1、 Rec. ITU-R M.1748 1 RECOMMENDATION ITU-R M.1748*Protection of the radio astronomy service in the band 1 400-1 427 MHz from unwanted emissions of MSS feeder links that may operate in the bands 1 390-1 392 MHz (Earth-to-space) and 1 430-1 432 MHz (space-to-Earth) (2006) Scope This Recommendation prov
2、ides epfd values for the protection of radio astronomy stations operating in the band 1 400-1 427 MHz from MSS feeder links (space-to-Earth) that may operate in the band 1 430-1 432 MHz, as well as a methodology to determine separation distances between radio astronomy stations operating in the band
3、 1 330-1 427 MHz and MSS feeder links (Earth-to-space) that may operate in the band 1 390-1 392 MHz. The ITU Radiocommunication Assembly, considering a) that WRC-03 allocated the bands 1 390-1 392 MHz and 1 430-1 432 MHz provisionally on a secondary basis to the fixed-satellite service (FSS) for fee
4、der links for non-geostationary mobile-satellite systems (MSS) operating below 1 GHz in the Earth-to-space and space-to-Earth directions, respectively (see No. 5.339A of the Radio Regulations (RR) and that Resolution 745 (WRC-03) applies; b) that Resolution 745 (WRC-03) calls for studies, including
5、the measurement of emissions from equipment that would be employed in operational systems, to validate that these systems meet all requirements for the protection of passive services in the band 1 400-1 427 MHz from unwanted emissions from MSS feeder links; c) that the band 1 400-1 427 MHz is alloca
6、ted to the Earth exploration-satellite service (EESS) (passive), radio astronomy (RAS) and space research (passive) services on a primary basis in all Regions, and that No. 5.340 of the RR applies to this band; d) that the 1 400-1 427 MHz band is extensively used by radio astronomers worldwide for o
7、bservations of the neutral hydrogen spectral line, as well as for continuum observations; e) that the threshold levels of interference detrimental to the radio astronomical observations are given in Tables 1 and 2 of Annex 1 to Recommendation ITU-R RA.769; f) that Recommendation ITU-R RA.1513 provid
8、es criteria for recommended levels of data loss to the RAS from any one network and that both the uplink and downlink associated with a network may contribute to data loss to the RAS in the 1 400-1 427 MHz band; *This Recommendation was jointly prepared by Radiocommunication Study Groups 7 and 8 and
9、 any future revision will also be undertaken jointly. 2 Rec. ITU-R M.1748 g) that data losses from earth stations operating in the 1 390-1 392 MHz band to the RAS operating in the 1 400-1 427 MHz band may be minimized using relatively modest separation distances, of the order of 100 km or less; h) t
10、hat Recommendation ITU-R RA.1631 describes the radio astronomy antenna pattern to be used in compatibility studies involving satellite constellations, Recommendation ITU-R M.1184 provides technical characteristics of mobile-satellite systems in frequency bands below 3 GHz for use in developing crite
11、ria for sharing between the MSS and other services, and Recommendation ITU-R M.1583 describes the methodology to be used in interference calculations between non-geostationary mobile-satellite service or radionavigation-satellite service systems and radio astronomy sites, noting a) that, for typical
12、 combinations of data rates and modulation techniques, it is feasible to reduce unwanted emissions in the 1 400-1 427 MHz band to the interference levels detrimental to the RAS given in Recommendation ITU-R RA.769, without a specific post-amplifier filter, by employing baseband processing techniques
13、; b) that when the baseband processing referred to under noting a) is not sufficient by itself to meet the required unwanted emission levels an additional post-amplifier filter can be used; c) that the band 1 330-1 400 MHz, which is used to observe the red-shifted neutral hydrogen spectral line, is
14、also included in No. 5.149 of the RR, recommends 1 that unwanted emissions of non-GSO MSS feeder links (space-to-Earth) of a single network that may operate in the band 1 430-1 432 MHz should be less than: an epfd of 259 dB(W/m2) in any 20 kHz bandwidth of the band 1 400-1 427 MHz for more than 98%
15、of integration periods of 2 000 seconds for spectral line observations; and an epfd of 243 dB(W/m2) in the entire 1 400-1 427 MHz band for more than 98% of integration periods of 2 000 seconds for continuum (broadband) observations; 2 that the methodology contained in Recommendation ITU-R M.1583 sho
16、uld be used to derive a pfd limit per satellite from the epfd limits given for MSS networks in recommends 1 above; 3 that earth stations that may operate in the band 1 390-1 392 MHz in conjunction with a given non-GSO MSS network should be separated from radio astronomy stations which conduct observ
17、ations in the band 1 400-1 427 MHz, so that the total data loss due to uplink and downlink does not exceed 2%; 4 that the methodology described in Annex 2 should be used to derive the separation distance between the radio astronomy station and the MSS feeder-link earth station on a case-by-case basi
