1、ERC REPORT 36 7 European Radiocommunications Committee (ERC) k-. .- within the European Conference of Postai and Telecommunications Administrations (CEPT) SHARING BETWEEN THE FIXED SERVICE AND THE RADIO ASTRONOMY SERVICE IN THE FREQUENCY RANGE 3.4 GHz - 105 GHz Stockholm, May 1995 STD-CEPT ERC REPOR
2、T 3b-ENGL 3995 = 232b434 0035472 339 = Copyright 1995 the European Conference of Postai and Telecommunications Administrations (0 STDeCEPT ERC REPORT 3b-ENGL 3795 m 2326434 0035473 275 = ERC REPORT 36 Page 1 SHARING BETWEEN THE FIXED SERVICE AND THE RADIO ASTRONOMY SERVICE IN THE FREQUENCY RANGE 3.4
3、 GHz - 105 GHz 1. INTRODUCTION This report provides guidance on sharing between the radio astronomy and fixed services operating in the frequency range 3.4 GHz - 105 GHz within Europe. The information presented has been taken hm the following sources: - draf extracts from the ITU-R Working Party 7D
4、radio astronomy Handbook - information supplied by the European Science Foundation Committee on radio astronomy frequencies (ESF-CRAP) - a working party established to study sharing aspects between the Fixed and radio astronomy services in one European country Annex I to this report provides a list
5、of radio astronomy frequencies which are used at the various observatories in Europe. 2. SHARING CONSIDERATIONS Most radio astronomy bands are shared with active services which transmit. Such sharing is particularly difficult for radio astronomy, which is a passive service. Because of the great dist
6、ances of astronomical sources the power flux density levels of the emissions under investigation are often 100 dB or more below those of man-made transmissions near the radio observatory. The strength and characteristics of the astronomical signais are determined by laws of nature and are beyond the
7、 control of the radio astronomer. Furthermore, because of the experimental nature of the science the radio astronomer is often unable to know in advance what the characteristics of the emissions will be. These factors make radio astronomy particularly vulnerable to interference. interference can be
8、damaging not only if it is strong and obliterates the astronomical signais, but also if it is weak. An insidious danger to radio astronomy lies in the interference which is just below the power level at which it can be. recognised in individual measurements and which is present for a large fraction
9、of the total time. In this case there may be no means during the experiment of detecting that interference has occurred, and subsequent data examination could lead to serious errors. Radio astronomy observatories are usually located at sites specially chosen to minimise interference from other servi
10、ces. The sites are usually at a considerable distance from the major terrestrial sources of interference and are frequently screened by nearby high ground. With this protection for the observatory and the protection afforded by the curvature of the Earth, sharing with terrestrial transmitters is pos
11、sible when the transmitter power is low and there is sufficient geographical separation. However, with the very sensitive systems used in radio astronomy, large separations are usually necessary. Sharing is not generally possible when the transmitter is within lie-of-sight of the radio astronomy ant
12、enna or the antenna feed. It is usuaily necessary for the transmitter to lie well over the horizon, at distances of 100 km or more. 3. PROTECTION CRITERIA FOR THE RADIO ASTRONOMY SERVICE An important protection criterion for radio astronomy is the power level of the interference considered harmful.
13、The harmful threshold depends on the frequency of observation and the type of measurement being made. Threshold interference levels for both continuum and spectral line observations are presented in Recommendation ITLJ-R RA.769. ERC REPORT 36 Page 2 A second criterion relates to the fraction of the
14、sky for which radio astronomy observations are to be protected. For ground-based sources of interference a value of O dBi is adopted for the gain of the radio astronomy antenna in the direction of the interferhg source, or in the direction of the horizon for a distant transmitter. The adoption of th
15、is value means that potential sources of interference at the harmful threshold levels given in Recommendation IT- R RA.769 will not cause harmful interference to observations made at elmtion angles greater than 19 degrees (based on the generased radiation pattem given in Recanmendation KU-R SA.509).
