1、STD-ITU-R RECMN S-73b-3-ENGL 1997 48552L2 0530324 O29 m Rec. -R S.736-3 1 RECOMMENDATION ITU-R S.736-3* ESTIMATION OF POLARIZATION DISCRIMINATION IN CALCULATIONS OF INTERFERENCE BETWEEN GEOSTATIONARY-SATELLITE NETWORKS IN THE FIXED-SATELLITE SERVICE (Question ITU-R 4214) ( 1992- 1994- 1995- 1997) Th
2、e ITU Radiocommunication Assembly, considering a) that more than one geostationary-satellite network in the fixed-satellite service (FSS) operates in the same frequency band; b) that interference between networks in the FSS contributes to noise in each network; c) that it is necessary to protect a n
3、etwork in the FSS from interference by other such networks; d) that the detailed estimation of mutual interference between satellite networks, due to increased orbit occupancy requires more accurate values of polarization discrimination, resulting from the use of different or identical polarizations
4、 by wanted and interferhg systems; e) that the use for actual coordination requirements of the values of polarization isolation factors in Appendix 29 to the Radio Regulations, would not provide a precise estimation of polarization discrimination in the calculation of actual interference margins, re
5、commends that, to estimate the polarization discrimination between two satellite networks, the method described in 1 Annex 1 should be used. ANNEX 1 Estimation of polarization discrimination 1 Polarization is defined as a vector of the electric field wave which is located in a plane orthogonal to th
6、e direction of the wave propagation. Generally, this vector describes an ellipse. Two particular cases arise, firstly circular polarization where the two axes of the ellipse are equal, secondly linear polarization where one of the axes is zero. If the radiated wave is linearly polarized, two orthogo
7、nal polarization planes exist, each polarization vector keeping a fixed direction. The polarization plane, for a linearly polarized wave, is the plane containing the direction of the wave propagation and the polarization vector. If the radiated wave is circularly polarized, right- and left-hand rota
8、tions exist. Definition of the polarization of a wave * This Recommendation should be brought to the attention of the Radiocommunication Working Party 10-1 1 S. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services STD-ITU-R RECMN S-73b-3-E
9、NGL 3797 W 4855232 0530325 Tb5 2 Rec. ITU-R S.7363 2 Definition of polarization angle and of relative alignment angle The polarization angle E is the angle between the vertical plane including the propagation direction (pointing of the earth station towards the satellite) and the polarization plane
10、of the linearly polarized wave transmitted by the satellite or by the earth station pointed towards the satellite. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesSTD-ITU-R RECMN S.73b-3-ENGL 1797 = LI855212 053032b 7Tl 3 Rec. ITU-R S.
11、736-3 The relative alignment angle is, in linear polarization, the angle between: - - the planes of polarization of the wanted and interfering signais (EI - 2) (see Appendix 2); or the plane of polarization of the received signal and the plane of polarization of the receiving antenna (see Appendix 1
12、). in the co-polarized case, the angle is given by: = lei - E21 -i 6 with: 6 : tolerances. For calculation of the angles and E, see Appendices 1 and 2. 3 The ratio of polarization decoupling Dp(cp) of an earth station or a satellite antenna is the ratio of the field component in the wanted polarizat
13、ion to the field component in the orthogonal polarization. cp is the angle between the directions of wanted and interfering signals. The polarization discrimination Y (factor of polarizationholation) of a receive antenna is the ratio of the received power of the two waves of different direction and
14、polarization. It should be noted that, if the interfering or the wanted network (or both of them) operates a set of transponders on one polarization, and a set of co-frequency transponders on the orthogonal polarization, then it is not valid to include the full polarization discrimination in calcula
15、tions of interference between the two networks. The degree of such discrimination will depend on the extent of the overlap of the pass-bands of transponders in one network with those of the other network. in the worst case, Le., when the transponders of the two networks are exactly aligned in freque
16、ncy and bandwidth, no inter-network polarization discrimination should be included in interference calculations between the two networks. Definition of polarization decoupling ratio and polarization discrimination 4 Calculation of polarization discrimination, Y, in linear polarization 4.1 The purpos
17、e of this calculation is to determine, in the case of a wanted receiving earth station, the discrimination with respect to an interfering wave. Earth-station radiation patterns have been established for CO- and cross-polarization planes using experimental data. The polarization angles are calculated
18、 for wanted and interfering signals using the coordinates of the two pointing directions of wanted and interfering satellite antennas and the coordinates of the reference earth station. The derived value of discrimination Yd takes into account the co-polarized wave coming from the interfering satell
