1、 Rec. ITU-R SF.1601-2 1 RECOMMENDATION ITU-R SF.1601-2 Methodologies for interference evaluation from the downlink of the fixed service using high altitude platform stations to the uplink of the fixed-satellite service using the geostationary satellites within the band 27.5-28.35 GHz (Questions ITU-
2、R 218/9 and ITU-R 251/4) (2002-2005-2006) Scope This Recommendation provides methodologies for the interference evaluation from the HAPS-to-ground transmission downlink of the fixed service (FS) using high altitude platform stations to the uplink of the fixed-satellite service using the geostationar
3、y satellites within the bands 27.5-28.35 GHz.This Recommendation contains three Annexes that provide methodologies for interference calculation, calculation of the e.i.r.p. of transmission from HAPS, interference evaluation in terms of C/I and examples of applications of the methodologies in the App
4、endix. 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 made provisions for operation of HAPS within the fixed service (FS) in the bands 47.2-47.5 GHz and 47.9-48.2 GHz; c)
5、that since the 47 GHz bands are more susceptible to rain attenuation in those countries listed in Nos. 5.537A and 5.543A of the Radio Regulations (RR), the frequency range 18-32 GHz has been studied for possible identification of additional spectrum in ITU-R; d) that since the 47 GHz bands are more
6、susceptible to rain attenuation in certain countries, WRC-2000 made a provision for the use of HAPS in the FS in the bands 27.5-28.35 GHz and 31.0-31.3 GHz in certain countries under the condition that it does not cause harmful interference to, nor claim protection from, other types of FS systems or
7、 other co-primary services (RR Nos. 5.537A and 5.543A); e) that Resolution 145 (WRC-03) urgently requested studies on technical, sharing and regulatory issues in order to determine criteria for the operation of HAPS in the bands 27.5-28.35 GHz and 31.0-31.3 GHz; f) that the band 27.5-28.35 GHz is al
8、located to the fixed-satellite service (FSS) (Earth-to-space direction) on a primary basis; g) that there is a need for methods to evaluate the interference from transmissions in the HAPS-to-ground direction within the band 27.5-28.35 GHz that could be caused to receivers of FSS satellites in the ge
9、ostationary orbit, 2 Rec. ITU-R SF.1601-2 recommends 1 that the methodology contained in Annex 1 may be used to assess the level of interference from the HAPS-to-ground (downlink) transmission in the FS to the Earth-to-space (uplink) of the FSS using geostationary (GSO) satellites within the frequen
10、cy band 27.5-28.35 GHz; 2 that administrations may consider Annex 2 as a method to estimate the e.i.r.p. of transmissions in the HAPS-to-ground direction within the band 27.5-28.35 GHz that would cause a given increase in the interference-to-noise ratio (I/N) of receivers of FSS satellites in the ge
11、ostationary orbit; 3 that the methodology contained in Annex 3 may be used to assess the carrier-to-interference power ratio (C/I) for determining the level of interference from the HAPS-to-ground (downlink) transmission in the FS to the Earth-to-space (uplink) of the FSS using GSO satellites within
12、 the frequency band 27.5-28.35 GHz. Annex 1 A methodology for interference evaluation from the downlink of the FS using HAPS to the uplink of the FSS using GSO satellites within the band 27.5-28.35 GHz 1 Introduction This Annex provides a methodology for interference evaluation from the FS using HAP
13、S to a GSO satellite system in the FSS within the band 27.5-28.35 GHz. This band is used for the Earth-to-space (uplink) direction by the GSO/FSS system. 2 A methodology for interference evaluation 2.1 Interference from a HAPS system Figure 1 shows the analysis model assumed for the evaluation of in
14、terference from a HAPS system to a GSO satellite. The interference power level in 1 MHz, I(g,h,b,r) due to a spot beam of a HAPS, received by a GSO satellite (g) is calculated using equation (1): dB(W/MHz),(),(),()(),( rghGhgFSLbhgGFbPrbhgIrxStxHlossH+= (1) where: PH(b) : transmitter power in 1 MHz
15、(dB(W/MHz) at the input of HAPS antenna for the beam (b) FLoss: feeder loss (dB)Rec. ITU-R SF.1601-2 3 ),( bhg : discrimination angle (degrees) at the HAPS (h) between the pointing direction of a HAPS spot beam (b) and the GSO satellite (g) GHtx),( bhg : transmitter antenna gain (dBi) of the HAPS (h
16、) for off-axis angle ),( bhg FSL(g,h) : free space loss (dB) between the GSO satellite (g) and the HAPS (h) (h,g,r) : discrimination angle (degrees) at the GSO satellite (g) between the pointing direction of a GSO FSS reference point (r) and a HAPS (h), see Fig. 2 GSrx(h,g,r): receiver antenna gain
17、(dBi) of the GSO satellite (g) for off-axis angle (h, g,r). 4 Rec. ITU-R SF.1601-2 To calculate the discrimination angle at a GSO satellite, a reference point must be established for the calculations. The reference point is selected as a specific location on the surface of the Earth. It is then assu
18、med that the boresight of the spot beam antenna of the GSO satellite is always directed to the reference point, regardless of the orbital location of the spacecraft. In cases where the reference point is not visible to the GSO satellite, then it is assumed that the reference point is moved to anothe
