broadcasting service (sound) BT Broadcasting service (television) F Fixed service M Mobile, radiodetermination, amateur and related satellite services P Radiowave propagation RA Radio astronomy RS Remote sensing systems S Fixed-satellite service SA Space applications and meteorology SF Frequenc
7、y sharing and coordination between fixed-satellite and fixed service systems SM Spectrum management SNG Satellite news gathering TF Time signals and frequency standards emissions V Vocabulary and related subjects Note: This ITU-R Recommendation was approved in English under the procedure detailed in
8、 Resolution ITU-R 1. Electronic Publication Geneva, 2015 ITU 2015 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without written permission of ITU. Rec. ITU-R RA.1513-2 1 RECOMMENDATION ITU-R RA.1513-2 Levels of data loss to radio astronomy observations
9、and percentage-of-time criteria resulting from degradation by interference for frequency bands allocated to the radio astronomy service on a primary basis (Question ITU-R 227/7) (2001-2003-2015) Scope This Recommendation addresses the levels of data loss to radio astronomy observations and percentag
10、e-of-time criteria resulting from degradation by interference for frequency bands allocated to the radio astronomy service on a primary basis. It includes studies of sharing situations for terrestrial and space-based applications, as well as an extensive section on measurement of data loss from weak
11、, pulsed interference. The ITU Radiocommunication Assembly, considering a) that research in radio astronomy depends critically upon the ability to make observations at the extreme limits of sensitivity and/or precision, and that the growing use of the radio spectrum increases the possibility of inte
12、rference detrimental to the radio astronomy service (RAS); b) that for some radio astronomy observations, such as those involving the passage of a comet, an occultation by the moon, or a supernova explosion, a high probability of success is desirable because of the difficulty or impossibility of rep
13、eating them; c) that since interference to radio astronomy can result from unwanted emissions of services in adjacent, nearby, or harmonically related bands, interference from several services or systems may occur in any single radio astronomy band; d) that burden sharing may be necessary to facilit
14、ate the efficient use of the radio spectrum; e) that mitigation techniques are a part of burden sharing, and more advanced techniques are being developed for future implementation, to allow more efficient use of the radio spectrum; f) that threshold levels of interference (assuming 0 dBi antenna gai
15、n) detrimental to the RAS for 2 000 s integration times are given in Recommendation ITU-R RA.769, but that no acceptable percentage of time has been established for interference from services with transmissions randomly distributed in time and either sharing a frequency band with the RAS, or produci
16、ng unwanted emissions that fall within a radio astronomy band; g) that administrations may require criteria for evaluation of interference between the RAS and other services in shared, adjacent, nearby, or harmonically related bands; h) that methods (e.g. the Monte Carlo method) have been developed
17、to determine the appropriate separation distance between radio astronomy sites and an aggregate of mobile earth stations, and that these methods require the specification of an acceptable percentage of time during which the aggregate interference power exceeds the threshold levels detrimental to the
18、 RAS; i) that studies of sharing scenarios and experience gained from long practice have led to values of tolerable time loss due to degradation of sensitivity, on time scales of a single observation, which are explained in more detail in Annex 1, 2 Rec. ITU-R RA.1513-2 recommends 1 that, for evalua
19、tion of interference, a criterion of 5% be used for the aggregate data loss to the RAS due to interference from all networks, in any frequency band allocated to the RAS on a primary basis, noting that further studies of the apportionment between different networks are required; 2 that, for evaluatio
20、n of interference, a criterion of 2% be used for data loss to the RAS due to interference from any one network, in any frequency band, which is allocated to the RAS on a primary basis; 3 that the percentage of data loss, in frequency bands allocated to the RAS on a primary basis be determined by usi
21、ng one of the following: (1) Recommendation ITU-R S.1586; (2) Recommendation ITU-R M.1583, or (3) the percentage of integration periods of 2 000 s in which the average spectral pfd at the radio telescope exceeds the levels defined (assuming 0 dBi antenna gain) in Recommendation ITU-R RA.769, whichev
22、er is appropriate; 4 that the criteria described in 3.3.2 of Annex 1 be used for evaluation of interference, in any frequency band allocated to the RAS on a primary basis, from unwanted emissions produced by any non-GSO satellite system at radio astronomy sites. Annex 1 Data loss resulting from inte
23、rference Page 1 Introduction 3 2 Data loss and sky blockage . 4 3 Sharing situations . 5 3.1 Interference due to variable propagation conditions 6 3.1.1 Terrestrial applications . 6 3.1.2 Space-based applications . 6 3.2 In-band sharing, where the transmission is variable in time and location 7 3.2.
