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    09/11/27 International Civil Aviation Organization




    Bangkok, Thailand, 8 18 December 2009

Agenda Item xx: Xxx



    (Presented by Joe Cramer US AVSI, Uwe Schwark Germany AVSI)


    The international aviation industry is studying characteristics of Wireless

    Avionics Intra-Communications systems intended for wireless

    communications applications between points on a single aircraft impacting the

    safety or regularity of flight. This paper presents initial thoughts on potential

    frequency bands for future WAIC systems.


    To provide guidance and support for the identification of suitable spectrum for

    future WAIC systems and to consider ICAO support for a potential proposal

    for a new agenda item at WRC-12 on the identification of spectrum for WAIC.


    Wireless Avionics Intra-Communication (WAIC) systems are considered as a replacement for existing aircraft systems employing wires for communications purposes and as an enabler for new on-board wireless communications applications. Deploying WAIC systems impacting safety or regularity of flight requires operating in spectrum recognized by the Convention on International Civil Aviation. The ITU-R Radiocommunication Assembly approved the study question 249/5 to determine the technical 1characteristics and operational requirements of WAIC systems. Resolution of this question is currently

     1 ITU Radiocommunication Assembly, QUESTION ITU-R 249/5 “ Technical characteristics and operational

    requirements of wireless avionics intra-communications (WAIC)”, 2009

    (7 pages)


    - 2 - ACP-WGF21/WP-xx

     2being conducted by ITU-R WP5B, which continues to study the issue. The United States and CEPT

    submitted contributions to the November 2009 ITU-R WP5B meeting providing technical characteristics, predicted accumulated data rates, and power level requirements for potential WAIC systems. Brazil submitted a document providing a glossary of terms. These documents were incorporated into the current Preliminary Draft New Report (PDNR) on this topic. The revised PDNR is submitted in Annex A. The Aerospace Vehicle Systems Institute (AVSI) is also working on the next update of this PDNR and is preparing a preliminary proposal for specific frequency bands that may be considered by the ITU and ICAO for accommodating WAIC applications. AVSI has informed ACP WG-F and WG-W about the 3WAIC effort through a series of informational documents and presentations.

    Based on preliminary analyses, it is most likely that radio frequency spectrum is required in aeronautical spectrum below 10 GHz for low data-rate WAIC systems and spectrum above approximately 20 GHz for the high data-rate applications. This information document addresses potential frequency bands below 10 GHz for WAIC systems with per-node data rates lower than 10 kbps and associated low power transmission. The AVSI member companies believe that a potential band can be found among one of the already existing aeronautical allocations. An advantage of such a solution is that coexistence studies may be essentially restricted to the incumbent and future aeronautical users of such bands. In many cases, the aeronautical applications utilizing the current aeronautical radio frequency spectrum are under regulatory and operational control of aviation regulators, aircraft manufacturers and operators who are also ultimately responsible for coexistence between WAIC and incumbent systems.

    This contribution presents three potential frequency bands for discussion. AVSI seeks feedback and guidance from ACP WG-F regarding the feasibility of utilizing WAIC applications in one of these radio frequency bands. These three bands are being initially considered based upon their potential technical suitability for WAIC systems as well as potential compatibility with incumbent systems. AVSI realizes that much more detailed analyses will be required to substantiate a future spectrum proposal. In addition to the ongoing compatibility studies and selection process the aerospace industry is considering establishing a new agenda item (under WRC-12 Agenda Item 8.2) identifying spectrum for WAIC systems. AVSI is asking ICAO to support this potential Agenda Item, e.g. by adding WAIC to the draft ICAO position paper dealing with WRC-12 matters.

    To date three frequency bands have been initially reviewed as potential candidate bands for accommodating low data-rate WAIC systems. This cursory analysis is not exhaustive. Our initial thoughts are described below:


    2.1 Potential WAIC candidate band 4200 4400 MHz

    The 4 200 4 400 MHz band is allocated to the aeronautical radionavigation service and is, according to footnote 5.438 of the ITU-R Radio Regulations exclusively reserved for radio altimeters installed on

     2 ITU-R Radiocommunication Study Groups Annex 15 to Document 5B/296-E, “Technical Characteristics and

    Operational Objectives for Installed Wireless Avionics Intra-Communications (WAIC)”, 2 June 2009. 3 ACP-WGF 17/WP19, “Dedicated Frequency Allocation for Aircraft On-Board Wireless Systems”, Nairobi, 19-25

