Rec. Itu-r s. 1555




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Rec. ITU-R S.1555

RECOMMENDATION ITU-R S.1555

Aggregate interference levels between closely spaced dual circularly


and dual linearly polarized geostationary-satellite networks in the
fixed-satellite service operating in the 6/4 GHz frequency bands

(Questions ITU-R 230/4 and 42/4)

(2002)
The ITU Radiocommunication Assembly,

considering

a) that in the 6/4 GHz frequency bands both dual circular polarization (CP) and dual linear polarization (LP) are used by different operational geostationary-satellite fixed satellite service (FSS) networks, and this situation is likely to continue because of the established infrastructure in those networks;

b) that such bands are heavily used resulting in the need for co-frequency and co-coverage networks to operate with relatively small orbital spacing;

c) that the existing ITU-R Recommendations, as well as Appendix 8 to the Radio Regulations (RR), only address the single entry interference between adjacent satellite networks, taking the interfering signal in each polarization at a time;

d) that it is important during coordination to be able to determine the aggregate effect of adjacent satellite interference arising from the simultaneous use of both orthogonal polarizations in each adjacent satellite network, whether the two networks use the same type of polarization (i.e. both CP or both LP) or whether they use different types of polarization (i.e. one using CP and the other using LP);

e) that the magnitude of the two orthogonally polarized signals of the interfered with and/or the interfering networks could be equal or unequal,



recommends

1 that, on the basis of the technical information contained in Annexes 1, 2 and 3, the aggregate interference between closely spaced adjacent satellite networks (up to 6° orbital separation) operating in the 6/4 GHz frequency bands using different types of polarization (i.e. CP in one network and LP in the other) should be assumed to be identical to that which would occur if both networks used the same types of polarization (i.e. both LP or both CP), under the following conditions:

 those networks simultaneously use both orthogonal polarizations co-frequency and co coverage and the magnitude of the two orthogonally polarized signals of the interfered with and the interfering networks are equal; or

 the magnitude of the two orthogonally polarized signals of the interfered with network are unequal, and the magnitude of the two orthogonally polarized signals of the interfering networks are equal;

2 that, on the basis of the technical information contained in Annex 3, when the magnitude of the two orthogonally polarized signals of the interfering network are unequal, the aggregate interference between closely spaced adjacent satellite networks (up to 6° orbital separation) operating in the 6/4 GHz frequency bands using different types of polarization (i.e. CP in one network and LP in the other) could be assumed to be identical to that which would occur if both networks used the same types of polarization (i.e. both LP or both CP) under the following conditions:

 these networks simultaneously use both orthogonal polarizations co-frequency and co coverage;

 an additional reduction of the magnitude of the two downlink orthogonally polarized signals of the CP network or an additional reduction of the magnitude of the downlink signal having the highest magnitude of the CP network should be applied.

3 that the technical information contained in Annex 1 should be used to determine the additional reduction of the magnitude of the two orthogonally polarized signals of the CP network when those networks simultaneously use both orthogonal polarizations co-frequency and co coverage, and the magnitude of the two orthogonally polarized signals of the interfering networks are unequal.

NOTE 1 – When the desired network uses dual LPs with equal magnitudes for the two orthogonal polarized signals and the adjacent network uses dual polarizations with a large difference between the magnitudes for the two orthogonal polarized signals (e.g. greater than 10 dB), the interference environment would differ depending on whether the adjacent satellite uses CP or LP. When LP is used the interference caused to the desired network would be primarily to one polarization (i.e. vertical or horizontal). When CP is used the interference caused to the desired network would be to both polarizations but at a reduced power level compared to the interference from a network using LP.

NOTE 2 – When both the desired and the interfering networks use a staggered channelization plan and when these networks transmit high spectral density in the central portion of the occupied bandwidth of the transponder (e.g. analogue TV/FM), an advantage exists in having adjacent satellites using the same polarization type (i.e. dual LP or dual CP). In these conditions, the signal energy in the centre of the channel falls within the guardband of the co-polarized channel of the adjacent network. The example figure below shows the co polar channelization plans for one of the polarizations on each adjacent satellite. The interference from the adjacent satellite is mitigated by the angular separation of the satellites and additionally by the frequency separation of the carriers due to filtering of the co-polarized channel of the adjacent satellites.

ANNEX 1


Interference between closely spaced dual circularly and dual linearly polarized satellite networks operating in the 6/4 GHz frequency bands

Abstract


This Annex introduces the issue of the aggregate interference between closely spaced adjacent satellite networks (up to 6° orbital separation) operating in the 6/4 GHz frequency bands when these networks use different types of polarization (i.e. CP in one network and LP in the other), and when those networks simultaneously use both orthogonal polarizations co-frequency and co-coverage. It provides the general expression of the equations which were used to perform the analyses.

It includes the main results of an analysis of the impact on the aggregate adjacent satellite interference levels when neighbouring satellites operating in the 6/4 GHz frequency bands use different types of polarization (i.e. LP versus CP) and when the magnitude of the two orthogonally polarized signals of the interfered with and the interfering networks are equal. In addition, it is assumed that the interfering and interfered with networks operate the same type of carriers at the same frequency. It compares the interference levels in these situations with those that exist when the satellite networks use the same type of polarization, either both using dual LP or both using dual CP. It concludes that in this case, for practical values of satellite and earth station cross-polar discrimination (XPD), the absolute worst-case additional interference, relative to the idealized case where both networks use the same type of polarization and are perfectly aligned, is less than approximately 0.5 dB for the downlink and less than approximately 1.5 dB for the uplink. The earth station antenna off-axis co-polar and cross-polar patterns are the main contributors to the interference. The analysis is worst case and uses simple template envelopes to represent the earth station antenna performance. In practice it is extremely unlikely that worst case conditions will occur on co-polar and cross-polar patterns of each of the two polarization transmitted by the earth station antenna simultaneously.


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