1、 Rec. ITU-R S.1782 1 RECOMMENDATION ITU-R S.1782 Possibilities for global broadband Internet access by fixed-satellite service systems (Question ITU-R 269/4) (2007) Scope In order to address issues raised both by the Radiocommunication Assembly and by WRC-03, a preliminary study into possibilities f
2、or providing access to the Internet at a high data-rate via satellite has been carried out. In one Annex an attempt is made to identify suitable fixed-satellite service (FSS) bands, and 500 MHz bandwidth pairs are selected within the 11/14 GHz, the 20/30 GHz and the 40/50 GHz FSS allocations. On the
3、 basis of direct satellite links from user terminals with 30 cm antennas, up and downlink characteristics for each case are developed, and the per-satellite capacities calculated. The total capacities of such systems to serve a 10 000 000 km2reference area are estimated. In a second Annex, up and do
4、wnlink characteristics in the 20/30 GHz and 11/14 GHz bands are developed for a system that would provide direct satellite links for user terminals with 1.2 m antennas, and again per-satellite and total capacities are calculated. In a third Annex the characteristics are developed of an example syste
5、m based on user access via terrestrial radio links to “community” earth stations and thence via a 20/30 GHz or 11/14 GHz satellite to a single central earth station, and again the corresponding per-satellite and total capacities are calculated. The ITU Radiocommunication Assembly, considering a) tha
6、t satellite telecommunication technology has the potential to accelerate the availability of high-speed Internet services in developing countries, including the least-developed countries, the land-locked and island countries, and economies in transition; b) that it is desirable to determine the tech
7、nical and operational characteristics of fixed-satellite service (FSS) systems that could facilitate the mass-production of simple user terminal equipment at affordable prices; c) that it is desirable to assess the global capacity that could be provided in FSS frequency allocations by systems having
8、 the characteristics determined in considering b); d) that the determinations in considering b) should take into account both the possibility of designing systems specifically for Internet access at high data-rates via small user terminals, and also the fact that some existing systems already includ
9、e broadband Internet access facilities; e) that a variety of earth station sizes are being employed for broadband Internet access via existing FSS systems designed to cater also for other applications and using several frequency bands; f) that development of standards for the satellite technology me
10、ntioned in considering a) for Internet applications facilitates the wider use of satellite for Internet access, 2 Rec. ITU-R S.1782 noting a) that Recommendation ITU-R S.1783 describes the characteristics of high-density fixed-satellite service (HDFSS) systems; b) that Recommendation ITU-R S.1709 de
11、scribes the technical characteristics of air interfaces of global broadband satellite systems, recognizing a) that the FSS frequency allocations can be used in the short, medium and long term for the global provision of high-speed Internet services, recommends 1 that the information in Annexes 1, 2
12、and 3 provides three possible examples that may be used in order to implement global access to the Internet at high data-rates via the FSS. Annex 1 Possibilities for global1broadband2Internet access by FSS systems designed for very small earth station antennas 1 Frequency band considerations 1.1 Sui
13、table bands “Short term” applies to bands for which satellite technology has already been developed. At the present time this is wholly true of the 4/6 GHz and 11/14 GHz FSS allocations, and partially true of the 20/30 GHz FSS allocations. It may be expected that in the “medium term”, say during the
14、 next ten years, satellite technology in the 20/30 GHz bands will become fully developed, and there will be some development in the 40/50 GHz bands also although experience suggests that it will be the “long term” before that development can be regarded as full. There are FSS allocations above 50 GH
15、z in Article 5 of the Radio Regulations (RR), but significant development in them seems unlikely to occur before the long term and they are not considered here. Preliminary studies ruled out the use of the 4/6 GHz bands for the subject application, on the grounds that low-cost terminals imply very s
16、mall antennas which would be unlikely to have adequate gain at those frequencies to operate to the wide-beam satellites typically involved. Furthermore, the 4/6 GHz bands are already heavily utilized so, even if spot-beam C-band satellites were provided, it would be difficult for very small-dish ear
17、th stations with their correspondingly wide beamwidths to share frequencies with the existing services. Therefore the 4/6 GHz bands are not considered further in this Annex. 1In this study the adjective “global” is interpreted to mean anywhere that may be served by geostationary satellite. 2In this
