CEPT ECC Electronic Communications Committee CPG-15 PTD CPG-PTD(12)019 CPG-15 PTD #1 Kristiansand, 18-20 September 2012 Date issued: 12 September 2012 Source: Subject: Eutelsat, Inmarsat, and SES Use of the band 3.4 4.2 GHz by FSS systems and potential use by terrestrial IMT systems Password protection required? (Y/N) N Summary: WRC-15 AI 1.1 addresses the issue of additional spectrum allocations to the mobile service on a primary basis and identifying additional frequency bands for International Mobile Telecommunications (IMT) to develop terrestrial mobile broadband applications. Eutelsat, Inmarsat, and SES provide their views on WRC-15 Agenda Item 1.1. Proposal: The potential use of the band 3400 4200 MHz for IMT systems has already been analysed (see Report ITU-R M.2109), and taking those studies into account, WRC-07 concluded that regulatory provisions in the band 3600-4200 MHz should not be changed. There is no reason to think that the potential for IMT operations has improved since then, or that the conclusions reached by WRC-07 might have changed. Therefore, the band 3400-4200 MHz should not be considered under WRC-15 Agenda Item 1.1. 1 Introduction Through its Resolution 807, the WRC-12 recommended to Council to include in the Agenda of WRC-15 an item (Agenda item 1.1) to consider additional spectrum allocations to the mobile service on a primary basis and identification of additional frequency bands for International Mobile Telecommunications (IMT) and related regulatory provisions, to facilitate the development of terrestrial mobile broadband applications, in accordance with Resolution 233 (WRC-12). CPM 15-1 decided to establish a Joint Task Group among Study Groups 4, 5, 6 and 7 (JTG 4-5-6-7) as responsible for conducting the relevant studies in accordance with the Terms of Reference specified in Annex 10 of the Administrative Circular CA/201. This document discusses potential use of the band 3.4 4.2 GHz by IMT systems, in the context of sharing with the FSS.
2 Background 2.1 C-band in Satellite Communications The bands 3.4 4.2 GHz (space-to-earth) and 5.925 6.725 GHz (Earth-to-space) are usually referred as C-band and are mainly used for satellite applications. The bands mentioned above are extensively used throughout the globe for different satellite applications, some of which are described below. The C-band was allocated to and used by the satellite industry since the first networks were deployed over 40 years ago. Even if today s satellite networks can also use higher frequency bands, the C-band remains of outstanding importance because of some properties of this part of the electromagnetic spectrum, often suitable to fulfil the communication needs of countries in areas near or within tropical or equatorial regions: C-band is very resilient to rain fade and is often the only alternative for satellite communications where adverse meteorological conditions make the use of higher frequency bands very difficult or impossible. Also, in addition to the above mentioned favourable propagation conditions, C-band allows satellite networks to cover large regions, making the use of low-cost receive-only hardware possible; this aspect is of high importance for developing countries, where the absence of or inaccessibility to alternative communication infrastructures makes satellite communications the only viable solution, especially for national broadcasters wanting to reach a large number of citizens for delivering TV content. Thanks to its robust qualities, satellite services operated in C-band also demonstrated the ability to play a vital role in recovery and relief operations for many disasters that occurred in recent years, such as the 2004 Asian tsunami, the 2010 Haiti earthquake and other major events. Some other services delivered through C-band satellite networks are distance learning, telemedicine and universal Internet access through low-cost VSAT equipment. C-band is also critical for the exchange of telemetry, telecommand and control (TT&C) information between satellites and earth stations used to manage their operations. This application requires particular protection from all interferences, due to the risk of losing control of the affected space station and the possibility of causing catastrophic damages to other spacecraft. Due to its high reliability, C-band is often used for TT&C for satellites even in cases where the main payload may be in other frequency bands. Finally, some satellite operators use the C-band for providing MSS feeder-links, through which hundreds of thousands of customers can enjoy connectivity on mobile platforms on land, at sea and in the air where other communication means are not available. This includes safety communication services, provided using C-band feeder links, for example, for GMDSS and AMS(R)S applications. The use of C-band for feeder-links for the MSS is of high importance for disaster recovery and relief, when terrestrial networks cannot fulfil the communication needs after a major disaster. 2.2 Recent WRC activity related to C-band Studies related to the possible use of the band 3.4 4.2 GHz for terrestrial IMT systems were conducted in preparation for WRC-07 (see Report ITU-R M.2109). Recognising the extensive use and importance of C-band for FSS applications, WRC-07 did not modify the allocations in this frequency band; however, some countries allowed the use of IMT in the band 3.4 3.6 GHz through footnotes (see Nos. 5.430A, 5.431A, 5.432A. 5.432B, 5.433A). In addition, WRC-07 imposed conditions to ensure protection of FSS earth stations in countries neighbouring those deploying IMT systems. The frequency band 3.6 4.2 GHz was not modified by WRC-07. Nothing has changed since WRC-07 to suggest that the feasibility of IMT operation in C-band is any less problematic now than it was then. On the contrary, in many areas where IMT has been deployed in the proximity of satellite receiving stations, the reception of the satellite has been severely disrupted. In some cases, such disruption has led to other customers/consumers 2
