Spectrum Alternatives for Aircraft Onboard Wireless Systems

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Spectrum Alternatives for Aircraft Onboard
Wireless Systems

• Date 2007-11-13

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What Kind of Spectrum Do We Want?

• Lower frequencies propagate better
• Less shadowing and better material penetration,
  signals will propagate throughout aircraft with
  low power
• Require larger antennas
• Higher frequencies are more attenuated
• More line of sight (LOS) propagation, shadowing
  and absorption become major factors
• Very small antennas can be used, but more power
  required
• Desirable to have aviation spectrum near
  unlicensed bands
• Can adapt COTS equipment to avionics use via
  firmware load
• Leverage significant wireless industry investment
  into technology upgrades and improvements

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Where Will the Spectrum Come From?

• Essentially all usable spectrum is already
  allocated to primary and secondary users around
  the world
• So how might we find spectrum? Two basic
  options
• Obtain new spectrum by taking it away from an
  incumbent user
• Resistance to getting more spectrum allocations
  will be high
• Maximum opportunity for new spectrum is above
  30GHz
• Reuse existing spectrum already allocated to
  aviation
• Aviation has a large number of dedicated
  frequency bands allocated in around the world
• Opportunities exist for more efficient use of
  existing aviation spectrum
• MLS is not deployed, DSB-AM still in use

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Obtaining New Spectrum

• Best opportunity for new spectrum is above
  30GHz
• Line of Sight (LOS) propagation
• High absorption due to rain, snow, etc. in
  atmosphere
• Resulting intra-airplane usage might be
  appropriate for
• Very short distance, high-bandwidth applications
• Very small devices, but with sufficient power
  availability
• Examples of suitable applications might include
• LRU-LRU communications within an equipment rack,
  within the flight deck, or multiple sensors with
  a nearby data concentrator
• Examples of ill-suited applications could include
• Extremely low-power devices attempting to
  communicate long distances or in a highly
  shadowed environment, such as along the length of
  the fuselage

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Reusing Existing Spectrum

• Existing aviation spectrum is largely below 10GHz
• Consequently, the advantages of low frequencies
  apply
• Is it be possible to reuse existing spectrum?
  Many factors apply
• Particular classification of existing spectrum
  (in ITU terms)
• Incumbent system characteristics
• Bandwidth potentially available for reuse
• How can we reuse existing spectrum? Two basic
  possibilities
• Cognitive the new systems can detect which
  parts of the frequency band the incumbent is
  using, and move elsewhere
• Underlayment the new systems operate at power
  levels below what the incumbent systems can
  detect (the UWB model)

