1、 Rec. ITU-R S.1712 1 RECOMMENDATION ITU-R S.1712 Methodologies for determining whether an FSS earth station at a given location could transmit in the band 13.75-14 GHz without exceeding the pfd limits in No. 5.502 of the Radio Regulations, and guidelines to mitigate excesses (2005) Scope WRC-03 adop
2、ted Resolution 144 to invite the ITU-R to develop Recommendations to establish technical or operational methods to facilitate sharing and greater flexibility in deployment of FSS earth stations smaller than 4.5 m in the band 13.75-14 GHz in conformity with Radio Regulations (RR) No. 5.502, and which
3、 may also be used to establish a basis for bilateral agreements between administrations. This Recommendation proposes three methods for determining whether FSS earth stations at a given location can transmit in the band 13.75-14 GHz without exceeding the pfd limit in RR No. 5.502. It also provides a
4、dditional measures that administrations of small and narrow countries can consider when deploying FSS earth stations. The ITU Radiocommunication Assembly, considering a) that WRC-03 revised the sharing constraints on the fixed-satellite service (FSS) (Earth-to-space) in the band 13.75-14 GHz; b) tha
5、t this FSS band is shared with the radiolocation and radionavigation services; c) that the revised sharing conditions approved at WRC-03 permit the operation of geostationary FSS earth stations in the band 13.75-14 GHz with antennas of diameter D, with 1.2 m D TP, this path is trans-horizon. Note th
6、at while Path 2 and Path 3 do not cross contours higher than the earth station, their lengths exceed the nominal radio horizon found in Step B. Therefore, these are known to be trans-horizon without application of the Recommendation ITU-R P.452 test. Path 4 is both longer than Path 1 and crosses a h
7、igher contour. Calculation of the angles shows this path is indeed trans-horizon. By inspection, there are no other paths that would be expected to produce results different from the paths shown in the map above. Therefore, this earth station site is not within LoS of any point on the coast (low-wat
8、er mark). The trans-horizon curve of Fig. 4 shows that the required separation distance for this earth station is 34 km. Since the shortest path is greater than this value, the earth station site is found to be compliant with the pfd limit criteria. Note that the true peak in the profile in Fig. 3 w
9、as not actually used in the calculations. The contour map in Fig. 2 only provided with certainty elevation data in 25 m increments. A higher resolution source of terrain data could have been used to take advantage of the true height of the intervening terrain. 8 Rec. ITU-R S.1712 FIGURE 4 Method 1:
10、Separation distance curves (minimum distance from the low-water mark as a function of the e.i.r.p. density toward the horizon) Note that the LoS curve is derived from the loss for LoS paths found in Recommendation ITU-R P.452-11. The trans-horizon curve is simply the LoS curve shifted up the e.i.r.p
11、. axis by Y dB. In reality, diffraction loss is not simply the LoS loss shifted by a constant value. Further analysis of the Recommendation ITU-R P.452-11 model may show that the trans-horizon curve may require some adjustment. Annex 2 Method 2: pfd contours based on actual terrain data, the propaga
12、tion model in Recommendation ITU-R P.452-11, the FSS earth stations e.i.r.p. in 10 MHz bandwidth and the diameter and height above ground of its antenna 1 Generalities This method produces a set of contours, using actual terrain data, showing the minimum separation distance from the low-water mark o
13、r neighbouring countrys land border, an FSS earth station would need to meet in order to respect the pfd limits in RR No. 5.502, as a function of the earth station e.i.r.p. and the diameter and height of its antenna. An FSS earth station deployed within the contour based on its on-axis e.i.r.p. is a
14、ssumed to meet the pfd limit criteria. No further analyses are required. This method, using more accurate data than Method 1, permits to obtain larger areas inside which an earth station can be deployed while meeting pfd limits of RR No. 5.502. However, it should be noted that deployment in areas ex
15、cluded by this method is still possible provided a Rec. ITU-R S.1712 9 potential site can be shown to meet the pfd limit criteria through application of Method 3 (Annex 3). To account for different path loss due to different antenna heights, contours are to be defined for a range of earth station he
16、ights above local terrain level. 2 Step-by-step description of Method 2 Step 1: Definition of contours: Assuming several typical combinations of antenna diameter and associated on-axis e.i.r.p., a set of contours can be defined as figuring the areas where the considered earth station can be deployed
17、 while respecting the limits of RR No. 5.502. Taking into account the earth station discrimination between its direction of pointing and the direction of the border, a value of necessary path loss can be associated with each defined contour. Step 2: Computation of contours: Knowing the value of the