further down the transmission chain not receiving services that they expect, e.g. loss of TV programming from television or cable head-end stations that receive their (video) content via C- band satellites (see Section 5.0). In view of the aforementioned advantages (and popularity) of C-band, FSS operators, including those submitting this paper, are continuing to procure and launch new C-band FSS satellites and new earth stations are being deployed throughout the world, confirming further the impossibility of operating IMT in these bands. These network and infrastructure projects involve considerable long term investments, being predicated on continued availability of the bands allocated to FSS as of WRC-07, with many already well-advanced in the construction phase. Loss of C-band spectrum by the FSS cannot be readily replaced by operation at higher frequency bands and will therefore cause additional financial losses at a time of unprecedented economic fragility around the world. 3 Compatibility and sharing issues between terrestrial and satellite services Many issues can be identified when assessing the potential sharing and compatibility between terrestrial and satellite systems using the C-band. Due to the limited power available on board of a spacecraft, satellite terminals on the ground are designed to receive very low-power signals transmitted by space stations located thousands of km away; considering GSO satellites, the distance (slant range) between the antenna on the spacecraft and that used by the receiving earth station is around 36,000 km 40,000 km. Because of that, receiving hardware is usually very sensitive to any external interference. This inherent system design makes the compatibility with wireless terrestrial systems hard to achieve. Such terrestrial networks normally make use of an extensive distribution of base stations transmitting high powers 1 simultaneously in every horizontal direction. The use of networks using carriers with the same centre frequency and wide bandwidths, as is the norm for terrestrial networks, means there is unlikely to be any possibility of being able to plan for an adequate frequency and geographical separation between IMT systems and FSS earth stations. As shown in Report ITU-R M.2109, required separation distances to avoid harmful interference to FSS earth stations are at least tens of kilometres, and in some cases more than 100 km. The requirement to protect ubiquitously deployed FSS earth stations by maintaining large separation distances leads to large holes in any potential coverage by terrestrial networks. In regions where FSS earth stations are densely deployed, the combined exclusion areas may consist of virtually the entire country, making IMT operations impractical/impossible. Conversely, implementation of IMT stations would preclude the use of C-band receiving stations within a relatively large area around each IMT station, thus restricting further development/expansion of C-band satellite services. There are significant numbers of receive only satellite earth stations in operation today, typically used for reception of on-air television programming. In order to encourage the use of satellite communications, in many countries licensing of receive-only stations is not required. Some administrations have proposed that such stations would no longer be entitled to protection from interference. Such a proposal could potentially lead any household that receives on-air television programming to experience an important disruption of service and could undermine decades of effort, time and money spent by satellite operators to build up their C-band service offerings and networks. 1 In Report ITU-R M.2109, the maximum EIRP assumed for terrestrial systems is 59 dbm. 3
4 Possible interference mitigation techniques and their applicability WP 5D and WP 4A have been collaborating on the development of a draft new Recommendation ITU-R M.[IMT.MITIGATION], to examine potential mitigation techniques that might improve the prospects for IMT operation in the band 3.4 3.6 GHz, without causing interference to FSS earth stations. This recommendation was recently sent back to WP 5D for further revision after approval at Study Group 5 was not achieved. In order to attempt to mitigate the interference and allow the co-existence of terrestrial and satellite systems in the C-band, a number of techniques have been identified. The description and applicability of each of them are discussed below. As explained below, no mitigation technique has been determined which can effectively overcome the basic incompatibility between IMT systems with FSS earth stations. 4.1 Band Segmentation Past studies by various regional and international organizations have evaluated whether the segmentation of the band could be a possible way forward to allow terrestrial services to coexist with satellite systems in the C-band. However, real-world deployments have proved that harmful interference could occur even when the two systems would operate in non-overlapping bands. Even when the terrestrial and satellite systems would operate in non-overlapping bands, a study made by the Asia-Pacific Telecommunity 2 showed that a separation distance from all satellite receivers of 2 km would still be required for preventing terrestrial mobile systems from causing harmful interference. This is due to the limited capability of terrestrial systems to limit their out-of-band emissions and of satellite receivers to filter out unwanted emissions in adjacent bands. Further discussion on this last point can be found in the technique listed below. 