Alternative Positioning, Navigation

1
Alternative Positioning, Navigation Timing
(APNT)Study Update

• Leo Eldredge
• October 14, 2010

2
Why APNT?

• The transformation of the National Airspace
  System (NAS) to the Next Generation Air
  Transportation System (NextGen) relies on
  GPS-Based PNT services and suitable alternate PNT
  services
• Current ATC system cannot be scaled up to handle
  2X traffic
• 2X traffic is more than a controller can handle
  using radar vectors
• RNAV and RNP procedures for trajectory-based
  operations (TBO)
• Automation will separate aircraft performing
  trajectory based operations (TBO)
• Controllers intercede to provide control by
  exception
• TBO Operations may require PNT performance that
  exceeds DME/DME/IRU
• GPS vulnerability to radio frequency interference
  (RFI) requires mitigation
• Waiting for the source of the interference to be
  located and turned off is not an acceptable
  alternative

3
Baseline Airspace Condition

• En Route
• Sector
• 01
• (BAASS)

• Ghost
• Sector
• (not depicted)

• Terminal
• Sector
• D

• En Route
• Sector
• 02 (GRUPR)

• Terminal
• Sector
• A

• Enabled by Legacy NAVAIDs
• VOR/DME, VORTAC, NDB
• Point-to-Point Navigation

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Big Airspace Concept

• Enabled by PBN
• GPS, WAAS, LAAS, DD, DDI
• Area Navigation (RNAV)
• Required Navigation Performance (RNP)

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TBO 3-Mile Separation with RNP
3 Mile Separation
DME / DME / IRU Performance Limit RNP-1.0
1 nm Overlap
2 x RNP 1.0
TBO (APNT) Requirement
2 x RNP 0.3
2 x RNP 0.3
Primary PNT Service GPS meets all TBO
requirements Alternate PNT Service DME/DME/IRU
wont support 3 NM separation
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GNSS Enables PBN and ADS-B
Navigation (gt 99.0 Availability) Navigation (gt 99.0 Availability) Surveillance (gt99.9 Availability) Surveillance (gt99.9 Availability) Surveillance (gt99.9 Availability) Positioning Positioning Positioning
Accuracy (95) Containment (10-7) Separation NACp (95) NIC (10-7) GNSS PNT (99.0 99.999) GNSS PNT (99.0 99.999) GNSS PNT (99.0 99.999)
En Route 10 nm 20 nm 5 nm 308m (7) 1 nm (5) GPS
En Route 4 nm 8 nm 5 nm 308m (7) 1 nm (5) GPS
En Route 2 nm 4 nm 5 nm 308m (7) 1 nm (5) GPS
Terminal 1 nm 2 nm 3 nm 171m (8) 0.6 nm (6)
LNAV 0.3 nm 0.6 nm 3 nm 171m (8) 0.6 nm (6)
RNP (AR) 0.1 nm 0.1 nm 2.5 nm DPA 171m (8) 0.2 nm (7) SBAS SBAS
LPV 16m/4m 40m/50m 2.5 nm DPA 171m (8) 0.2 nm (7)
LPV-200 16m/4m 40m/35m 2.5 nm DPA 171m (8) 0.2 nm (7)
GLS Cat-I 16m/4m 40m/10m 2.0 nm IPA 121 m (8) 0.2 nm (7) GBAS GBAS
GLS Cat-III 16m/2m 40m/10m 2.0 nm IPA 121 m (8) 0.2 nm (7) GBAS GBAS
APNT
3 nm 171m (8) 0.6 nm (6) DME Only Gap
LNAV 0.3 nm 0.6 nm 3 nm 171m (8) 0.6 nm (6) DME Only Gap
Operational requirements are defined for total
system accuracy, which is dominated by fight
technical error. Position accuracy for
these operations is negligible. Containment
for RNP AR is specified as a total system
requirement value representative of current
approvals.
Dependent Parallel Approach (DPA) Independent
Parallel Approach (IPA)
Surveillance Integrity Level (SIL) Navigation
Integrity Category (NIC)
Navigation Accuracy Category for Position (NACp)
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PNT Performance Zones
27 SM
89 SM
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Zone 1, 2, and 3 Geographic Areas
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GNSS Challenges GPS Testing by DOD

