UAS Control and Non Payload UAS Control and Non Payload Communications (CNPC) Link Communications (CNPC) Link

AvailabilityAvailability

ICAO ACP-WG-F Meeting #24

Paris, March 2011

Michael Neale and Brooks Cressman

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OverviewOverview

What levels of UAS Control and Non-Payload Communications (CNPC) Link Availability will be required?

Safety driven analysis of Collision Avoidance Scenario.

Dependent on Aircraft type, Class of Airspace, Operation.

ICAO AMS(R)S Manual.

What levels of Availability can be achieved?LOS and BLOS (satellite).

Using frequencies likely to be approved at ITU WRC-12.

An overall system view.

A candidate UAS CNPC design solution

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Safety AnalysisSafety Analysis

Analysis of a Collision Avoidance ScenarioConflict Avoidance Period 5-10 seconds.

Collision Avoidance Period 5-10 seconds.

CNPC Link temporary outage must last for less than 1-2 seconds during this 10-20 second period.

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Safety AnalysisSafety AnalysisTarget UAS Midair Collision Rates per flight hour to be the same as manned aircraft

AOPA NALL Report shows about 10 Part 91 (GA) manned aircraft midair collisions per year during approximately 25 million flight hours = 4x10^-7 per flight hour.

NTSB and FAA data shows for manned Part 121 (airline and large cargo) aircraft no midair collisions during over 400 million flight hours = 2.5x10^-9 per flight hour.

Collision LikelihoodCurrent estimates of the likelihood of an intruder, on a collision course with a UA, entering the UA's self conflict avoidance volume (self separation volume) is once every 10,000hrs. Collision Likelihood = 1x10^-4 per flight hour.

Sense and Avoid and CNPC systems must reduce this Collision Likelihood to the target Midair Collision rates achieved by manned aircraft

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Safety AnalysisSafety AnalysisAssuming no autonomous UA operation

Collision Likelihood x SA & CNPC Unavailability < Manned Aircraft Midair Collision Rate

Part 91 Type UA Unavailability Case4x10^-7/1x10^-4 = 4x10-3

Assume SA and CNPC systems share equal Unavailabilities.

CC link Unavailability 1/2 x 4x10^3 = 2x10-3 = 0.2%

99.8% CNPC Link Availability = Total outage of 2.88min per day.

Part 121 Type UA Unavailability Case2.5x10^-9/1x10^-4 = 2.5x10-5

Assume SA and CNPC systems share equal Unavailabilities.

CNPC Link Unavailability 1/2 x 2.5x10-5 = 1.25x10-5 = 0.00125%

99.99875% CNPC Link Availability = Total outage of 1.08 seconds per day.

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Safety AnalysisSafety AnalysisPart 91 Type UA Unavailability Case

Required CNPC Link Availability approximately 99.8%

Part 121 Type UA Unavailability CaseRequired CNPC Link Availability approximately 99.99875%

ICAO Manual on Required Communications Performance Doc 9869 AN/462, 2008 prescribes a similar level of availability based on supporting ATC separation service.

RCP Type Transaction Time (secs)

Continuity per flight hr

Availability per flight hr

Integrity per flight hr

Usage

RCP 10 10 0.999 0.99998 10-5 Controller voice intervention supporting separation assurance in a 5nm radius environment

RCP 60 60 0.999 0.9999 10-5 Controller routine communication in a 5nm radius environment - data

RCP 120 120 0.999 0.9999 10-5 Controller intervention supporting separation assuarance in a 15nm radius environment

RCP 240 240 0.999 0.999 10-5 Controller intervention supporting separation assuarance in a 30/50m radius environment

RCP 400 400 0.999 0.999 10-5 Controller intervention supporting separation assuarance outside a 30/50m radius environment

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LOS CNPC Link AvailabilityLOS CNPC Link AvailabilityLOS Availability impairments compared to free space

Multipath and Diffraction – low altitude e.g. takeoff and landing as well as earth curvature obstruction near maximum range.

Airframe antenna obstruction - maneuvering during takeoff and landing as well as when flying straight and level en-route.

LOS MultipathUsing ITU-R P.530 Propagation data and prediction methods required for the design of terrestrial line of sight systems – Section 2.3.2.

Additional propagation loss of 11-19dB (depending on frequency and aircraft altitude) added for 99.8% availability.

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LOS CNPC Link AvailabilityLOS CNPC Link AvailabilityLOS Installed antenna performance analysis

Using a single antenna yields 20-25dB nulls.

Using two diversity controlled antennas gives 12dB nulls.

Additional loss (12dB) added to link budgets to account for airframe obstruction

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LOS CNPC Link AvailabilityLOS CNPC Link AvailabilityAssuming

Control - Telecommand and telemetry data rates 10kbps

Pilot Voice Communication data rates 5kbps

SA/TCAS support data rates 10kbps

Weather radar and nose camera video 270kbps

L Band (circa 1GHz) and C Band (circa 5GHz) ITU preferred AM(R)S LOS frequencies.