18、s. Rec. ITU-R M.1748 3 Annex 1 Example calculation of the pfd per satellite required to respect epfd limits for the protection of the radio astronomy service operating in the band 1 400-1 427 MHz from unwanted emissions of MSS feeder links that may operate in the band 1 430-1 432 MHz 1 Methodology R
19、ecommendation ITU-R S.1586 (or Recommendation ITU-R M.1583) provides a methodology to evaluate the levels of unwanted emissions produced by a non-geostationary satellite system at a radio astronomy site. It is based on a division of the sky into cells of nearly equal size and a statistical analysis
20、where the pointing direction of the RAS antenna and the starting time of the satellite constellation are the random variables. For each trial, the unwanted emission level (expressed in terms of epfd) is averaged over a 2 000 s period. Moreover, Annex 1 to Recommendation ITU-R RA.769 provides the thr
21、eshold levels for interference detrimental to the RAS and Recommendation ITU-R RA.1513 provides a criterion of 2% for maximum allowable data loss to the RAS due to interference from any one network, which is determined as the percentage of integration periods of 2 000 s in which the average spectral
22、 power flux-density (pfd) at the radio telescope exceeds the levels defined in Recommendation ITU-R RA.769. The purpose of the present study is to determine the maximum pfd level required for unwanted emissions of non-GSO MSS system feeder links in the band 1 430-1 432 MHz to comply with the criteri
23、a for the protection of radio astronomical observations in the band 1 400-1 427 MHz as given in Recommendations ITU-R RA.769 and ITU-R RA.1513, using the methodology of Recommendation ITU-R S.1586, which is designed to take into account the non-geostationary nature of these systems when assessing th
24、eir unwanted emission levels at radio telescope sites. 2 MSS system characteristics The characteristics of the MSS system are summarized in Table 1. It is assumed that the satellites are outfitted with an isoflux antenna, capable of producing a constant pfd on the ground. TABLE 1 MSS system characte
25、ristics Orbital altitude 1 000 km Orbital inclination 50 (and 83 for polar coverage) Number of planes 6 (+ one more for polar coverage) Number of satellites per plane 4 4 Rec. ITU-R M.1748 3 RAS station characteristics and protection criteria The Effelsberg radio telescope in Germany was chosen for
26、this analysis. Its geographical coordinates are: latitude: N 50.7, longitude: E 7.0. The antenna pattern and peak gain at boresight used are given in Recommendation ITU-R RA.1631. TABLE 2 pfd levels detrimental to the RAS Frequency band (MHz) Interference level (dB(W/m2) Reference bandwidth (MHz) Ty
27、pe of observation 1 330-1 400 1 400-1 427 1 400-1 427 196(1)180 196 0.02 27 0.02 Spectral line Continuum Spectral line (1)There is no detrimental threshold level defined in Recommendation ITU-R RA.769 for the band 1 330-1 400 MHz (see RR No. 5.149). The protection criterion listed above for this ban
28、d was derived from the one used in the band 1 400-1 427 MHz in case of for spectral line observations. The simulations were performed considering minimum telescope elevation angles of 0 and 3. In terms of an epfd level, the detrimental pfd threshold level corresponds to: maxlimlimGpfdepfd = TABLE 3
29、epfd levels detrimental to the RAS Frequency band (MHz) epfd interference level (dB(W/m2) Reference bandwidth (MHz) Type of observation 1 330-1 4001 400-1 427 1 400-1 427 259 243 259 0.02 27 0.02 Spectral line Continuum Spectral line 4 Determination of the required maximum pfd per satellite level fo
30、r the protection of the radio astronomy service 4.1 Procedure The following approach is used (see Recommendation ITU-R S.1586): Step 1: Select a pfd value per satellite. In a first approximation (and as a worst-case scenario) this value may be considered constant for all elevation angles. In the par
31、ticular example under consideration, the satellite is assumed to be equipped with an isoflux antenna. Rec. ITU-R M.1748 5 Step 2: Select a radio astronomy station. Step 3: Division of the sky into 2 334 cells of about 9 square degrees solid angle each (see Table 1 in Annex 3 to Recommendation ITU-R
32、S.1586). Step 4: For each cell t the radio astronomy station may observe (taking into account the minimum elevation angle minat which the radio astronomy station is capable of conducting observations in the frequency band, as defined in Appendix 4 of the RR), point the radio telescope towards a rand
33、omly chosen direction within the cell, and start the satellite transmissions at a randomly chosen point in time. The epfd is then evaluated for each time sample over a 2 000 s integration time, with a time Step of 1 s. The average epfd corresponding to this trial is then calculated. Step 5: If the e