16、 In fact radio astronomas may be prepared to accept this restriction of their sky covexage, provided that earth-miation allows all available parts of the celestial sphere to be accessed at some time. A third aiterion which must be amsidered is the pacentage of time that a harmful interference level
17、may be exceeded without seriously demg the operation of the service. in this report a singie permtage value has been chosen for all cases although it is clear that some observatiOns are more susceptible to brief periods of interference thau othas. For the calculations presented in this report it has
18、 been accepted that the harmful interfaence levels given in Recarmnendation ITU-R RA.769 may be exceeded due to propagation effects for no more than 10 % of the time. Strong interference Occumng oniy 10 % of the time because transmissions are limited to that period of time would not be acceptable. I
19、t should be noted that the detailed characteristics of the intedemm and their relation to the particular type of radio astroncanical observation will need to be taka into account. It must be emphasised that for some types of observation a 10 % mure rate due to interference imposeS severe restriction
20、s on the radio astronomer. For some observations a high probability of success is desirable because of the difcuity or impossibility of repeating them An example is an observation of a comet, which may produce rapidly Varying emissions during its passage, and which may not return for many hundreds o
21、f years. Some other types of observation require simukanecjus measurements at different wavelengths and at a number of sites, at each of which success must be obtained if the a-nt as a whole is to be successful. An example is a c BI then: Pt(dBW) = PTBW) - 10 log U) the number and distribution of th
22、e transmitters; iii) the transmitter e.ir.p. in the direction of the radio astmnomy site; iv) the fraction of the time the transmitter is active; v) the proie of the terrain; vi) the local presence of treeshiidings; 6) atmospheric conditions. Because of the my factors involved the boundaries of the
23、cc+ordination zones need to be established indiividually for each radio astronomy site at which such a zone is required taking due acmmt of any special features of the radio astronomy measurements and of the active service which shares the band. It should be reaiised that the size of the co- ordinat
24、ion me auld be a hundmi kilometres or more. Por many small mtries the mordhation zone required may extend beyond the national bomdaries into countries where the frequency allocations may be different. Thus special conditions may need to be applied when determining coordination zones to protect radio
25、 astronomy in smali colmtries. The Co-ordination zone dehes a region arcund the radio observatory autside of which the usen of the active service can transmit hiy withcut causing harmful interference to the radio astconomy observations. For users within the ce ordination me some means must be found
26、to avoid harmful interference to the radio astronomy service, for example by pointing the Fmed link away from the observatory or taking advantage of naturai shielding. Sharing in the band 3.4 GEIZ - 50 GHz This section describes the results of sharing calculations which have been Camed out for share
27、d radio astronomy bands below 50 GHz. coordination distances have been calculated between a hypothetical transmitter and radio asmmy receiver. For a time percentage of 10 % and distances greater than approximately 100 the tropospheric scatter mechaukm is dominant. Por shorter distances difhction dom
28、inatec. Recommwdaticn ITU-R FN.4525 provides procedures for evaluating the available propagation loss between stations on the surface of the Earth within the frequency range of about 0.7 GHz to 30 GHz. Table 1 presents co-ordination distances which have been calculated to the nearest 5 km, using the
29、 tropospheric scatter prediction prdure provided in this Reammendation. In the absence of an alternative approach kthh Study Group 3 documentation, this predication procedure has been used for frequencies up to 50 GHz. Results are given for three sites having horizon angles of O“, 1“ and 4“ respecti
30、vely. In some cases the transmitter bandwidth is less than the receiver bandwidth and hmce a number of transmittllig channels within the receiver bandwidth can be occupied. For the purposes of prcducing Table 1 it has been assumed that at a specrfic distance from the observatory, only one transmitte
31、r is pointing in the direction of the obsenratory and Operating within the receiver bandwidth. For Co-ordination distances less than 100 km the dominant pmpagation mechanism is dif transmitter power; gain of the transmitter in the direction of the radio astronomy obSmtw, transmitter e.i.r.p. in the
32、direction of the radio astronomy observatory; transmitter bandwidth; the type of radio astronomy observafioli (C denotes continuum and SL denotes spectral he obSmtim); threshold for hamiful intedmn, taken from column 7 of Tables 1 and 2 of Recommendaticai ITU-R RA769, for continuum and spectral he o