10 Watt transmitters

2dB Noise Figure receivers

Realistic system losses

Two Omnidirectional antennas on the aircraft

High gain antenna(s) at Control Station

Include 6dB safety margin

Approximately 150km (80nm) range

Single Link Availability of 99.8% can be achieved

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BLOS CNPC Link AvailabilityBLOS CNPC Link Availability

BLOS Satellite Availability impairments compared to free space

L and C Band scintillation loss (<0.5dB).

Ku and Ka Band.Rain and scintillation fading.

Use ITU-R P.618 - Propagation data and prediction methods required for the design of Earth-space telecommunication systems - Section 2.2.1.1.

Additional propagation loss of 1.6-14dB depending on rain rate and altitude for 99.8% availability.

Other Ku and Ka Band limitationsAircraft size and power capability, limits antenna size and transmit amplifier power output which limits EIRP and G/T and link margin.

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BLOS CNPC Link AvailabilityBLOS CNPC Link AvailabilityRain at lower altitudes causes additional propagation loss on Ku/Ka satellite links

UA can only use Ku/Ka Band satellites at aircraft altitudes where rain loss is not excessive. This limits the lowest altitude the UA can fly. UA will switch to LOS for takeoff and landing.

Manned Aircraft avoid weather radar level 3 (red) and above regions where rain is higher than an R 0.01 of approximately 20mm/hr.

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3

6

9

12

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10 20 30 40 50 60 70 80 90 100

Rq

. Fad

e M

argi

n (d

B)

Rain Rate (mm/hr)

.1 km

.5 km

1 km

1.5 km

2.0 km

3.0 km

UA - Fade Margin

UA Altitude

Freq:20 GHzLink Availability: 99.85%

6.7 dB Fade Margin(-118 dB(W/m²/MHz) & 0.5 m antenna)

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BLOS CNPC Link AvailabilityBLOS CNPC Link Availability

AssumingControl - Telecommand and telemetry data rates 10kbps

Pilot Voice Communication data rates 5kbps

SA/TCAS support data rates 10kbps

Weather radar and nose camera video 270kbps

L Band (circa 1.6GHz), C Band (circa 5GHz), Ku (12/14GHz) and Ka Band (20/30GHz) frequencies

10 Watt transmitters

Realistic system losses

Omnidirectional antennas on the aircraft at L and C Band

0.8m and 0.5m dish antennas on aircraft at Ku and Ka Band

EIRP limited by uplink power flux density regulations

Single Link Availability 99.8% can be achieved

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Candidate DesignCandidate DesignA single CNPC link is probably adequate for Part 91 Type UA operating in class E or G airspaceA very effective way to achieve the availability needed for a Part 121 Type UA operating in class A, B or C airspace is to use two non-correlated CNPC systems

1- 0.998 x 1-0.998 = 1-0.999996 or 99.9996% Availability

Also mitigates against hardware and software failures.

Use the multiple frequency bands that are being considered by ITU to provide the diversity.

Dual links for larger UA already assumed in ITU-R M.2171 spectrum analysis.

Allows some margin for other parts of the CNPC link.

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Candidate DesignCandidate Design

Part 91 Type UA Operation in Class E or G airspace.

LOS - Use Single L (1GHz) or C (5GHz) Band LOS link.

BLOS - Use Single L (1.6GHz) or C (5GHz) BLOS link – only required for operation outside Visual LOS.

If desiring to operate in class A, B or C airspace may be treated as a Part 121 Type UA if suitably equipped.

Part 121 Type UAOperation in Class A, B, C or D airspace.

LOS - Use Dual L (1GHz) and C (5GHz) Band LOS Links.

BLOS – Use Dual L(1.6GHz) or C (5GHz) Band link and Ku (12/14GHz) or Ka (20/30GHz) Band Link.

If desiring to operate in Class E, or G airspace may do so.

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ConclusionsConclusions

A flexible dual band approach can deliver the levels of safety anticipated while affording a number of advantages:Redundancy

Using two non-correlated frequencies offers protection against equipment failure as well as improvements in availability.

ScalabilityA smaller UA only requires a simple single AM(R)S L (1GHz) or C (5GHz) Band system for Visual LOS or Radio LOS operation.

A larger UA, that can support more equipment, can achieve higher levels of availability.

Interference ProtectionCombining an L(1.6GHz) or C (5GHz) Band AMS(R)S BLOS system with a Ku or Ka Band FSS system provides the interference protection of AMS(R)S with the ubiquity and payload data rate capability of FSS.

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Future LiaisonFuture Liaison

RTCA SC203 Control and Communications Work Group has developed a number of papers on:

UAS CNPC Spectrum

UAS CNPC Security

UAS CNPC messaging and data requirements

UAS Candidate CNPC Architectures

UAS CNPC Required Communications PerformanceLatency, Availability Continuity, Integrity etc.

Contact Michael Neale for copies of SC203 papers or to participate in RTCA UAS MASPS and MOPS development

Michael Neale – michael.neale@uav.com

Brooks Cressman – brooks.cressman@itt.com