1、 Rec. ITU-R M.1583-1 1 RECOMMENDATION ITU-R M.1583-1*Interference calculations between non-geostationary mobile-satellite service or radionavigation-satellite service systems and radio astronomy telescope sites (Question ITU-R 236/8) (2002-2007) Scope This Recommendation describes a methodology to b
2、e used to calculate the amount of data loss due to interference produced by a non-GSO mobile-satellite or radionavigation-satellite service system at a radio astronomy site. This methodology is based on the calculation of the epfd produced by the considered active system at the radio astronomy site.
3、 The ITU Radiocommunication Assembly, considering a) that, in some cases, the radio astronomy service and space services (space-to-Earth) have been allocated to adjacent or nearby frequency bands; b) that the radio astronomy service is based on the reception of emissions at much lower power levels t
4、han are generally used in other radio services; c) that, due to these low received power levels, the radio astronomy service is generally more susceptible to interference from unwanted emissions than other services; d) that due to the characteristics of non-geostationary (non-GSO) satellite systems,
5、 and in particular to the time-varying nature of interference, the level of interference from such satellites into radio telescopes cannot be evaluated in the same way as for the case of GSO satellites, recommends 1 that the determination of unwanted emission levels produced by a non-GSO radionaviga
6、tion-satellite service (RNSS) or a mobile-satellite service (MSS) systems on radio astronomy sites should be based on the method described in Annex 1; 2 that when performing this determination, the antenna pattern described in Recommendation ITU-R RA.1631 should be used to model radio astronomy ante
7、nnas; 3 that the percentage of time during which an equivalent power flux-density (epfd) threshold level is exceeded should also be determined in accordance with the method described in Annex 2. *This Recommendation should be brought to the attention of Radiocommunication Study Group 7. 2 Rec. ITU-R
8、 M.1583-1 Annex 1 Calculation of unwanted emission levels produced by a non-GSO RNSS or an MSS system at radio astronomy sites The methodology described here, based on the “equivalent power flux-density” (epfd) concept, is intended for use in calculating the power flux-density (pfd) levels produced
9、by unwanted emissions of a non-GSO satellite system into radio telescopes, taking into account the characteristics of both the satellite system and the radio telescope antenna. The value of the epfd is the aggregate of the contributions from all satellite emissions expressed as the pfd of a single e
10、quivalent source on the boresight (peak of main beam) of the radio telescope. 1 Required parameters Due to the particular characteristics of non-GSO satellite systems, it is clear that the level of the interference from such satellites into a radio telescope cannot be evaluated in the same way as fo
11、r GSO satellites. A statistical approach is needed which takes into account the dynamic aspect of non-GSO satellites. The evaluation of interference resulting from the satellites at the radio telescope during the integration time (2 000 s) should be based on statistical calculations and should take
12、into account the parameters of both the satellites and the radio telescope. Non-GSO satellite system parameters: the number of satellites visible in the sky at the radio astronomy station; the detailed orbital characteristics of the satellites; the pfd radiated by each satellite at the radio telesco
13、pe within the radio astronomy band considered, which may be estimated using a model of unwanted emissions mask. Radio telescope parameters: the antenna location; the antenna pattern and antenna gain; the practical range of pointing directions; the boresight pointing direction; the off-axis angles be
14、tween the boresight of the antenna of the radio astronomy station and the directions of the transmitting satellites; the integration time (2 000 s). 2 Calculation of epfd at radio astronomy sites The receiving gain of a radio telescope in the direction of a non-GSO satellite (as opposed to GSO) vari
15、es with time chiefly because of the movement of the satellite and the fine angular structure of the radio telescopes side-lobe pattern. There will be times when the telescope gain in the direction of a satellite is much higher than 0 dBi, and other times when it is less. In addition, in the case of
16、multiple satellites of a non-GSO system, all their contributions must be included and properly taken into account. Rec. ITU-R M.1583-1 3 This may be done using the concept of epfd originally defined to assess possible sharing conditions between GSO and non-GSO systems. In the section below the conce
17、pt is developed for the case of a radio astronomy station subject to interference from non-GSO satellites. 2.1 Definition of epfd When an antenna receives power, within its reference bandwidth, simultaneously from transmitters at various distances, in various directions and at various levels of inci
