ACP WGF21 WP11
Aeronautical Communications Panel (ACP)
Working Group F Meeting
(Bangkok, 8 - 18December 2009)
Agenda Item 4: Development of material for ITU-R meetings
Satellite Spectrum to Support Unmanned Aircraft Systems (UAS)Control Links
(Presented by Brandon Mitchell)
1 Introduction
A wide range of satellite systems operate above 10 GHz, offering mature technologies and worldwide coverage. For example, satellite systems operating in the 11-12/14 GHz Bands have been used successfully for over a decade to provide many hundreds of thousands of hours of beyond line-of-sight (BLOS) communications for Unmanned Aircraft Systems (UAS) operating in segregated airspace. These BLOS communications include unmanned aircraft (UA) Control, air traffic control (ATC) Communications, and transfer of sensor products.
The frequencies above 10 GHz include bands allocated worldwide to the FSS where many hundreds of satellites are currently operating, all supporting multi-megahertz-bandwidth transponders.[1] Current technology has shown that a fair compromise between antenna size and power (RF and DC) for UAS operations services with small-size and low-cost antennas exists in these frequencies. This makes these frequencies very attractive for UA use because of the limitations on UA equipment size, weight, and power.
Certain portions of FSS bands have characteristics that make them attractive for consideration for protected UAS operations. While these satellite bands do not carry an aeronautical mobile satellite (R) service (AMS(R)S) allocation or indeed any aeronautical spectrum designation, potential interferers are limited to neighboring satellite systems and levels of interference are therefore calculable. However, it must be recognized that many of these FSS bands are heavily utilized by commercial satellite systems.
The International Civil Aviation Organization (ICAO) may require that UAS satellite control communications utilize frequency bands with an AMS(R)S allocation when the UAS is operating in non-segregated airspace. However, commercial FSS operators are greatly concerned that if any portion of an existing FSS band is allocated to AMS(R)S, they would be unable to offer that segment to other customers due to the safety service attribute of an AMS(R)S allocation. Additionally, there is a concern that AMS(R)S traffic on one satellite network could place additional protection requirements on neighboring satellite networks not carrying AMS(R)S traffic, due to the safety service aspect of AMS(R)S, thereby creating difficulties in the current Article 9 coordination regime. These concerns have made it difficult to consider bands with existing commercial satellite operations. Further, some allocations have sharing issues because they are heavily utilized or because they are allocated to both Earth-to-space and space-to-Earth transmissions allowing little opportunity to provide the low levels of interference necessary for safe operation of UAS. There are also radio astronomy allocations in some of these frequencies to be considered.
In addition, there are a number of ITU-R designated Plan bands above 10 GHz. These bands are not under consideration.
Based on the analysis performed in ITU-R M.[UAS-SPEC], it has been shown that for a spot-beam based system that incorporates frequency reuse, approximately 46 MHz of spectrum will be needed. Approximately 56 MHz of spectrum will be needed for a regional-beam satellite system, which would require multiple co-coverage geostationary satellites, a directional antenna on the UA and operation at higher frequencies. Both the spot-beam and regional-beam satellite spectrum requirements include uplink and downlink spectrum to and from the satellite for both the UA and the control station (CS). This spectrum does not need to be contiguous nor in the same band. The analysis in ITU-R M.[UAS-SPEC] does not differentiate between spectrum required for feeder links (CS or mobile satellite service gateway to satellite) and spectrum required for service links (UA to satellite or CS to satellite in a double hop mobile satellite service solution). Further analysis may be required to differentiate the amount of spectrum needed for feeder links and service links once suitable bands have been identified. Conversely, availability of only specific bands may dictate the type of satellite system that can be used and therefore the amount of spectrum required for service and feeder links.
2 Approaches
Based on the discussion above, four options for accommodating the UAS satellite spectrum requirements are identified below.
2.1 Introduce AMS(R)S in bands, or portions of bands, with existing FSS allocations.
This option would introduce an additional allocation to the AMS(R)S in bands, or portions of bands, with existing FSS allocations. The AMS(R)S allocation could be limited to use by only the UAS. Additionally, an ITU-R Recommendation or WRC Resolution as described in 2.3 below would be developed to ensure compatibility with FSS and to specify UAS control link performance requirements. This approach could have the undesired result of precluding or severely limiting commercial operators from using the bands allocated to AMS(R)S for applications other than UAS. In addition, this could lead to difficulties in the coordination process, as satellite networks carrying the AMS(R)S traffic could claim additional protection requirements for the safety service aspects of AMS(R)S, as compared to the protection requirements of conventional commercial traffic.
2.2 Introduce Aeronautical Mobile Satellite Service (AMSS) in bands, or portions of bands, with existing FSS allocations.
This option would introduce an additional allocation to the AMSS in bands, or portions of bands, with existing FSS allocations along with an ITU-R Recommendation or WRC Resolution as described in 2.3 below. The AMSS allocation would be limited to use by only the UAS and performance and protection aspects of the UAS would be addressed in the ITUR Recommendation or Resolution described in 2.3 below. This approach would eliminate the potential for satellite network operators to claim additional protection for AMS(R)S and the need for satellite network operators to limit commercial operations in these AMSS bands.
2.3 Introduce a new ITU-R Recommendation or WRC Resolution addressing how to provide UAS control communications within existing FSS allocations.
This option would provide guidelines for the operation of UAS control links within existing FSS allocations with no change to the allocation status or as part of a new AMS(R)S or AMSS allocations as noted in 2.1 and 2.2 above. The Recommendation or Resolution would ensure the UAS equipment meets certain performance requirements in order to ensure that the UAS control link does not require additional interference protection as compared to conventional satellite links and their associated earth terminal equipment. Additionally, a Recommendation or Resolution would provide characteristics to ensure compatibility with co-frequency satellite networks. These guidelines would also need to address the required link availability.
2.4 Introduce new AMS(R)S allocations to bands that do not currently have a FSS allocation.
This option would consider non-satellite frequency bands. There are a variety of bands that are used for terrestrial communications, radars, and scientific purposes. Some of these bands are already allocated for aviation systems. Sharing in some of these bands may present difficulties; however, sharing in others should be possible. It may also be necessary to specify the performance and compatibility aspects of the UAS in an ITU-R Recommendation or Resolution as described in 2.3 above.
3 Conclusion
The approaches mentioned above are listed as discussion points and more options may be available. ICAO WG F should discuss these issues in an effort to assist ITU-R Working Party 5B with resolving studies under WRC-12 agenda item 1.3.
[1] The recently approved modification to ITU-R Recommendation S.1001-1 contains a listing of existing FSS allocations by ITU Region and an estimate of the number of satellite networks that use these allocations.