33、bservations respective the required transmission loss ddated ushg equations (2) and (3); co-ordination distance required to avoid harmful intedemm to the radio astnxiomy observaticais in the case where the horizon at the observatory is at an elevation angle of O degree; cordjnation distance required
34、 to avoid harmful intdmce to the radio astnniomy observations in the case where the horizon at the obsmtory is at an elevation angle of 1 degree; ordinatiun distance required to avoid harmful intdm to the radio astronomy observations in the case where the horizon at the obsmtq is at an elevation ang
35、le of 4 degrees. Frequency MHz (1) 4830 5000 10600 22200 31000 49000 TABLE 1 - Sharing paramters and Co-ordination distances Assumed interfering Assumed radio Required transmitter astronomy receiver transmission loSS PI iBW (7) - - -218 -218 -207 -207 -202 -202 -210 -192 -207 - BI L MHz dB km (8) (9
36、) (1 0) 0.05 243 520 0.05 199 110 10 255 650 10 21 1 195 100 253 535 100 209 130 0.25 225 130 500 227 150 0.50 219 400 STD-CEPT ERC REPORT 3b-ENGL 1995 232h4L4 0015478 857 9 ERC REPORT 36 Page 6 4.4. 5. 6. 6.1. Sharing in radio astronomy bands above 50 GHz There are allocations above 50 GHz to the r
37、adio astronomy service for both conhum and spectral line observations. Some of these allccations are shared with a variety of active services. Until recently there have been relatively few active systems operating above 50 GHz, and consequently few reported cases of interfmn to radio astronomy. Shar
38、ing with active services above 50 GHz will be made easier by several facts: i) high transmitter gains are easier to achieve with antennas of modest size, ii) atmosphaic attenuation is higher; Ui) the troppherk scatter signai decreases mnotonically with increasing frequency. TIMESHARING Becaw of the
39、nature of the phenomena observed in radio astraiomy, dy under special cmditions will it be feasible to devise timesharing programmes between radio astronomy and otha services. purthme adve usas who provide a service to customers may be unwilling or unable to adopt tirne sharing. Time sharing may som
40、etimes be possible in principle, but in practice the difficulties associated with it are operational rather than technical. For these and other reasons time sharing has not yet been a feature of any extended radio astronomy programme. Nevertheless limited tine sharing to permit observatiOns at a rad
41、io astronomy site may be possible, and may indeed be necessary on occasion. Radio astrongners sometimes need to obsave cutside the frequency bands allocated to their service, and in such cases time sharing with active services may be the only available option. Recommendation ITU- R RA.3 14-8 acknowl
42、edges this fact, and urges administrations to provide assistance in the awrdination of expahmtal observations of specrral hes in bands not allocated to radio astronomy. GUIDANCE ON ESTABLISHING COORDINATION ZONES LESS THAN 100 km Table 1 shows that in the cases where the fixed link has a low e.i.r.p
43、. or the kquency is sufficiently high, the ce ordination distance is often less than 100 km. Ihmfore the co-ordhation zone should be determined using an appropriate dikction model. In order to calculate diffraction loss accurately a detailed knowledge of the terrain is required for each azimuth arou
44、nd the radio observatory and hence it may be useful to computerise the procedure. In the absence of detailed terrain knowledge, a mordjnation zone can be established based upon practical sharing experience. The following sections provide guidance on establishing CO-ordination zones based upon the pr
45、actical sharing experiences of one European country. Practical experience ofsharii at 22 GHz Within one Eu- country, the radio astronomy and fixed services have successfully shared the bands 22.21 - 22.5, 22.81- 22.86 and 23.07 - 23.12 since 1988. A -odinaticm zone with a radius of 50 kmhas been in
46、operation and both services have agreed that this arrangement has been smful. Typical parameters for the fixed service in this band are: Power -15 dBW, Gain 41.5 &i, Bandwidth 3.5 MHz. The radio astronomy observatories in this country have horizon angles of apprOximately 1 degree. ERC REPORT 36 Page
47、 I _ Gain (ai) Bandwidth (MHz) 6.2. 6.3. 13 34 2 2 Sharing at 10 GHz The radio astronomy and fixed services have a shared allocation in the band 10.6 - 10.68 GHz. Table 1 shows that at 10 GHz, the uxmination distance can be less than 100 km if the e.i.r.p. is suciently low and thm is a sufficient ho
48、rizon angle at the observatory. Within one Europeau country a “DMA Point to Muitipint system is in operation. This system has the following parametas: TABLE 2 II (Basestation loutstation Compared with the situation at 22 GHz, both the propagation loss and the required transmission loss are less at 1
49、0 GHz. Hence in order to calculate an appropriate Co-ordination disiance it is necessary to carefully compare the frequency dependent tenns used to caldate propagation loss and the required transmission loss for the two bands. The outstation has the higher e.ir.p. and hence has been used in the following table: TABLE 3 Frequeneg Required transmission I loss Frequency dependent terms used in propagation calculations 10.6 I 200 I 20.5 I 0.5 I The table shows that at 10 GHz the lower required transmission loss more than compensates for the smaller propag