34、pfd level averaged over the 2 000 s integration interval of the trial exceeds the interference threshold level, that particular 2 000 s observation is considered to be affected. Step 6: Repeat Steps 4 and 5 to get a representative number of trials (100 trials were found to be statistically sufficien
35、t). Step 7: Determine the percentage of affected integration periods of 2 000 s over the whole sky accessible to the radiotelescope as defined in Step 4. Step 8: Change the pfd level of the non-GSO MSS system until this percentage is below 2%. 4.2 Results The simulation leads to the required pfd lim
36、its per MSS satellite given in Table 4. TABLE 4 Maximum pfd levels per MSS satellite to protect a radio astronomy station Band and type of observation pfd limit per satellite (dB(W/m2) Reference bandwidth (MHz) 1 330-1 400 MHz (spectral line) 201 0.02 1 400-1 427 MHz (continuum) 185 27 1 400-1 427 M
37、Hz (spectral line) 201 0.02 The total amount of data loss is 2.07% when considering the minimum elevation angle of 0, and 1.65% when considering a minimum elevation angle of 3. Figure 1 shows, for the radio astronomy site of Effelsberg, for each cell over the whole sky, the percentage of observation
38、s where the epfd criterion has been exceeded. The total number of trials per cell is 100. The intensity scale represents the number of trials for which the epfd criterion has been exceeded. 6 Rec. ITU-R M.1748 FIGURE 1 Simulation results for Effelsberg 5 Conclusions The study shows that a pfd limit
39、of 185 dB(W/m2) (for continuum observations) per MSS satellite in the whole band 1 400-1 427 MHz and 201 dB(W/m2) (for spectral line observation) per MSS satellite in any 20 kHz bandwidth of the band 1 400-1 427 MHz is sufficient for the protection of the radio astronomy service for the system consi
40、dered. The spectral line pfd limit is also applicable to the band 1 330-1 400 MHz. Rec. ITU-R M.1748 7 Annex 2 Separation distance between radio astronomy stations operating in the band 1 400-1 427 MHz and MSS feeder-link earth stations that may operate in the band 1 390-1 392 MHz 1 Introduction The
41、 purpose of this Annex is to determine the separation distance between a radio astronomy station that may operate in the band 1 400-1 427 MHz and an MSS feeder-link earth station operating in the band 1 390-1 392 MHz, to avoid interference detrimental to the radio astronomy station. Recommendation I
42、TU-R RA.1513 deals with the issues of maximum levels of data loss and percentage-of-time criteria acceptable for radio astronomy observations that are central to sharing studies. The threshold levels of interference detrimental to radio astronomical observations are given in Recommendation ITU-R RA.
43、769. 2 Methodology For radio astronomy, the power received is integrated over a period of time in order to reach a better sensitivity. The result of this integration is called an observation in the following paragraphs. The power received from an interferer during an observation may be expressed as
44、follows: () () ()()=N1N1ibrttiLiGiGiPI (1) where: Lb(i): propagation loss at instant i Pt(i): transmitting power level (W) in the RAS bandwidth at the input to the antenna at instant i Gt(i): gain of the transmitting antenna in the direction of the radio astronomy antenna at instant i Gr(i): gain of
45、 the radio astronomy antenna in the direction of the transmitter at instant i N: number of samples I: interference power (W) in the reference bandwidth at the receiver input averaged over the observation period T. Usually (and to be consistent with the detrimental threshold levels given in Recommend
46、ation ITU-R RA.769) the calculation is performed over an integration period T of 2 000 s. During this period of time, some of the parameters may vary. For this particular application, Ptis considered constant. As the transmitter is an earth station following a satellite or a constellation of satelli
47、tes, Gtvaries during the integration time and also from one observation to the next. We assume that the radio astronomy antenna properties are fixed during the integration time (e.g. that Grdoes not vary in the 2 000 s period), but that the RAS antenna pointing direction varies from one observation
48、to the next. 8 Rec. ITU-R M.1748 Observations performed over a given integration time are considered lost when the interference power received, I, averaged over T exceeds the threshold value given in Recommendation ITU-R RA.769. Therefore: () ()=N1N1irtHtbiGiGPPL (2) where: Pt: transmitting power le
49、vel (W) in the RAS bandwidth at the input to the antenna (including feeder loss) Gt(i): gain of the transmitting antenna in the direction of the radio astronomy antenna at instant i Gr(i): gain of the radio astronomy antenna in the direction of the transmitter at instant i N: number of samples PH: interference power (W) threshold given in Recommendation ITU-R RA.769. It is necessary to perform the calculation over several periods of time in order to verify that the percentage of observations lost is lower than the 2% criterion given in Recommendation IT