18、path loss to be associated with each contour, and taking into account an actual terrain database, it is possible to compute the position of each contour on a map. The propagation model to be used is the one described in Recommendation ITU-R P.452-11. Step 3: Compliance with the pfd limits criteria i
19、n RR No. 5.502: This compliance is assessed by the comparison of the position of the earth station intended to be deployed with the contour associated with the corresponding profile: if the position of the earth station intended to be deployed is inside the associated contour, the earth station can
20、be deployed with no additional measures while respecting the criteria of RR No. 5.502; if the position of the earth station intended to be deployed is outside the associated contour, additional considerations on the actual site environment are required. 3 Possible application of Method 2 3.1 Interfe
21、rence scenario The scenario for interference at the border of a country produced by an earth station within the country is illustrated in Figs. 5 and 6. 10 Rec. ITU-R S.1712 E: earth station e.i.r.p. toward satellite (dB(W/10 MHz) Gm: on-axis gain of earth station antenna (dBi) G(): earth station an
22、tenna gain in direction of horizon along the lowest-loss path to border (dBi) a: azimuth angle of earth station antenna axis (degrees West of South) e: elevation angle of earth station antenna axis (degrees) h: elevation angle of the horizon in the direction of the lowest-loss path (degrees) hE: hei
23、ght above local ground level of earth station antenna focal point (m) hR: height above local ground level of radar antenna focal point (m) pfd: power flux-density of interference at border (dB(W/(m2 10 MHz) : azimuth angle of lowest-loss path to the border (degrees West of South) It should be noted
24、that the off-axis angle, , of interest here is the angle between the main beam axis and the axis representing the first part of the lowest-loss interference path, which in general will include a small elevation angle, h (usually between about 1 and +3) (see Fig. 6). Rec. ITU-R S.1712 11 The pfd at t
25、he low-water mark or land border may be calculated by equation (1): pfd = E Gm+ G() L 10 log (2/4) dB(W/m2) (1) where: L: path-loss between isotropic antennas exceeded for all but 1% of the time (dB) : wavelength (m) At the mid-band frequency of 13.875 MHz, = 0.02162 m, so 10 log (2/4) = 44.29. Then
26、, to meet the required pfd limit, rearranging equation (1) gives: L = E (Gm G() + 159.29 dB (2) If the factors in the right hand side of equation (2) could be reduced to constants, the areas in which an earth station would meet the pfd limit would be indicated by contours of constant L. The factor (
27、Gm G() is the discrimination afforded by the earth station transmit antenna pattern in the direction of the interference path, and it depends on the antenna diameter and radiation pattern and on the off-axis angle . For the radiation pattern, it is appropriate to employ the algorithms in Recommendat
28、ion ITU-R S.580 for the side lobes, and to add a main-beam with a square-law roll-off (i.e. G() = Gm 12(/3dB)2) and a peak gain, Gm, corresponding to an illumination efficiency of 65% (i.e. Gm= 10 log (0.65) (D/)2 where D is the antenna diameter (m), and 3dB= 70/D). Thus, for any given earth station
29、 e.i.r.p. and antenna diameter, the value of L required to just meet the pfd limit may be calculated if the relevant value of is known. The earth station height above the terrain, hE, should be determined by the concerned administration according to the type of deployment intended. For example, the
30、contours shown later in this Annex were computed for hE= 11.2 m. This level implies highly-mounted terminals. If the earth station were contemplated for mounting on single-story flat roof structures (such as a gas station), 5 to 6 m would be appropriate. Caution should be used to avoid mounting eart
31、h stations above the height used to construct the contours so as to avoid exceeding the permitted pfd at the low-water mark. For mounting on taller buildings in an urban environment, even higher values for hEwould be necessary. In an urban environment, off-axis earth station paths in such locations
32、may be blocked by considerable clutter. In any case, such level of detail goes beyond the intent of Method 2. This method should be based on “typical” deployments rather than extreme cases. 12 Rec. ITU-R S.1712 3.2 Earth station off-axis angle for maximum pfd at low-water mark or land border It can
33、be seen in Fig. 5 that the off-axis angle depends on the direction toward the low-water mark or land border, and on the azimuth, a, and elevation, e, angles in which the earth station antenna is pointing. From Fig. 6 it can be seen that, to a small extent, depends also on the elevation angle, h, of
