1、 Rec. ITU-R S.1555 1 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 R
2、adiocommunication 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
3、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), onl
4、y 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
5、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 polariz
6、ed 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) operat
7、ing 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 netw
8、orks 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
9、unequal, and the magnitude of the two orthogonally polarized signals of the interfering networks are equal; 2 Rec. ITU-R S.1555 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,
10、 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 n
11、etworks 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 ne
12、twork 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 sig
13、nals 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 t
14、wo 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. Whe
15、n 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 usi
16、ng 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 usi
17、ng 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 o
18、n 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. 1555-00Satellite 1: vertical polariza
19、tionSatellite 2: vertical polarizationRec. ITU-R S.1555 3 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
20、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-coverag
21、e. 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
22、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
23、 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 (
24、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-a
25、xis 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-pola
26、r patterns of each of the two polarization transmitted by the earth station antenna simultaneously. 1 Introduction 6/4 GHz satellites operate co-frequency and co-coverage along the geostationary arc with small orbital spacing between adjacent satellites, typically in the range of 2 to 6. Coordinatio
27、n between these networks often assumes that they operate co-polar to each other, where no polarization isolation is assumed, such as when both networks use dual orthogonal LP or dual orthogonal CP. Cases arise where some polarization isolation exists between adjacent networks such as when adjacent n
28、etworks only use opposite senses of the same type of polarization (e.g. vertical polarization (VP) adjacent to horizontal polarization (HP), or right-hand circular (RHC) adjacent to left-hand circular (LHC) polarization). With the satellite antenna XPD of the order of 30 dB, the earth station antenn
29、a off-axis cross-polar gain will be the dominant cross-polarization effect in these cases. It essentially controls the cross-polar interference between two adjacent satellite networks regardless of whether they are operating in LP or in CP. 4 Rec. ITU-R S.1555 Another situation can arise in which ad
30、jacent satellite networks use different types of polarization CP in one network and LP in the other. Such situations occur regularly with networks operating in the 6/4 GHz frequency bands where historical choices of polarization (CP versus LP) made decades ago are still maintained in the current ope
31、rational networks, a situation that is likely to continue in the future due to the considerable infrastructure investment in these networks. The off-axis polarization isolation between networks in these cases has been studied, but only taking account of one polarization at a time1. Paragraph 2.2.3 o
32、f RR Appendix 8 provides guidance to administrations in terms of the isolation between a single CP interfering signal and an LP wanted signal (or vice versa) with a recommended worst-case numerical isolation factor of 1.4 times (= 1.46 dB) as an envelope value for all ranges of orbital separation. T
33、he situation that has not been adequately studied, and which is addressed in this Recommendation, is when the interfering network uses both senses of polarization (either CP or LP) and the wanted network uses the other type of polarization (either LP or CP, respectively). In this case it is importan
34、t during coordination to calculate the aggregate interference resulting from the combined effect of the two orthogonally polarized signals in the interfering network. In fact, this is the case that exists in practice in most situations with currently operational satellite networks, where both are us
35、ing dual orthogonal polarization for spectral efficiency reasons. 2 Generic vector equations This section summarizes the general expressions of the equations that should be used to assess the coupling from the two polarization components of the interfering network into one component of the interfere
36、d with network. The equations are provided for each possible case of interference (i.e. CP into LP, LP into CP, LP into LP). 2.1 Interference from circularly polarized into linearly polarized antenna systems In this section we first derive general expressions for the coupling from the two types of c
37、ircular polarization into a linearly polarized antenna. Then, we consider the two special cases: A dual circularly polarized satellite illuminates a linearly polarized earth station. A dual circularly polarized earth station illuminates a linearly polarized satellite. The incident field at the locat
38、ion of the receive antenna is, for each polarization of the circularly polarized transmit antenna: LRjLXLLjRXRRjejejeje + += + =e22e22vhvhevhvhe(1) _ 1See ex-CCIR Reports 555 and 1141 and Recommendation ITU-R S.736. Rec. ITU-R S.1555 5 where: eR, eL: incident electric field vectors for the right-han
39、d and the left-hand circularly polarized signals eR, eRX: co-polarized and the cross-polarized field amplitudes of the right-hand circularly polarized signal eL, eLX: co-polarized and the cross-polarized field amplitudes of the left-hand circularly polarized signal h, v: horizontal and vertical unit
40、 vectors at the location of the receive antenna R, L: unknown phases of the cross-polarized field relative to the co-polarized field for the right-hand and the left-hand circularly polarized signals2. Each port of the linearly polarized receive antenna can be characterized by an effective length3, i
41、.e. for the HP and the VP: +=+=jxvjxhggggeehvhvhh(2) where: g, gx: proportional to the co-polar and the cross-polar gain of the receive antenna h, v : horizontal and vertical unit vectors at the location of the receive antenna : unknown phase of the cross-polarization voltage relative to the co-pola
42、rization voltage received in a port of the linearly polarized antenna. The actual values of g, gxand will in general be different for the two receive antenna ports, although the worst-case interference (based on using the gain masks and the appropriate value for ) will be the same for both antenna p
43、orts. The analysis here is of the aggregate interference for one receive antenna port at a time. The received voltages for the two incident signals in equation (1) in the horizontal polarization receive port are therefore: )(e2e2e22RRjRXxjRxjRXRRhRhegjegjegegv+= eh(3) )(e2e2e22LLjLXxjLxjLXLLhLhegjeg
44、jegegv+= eh(4) _ 2As in most antenna analyses, simple carriers with the time factor e jtare assumed. The carrier and the signal in one polarization are assumed to be uncorrelated with the carrier and the signal in the other polarization. 3The concept of effective length applied originally to dipole
45、antennas and linear polarization. It has over the years been extended to general polarization states and more general antennas. The effective length of an antenna may be defined as a complex vector so that the received open-circuit voltage is the scalar product of effective length vector h and the i
46、ncident electric field vector e, i.e. voc= h e. 6 Rec. ITU-R S.1555 The power received in the horizontal polarization port is proportional to the sum of the voltages squared assuming that the two signals are uncorrelated. The last term on the right-hand sides of equations (3) and (4) is the product
47、of the cross-polarization of the two antennas and will therefore be the smallest for practical cross-polar performance values. As a result some of the terms resulting from the squaring of equations (3) and (4) are so small that they can be ignored, and these are the ones involving the product of the
48、 last term with any other terms except the first. By simplifying in this way the power in the horizontal polarization receive port is proportional to: ()()()()+=+cossinsin2sincoscos222222222222LLXLRRXRxLRxLLXLRRXRLRxLXRXLRLhRheeeeggeeggeeeegeegeeeegvv(5) Similarly, the power in the vertical polariza
49、tion receive port is proportional to: ()()()()+=+cossinsin2sincoscos222222222222LLXLRRXRxLRxLLXLRRXRLRxLXRXLRLvRveeeeggeeggeeeegeegeeeegvv(6) 2.2 Interference from linearly polarized into circularly polarized antenna systems This section investigates the opposite scenario of that of the previous section. We derive general expressions for the coupling from two orthogonal linear polarizations into a circularly polarized antenna and consider