18、study, the example of “broadband” used is a user rate of 2 Mbit/s. Rec. ITU-R S.1782 3 The preliminary studies also considered that to some degree the considerations in the previous paragraph apply also to the 11/14 GHz bands. The constraint on earth station antenna size is less severe than at 4/6 G
19、Hz because gain is higher and (medium) spot-beam operation is more common but, like 4/6 GHz, the non-planned frequencies at 11/14 GHz have been heavily utilized for many years so frequency-sharing may be a problem. The 20/30 GHz FSS allocations are believed to be intrinsically the most suitable for
20、broadband Internet access in the near term, because the wavelength is consistent with very small antennas, the technology is reasonably well developed, and utilization is as yet relatively low. Moreover, Internet access by individuals is incompatible with the way in which the great majority of inter
21、national use of the FSS bands has been regulated up to now, i.e. by coordination of individual earth stations. The likelihood, that the user terminals will be sold by “high street” retailers in large numbers and installed in homes as well as offices, necessitates a regulatory regime such as that whi
22、ch is being developed to accommodate HDFSS. RR No. 5.516B, referenced by WRC-03 in its call for studies on possible global broadband FSS systems for Internet applications, is partially repeated below for convenience: “The following bands are identified for use by high-density applications in the fix
23、ed-satellite service: 17.3-17.7 GHz (space-to-Earth) in Region 1, 18.3-19.3 GHz (space-to-Earth) in Region 2, 19.7-20.2 GHz (space-to-Earth) in all Regions, 39.5-40 GHz (space-to-Earth) in Region 1, 40-40.5 GHz (space-to-Earth) in all Regions, 40.5-42 GHz (space-to-Earth) in Region 2, 47.5-47.9 GHz
24、(space-to-Earth) in Region 1, 48.2-48.54 GHz (space-to-Earth) in Region 1, 49.44-50.2 GHz (space-to-Earth) in Region 1, and 27.5-27.82 GHz (Earth-to-space) in Region 1, 28.35-28.45 GHz (Earth-to-space) in Region 2, 28.45-28.94 GHz (Earth-to-space) in all Regions, 28.94-29.1 GHz (Earth-to-space) in R
25、egion 2 and 3, 29.25-29.46 GHz (Earth-to-space) in Region 2, 29.46-30 GHz (Earth-to-space) in all Regions, 48.2-50.2 GHz (Earth-to-space) in Region 2.” It is noteworthy that these designations add up to the following aggregate bandwidths: 20/30 GHz bands Global plus Region 1 Region 2 Region 3 Down 5
26、00 MHz 400 MHz 1 000 MHz Up 1 030 MHz 320 MHz 470 MHz 160 MHz 40/50 GHz bands Down 500 MHz 2 000 MHz 1 500 MHz Up 2 000 MHz 4 Rec. ITU-R S.1782 Thus, assuming that frequencies in the bands designated for global use can be reused in two or three Regions simultaneously, the total spectrum identified f
27、or HDFSS in these bands is, Region-by-Region: Region 1 3 400 MHz down, 1 350 MHz up; Region 2 3 500 MHz down, 3 500 MHz up; Region 3 1 000 MHz down, 1 190 MHz up. These totals suggest that much more downlink than uplink bandwidth may be needed to meet the needs of HDFSS applications in Region 1, but
28、 that in the other two Regions the needs may be of the same order in both transmission directions. Insofar as the 20/30 and 40/50 GHz bands are concerned, the considerations in this Recommendation are confined to the bands identified in RR No. 5.516B for all three Regions, i.e. 19.7-20.2 GHz, 28.45-
29、28.94 GHz, 29.46-30.0 GHz and 40.0-40.5 GHz (see Table 1). Although the invitations for ITU-R study on the present topic by both WRC-03 and the Radiocommunication Assembly envisage use of FSS bands, the analyses in this Annex for the 11/14 GHz FSS bands would yield similar results if carried out for
30、 the adjacent BSS bands (i.e. 11.7-12.5 GHz in Regions 1 and 3, and 12.2-12.7 GHz in Region 2). 1.2 Current FSS use of the bands In order to assess the extent to which broadband Internet access requirements could be met by future satellites in the bands discussed in 2.1, it is necessary to determine
31、 the degree to which the orbit/spectrum resource of those bands is either already utilized by existing satellite systems, or will soon be in use by systems already under development for other FSS applications. Noting that an indication of the variation in current and planned usage from band to band
32、may be obtained from the Radiocommunication Bureaus SNS database, Table 1 compares the numbers of applications for spectrum for GSO/FSS networks up to January 2005 in a 500 MHz segment of each of the FSS allocations in the 11/14 GHz, 20/30 GHz and 40/50 GHz ranges. Each of these 500 MHz bands (excep
33、t the last one) is allocated to the FSS in all three Regions: TABLE 1 Comparison of applications for spectrum assignments FSS allocation Bandwidth Transmission direction Main purpose Number of filings 10.95-11.2 GHz 11.45-11.7 GHz 500 MHz Space-to-Earth 12 417 14.0-14.5 GHz 500 MHz Earth-to-space Ge