18、dent pfd, the epfd is that pfd which, if received from a single transmitter in the far field of the antenna in the direction of maximum gain, would produce the same power at the input of the receiver as is actually received from the aggregate of the various transmitters. The instantaneous epfd is ca
19、lculated using the following formula: =maxririitNiPGGdGepfdai,2l1010)(4)(10log10 (1) where: Na : number of non-GSO space stations that are visible from the radio telescope i: index of the non-GSO space station considered Pi :RF power of the unwanted emission at the input of the antenna (or RF radiat
20、ed power in the case of an active antenna) of the transmitting space station considered in the non-GSO system (dBW) in the reference bandwidth i : off-axis angle (degrees) between the boresight of the transmitting space station considered in the non-GSO system and the direction of the radio telescop
21、e Gt (i): transmit antenna gain (as a ratio) of the space station considered in the non-GSO system in the direction of the radio telescope di : distance (m) between the transmitting station considered in the non-GSO system and the radio telescope i : off-axis angle (degrees) between the pointing dir
22、ection of the radio telescope and the direction of the transmitting space station considered in the non-GSO system Gr(i): receive antenna gain (as a ratio) of the radio telescope, in the direction of the transmitting space station considered in the non-GSO system (see Recommendation ITU-R RA.1631) G
23、r,max : maximum gain (as a ratio) of the radio telescope epfd: instantaneous equivalent power flux-density (dB(W/m2) in the reference bandwidth at the radio telescope. The epfd calculation in equation (1) assumes that the pfd due to all interfering sources is directed at the boresight of the receivi
24、ng antenna, where the antenna gain is maximum. However, radio astronomy protection criteria are based on a 0 dBi contour of the radio astronomy antenna. Using the approach in equation (1), the pfd due to all interfering sources directed at the 0 dBi gain of the receiving antenna, can be determined a
25、s follows: =)(4)(10log102l1010dBi0 iriitNiPGGdGepfdair(2) 4 Rec. ITU-R M.1583-1 The dBi0=rGepfd values resulting from equation (2), averaged (in linear form) over a 2 000 s integration time, can be compared with pfd levels (defined assuming a 0 dBi receiving antenna gain in the direction of interfer
26、ence and given this integration time). NOTE 1 It is assumed that each transmitter is located in the far field of the radio telescope (that is, at a distance greater than 2D2/ where D is the effective diameter of the radio telescope and is the observing wavelength). Though this may not always be sati
27、sfied, it is considered to be an adequate approximation. NOTE 2 For some telescopes, the direction of maximum gain (boresight direction) may not always coincide with the geometrical axis of the radio telescope. NOTE 3 In the case of active antennas, Pishould be taken as the radiated RF power rather
28、than the power at the input to the antenna. NOTE 4 The antenna gain of the transmitting station, Gt(i) is taken at the frequency of the radio astronomy band considered. This may differ from the gain at the frequencies of the intended transmissions. Annex 2 Distribution of epfd levels This Annex desc
29、ribes a way to derive epfd statistics over the whole sky. 1 Division of the sky into cells of approximately equal solid angle The first step of this approach is to divide the sky into M rings parallel to the horizon and equally spaced in terms of elevation angle, from 0 to 90. The width of each ring
30、 is 90/M. The next step is to divide these rings into cells whose azimuth width is chosen to provide an integer number of cells per ring and is approximately equal to: )cos(/90elevationMdegrees Figure 1 provides an example of division based on a step of 3 width in elevation, this divides the sky int
31、o 30 rings of 3 of elevation angle. Then, the azimuth width is approximately equal to: )cos(30/90elevationdegrees Elevation is a mean elevation in a given ring. Rec. ITU-R M.1583-1 5 This leads to a division of the sky into 2 334 cells of approximately 9 square degrees of solid angle each. Table 1 p
32、rovides the number of cells for each ring corresponding to this example. TABLE 1 Example of division of the sky into square cells of about 9 square degrees solid angle Lower elevation of the ring (degrees) Ring solid angle (square degrees) Cumulative solid angle (square degrees) Azimuthstep (degrees
33、)Number of cells in the ring Cell solid angle (square degrees)Cumulative number of cells Percentage of solid angle (%) Cumulativesolid angle (%) 0 1 079.51 1 079.51 3 120 9.00 120 5.23 5.23 3 1 076.55 2 156.05 3 120 8.97 240 5.22 10.45 6 1 070.64 3 226.69 3 120 8.92 360 5.19 15.64 9 1 061.79 4 288.4
34、9 3 120 8.85 480 5.15 20.79 12 1 050.04 5 338.53 3 120 8.75 600 5.09 25.88 15 1 035.41 6 373.93 3 120 8.63 720 5.02 30.90 18 1 017.94 7 391.87 3 120 8.48 840 4.94 35.84 21 997.68 8 389.55 3 120 8.31 960 4.84 40.67 24 974.68 9 364.23 3 120 8.12 1 080 4.73 45.40 27 949.01 10 313.24 3 120 7.91 1 200 4.