    September 2007. ACP-WGF 18/WP05, “The Technical Characteristics and Performance Objectives for Installed Wireless Avionics Intra-Communications (WAIC) Systems”, Montreal, 15-19 May 2008. ACP/WGF 20/WP07,

    “Draft Revisions to Working Document on Technical Characteristics and Operational Objectives for Installed Wireless Avionics Intra-Communications (WAIC)”, Montreal, 24 March – 3 April 2009

    - 3 - ACP-WGF21/WP-xx

    board aircraft and associated transponders on the ground. This band is predominantly used for low range radio altimeter applications on board civil and military aircraft depending on the implementation of the Radio Regulations on individual national level. For civil aircraft the predominant radar principle used is FMCW (Frequency Modulated Continuous Wave). Military aircraft apply both FMCW and pulsed type radars.

    Typical characteristics and the usage profile of low range radio altimeters on board civil aircraft suggest that coexistence with future WAIC applications could be possible due to the following:

    a) Low range radio altimeters apply radio magnetic waves emitted and received predominantly over

    transmit/receive paths, which are orthogonal to the earth's surface using directive antennas

    usually installed underneath the aircraft fuselage. This fact suggests that coexistence of both

    applications in the same band is viable by adequate spatial separation and a thorough design of

    the antennas applied by both applications. A joint optimization of the antennas on the aircraft is

    reasonable since both systems including their installation are under the full control and

    responsibility of the aircraft manufacturer. The directivity of radio altimeter signals and low

    power transmissions of WAIC systems may also ensure that WAIC systems do not cause

    interference to the radio altimeter of another aircraft.

    b) In radar systems, the signal-to-interference ratio at the radar receiver input increases as the

    distance to the target decreases, assuming the interference power level remains constant. With

    respect to the low range radio altimeter case, this means the reception quality and hence the

    precision of the altitude-over-ground measurement, increases with decreasing altitude during an

    approach to an airport. This factor makes the low range radio altimeter inherently robust against

    in-band and adjacent band interference.

    c) The commonly used principle in low range radar altimeter implementations for commercial

    aircraft is the FMCW principle. FWCW-based radars apply a linear up-chirp followed by a down-

    chirp signal with a given constant frequency variation rate. The difference in frequency between

    the instantaneous transmit frequency and the frequency of the receive signal reflected by the

    target object (the ground) is proportional to twice the distance between the radar antenna and the

    target object. Usually the frequency sweep of the chirp signal occupies between 100 and

    150 MHz of bandwidth in state-of-the-art implementations. But, in a given time interval, the

    bandwidth instantaneously occupied, is only a few kHz. This fact may be exploited when

    designing a medium access protocol for WAIC systems actively avoiding interference with radio

    altimeter transmissions.

    2.2 Potential WAIC candidate band 5 030 5 091 MHz

    The 5 030 5 091 MHz band is currently allocated to two aeronautical services:

    Aeronautical Radio Navigation Service (ARNS)

    This allocation supports implementation of the Microwave Landing Systems (MLS) and takes precedence in this band (per footnote 5.444 of the ITU-R Radio Regulations). MLS is a precision approach and landing guidance system that provides position information and various ground-to-air data from ground transmitters to airborne receivers at altitudes up to 20,000 feet and ranges out to 22.5 nautical miles. A regional frequency assignment and implementation plan for MLS has been prepared for Europe. In March 2009 an MLS system was commissioned at Heathrow airport that supports Cat III operations. Additionally, mobile MLS stations are utilized to support precision approach capability at military airfields that have limited or no installed navigation aids.

    - 4 - ACP-WGF21/WP-xx

    Typical broad characteristics and usage profiles of MLS systems suggest that coexistence with future WAIC applications could be possible due to the following:

    a) For WAIC systems collocated on the same aircraft with an MLS receiver, the WAIC system

    could be designed to have knowledge of the selected MLS channel, and avoid utilizing that


    b) The low power level of WAIC systems combined with aircraft attenuation and free-space loss due

    to minimum aircraft separation requirements may ensure that WAIC systems do not interfere with

    MLS receivers on adjacent aircraft (operating in the same airspace or at the same airport).

    c) WAIC systems could also deploy algorithms, which would detect MLS transmitters and select

    not-occupied channels to ensure reliable WAIC operation. This would also serve to prevent

    WAIC interference to MLS receivers on adjacent aircraft.