4.2 Additional filtering There are two interference mechanisms related to adjacent band issues: firstly, unwanted emissions from terrestrial base/mobile stations operating in the C-band can generate interference to earth stations in other parts of the same band. Secondly, since LNBs and LNAs commonly used on FSS earth stations are designed to receive the entire C-band, the power radiated by terrestrial base/mobile stations can cause the overdrive of the amplifier of the first block, compromising its linear response. The effect of LNB overdrive could be reduced if some additional filtering could be applied on the FSS earth stations. However, applying some rejection and/or bandpass filtering to a given FSS earth station would prevent it to use parts of the C-band, compromising then the future development of the service. Furthermore, this solution would be difficult to apply to transportable earth stations, since, by the nature of their operations, their geographical location and receiving frequencies can change significantly and very often over time: for example, a typical Satellite News Gathering (SNG) earth station can be employed to transmit and receive carriers on different satellite transponders, potentially from different geographical locations, in a relatively short interval of time. It should also be noticed that introducing an RF filter between the FSS earth station antenna output and the input to the amplifier of the first receiving block generates loss and, consequently, increases the system equivalent noise temperature by around 8% for any 0.1 db of attenuation. Taking into account that filters typically used in this band have an insertion loss of circa 0.5 db, leading to an increase in the noise temperature of about 43% or 1.54 db, a new margin should then be foreseen in any link budget for transmissions operated in this band. At 2 Report APT/AWF/REP-05 March 2008. 4
the same time, having to increase the satellite downlink carrier e.i.r.p. will reduce the capacity of the satellite system. It should be noted that there are practical constraints to applying such filtering to the concerned FSS earth stations, since many of them are receive-only and are therefore typically unlicensed or blanked licensed. Consequently, administrations would not have access to all the information required for the correct implementation of this technique. To address interference from the unwanted emissions of terrestrial systems to FSS earth stations, it should also be highlighted that some rejection filtering could be applied to the transmitting terrestrial base/mobile stations, in order to reduce the emissions outside their assigned frequency blocks. The CEPT ECC Report 100 already mentioned above is again a good reference for describing this issue. It concludes that, even when such additional filtering is installed, interference can still occur and a separation distance of up to circa 4 km still needs to be observed to avoid harmful interference. 4.3 Dynamic Spectrum Access Techniques Another class of mitigation technique that has been studied for allowing the co-existence between terrestrial and satellite services in the C-band deals with a dynamic allocation of the spectrum between the two systems. These techniques foresee that, within a given territory, terrestrial systems would be allowed to use only those parts of the C-band not already used by ground-based satellite systems in the vicinity. Terrestrial systems would be capable of choosing the right frequency of operation thanks to the real-time information collected through an auxiliary system, such as a network of beacons installed on the FSS earth station antennae or a database with geographical data. The design and implementation of such auxiliary systems are complex and their maintenance expensive. In every geographical area, the terrestrial system network manager would have to make the decision of letting a base/mobile station transmit or mute any transmission on the basis of the information concerning the real-time usage of the C-band by FSS earth stations in the surrounding area, and keep updating those decisions. Therefore, the absence of any interference would be strongly dependent on the correct functioning of these auxiliary systems and the accuracy of the information delivered. In order to provide the maximum flexibility in responding to constant and rapid variations in operational requirements of FSS downlinks earth Stations are usually designed to receive multiple carriers of bandwidth, typically between 4 khz and 72 MHz in any part of the C-band. Moreover, the frequencies at which any station can operate and the pointing direction of its antenna are not fixed and can be varied at any point in time by the relevant satellite operator according to various operational circumstances, often unforeseeable. It is therefore essential that earth stations can access the entire space segment in order to respond, without any disruption, to changes in operational conditions which typically occur instantly and without notice. It would be very challenging, not to say impossible, for any auxiliary system to be kept up to date in a way that would ensure the viability of FSS service offerings. 5 Reported cases of interference In many countries which have authorised wireless access systems in some parts of the C-band, interference cases have been reported. Public reports were made in Bolivia, Fiji and Indonesia, and field trials in Hong Kong have confirmed this interference. At the beginning of 2012, the British Broadcasting Corporation (BBC) confirmed that FSS earth stations operating in the C-band and used for their international satellite distribution network of radio and TV content had been affected by harmful interference in the following countries: D.R. of the Congo, Gabon, Guinea, Morocco, Nigeria, Tanzania, Uganda, Burkina Faso, Burundi, Rwanda, Pakistan, Cambodia, Trinidad, South Sudan and Jamaica. 5
Furthermore, a recent press release reported that Bangladeshi broadcasting, cable and satellite TV operators, in co-ordination with the international satellite communications industry, have called for the Government of Bangladesh to take rapid action to halt the disruption of TV services suffered by millions of citizens due to the operation of WiMAX services in the 3.5 GHz band. These cases are generally limited to the wireless access systems deployed in the lower part of the C-band, typically a band of 200 MHz. If wireless access systems were to be deployed in additional parts of the band 3.4 4.2 GHz, many more interference cases must be expected. 6 Conclusions The potential use of the band 3400 4200 MHz for IMT systems has already been analysed (see Report ITU-R M.2109), and taking those studies into account, WRC-07 concluded that regulatory provisions in the band 3600-4200 MHz should not be changed. There is no reason to think that the potential for IMT operations has improved since then, or that the conclusions reached by WRC-07 might have changed. Therefore, the band 3400-4200 MHz should not be considered under WRC-15 Agenda Item 1.1. 6