19、ite, received by the earth-station receiver (Co-polarized All(cp) and cross-polarized A+(cp) patterns). The cross-polarized wave coming from the interfering satellite intercepted by the co-polarized pattern of the station is also taken into account. However, the additional isolation afforded by the
20、ratio of crossed polarization transmit-to-crossed polarization receive may be neglected. Calculation of polarization discrimination, Yd, in the down-link dB where: Pb topocentric separation between satellites Dp(cpb) : polarization decoupling of the wanted earth station: Dp(Pb) = A/(Vb) - A+( (on-ax
21、is and off-axis $i) Pv za Zp2 COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesRec. ITU-R S.7363 23 a- COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services24 STD-ITU-R RECMN S
22、.73b-3-ENGL 2997 = Li855212 0530347 b2b Rec. ITU-R S.736-3 COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services STD-ITU-R RECMN S-73b-3-ENGL 1777 m 4855222 0530348 5b2 Rec. ITU-R S.736-3 25 APPENDIX 3 TOANNEX 1 Depolarization due to rain:
23、Cross-polarization of waves in the troposphere for Earth-space telecommunications systems 1 Definition of cross-polarization discrimination due to rain The cross-polarization discrimination due to rain, Dx, is the ratio of the received power on the transmitted polarization over the received power on
24、 the orthogonal polarization. where: Ap: rain attenuation (dB) exceeded for the required percentage of time p, for the path in question, commonly called CO-polar attenuation (.e. on the transmitted polarization transmitted) Vcf): value near 20 between 8 and 15 GHz u = uy; Es, r, 4 where: f: frequenc
25、y (GHz) : path elevation angle (degrees) T: tilt hgle (degrees) of the polarization of the linearly polarized vector with respect to the horizontal local plan, (for circular polarization, use T = 45O) Q: deviation of the raindrop canting angle distribution. From the cross-polarization discrimination
26、, it is possible to calculate cross-polarization angle YX, (rotation angle of the polarization vector) for calculating the level of depolarization. 2 Executive summary of a method for calculating long-term statistics of hydrometeor- induced cross-polarization (see Recommendation ITU-R P.618) Differe
27、nt depolarization mechanisms, particularly hydrometeor effects, are important in the troposphere. Cross- polarization effects are given in Recommendation IT-R P.618, as also are the calculation of long-term statistics of hydrometeor induced cross-polarization. The method described allows the calcula
28、tion of cross-polarization statistics from rain attenuation statistics for a same path for 8 I f I 35 GHz and I 60, the method allowing scaling of results at similar frequencies is also presented. with: U = Cf + C, + CE, + Co and CA = Vv log Ap DXraifi = Cf + CT + CE, + Cc - CA dB COPYRIGHT Internat
29、ional Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesSTD-ITU-R RECMN S.73b-3-ENGL L777 4855232 0530347 qT7 26 Rec. ITU-R S.736-3 with the following parameters: Cj: fiequency-dependent term Cf = 30 log f polarization improvement factor dependent on tilt angle
30、 T: for8 If I35GHz C, : C, = -lOlogI - 0.484(1 + COST) if T = 45“, CT = O and if T = O“ or 90, C, is maximum and reaches the value of 15 dEi (in the case of circular polarization, z = 45“); elevation angle dependent term CES : CEs = -40 log (COS ES) forEs I 60“ C, : rain drop canting angle dependent
31、 term: C, = 0.0052cr2 with o (degrees) the effective standard deviation of the distribution of the raindrop canting angle. The values of o are O“, 5“, 10“ and 15“ for respectively 1%, 0.1%, 0.01% and 0.001% of the time rain attenuation dependant term: CA : CA = vcf) 10gAp where: Vm = 12.8 foal9 Vcf)
32、 = 22.6 for 8 If I 20GHz for20 e f I35GHz 3 Executive summary of a method for calculating long-term rain attenuation statistics from point rainfall rate (see Recommendation ITU-R P.618) The attenuation due to the precipitation is also given in Recommendation IT-R P.618, the general method described
33、allows prediction of the attenuation from precipitation and clouds along a slant propagation path. The parameter Ro.01 (mmh) is the point rainfall rate for the location and for 0.01% of an average year. The attenuation Ap exceeded for a percentage p% of an average year, in the range 0.001% to 1% is
34、determined from the attenuation Ao.01 exceeded for a percentage 0.01% of an average year by using the following formulae: - AP - - O. 12 p-(O.546 + 0.043 1% P) Ao.01 for p% of the time of an average year and Ao.01 = YRLSq)01 for 0.0 1 % of the time of an average year The parameters are the following
35、: : specific attenuation due to precipitation: YR = kef) (Ro.01)cf) (dBkm) (see Recommendation IT-R P.838) kv) and acf) are coefficients which depend on frequency among others factors Ro.01: r0.01: rainfall rate (mmh) exceeded for 0.01% of an average year (integration time of 1 mn) reduction factor
36、of the length of the precipitation path: I - rO.O1 - I + LG/Lo COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesSTD-ITU-R RECMN S.73b-3-ENGL 1997 4855232 0530350 110 Rec. ITU-R S.736-3 where LO = 35 exp (-0.015 R0.01) L, : slant path le
37、ngth above the rain height: where the horizontal projection LG = L, cos E, (km) h, : height above mean sea level of the earth station (km) hR : effective rain height for the latitude of the earth station (km) for O I yP 36“ for wp 36“ 27 where y+, is the absolute value of the earth station latitude.
