1、 STD-ITU-R RECMN P-LhLZ-ENGL 1999 4855212 0537283 037 300 Rec. ITU-R P.1412 RECOMMENDATION ITU-R P.1412 PROPAGATION DATA FOR THE EVALUATION OF COORDINATION BETWEEN EARTH STATIONS WORKING IN THE BIDIRECTIONALLY ALLOCATED FREQUENCY BANDS (1999) The IT Radiocommunication Assembly, considering a) that t
2、he Radio Regulations allocate some frequency bands for the bidirectional use of Earth-space systems; b) for two earth stations being operated bidirectionally; c) nation area around an earth station in frequency bands between O. 1 GHz and 105 GHz; that different propagation paths should be taken into
3、 account for the assessment of the need for coordination that studies have been undertaken by Radiocommunication Study Group 1 on the determination of the coordi- recommends 1 dering the need for coordination between earth stations operated bidirectionally. that the information and illustrative exam
4、ples contained in Annex 1 should be taken into account when consi- ANNEX 1 1 Introduction The possible requirements for operating earth stations in bidirectional frequency allocations raises a number of considerations which need to be consolidated in order to demonstrate that sharing is feasible in
5、many cases. This Annex demonstrates this feasibility and then extends the assessment to particular areas where such operations require more careful scrutiny. By facilitating the evaluation of interference potential within the coordination area determined by Recommendation ITU-R IS .848, the feasibil
6、ity of such operations is emphasized. The purpose here is to provide a simplified procedure, applicable to representative geometrical configurations, concentrating on the evaluation of the effect of rain scatter in bidirectional coordination. 2 Interference scenarios Three interference configuration
7、s are considered: - between two (large) earth stations, with both transmitter and receiver operating to two separate geostationary satellites; between a geostationary-satellite orbit (GSO) terminal and a feeder link for a non-GSO satellite of the mobile- satellite service (i.e. earth station with a
8、large antenna); between a GSO terminal and a large number of non-GSO fixed-satellite service (FSS) terminals (small antennas). - - COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services STD-ITU-R RECMN P.1412-ENGL 1999 4855232 0537284 T53 Re
9、c. ITU-R P.1412 301 For the first two of these configurations, which employ mediumhigh gain antennas, the narrow-beam approximation of the bistatic radar equation may be used. For the third configuration, with one mediumhigh gain antenna and many small earth stations with widebeam antennas, the narr
10、ow-beam approximation can be used for the main lobe of the high gain antenna to the side lobe of the widebeam antenna. In this case, it is assumed that the small earth stations may be limited to elevation angles above 40“; other cases with elevation angles down to 15“ may need a different approach,
11、e.g. using the auxiliary contour method. 3 Basis of the method 3.1 Mode (i), clear air propagation For mode (1), the interference along the great circle plane containing the boresight will be reduced by at least 22 dB when the elevation angle of the earth station antenna is increased from 5“ to at l
12、east 40“. At other azimuths, not along the boresight azimuth, the reduction will be smaller but it will be from a lower initial value of antenna gain in that direction. 3.2 Mode (2), hydrometeor scatter For mode (2), the computation is more complex but a reduction in coupling can be inferred qualita
13、tively from the reduced common volume within the atmosphere which will result from raising the earth station elevation angles from 5“ to at least 40“. The geometry assumed for the method is shown in Fig. 1, where T is the transmitter and R is the receiver. It is assumed initially, that the beam from
14、 T is in, or near, the vertical direction with an isolated rain cell located so as to fill the beam, i.e. a “worst case“ situation. Applying the general equation for bistatic scatter to an element 6V in the beam as shown in Fig. 1: P,./P, = (G,/4ny2)(rl.6V14xx2)G,h2/4n) where: x : distance from 6V t
15、o R y : distance from 6V to T G, : transmitter antenna gain G,: receiver antenna gain q : h : wavelength average cross section per unit volume and no attenuation is assumed outside the beam from T. Suppose d, the separation between T and R, is appreciably greater than the rain height, h. Then if the