24、1 Terrestrial applications . 7 3.2.2 Space-based applications . 7 3.2.3 Space-based radio astronomy applications 7 3.3 Unwanted emissions into a radio astronomy frequency band, where the transmission is variable in time and/or direction of arrival 7 3.3.1 Terrestrial applications . 7 3.3.2 Space-bas
25、ed applications . 7 3.4 Measurement of data loss from weak, pulsed interference . 9 Rec. ITU-R RA.1513-2 3 3.4.1 Method . 10 3.4.2 Effect of regular pulses 11 3.4.3 Long period pulses . 12 3.4.4 Mitigation methods 12 3.4.5 Equivalence of rapid pulses and continuous emission . 12 3.4.6 Summary 13 4 C
26、onclusions 13 1 Introduction An important parameter for all radiocommunication services is the percentage of time lost to interference. Administrations may need quantitative criteria relative to radio astronomy operations with active services operating in the same, adjacent, nearby, or harmonically
27、related bands. For example, Recommendation ITU-R M.1316 uses this percentage of time lost to interference in the calculation of the separation distance by default between stations operating in the MSS (Earth-to-space) and a radio astronomy observatory, by using the Monte Carlo methodology. Existing
28、limits to the aggregate time losses tolerated by various other science services are given in Table 1, for comparison. TABLE 1 Example of criteria for aggregate percentage of time of data loss use for other science services Radio telescopes are designed to operate continuously, following a schedule o
29、f observing programs requested by astronomers. As a rule, access to radio telescopes is on a competitive basis, with research proposals often exceeding available telescope time by a factor of 2-3. Virtually all radio astronomy installations are operated out of public funds, and must be used very eff
30、iciently. Some loss of observing time resulting from maintenance or upgrading of hardware or software, however, cannot be avoided. Experience over many years of operation with major instruments by one Earth exploration-satellite service (EESS) (passive sensors) (%) (Recommendation ITU-R SA.1029-2):
31、3-D atmospheric sounding All other sensors 0.01 1.0-5.0 Command and data transmission systems operating in the earth exploration-satellite and meteorological-satellite services (%) (Recommendation ITU-R SA.514-3) 0.1-1.0 EES and MetSat services using spacecraft in geostationary orbit (%) (Recommenda
32、tion ITU-R SA.1161-1) 0.0025-0.1 Space operations systems S/N 20 dB for 99% of time (%) (Recommendation ITU-R SA.363-5) 1.0 4 Rec. ITU-R RA.1513-2 administration shows that such losses need not exceed 5% of time, for example one 8 h day per week. Considerations of overall efficiency and cost of oper
33、ation indicate that the additional aggregate time loss due to interference should be limited to a similar 5% figure. In order to achieve the figures shown in Table 1, individual services should design their systems and control their operations to an appropriate fraction of these figures. Prudence di
34、ctates that individual systems be allowed only a fraction of the interference budget, depending on factors related to the actual allocation situation, such as band sharing and the interference potential due to unwanted emissions from other services. It should be noted that the concept of aggregate d
35、ata loss is not fully developed at present. Simulation tools, such as the one described in Recommendation ITU-R M.1316, allow the case of interference resulting from a single system to be considered. Other methodologies for single systems are also being developed. At this time there is no similar to
36、ol for the case of aggregate data loss resulting from several systems. A method that takes into account the characteristics of several systems may be difficult to develop. A particular difficulty is the apportionment of the aggregate data loss among the various systems. Further studies of these prob
37、lems are needed. The advent of radio services using space stations and high-altitude platform stations requires reassessment of the measures by which the RAS is protected from interference. Frequency sharing with such services is normally impossible, but potentially negative effects upon the RAS by
38、services in nearby bands arise through two factors: a) unwanted emissions falling in bands allocated to the RAS; b) intermodulation and departures from linearity in radio telescope systems due to strong signals in adjacent bands. It is assumed that the satellite operators will use all practical mean
39、s to minimize unwanted emissions, and radio astronomers all practical methods to minimize sensitivity to signals in adjacent or nearby bands. Nevertheless, item b) should be an important consideration when operating systems in bands adjacent or close to bands allocated to the RAS. 2 Data loss and sk
40、y blockage Whenever data loss is mentioned in this Recommendation, it refers to data that have to be discarded because they are contaminated by the aggregate interference, from one or more sources that exceeds the levels of Recommendation ITU-R RA.769, under the assumptions stated therein. The term
41、blockage is used here to indicate antenna directions in which the level of interference received exceed those given for detrimental interference in Recommendation ITU-R RA.769. In the presence of such interference, data useful for research at the frontiers of knowledge is generally not obtainable. D
42、ata loss may result from loss of part of the observing band, part of the observing time or from blockage of part of the sky. All of these can be expressed as loss of effective observing time. It is stated in Recommendation ITU-R RA.1031 that many radio astronomy measurements can tolerate interferenc
43、e from a shared service which exceeds the thresholds given in Recommendation ITU-R RA.769, for 2% of time. It should be noted that such observations, which can tolerate enhanced measurement errors, represent observations such as solar radio flare patrols. Observations of significance in radio astron
44、omy are those which result in new knowledge of astronomical phenomena, which either require making observations of objects not previously studied, or observing known objects with increased precision. Both such cases call for observations at the highest achievable sensitivity. As radio astronomy has
45、matured, the usefulness of data which is limited in accuracy by the presence of interference has declined, and it is the usual practice of astronomers to delete data for which there is any evidence of interference. Thus it is a matter of Rec. ITU-R RA.1513-2 5 practical reality that interference occ
46、urring at any identifiable level results in loss of the contaminated data. The 0 dBi contour of the pattern for large antennas between 2 GHz and about 30 GHz defined in Recommendation ITU-R SA.509 has a radius of 19. When a radio telescope points less than 19 from a transmitter, emitting in a radio
47、astronomy band at the detrimental level defined in Recommendation ITU-R RA.769, interference results. This effectively blocks radio astronomy observation within a region of the sky 19 in angular radius. Fractional sky blockage is the ratio of sky blockage (above the horizon), as defined above, to th
48、e solid angle of the visible hemisphere. Figure 1 shows the effect of a hypothetical transmitter on the horizon at the origin of the azimuth scale, which just meets the spectral pfd level of Recommendation ITU-R RA.769 at a radio astronomy station. The contours in the figure show the decibel level b
49、y which the received power from the transmitter exceeds the level at which it is detrimental to radio astronomy, as a function of the pointing angle of the radio astronomy antenna. The received transmission causes detrimental interference when it is received in sidelobes of the radio astronomy antenna with gain greater than 0 dBi. Table 2 shows the percentage of sky receiving such detrimental interference, for pointing angles of the antenna at elevations above 5. Since radio astronomy antennas are rarely pointed below 5, this is the lowest elevation considered. Fo