19、r point under the condition that the elevation angle toward the GSO satellite is the minimum value. Figure 2 shows the geometric model of the example including the reference point. Based on an operational scenario of the HAPS system in which a HAPS can transmit multiple carriers in each spot beam, i
20、t is assumed that HAPS downlink multiple carriers could exist in the entire receiver bandwidth at the GSO satellite. The aggregate interference from a HAPS system is expressed as Isingleand calculated as a sum of the spectral density I(g,h,b,r) of all the possible spot beams of the HAPS which could
21、use the same frequency as shown in equation (2). =bbhhInrb,h,g,Insingle1101log10)/10(dB(W/MHz) (2) where bnindicates the number of spot beams which could use the same frequency and hnindicates the number of HAPS which one HAPS system consists of. Once the interference level received by the FSS has b
22、een assessed, the I/N ratio can be assessed as follows: 60)(log10/ =satsinglesinglesingleTkININI (3) where: I/Nsingle : interference-to-thermal noise ratio (dB) N : thermal noise power of satellite receiver in 1 MHz (dB(W/MHz) k : Boltzmanns constant (W/(K Hz) Tsat : system noise temperature of a GS
23、O/FSS satellite (K). Rec. ITU-R SF.1601-2 5 The calculated aggregate interference level would then be compared with an appropriate interference threshold in order to determine if the HAPS system is causing harmful interference to the FSS. 2.2 Interference from multiple HAPS systems Situations could
24、arise in which several operational HAPS systems could cause interference to a certain GSO satellite. The aggregate interference from multiple HAPS systems is expressed as Imultipleand derived from the sum total of each interference level from each HAPS system to the GSO satellite as shown in equatio
25、n (4). dB(W/MHz)11110log1010)/(=nn nrb,h,g,ImultiplesshhbbI (4) where snindicates the number of HAPS systems. The other terms are as described above for the case of interference from a single HAPS system. For an exact evaluation of a multiple HAPS situation, the characteristics of each HAPS system s
26、hould be used in the calculations. In the absence of such information for one or more of the systems, an approximate indication of the resulting interference can be obtained by using the characteristics of a reference HAPS system in the calculations. Once Imultiplehas been found, it can be used inst
27、ead of Isinglein equation (3) in order to assess the impact of the interference upon the FSS. 2.3 Downlink power control The interference from HAPS downlink to GSO/FSS uplink is maximum under the condition of maximum transmission power of HAPS downlink or under the rain condition. When using downlin
28、k power control in HAPS system, aggregate transmission power of HAPS downlink can be reduced under clear-sky conditions. As a result, the interference received at the FSS spacecraft is reduced in clear-sky conditions. 2.4 Input parameters Interference studies applying the methodology of this Annex s
29、hould use actual characteristics of FSS and HAPS systems under consideration if available. In their absence, the following values may be used: 2.4.1 HAPS characteristics See Recommendation ITU-R F.1569. 2.4.2 FSS input characteristics Tsat : 500 K Antenna beamwidth (small stations): 0.3 Antenna beam
30、width (hub stations): 2 Antenna gain: Recommendation ITU-R S.672, Annex 1, (Ls= 20 dB)1. 1Recommendation ITU-R S.672 provides design objectives for spacecraft antenna designers. Providing objectives for a shaped beam is not possible for typical cases as there is no knowledge of the FSS service area.
31、 A specific roll-off performance of Ls= 10 dB may be used so as to characterize the shaped beam case. Further study is required on the roll-off performance. 6 Rec. ITU-R SF.1601-2 Appendix 1 to Annex 1 An example of the application of the methodology of Annex 1 1 Interference model It is assumed a H
32、APS system consisting of a number of HAPS platforms is operating in a rectangular area as shown in Fig. 3. A platform located at the centre of the area is the reference point in this example calculation and all other platforms are deployed on the plane which is perpendicular to the line connecting t
33、he reference point and its nadir point on the Earth. When the reference point is taken as the origin of the x-y coordinates on that plane, it is assumed that the HAPS platforms are placed at every lattice point in the area which has the coordinates of (Lx, Ly), (Lx Ly), (Lx, Ly) and (Lx, Ly). Also a
34、ssuming that the numbers of HAPS platforms are nxand nyas counted on the x and y axes, respectively, then the total number of platforms, nt, in consideration becomes nx ny(nx and nyare odd numbers). In this deployment model, the separation distance between neighbouring HAPS are expressed as dxand dy
35、as measured along with the x and y axes, respectively. The dxand dyare given by 2Lx/(Nx 1) and 2Ly/(Ny 1), respectively. It is also assumed that the GSO satellite to be interfered is positioned in the direction of the assumed x axis and the satellite antenna is always pointed to the reference point.