35、60 50.00 30 920.75 11 233.99 4 90 10.23 1 290 4.46 54.46 33 889.95 12 123.94 4 90 9.89 1 380 4.31 58.78 6 Rec. ITU-R M.1583-1 TABLE 1 (end) Lower elevation of the ring (degrees) Ring solid angle (square degrees) Cumulative solid angle (square degrees) Azimuthstep (degrees)Number of cells in the ring
36、 Cell solid angle (square degrees)Cumulative number of cells Percentage of solid angle (%) Cumulativesolid angle (%) 36 856.72 12 980.66 4 90 9.52 1 470 4.15 62.93 39 821.14 13 801.81 4 90 9.12 1 560 3.98 66.91 42 783.31 14 585.12 4 90 8.70 1 650 3.80 70.71 45 743.34 15 328.46 4 90 8.26 1 740 3.60 7
37、4.31 48 701.32 16 029.79 5 72 9.74 1 812 3.40 77.71 51 657.39 16 687.17 5 72 9.13 1 884 3.19 80.90 54 611.65 17 298.82 5 72 8.50 1 956 2.97 83.87 57 564.23 17 863.06 6 60 9.40 2 016 2.74 86.60 60 515.27 18 378.33 6 60 8.59 2 076 2.50 89.10 63 464.90 18 843.23 6 60 7.75 2 136 2.25 91.35 66 413.25 19
38、256.48 8 45 9.18 2 181 2.00 93.36 69 360.47 19 616.95 9 40 9.01 2 221 1.75 95.11 72 306.70 19 923.65 10 36 8.52 2 257 1.49 96.59 75 252.09 20 175.74 12 30 8.40 2 287 1.22 97.81 78 196.79 20 372.53 18 20 9.84 2 307 0.95 98.77 81 140.95 20 513.49 24 15 9.40 2 322 0.68 99.45 84 84.73 20 598.21 40 9 9.4
39、1 2 331 0.41 99.86 87 28.27 20 626.48 120 3 9.42 2 334 0.14 100.00 2 epfd distribution for a cell First, a random choice is made for a pointing direction of the radio astronomy service antenna which will lie within a specific cell on the sky as defined in 1. Then, the starting time of the constellat
40、ion is randomly chosen. The epfdis then evaluated for each time sample over a 2 000 s integration time. The average epfd corresponding to this trial is then calculated for the chosen pointing direction and starting time of the constellation. This operation is repeated to obtain a statistical distrib
41、ution of the epfd in the considered cell. The methodology involves a number of trials, each of which calculates the averaged epfd level over a 2 000 s integration interval. The greater the number of trials, the more accurate this distribution will be. A sufficient number of trials is needed to achie
42、ve the required confidence level in the results. In particular, the number of trials multiplied by the 2 000 s integration time should be significantly higher than the period of the constellation. It is also necessary to ensure adequate statistical sampling over the full period of the constellation.
43、 Once it is found that no further significant change occurs in the distribution, it can be concluded that a sufficient number of trials has been performed. This check can be done either automatically as an integral part of the simulation, or manually, by stopping the simulation at regular intervals.
44、 Rec. ITU-R M.1583-1 7 3 Output in terms of percentage of data loss The epfd determination described in 2 provides a distribution of epfd levels for each cell of the sky which can be compared to the threshold levels used for radio astronomical measurements. When these levels are exceeded, some radio
45、 astronomy data will be lost. The percentage of this loss is defined as the sum of these losses in all cells over the number of trials. Figure 2 shows an example of the percentage of data loss per cell over the whole sky for a non-GSO RNSS constellation. FIGURE 2 Distribution of data loss over the sky