    The frequency band study to support control links for UAS, Preliminary Draft New Report under WRC-12 Agenda Item 1.3, provides a good description of and protection requirements for MLS systems. This document will be utilized for future potential compatibility studies.

    Aeronautical Mobile-Satellite (Route) Service (AMS(R)S)

    A primary allocation for AMS(R)S is also provided per footnote 5.367 of the ITU-R Radio Regulations. Footnote 5.367 states that AMS(R)S has a primary allocation from 5 000 to 5 150 MHz. Since footnote No. 5.444 states that the requirements of MLS take precedence over other uses of the 5 030-5 091 MHz frequency range, any 5 030-5 091 MHz AMS(R)S or WAIC system would have to give precedence to MLS.

    A proposal to develop a satellite-based UAS control link within the 5 000-5 150 MHz band was recently 4introduced in the European Organization for Civil Aviation Equipment (EUROCAE) and other forums.

    52.3 Potential WAIC candidate band 9 300 9 500 MHz

    The 9 300 9 500 MHz band is allocated to a variety of primary status services including:

    - Airborne weather radar (AWR) systems (according to footnote 5.475 of the ITU-R Radio


    - Radionavigation, including ground based meteorological, maritime coast and shipborne radars, - Earth-Exploration Satellite Service (EESS) and

    - Space Research Service.

    Initial compatibility assessments between potential WAIC applications and incumbent services must address the following:

    a) Radars operated in the band 9 300 9 500 MHz are likely to remain in service for many

    years into the future. Sharing between AWR and meteorological radars on one hand and

    maritime radars on the other hand is possible and practical because of the different

    geographical usage, and good coordination between these services. Sharing with other

    services including WAIC needs careful study.

     4 A. Klaeyle, The 5 GHz “Safety Satcom” Infrastructure, UAS_305.1, EUROCAE WG-73, 31 December 2008. 5 The 9 000 9 200 MHz band may also be a viable candidate but has not yet been analyzed in detail.

    - 5 - ACP-WGF21/WP-xx

    b) Ground-based radars may interfere with WAIC systems. This may even be true for the

    case of WAIC applications located inside the aircraft fuselage. Dynamic channel

    selection methods, similar to those used by RLANs in the 5 GHz radar bands, may

    support co-existence.

    c) Maritime and shipborne radars may interfere with WAIC systems under certain

    circumstances, e.g. when aerodromes and maritime facilities are located in close vicinity.

    As in the case of ground-based radars, techniques actively avoiding interference may

    support coexistence between these radars and WAIC systems.

    d) AWR signals may interfere with WAIC transmissions and vice versa. In particular this is

    true for the case of landing gear sensors. Appropriate mitigation strategies will have to be


    e) Co-existence between the EESS and WAIC applications

    f) Co-existence between the Space Research Service and WAIC applications

2.4 Future band candidates for high data-rate systems

    This document addresses only candidate frequency bands for low data-rate WAIC systems. A parallel effort is under way at AVSI to identify suitable candidate bands for high data-rate WAIC systems. Because of the wider bandwidth required, this will most likely yield bands above 20 GHz that do not currently include aeronautical safety allocations. A future contribution to ITU-R WP5B will provide a spectrum proposal for low data-rate systems, based on feedback to this document, and a spectrum proposal for high data-rate systems, which is not addressed here.


    The ability to use WAIC applications globally is extremely important to the commercial aviation industry and presents a significant challenge given the international nature of air travel. The aviation industry is striving to utilize wireless systems for both system upgrades on current aircraft, and in new aircraft design that will be at least as safe as current wired systems, while reducing costs. The support of ICAO in enabling WAIC applications to benefit from the certification efficiencies provided to avionics systems and to benefit from the protections provided to aviation spectrum is essential for implementing such applications. WAIC systems will require to be defined as a safety service on a global basis. First analysis of suitable frequency bands indicates that sufficient spectrum necessary for accommodating the identified WAIC applications may not be obtained without modification of the existing Radio Regulations. The aviation industry will depend upon ICAO and its member administrations in order to obtain the necessary spectrum. Early indication of support for a potential Agenda Item from ICAO in this matter will help in acquiring support from Administrations.


    The ACP WGF is invited to:

    a) provide guidance and support for the identification of suitable spectrum for future WAIC systems.

- 6 - ACP-WGF21/WP-xx

b) consider ICAO support for a potential proposal for a new agenda item at WRC-12 on the

identification of spectrum for WAIC.

    - 7 - ACP-WGF21/WP-xx



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