38、 4 Degradations of polarization Rain and snow may deteriorate the polarization vector direction. The drops of rain have a shape, not spherical but generally rather ellipsoidal. When a linearly or circularly polarized wave goes through such drops of rain, the components of polar vector have various a
39、ttenuations and phase-shift according to the axis of the ellipsoid of drops. Consequently, the wave is linearly polarized, and has therefore a component in the orthogonal direction at that of the transmit wave. It is the phenomenon of cross-polarization or depolarization. The orthogonality of two wa
40、ves polarized perpendicularly is kept with the differential phase-shift effect; on the other hand, it is not kept with the differential attenuation effect. The differential phase-shift effect is preponderant over the differential attenuation effect. The differential attenuation effect is low particu
41、larly at 6/4 GHz, but its effect is not negligible for the higher frequencies. The levels of depolarization are functions of the precipitation rate. In the not very rainy regions, the cross-polarization effects are relatively light and decrease only lightly the cross-polarization discrimination. On
42、the other hand, in the very rainy regions, cross-polarization effects are strong and decrease in an unacceptable way the cross-polarization discrimination. In the case of a wave with a circular polarization or in a linear polarization with a tilt angle T = 45“, the degradation of the cross-polarizat
43、ion discrimination is maximum. On the other hand, the degradation is reduced if the polarization is near a horizontal or vertical polarization due to the symmetry of the drops of rain. 5 Effects of rain on the attenuation of waves 5.1 Estimations of attenuations The structure of precipitations is no
44、t well known for the rain rate and for its horizontal and vertical extent. The effect of rain is relatively low below 10 GHz, on the other hand, its effect is significant above 10 GHz. The calculation of the attenuation due to rain is based essentially on the knowledge of rainfall rates. The strong
45、attenuations during a very small percentage of the time correspond to rare events with a time span of a few min. A percentage of 0.01% of an average year corresponds to a time span of 50 min. These relatively short time-scale events have a periodicity of several years, it is therefore necessary to t
46、ake measures during several years to obtain statistically significant data. However, the effect of rain is still a new and incomplete area of study, and the methods of calculation are not fully defmed. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Ha
47、ndling Services STD-ITU-R RECMN S.73b-3-ENGL L777 = 4855232 0530353 057 28 Rec. ITU-R S.736-3 The main factors are the following: a) Elevation angle Strong rains have a structure which is more vertical than horizontal. For angles greater than 15O, strong attenuations depend very little on the elevat
48、ion angle (compact regions with intense rainfall). For very small intense rains, the attenuation is light and with a cosecant law. b) Frequency The frequency effect on the determination is complicated, but there are empirical laws independent of the rain intensity. There are also semi-empirical laws
49、 connecting the attenuations Apl and Ap2 at fiequenciesfi andf2 for frequencies lower than 50 GHz (similarity in frequency: Recommendation ITU-R P.618). c) Climate Attenuations depend mainly on the statistic distribution of the rain intensity in a point. From this distribution, the calculation of attenuations may begin (see Recommendations IT-R P.837, IT-R P.838 and IT-R P.839). COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services
