Managing Separation ofUnmanned Aerial Vehicles Using
High-Integrity GNSS Navigation
Sam Pullen
Stanford University
spullen@stanford.edu
EIWAC 2013

Tokyo, Japan
20 February 2013

Outline• Unmanned Aerial Vehicle (UAV) Networks– Applications– Ground-driven architecture– Local-Area Differential GNSS (DGNSS) Navigation• Concept of Operations• Risk Model for Safe Separation• Error Model for Safe Separation• Future Work: KAIST flight testing
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Separation for UAV Networks using GNSS2

UAV Applications (1): Scientific
Observations, Photography
Ice Monitoring in Arctic

Volcanic Ash Monitoring

Source: A. Armstrong, NOAA(New York Times, Oct. 2007)

Source: (concept) G. Gao,(picture) H. Thorburn, Wikimedia
Commons, 2010

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UAV Applications (2):Reconnaissance, SurveillanceWhite Sands
Missile Range, NM

Boeing/PaineField, WA

Source: USGS/
Wikimedia Commons

4.3km

90 km

Source:Google Maps

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UAV Applications (3):Reconnaissance, Surveillance
Inwood and nearby (gated) subdivisions, San Antonio, TX

1.5 km

4.5 kmSource:Google Maps20 February 2013

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Concerns over Threat to Privacy
Source: TIME Magazine (cover), 11 February 2013.

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Constraints of Commercial
UAV Network Environment• Service must be cost-effective• UAV design and flight operations dominate achievable
performance– Low-power/weight/cost receiver chipsets– Airborne dynamics are larger than for manned aircraft.
– Flying (relatively) close to ground objects
significant
airborne multipath from ground reflections• Two-way datalink required for guidance‒ Monitoring separation is a key responsibility of the groundcontroller

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Separation for UAV Networks using GNSS

7Local-Area UAV Network Concept

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Separation for UAV Networks using GNSS

8Simplification of GBAS for UAV Networks• See: S. Pullen, et al, “LADGNSS Architectures Optimized to
Support UAVs” ION ITM 2013, San Diego, CA, Jan. 2013

Ground Facility

Aircraft

SDM
MLA

RFI

RR

VDB

VDB
Rec.

RFI

X-corr.

MLA

RR

Accel.

»MLA

RR

CMC

MQM
VDB
EXM »Xmit.

AR
CMC

AREphem.

»

B-Val/µσµσ

MLA

RR
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Ground-to-air
datalink

Iono.
screenVDB
Mon.

ARAdd air-to-ground datalink
Separation for UAV Networks using GNSS

DVVPL

9

Safe Separation: Definitions of Terms• “In-network” UAVs: UAVs in the same network– Share the same source of guidance– Share the same LADGNSS differential corrections• “Out-of-network UAVs”: all other UAVs
– May share use of GNSS, but do not share guidance ordifferential corrections– Fly in the same general airspace allocated to UAVs

• “Manned aircraft”: aircraft with human occupants‒ Assumed to fly in their own airspace (separate from UAVs)• “Ground obstructions”: the ground and any people,
buildings, etc. attached to the ground
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Components of Separation Budget“In-network” UAVUAV Navigation Error (Unav)UAV Path-Following Error (Upath)

UAV Guidance Error (Uguidance)

Target Guidance Error (Tguidance)

Min.
Sep.
(bx)

Target Path-Following Error (Tpath)
Target Navigation Error (Tnav)

Altitude Limit or Other Vehicle (“Target”)
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Risk Model for Total Separation(example numbers for suburban applications)
Pr(HH | SV) = Pr(HH | CO) × Pr (CO | SV)
harm tohumans

separation
violationx

Scenario

collision=Pr (CO|SV) Pr (HH|CO)Pr(HH|SV)

Pr(HH|SV)(mean)(mean)(mean)(worst case)In-network
UAV

10-4

10-5

10-9

10-5

Out-ofnetwork UAV

10-5

10-4

10-9

10-4

Upper limit(manned a/c)

10-7

10-2

10-9

10-2

Lower limit(ground)

10-4

10-3

10-7

10-320 February 2013

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Required Prob. of Separation Violation
Solve for Pr(SV) to meet total safety requirement:
Pr(HH | SV) × Pr(SV) ≤ 10-920 February 2013

Separation for UAV Networks using GNSS

Target levelof safety13Preliminary Error Budget(3-D separation between in-network UAVs)

Very highly
correlated

highlycorrelated

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Preliminary Error Budget(vertical separation from manned aircraft)

potentiallycorrelated,but assumed
independent

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Out of Network UAVs:“Sense and Avoid”• Safe separation from out-of-network UAVs requires
some form of “sense and avoid” technology.
• Most practical solution: requirement for UAVs tobroadcast position information at regular intervals– “ADS-B-OUT” for UAVs, but with much simpler, miniaturizedcomponents.
– Report aircraft type, position, velocity, and source ofnavigation (e.g., a variation of GNSS)– “ADS-B-IN” function may be delegated to ground controller
for short-range systems• Guidance adaptation to out-of-network UAVs,
particularly “non-friendly” ones, is a major challenge.
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Future Work: KAIST Experiments• Test elements of UAV network architecture with flyingairborne vehicles.
• Utilize “IMT” GBAS prototype developed by Prof.
Jiyun Lee at KAIST (Daejeon, Korea) along withexisting commercial DGPS system.
• Key test objectives:– Examine receiver performance of existing UAVs in different
environments (using static “pseudo-user” as control).
– Evaluate correlated errors of UAVs close to each other.
– Map resulting UAV error models to separation standards
proposed here.
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GBAS IMT Reference Receivers
at KAISTIMT Antennas/Receivers (2013)
Pseudo-User
Antenna/Receiver
73 m

79 m

IMT Antennas/
Receivers (now)

83 m

16 m
44 m

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46 m

70 m

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Vicinity of KAIST GBAS

P-UserExpanded

Existing~ 500 m20 February 2013

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Summary• A concept for autonomous UAV networks supportedby local-area DGNSS has been proposed.
– Medium-range photography / data-collection– Short-to-medium reconnaissance / surveillance• A model for separation standards between networked
UAVs and obstacles/other aircraft (including otheraircraft) has been developed.
– Based on risk and consequences of potential UAV collisions• Flight tests to come using KAIST GBAS prototype.
– Identify UAV navigation and flight technical errors undervarious conditions.
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20SummaryEnding• A concept for autonomous UAV networks supportedby local-area DGNSS has been proposed.

• Thank
you for your attention。
– Medium-range photography / data-collection– Medium-to-short range reconnaissance / surveillance

ご清聴、ありがとうございました。
• A model for separation standards between networkedUAVs and obstacles/other aircraft (including otheraircraft) has been developed.
– Based on risk andconsequencesof potential UAV collisions• Questions
arewelcome!

• Flight tests to come using KAIST GBAS prototype.

ご遠慮なく、英語でも日本語でも質問し– Identify UAV navigation and flight technical errors undervarious conditions.てください。
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Backup Slides follow…

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GBAS Architecture Overview(supports CAT I Precision Approach)airport boundary

Corrected carrier-smoothed-code processing(encloses GBAS Ground Facility)− VPL, LPL calculations

Cat I

GPS Antennas
GPS, L1 only

LGF Ref/Mon Receivers
and Processing
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VHF Antennas
VHF Data Broadcast

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