34、neral FSS commercial applications 16 467 19.7-20.2 GHz 500 MHz Space-to-Earth 5 245 29.5-30.0 GHz 500 MHz Earth-to-space Identified for HDFSS 4 830 40.0-40.5 GHz 500 MHz Space-to-Earth 1 205 (48.2-48.7 GHz(1) 500 MHz Earth-to-space Identified for HDFSS (797) (1)This is part of a band identified by W
35、RC-03 for HDFSS uplinks in Region 2. Although it was not similarly identified in respect of Regions 1 and 3, it is added in order that the Table can cover uplinks to complement the 40 GHz downlinks. Rec. ITU-R S.1782 5 Together with the fact that there are many more 11/14 GHz satellite payloads in o
36、peration today than payloads in the higher frequency bands, the information in Table 1 leads to the following deductions: The main global FSS allocations at 11/14 GHz are currently much more heavily utilized than those parts of the 20/30 GHz allocations that have been identified for future global HD
37、FSS use. FSS use of the 40/50 GHz frequencies identified for future HDFSS has yet to begin. 2 Possible technical characteristics 2.1 Satellite beams Studies have found that the objective of providing facilities to access the Internet via satellite at high-data-rates to individual user terminals at a
38、ffordable prices would best be met by systems designed to accommodate ultra-small aperture terminals (USATs) at the user end of the links 30 cm diameter is the example used in this study. The relatively low antenna gain of such terminals, especially at the lower frequencies under consideration, woul
39、d lead to modest capacity per satellite and hence to relatively high space-sector cost per bit of information, unless each satellite was designed for frequency reuse via multiple spot-beams. Tables 3, 4 and 5 summarize relevant parameters from the Annexes to Recommendation ITU-R S.1328, that are rel
40、evant to this study, and give an indication of the dimensions of spot-beams likely to be available either now or in the near future. In the case of the 11/14 GHz bands the data in Table 3 is augmented by satellite antenna receive gain figures deduced from replies to a Radiocommunication Bureau Quest
41、ionnaire in 1998. It may be assumed that satellites designed in the immediate future to provide broadband Internet access will incorporate multiple spot-beams toward the narrow (i.e. high gain) end of the ranges in Tables 3, 4 and 5. Accordingly the parameters in Table 2 are selected as bases for th
42、e characterization of the user links of suitable satellite systems. It is assumed here that, for operational convenience, the satellite antenna sub-systems will be designed so that each pair of transmit and receive beams have the same beamwidths and their footprints have the same fixed positions on
43、the Earths surface. TABLE 2 Satellite spot-beam characteristics selected FSS frequency range 11/14 GHz 20/30 GHz 40/50 GHz Gain at beam centre (dBi) 42 50 55 3 dB beamwidth (degrees) 1.4 0.6 0.3 Number (n) of dual-polar transmit/receive beams per satellite 12 32 64 It is important to note here that,
44、 as the beamwidth reduces, the pointing accuracy requirement increases, and hence the difficulty and cost of controlling the beam footprints increases. In the light of spacecraft development in recent years it is reasonable to assume antenna feed arrangements that compensate for the curvature of the
45、 Earths surface to enable all beams generated by a given satellite to have circular footprints of the same diameter regardless of pointing direction. Thus, with the exception of a beam pointing at the sub-satellite point, each beam will have an approximately elliptical cross-section, and its axial r
46、atio and orientation will depend on its pointing 6 Rec. ITU-R S.1782 direction relative to the direction of the sub-satellite point. The beamwidths of the major (a) and minor (b) axes will be such that (a)(b)0.5= (0), where (0) is the 3 dB beamwidth of the (circular) beam pointing to the sub-satelli
47、te point. For continuous coverage via multiple beams with circular footprints a hexagonal pattern of overlaps may be assumed, as in Fig. 1. FIGURE 1 Hexagonal pattern for footprints of overlapping satellite beams A one-in-four frequency reuse pattern is shown in Fig. 1, and each beam is assumed to b
48、e dual-polarized. Given practicable rates of roll-off and first-sidelobe levels such as those described by the equations in Recommendation ITU-R S.672, the discrimination between the centre of a beam and the nearest edge of the next co-frequency beam should be just about adequate to support this mod
49、e of operation. For example, at point “o” at the edge of one of the hexagonal areas served by a frequency f2beam, the interference contributions from the nearest six co-frequency beams can be calculated from the off-axis angles oa, ob, oc, od, oe, and og, subtended at the satellite. From the geometry of the diagram: oa = 5(0/2) cos(30) = 2.165(0) ob = og = (2(0/4) + 02+ 3(0/2) cos(30)2)0.5= 1.984(0) oc = oe = (0/2) cos(30)2+ 2(0/4) + 02)0.5= 1.561(0) and od = 3(0/2) cos(30) = 1.299(0) Rec. ITU-R S.1782 7 TAB