34、the local horizon. From the ITU-R reference patterns it is seen that, for relatively small off-axis angles the antenna discrimination increases fairly rapidly (proportionally to 25 log (), but for larger angles it tends to flatten out. The direction of the lowest-loss path toward the low-water mark
35、or border depends partly on the geography of the terrain between the border and the earth station i.e. there is a tendency for the lowest-loss path to lie in an azimuth direction near to that in which the distance to the border is shortest, and partly on the nature of the terrain (in hilly terrain t
36、he lowest-loss path may not coincide with the shortest path). If the direction of the shortest path is near to the azimuth pointing direction of the earth station antenna and the antenna elevation angle is low then, even if the shortest path is not the lowest-loss path, the highest pfd may be produc
37、ed because the effect of the antenna discrimination outweighs the effect of the terrain. However, since the azimuth bearing, , of the lowest-loss path to the border may be anything from 0 to 180 with respect to due-South, it is instructive to review how varies with for different combinations of a an
38、d e. The values of a and e themselves depend on the latitude of the earth station, E, and on its longitude, E, relative to longitude, S, of the satellite to which it is transmitting. From the geometry of Fig. 7 the off-axis angle (when h = 0) was calculated for values of the bearing in 5 steps from
39、180 to + 180, for earth stations at various different latitudes, and in each case for a range of differences in longitude between earth station E and its satellite S, thus spanning most practicable situations. Considering earth stations in general, all bearings for the lowest-loss path to the low-wa
40、ter mark or the land border are equally likely. Hence it was possible to convert the data thus obtained into cumulative probability distributions of . By adjusting these results to allow for h = +3 it was found that in the case of earth stations at 10 latitude, for example, exceeds 48 for 96% of azi
41、muth bearings. Similarly, for earth stations at 35 latitude exceeds 48 for 92% of azimuth bearings, and for earth stations at 60 latitude exceeds 48 for 91% of azimuth bearings. Since 48 is the off-axis angle at which the gain patterns in Recommendation ITU-R S.580 flatten off, the earth station ant
42、enna discrimination may thus be Rec. ITU-R S.1712 13 regarded as constant in 91% to 96% of cases. The value of that discrimination depends on the antenna diameter, and is as given in Table 1 for antennas with 65% efficiency: TABLE 1 Maximum antenna discrimination from Recommendation ITU-R S.580 Ante
43、nna diameter (m) 1.2 1.5 1.8 2.1 2.6 3.1 4.5 Discrimination (Gm G() for 48 (dB) 53.0 54.9 56.5 57.8 59.7 61.2 64.4 From the results of the calculations described in the foregoing paragraph it was found that the minimum values of off-axis angle occur for values of not far from the difference in longi
44、tude between the satellite and the earth station. Therefore, although it is “safe” to employ the present methodology for the great majority of cases, if an earth station site is on or close to the contour relevant to its e.i.r.p. and antenna size and there is reason to believe that the lowest loss p
45、ath to the low-water mark or land border (e.g. the path to the nearest point is in approximately the azimuth direction of the satellite, and the elevation angle to the satellite is less than (48+ h), it will be necessary to make an individual calculation of the pfd rather than relying on the contour
46、. However, this will only be necessary in a small minority of cases, depending mainly on the latitude of the country in which the FSS earth station is intended to be deployed. In those instances where the FSS earth stations operate above a certain elevation angle (e.g. above 48 + h for Recommendatio
47、n ITU-R S.580 antenna pattern) the e.i.r.p. density towards the horizon will be constant for all azimuths. In such cases, the contours corresponding to the required distance can be computed as a function of input power into the antenna and are independent of the antenna size. In the exceptional case
48、s where an earth station site is within but close to the contour relevant to the e.i.r.p. and antenna size concerned, the elevation angle is less than 51 (i.e. 48 + 3), and the azimuth bearing toward the satellite is near to the bearing of the lowest-loss path to the border, the off-axis angle, shou
49、ld be calculated from the expression = cos1cos( a) cos(e) cos(h) + sin(e) sin(h) (degrees). If the result is less than 48, then the earth station might exceed the pfd limit at the border by the difference between the off-axis gain derived according to Recommendation ITU-R S.580 for that particular off-axis angle and 10 dBi, if it was exactly on the contour, or less if inside the contour. This excess could be removed by either relocating the earth stat