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Existing Aeronautical Allocations
Avionics Receivers Freq Range (MHz) Allocation (Service) Limiting Footnotes
ADF 0.190-1.750 ARNS No limiting footnotes. Service Definition Aeronautical Radionavigation - A radionavigation service intended for the benefit and for the safe operation of aircraft
HF Voice HF Datalink 2-30 AM(R)S AM(OR)S No limiting footnotes. Service Definitions Aeronautical Mobile (Route) Service reserved for communications relating to safety and regularity of flight (Air Traffic Control) Aeronautical Mobile (Off-Route) Service - intended for communications, including those relating to flight coordination (Aeronautical Operational Control)
Marker Beacon 75 ARNS 5.180 The frequency 75 MHz is assigned to marker beacons. Administrations shall refrain from assigning frequencies close to the limits of the guardband to stations of other services which, because of their power or geographical position, might cause harmful interference or otherwise place a constraint on marker beacons.
ILS Localizer VHF Data Broadcast VHF Omnirange (VOR) 108-118 ARNS No AR limiting footnotes. AM(R) (VHF Radio) allocation by footnote 5.197A The band 108-117.975 MHz may also be used by the aeronautical mobile (R) service on a primary basis, limited to systems that transmit navigational information in support of air navigation and surveillance functions in accordance with recognized international aviation standards.
VHF Voice Data Link 118-137 AM(R)S No limiting footnotes.
ILS Glide Slope 329-335 ARNS 5.258 The use of the band 328.6-335.4 MHz by the aeronautical radionavigation service is limited to Instrument Landing Systems (glide path).
DME UAT Mode AC Transponder Mode S Transponder TCAS Interrogator GNSS L5/E5 962-1213 982 1030 1030 1090 1164-1215 ARNS 5.328 The use of the band 960-1 215 MHz by the aeronautical radionavigation service is reserved on a worldwide basis for the operation and development of airborne electronic aids to air navigation and any directly associated ground-based facilities. (WRC-2000)
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Existing Aeronautical Allocations
Avionics Receivers Freq Range (MHz) Allocation (Service) Limiting Footnotes
AMS(R)S SATCOM 1530-1559 No Allocation Footnote Only 5.357A In the bands 1 545-1 555 MHz and 1 646.5-1 656.5 MHz, priority shall be given to accommodating the spectrum requirements of the aeronautical mobile-satellite (R) service providing transmission of messages with priority 1 to 6 in Article 44. Aeronautical mobile-satellite (R) service communications with priority 1 to 6 in Article 44 shall have priority access and immediate availability, by pre-emption if necessary, over all other mobile-satellite communications operating within a network.
GNSS/ GPS 1559-1610 ARNS No Limiting Footnotes
Radio Altimeter 4200-4400 ARNS 5.438 Use of the band 4 200-4 400 MHz by the aeronautical radionavigation service is reserved exclusively for radio altimeters installed on board aircraft and for the associated transponders on the ground. However, passive sensing in the Earth exploration-satellite and space research services may be authorized in this band on a secondary basis (no protection is provided by the radio altimeters).
MLS MLS Extension Band 5030-5090 5090-5150 ARNS 5.444 The band 5 030-5 150 MHz is to be used for the operation of the international standard system (microwave landing system) for precision approach and landing. The requirements of this system shall take precedence over other uses of this band. 5.367 Additional allocation The bands 1 610-1 626.5 MHz and 5 000-5 150 MHz are also allocated to the aeronautical mobile-satellite (R) service on a primary basis, subject to agreement obtained under No. 9.21
Weather Radar 5350-5470 ARNS 5.449 The use of the band 5 350-5 470 MHz by the aeronautical radionavigation service is limited to airborne radars and associated airborne beacons.
Weather Radar 9300-9500 No Allocation - Footnote Only 5.475 The use of the band 9 300-9 500 MHz by the aeronautical radionavigation service is limited to airborne weather radars and ground-based radars. In addition, ground-based radar beacons in the aeronautical radionavigation service are permitted in the band 9 300-9 320 MHz on condition that harmful interference is not caused to the maritime radionavigation service. In the band 9 300-9 500 MHz, ground-based radars used for meteorological purposes have priority over other radiolocation devices.
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Cognitive Approaches

• What is Cognitive Radio, and what does it have to
  do with reality?
• Cognitive radio is the concept of a coexisting
  system detecting another system, and moving out
  of the way
• Regulatory authorities world-wide are looking at
  cognitive as an answer to the shortage of good
  spectrum
• IEEE 802.11a/n operation in 5GHz band using DFS
  is an early implementation of cognitive
  capability
• Thus, to reuse existing avionics spectrum the new
  systems would
• Need to know where the incumbent system is
  operating, and
• Operate around it or under it
• How?
• Announcements (via a systems bus, beacon, etc.)
• Detection of emissions (proven, but difficult)

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Underlayment Approaches

• What is underlayment, and what does it have to do
  with reality?
• Underlaying an existing spectrum allocation
  relies upon operating a new system in such a way
  that the existing system is not interfered with
  in a harmful way (FAA/FCC nomenclature)
• Again, a major push by regulators looking for
  ways to gain more utility from over-desired
  spectrum
• Thus, to reuse existing avionics spectrum, the
  new systems would
• Operate at power levels which would not interfere
  with the input receivers of incumbent systems
• How? Two factors
• Output power, directionality, and gain of new
  system
• Interference path loss (IPL) between new system
  and the incumbent receiving antenna

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How Much Bandwidth is Available?

• Shannons Law
• The theoretical maximum bit-rate through any
  noise-limited channel is
• where Cchannel capacity in bits, Bchannel
  bandwidth in Hz, and ? is numeric signal-to-noise
  ratio
• Shannons law can be modified by MIMO technology
  to
• Where ?(H) is a bunch of channel and path
  correlation factors, and N is the number of MIMO
  channels

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How Close to Shannon Are We?
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Underlaying Existing Systems
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Conclusions

• Two approaches to obtain dedicated and protected
  spectrum for intra-airplane use
• Pursue a new aviation allocation through
  international treaties organizations
• Develop methodology to re-use existing spectrum
  in a safe and efficient manner
• A new allocation
• Would likely be challenging to obtain spectrum
  below 10GHz, due to strong competition for
  spectrum resources
• Would likely take several cycles of the World
  Radio Conference to approve
• Reusing existing allocations
• Significant engineering challenges in ensuring
  that multiple communications systems can use the
  same spectrum without harmful interference
• Regulatory challenges pertaining to avoiding
  being limited by the current regulatory language
  and footnotes on existing bands