36、 The angle in Fig. 4 is defined as the elevation angle of the satellite at the reference point measured from the x-y plane. The aggregate interference from the nTHAPS platforms are evaluated in terms of the interference to satellite noise power ratio, I/N, of the GSO satellite as a function of the e
37、levation angle, for combinations of typical HAPS deployment and satellite characteristics. Rec. ITU-R SF.1601-2 7 2 HAPS characteristics Typical parameters of HAPS systems at the 28 GHz band are given in Recommendation ITU-R F.1569. Table 1 shows the parameters used for the calculations. TABLE 1 HAP
38、S characteristics Parameters HAPS-1 HAPS-2 Altitude of HAPS (at the reference point) (km) 20 20 Aggregate e.i.r.p. of a HAPS sideward or backward(1)5 dBW in 20 MHz bandwidth 5 dBW in 20 MHz bandwidth Length of HAPS deployment area (2 Lx) (km) 1 000 600 Width of HAPS deployment area (2 Ly) (km) 1 000
39、 600 Number of HAPS on x axis (nx) 11 9 Number of HAPS on y axis (nyTotal number of HAPS (nT) 121 81 Distance between HAPS on x axis (dx) (km) 100 75 Distance between HAPS on y axis (dy) (km) 100 75 (1)The practical model with the 397 spot beams shown in Fig. 3 of Recommendation ITU-R F.1569. 3 GSO
40、satellite characteristics The parameters of the GSO satellite are shown in Table 2. 8 Rec. ITU-R SF.1601-2 TABLE 2 GSO satellite characteristics Parameters GSO-1 GSO-2 System noise temperature (K) 500 500 Antenna half-power beamwidth (degrees) 0.3 2 Antenna side-lobe level (dB) (Lsin Annex 1 of Rec.
41、 ITU-R S.672-4) 20 20 Antenna peak gain(1)(dBi) 55.0 38.5 (1)Calculated using the equation of Gmax(dBi) = 44.5 20 log ( is a 3 dB beamwidth (degrees). 4 Calculation results Figures 5 and 6 indicate the calculated I/N of the GSO satellite. It is obvious from the methodology that the I/N of the GSO sa
42、tellite largely depends on the peak gain of the antenna of the GSO satellite when the antenna is pointed towards the interference source. An antenna with the narrow beamwidth (0.3) receives more interference when the reference point has lower elevation angles because the number of the HAPS within th
43、e main beam is limited at the high elevation angles and increased at the lower elevation angles. On the other hand, an antenna with the wider beamwidth (2) receives less interference because of lower antenna gain and the interference level is rather constant because it almost covers the entire HAPS
44、deployment area within the main beam even for the high elevation angles. The interference level mainly depends on the propagation distance of the interference signal. For these cases results show that the I/N of the GSO satellite is less than 20 dB (1%) for both GSO satellite cases under usual opera
45、ting condition where the earth stations are assumed to have elevation angles of 20 or higher against the satellite. Rec. ITU-R SF.1601-2 9 Annex 2 A methodology for the calculation of the e.i.r.p. transmissions from HAPS in the HAPS-to-ground direction within the band 27.5-28.35 GHz that would cause
46、 a given increase in the I/N of receivers of FSS geostationary satellites 1 Introduction The measure of interference used in this method is the I/N of the FSS receiving system. The determinative interference characteristics of the FSS receiving system are its antenna gain and system noise temperatur
47、e. This method can be used to estimate the e.i.r.p. density of transmissions from HAPS in the HAPS-to-ground direction that could cause a given increase in the I/N of FSS receiving systems in the GSO orbit. 2 Description of the method The first step of the method is to calculate the given increase i
48、n interference-to-noise ratio, I/N, by determining the noise power in the assumed receiving system noise power density in 1 MHz. N = k T B (5) 10 Rec. ITU-R SF.1601-2 where: k: Boltzmanns constant (W/(K Hz) T: FSS receiving system noise temperature (K) B: reference bandwidth (1 MHz). Next, the assum
49、ed I/N is used to determine the interference power (dB(W/MHz). I = N + I/N (6) Then the power flux-density (PFD) that would produce the assumed interference at the GSO orbit is calculated: PFD = I GR+ 20 log ( f ) + 21.45 dB(W/(m2 MHz) (7) where: Gr:effective gain (dBi) of the FSS receive antenna in the direction of the interfering HAPS platforms, f: frequency of transmission (GHz). Then, the total e.i.r.p. from all HAPS transmissions that would produce this PFD at the GSO is (
