1、 Rec. ITU-R F.1820 1 RECOMMENDATION ITU-R F.1820 Power flux-density at international borders for high altitude platform stations providing fixed wireless access services to protect the fixed service in neighbouring countries in the 47.2-47.5 GHz and 47.9-48.2 GHz bands (Question ITU-R 212/9) (2007)
2、Scope This Recommendation provides power flux density (pfd) values for the purpose of protecting conventional fixed service stations in neighbouring administrations from co-channel interference from a high altitude platform station (HAPS) operating in the frequency bands 47.2-47.5 GHz and 47.9-48.2
3、GHz. Acronyms UAC Urban area coverage SAC Suburban area coverage RAC Rural area coverage The ITU Radiocommunication Assembly, considering a) that new technology utilizing high altitude platform stations (HAPS) in the stratosphere is being developed; b) that WRC-97 designated the 47.2-47.5 GHz and 47
4、.9-48.2 GHz bands for use as a co-primary fixed service for HAPS deployment; c) that Recommendation ITU-R F.1500 contains the characteristics of systems in the fixed service planned for HAPS usage in the 47.2-47.5 GHz and 48.2-48.5 GHz bands; d) that, while the decision to deploy HAPS can be taken o
5、n a national basis, such deployment may affect neighbouring administrations, particularly in small countries, recommends 1 that for the purpose of protecting conventional fixed service stations in neighbouring administrations from co-channel interference, based on the methodology described in Annex
6、1, a HAPS operating in the frequency bands 47.2-47.5 GHz and 47.9-48.2 GHz should not exceed the following power flux-density (pfd) values at the Earths surface outside an administrations borders, unless explicit agreement of the affected administration is provided at the time of the notification of
7、 HAPS: 141 dB(W/(m2 MHz) for 0 3 141 + 2.0( 3) dB(W/(m2 MHz) for 3 1), this is possible, although HAPS platforms station keeping is considerably looser than that of the GSO satellite if the fixed service antenna is pointed too closely to the nominal position of HAPS. However, a fixed service antenna
8、 typically is aimed horizontally toward another distant fixed service antenna, whereas HAPS platform antennas minimum elevation angle is about 4, hence the difference in the elevation angles between the interfering HAPS antennas and the fixed service antenna alone can provide at least a 25 dB reduct
9、ion of the interference signal. 8 Rec. ITU-R F.1820 Environmental screening of the fixed service antenna also helps to further reduce off-boresight interference. The solid curve in Fig. 5 depicts the computed pfd bound as a function of the elevation angle of the HAPS platform as viewed from the fixe
10、d service station. The dashed curve shows the same bound after the 20 dB rain attenuation margin has been subtracted. Note that the computed pfd bound (20 dB) is fairly flat for elevation angles above 13, and drops off abruptly for elevation angles below 3. FIGURE 5 pfd bound vs. elevation angle FIG
11、URE 6 Atmosphere attenuation vs. elevation angle Rec. ITU-R F.1820 9 Figure 6 depicts the variation of the minimum propagation attenuation due to atmospheric gases in the 47.2-48.2 GHz band as a function of the elevation angle of the HAPS platform viewed from the fixed service station, in accordance
12、 with Recommendation ITU-R F.1501. It indicates that the atmospheric attenuation remains small (0.57 dB at 90 and 1.9 dB at 22.5 or 50 km from nadir), until the elevation angle drops below 13 (attenuation = 3.4 dB, distance 90 km from nadir), at which point the attenuation increases almost exponenti
13、ally, reaching a value of 42.2 dB at 0.154 (approximately 500 km from nadir). At 3 ( 280 km from nadir) the atmosphere attenuation is 13.9 dB. Notice that the atmospheric attenuation decreases rapidly with altitude of the ground station. Above 10 km in altitude, the atmospheric attenuation varies fr
14、om 0.47 dB to 1.22 dB between 76 km and 200 km (from nadir). 3 Proposed HAPS pfd limit at international borders to protect fixed service Based on the results of this study it is proposed that for the purpose of protecting fixed service ground stations in neighbouring administrations from co-channel
15、interference, a HAPS operating in the frequency bands 47.2-47.5 GHz and 47.9-48.2 GHz should not exceed the following co-channel pfd at the Earths surface outside an administrations borders, unless explicit agreement of the affected administration is provided at the time of the notification of HAPS;
16、 141 dB(W/(m2 MHz) for 0 3 141 + 2.0( 3) dB(W/(m2 MHz) for 3 13 121 dB(W/(m2 MHz) for 13 90 where is the angle of the arrival above the horizontal plane of the Earth. The rationale for selection of an angle of arrival range smaller than 3 is that there is a greater likelihood that the fixed service
17、antenna may receive boresight or near-boresight interference from a HAPS platform, hence full protection is required. For angles of arrival 13 or above, boresight interference is highly unlikely, hence a 20 dB reduction of the fixed service antenna gain is assumed to reduce the pfd protection requirement from HAPS.