16、 beam from R is directed in azimuth and elevation so that it is at least 45“ from any portion of the rain in the beam from T, there is a simple expression for the side-lobe gain of R in the rain direction. Also, most of the rain in the beam from T will contribute to the scatter (assuming no signific
17、ant site shielding) until d becomes much larger than, say, 100 km. Even for d = 200 km, 80% of the rain volume in the beam will still be effective, assuming h = 4 km and a “4/3 Earth“ model. Substituting for 6V, in terms of G, and integrating for the whole volume, it can easily be shown that the rat
18、io of received to transmitted power is given by: P,. / pt = G,. q h2 h)/256 d2 for the conditions assumed, where G, is the side-lobe gain (assumed uniform) as shown in Fig. 1, and the beam T is in, or near, the vertical direction. COPYRIGHT International Telecommunications Union/ITU Radiocommunicati
19、onsLicensed by Information Handling ServicesSTD.ITU-R RECMN P-1412-ENGL 1999 302 Rec. ITU-R P.1412 D 4855212 0537285 99T FIGURE 1 Bidirectional scatter geometry I h I A: side-lobe coupling B: rain cell The estimation of the additional loss due to attenuation outside the common volume is a complex pr
20、oblem of statistical variability in both rainfall rate, and rain cell size. However, recognizing that a “conservative“ estimate is necessary in coordination, an isolated rain cell may be assumed. The additional loss will depend, at a given frequency, on the size of the cell and its location. If it i
21、s located so that an appreciable portion of the cell is between T and R, the extra loss may be significant. If its centre lies on the other side of T from R (but still filling the T beam), the extra loss will be small. It has been shown that, due to the compensating effects of decreasing cell diamet
22、er and increasing rate of attenuation (dB/km) as rainfall rate increases, the additional loss is not strongly dependent on rainfall rate, being approximately 4 dB, for rainfall rates in the range 10-60 mm/h, at 18 GHz; about 2 dB at 12 GHz; and negligible at 4 GHz. Although the geometry would be som
23、ewhat different, the same values could be assumed for attenuation outside the rain-scatter volume. With this addition, plus a small correction for gaseous absorption where necessary, the transmission loss can be calculated as a function of distance, frequency, and of reflectivity (Le. rainfall rate)
24、. It is appropriate to assume a value of 4 km for the rain height, h, a value which is representative of a time percentage of about 0.01% for latitudes of O“ to 55“. For the third configuration, listed in 0 2, use Recommendation IT-R P.620 as a basis for the computations if the elevation of the wide
25、beam antenna goes below 30“. 4 Illustrative examples of the application of the method to the three configurations 4.1 Bistatic scatter calculations for GSO/FSS Numerical integrations using the bistatic radar equation have been performed for main lobe - side-lobe coupling between two stations working
26、 in the bidirectional mode. Calculations were made assuming the transmitter and receiver have similar gains of 57.5 dB, with a side-lobe pattern given by: The transmitter elevation angle was fixed at 30“. The receiver was assumed to be pointing away from the transmitter direction, i.e. with an eleva
27、tion angle greater than 90“. The geometry is shown in Fig. 2. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesSTD=ITU-R RECMN P-1412-ENGL 1999 W 4855212 0537286 82b W Rec. ITU-R P.1412 303 Calculations were made for a frequency of 18 G
28、Hz, and for four rainfall rates, 2, 8,28 and 78 mmh, corresponding to Climate F for time percentages of 1%, 0.1%, 0.01% and 0.001%. Attenuation due to rain between the two beams was arbitrarily set to 4 dB at 18 GHz, independent of rainfall rate. Although higher specific attenuation may be expected
29、for higher rainfall rates, the precipitation may be more widespread for lower rainfall rates, giving a similar path attenuation over a wide range of rainfall rates. This is a coarse but appro- priate approximation. The results are shown in Fig. 3. FIGURE 2 Geometry with fixed transmitter and receive
30、r 150 160 v v1 O e .: 170 v) .- E c 180 Rx Tx i&az FIGURE 3 Variation of transmission loss with distance 190 10 20 50 100 Distance (km) Tx elevation = 30“ Rx elevation 90“ Frequency = 18 GHz 141243 COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handli
31、ng Services STD-ITU-R RECMN P-LI12-ENGL 1999 W 4855212 0537287 7b2 = 304 Rec. ITU-R P.1412 4.2 Elevation angle dependence for bistatic scatter: Coupling between a widebeam receiver and a narrow-beam transmitter 4.2.1 The transmitter elevation angle was fixed at 30“ and the receiver elevation varied
32、from 5“ to 155“ as in Fig. 4. Widebeam antenna tracking over a broad range of elevations FIGURE 4 Geometry with elevation angles fixed for the transmitter and variable for the receiver Rx Tx (Variable elevation) (Fixed elevation) The computed transmission loss results are shown in Fig. 5, for three
33、different distances between the transmitter and receiver sites. This shows that when the receiver elevation angles are less than 30“, main beam intersection will occur, giving high coupling. For angles greater than 30“, only coupling from transmitter main lobe to receiver side lobe occurs, which is
34、then independent of elevation angle. A similar behaviour is seen for all distances, though with different levels of transmission loss. FIGURE 5 Variation of transmission loss with elevation of a widebeam receiver 100 rn O .- 8 140 Co rn E 160 P 180 O 20 40 60 80 100 120 140 160 Angular separation al
35、ong great circle path (degrees) 10 km - 20km 30 km - . Tx elevation = 30“ 1412-05 COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesSTDmITU-R RECMN P-1432-ENGL 3999 4855232 0537288 bT9 Rec. ITU-R P.1412 305 Frequency (GHz) 5 Further calc
36、ulations with a fixed transmitter elevation of 30“ and a widebeam receiver with elevations between O“ and 60“ have been performed assuming a high intensity raincell of 60 mm/h in the common volume, for three frequencies 5, i5 and 30 GHz. The attenuation within the common volume at each frequency is
37、listed in Table 1. Attenuation (a) O TABLE 1 Attenuation assumed at each frequency 15 4 30 12 I I The results are shown in Fig. 6. These indicate that the transmission loss is, to a first approximation, independent of frequency. At a separation between Tx and Rx of 5 km, the minimum transmission los
38、s is about 98 dB. This can be scaled to other distances, D, using the relation: L = 98 + 15(logD -0.7) for D21 (4) 4.2.2 Figure 7 shows the second geometry considered, where the receiver has an elevation of 30“, and computations of loss are made for various elevations of the narrow-beam transmitter.
39、 Narrow-beam antenna tracking over a range of elevations The results are shown in Fig. 8. For a 10 km separation, there is very little coupling between the two systems for transmitter elevation angles below 60“, but as the elevation increases beyond this point, coupling rapidly increases as the tran
40、smit beam enters the main beam of the receiver. This happens at a height of 10 km with this geometry. For wider separations, the angles are correspondingly larger. The results depicted in Fig. 5 indicated that for receiver elevation angles greater than 30“ the loss is virtually independent of elevat
41、ion angle. Consequently, Fig. 9 shows the dependence of loss on distance, at a frequency of 18 GHz, with a transmitter elevation of 30“, a receiver elevation of 80“, and two rainfall rates, 30 and 60 mm/h. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Informatio
42、n Handling Services306 STD-ITU-R RECMN P.3432-ENGL 3999 W 4855232 0537289 Rec. ITU-R P.1412 FIGURE 6 Variation of transmission loss with elevation angie for a widebeam receiver O IO 20 30 40 50 60 70 Angular separation along great circle path (degrees) a) 5 km Tx - Rx separation 535 m 90 100 110 120
43、 130 140 150 1 60 170 O 10 20 30 40 50 60 70 Angular separation along great circle path (degrees) b) 10 km Tx - Rx separation 100 1 IO 1 20 1 30 140 150 160 170 O 10 20 30 40 50 60 70 Angular separation along great circle path (degrees) c) 20 km Tx - Rx separation 1412-06 COPYRIGHT International Tel
44、ecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services- STDmITU-R RECMN P-3432-ENGL 1779 4855232 0537290 257 H 307 Rec. ITU-R P.1412 FIGURE 7 Geometry with fixed receiver and variable elevation transmitter Rx Tx (Fixed elevation) (Variable elevation) FIGURE 8 Variatio
45、n of transmission loss with elevation of narrow-beam transmitter 100 v 120 .d 5 140 v1 .- Ei = 160 E! c I 80 O 20 40 60 80 100 120 140 160 Angular separation along great circle path (degrees) 10 km - 20km 30 km - . Rx elevation = 30“ 1412-08 COPYRIGHT International Telecommunications Union/ITU Radio
46、communicationsLicensed by Information Handling Services308 STD-ITU-R RECMN P-II4L2-ENGL 1999 W 4855232 0537293 II93 Rec. ITU-R P.1412 E .$ 170 y .- E fi E 180 FIGURE 9 Variation of transmission loss with distance 150 160 v 190 10 20 50 Distance (km) Tx elevation = 30“ Rx elevation = 80“ Frequency = 18 GHz 100 141249 COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services
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