• Duration

9 Month Duration

• Geographical Area Impacted

Geographical Area Impacted

• 141

• NOTAMs

141
NOTAMs

• Minimum

• Average

Minimum
Average

• Maximum

Maximum

• 2

• Shortest

• 1.0 hour

Shortest
1.0 hour

• 2

• 2

2
2
2

• Miles

Miles

• Miles

• Miles

Miles
Miles

• 139,795

• 66,018

• 455,805

139,795
66,018
455,805

• Average

• 6.63 hours

Average
6.63 hours

• Longest

• 72 hours

Longest
72 hours

• 782 Hours

782 Hours

• Cumulative

Cumulative

• 90 days

90 days
10
Commercially Available GPS Jammer(so called
Personal Privacy Device)
11
LAAS Antenna Location
12
Zeta SnapShot System Data

• Broadband RFI straddling L1

• Baseline/Nominal L1 RF

13
and a few more Personal Privacy Devices
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RFI Challenges without APNT

• Transitioning from 3-mile to 5-mile separation en
  route and on arrivals outside of 40 nm when a GPS
  RFI event occurs
• Shifting some aircraft to radar vectors
  significant implications
• Rerouting aircraft around interference area to
  reduce demand
• Throttle back demand to compensate for loss of
  capabilities like parallel runway approaches
• Limit RNAV/RNP arrivals and departures and reduce
  options to handling arrivals

15
APNT Alternative 1Optimized DME Network
16
1100 DMEs in Current Nework
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DME-DME Alternative

• Strengths
• Leverage existing technology and systems
• Least Impact on Avionics for Air Carriers
• Weaknesses
• General Aviation generally does not equip with
  DME
• DME-DME equipped aircraft without Inertial are
  not currently authorized to fly RNAV/RNP routes
• DME-DME, even with Inertial, is not authorized
  for pubic approach operations less than
  RNAV/RNP-1.0
• DME-DME interrogations saturate in very high
  traffic environments
• Will require retention and capitalization of
  nearly half the VORs unless GA equipped with
  DME/DME inertial

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APNT Alternative 2Wide Area Multi-Lateration
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Passive Wide-Area Multi-Lateration (WAM)
1 Aircraft Transmits ADS-B Signal 6 Aircraft
Uses Own Position for Navigation
Combined DME/GBT Network 2 - WAM Receives
Signal 3 - Aircraft Position Determined 4 -
Aircraft Position Sent to GBTs
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656 GBTs for National Coverage
Communication Coverage Not Navigation
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Combined Network of DMEs and GBTs
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Approaches Histogram NavCanada Independent
Verification Of Data
 Instrument Procedures  Instrument Procedures  Instrument Procedures
Meters Feet
Average 9.4 30.8
Max 81.3 266.9
Min 0.0 0.0
Median 8.0 26.1
Std. dev 8.0 26.3
1-sigma 11.0 36.1
2-sigma 23.0 75.5
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MLAT Alternative

• Strengths
• Accuracy Demonstrated to be within target levels
• Compatible with existing WAM Systems
• Weaknesses
• Throughput on 1090ES may limit availability
• Minimum of 3 sites required to compute aircraft
  position
• Integrity monitoring and Time to Alert may be
  challenging
• More sites may be needed due to limited signal
  range
• Requires a GPS-Independent common time reference
• Significant investment in processing facilities
  and terrestrial communications network may be
  required
• Use of MLAT for Navigation will require avionics
  changes

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APNT Alternative 3DME Pseudolites (DMPL)
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Pseudolite Alternative Concept

• Aircraft Calculates Position
• RAIM Based Integrity Solution

• Combined Network of DME/GBTs etc
• GPS-Independent Time Reference
• 1 Hz Message ID and Time _at_ Transmit
• PNT Data Broadcast Channel

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Pseudolite Alternative

• Strengths
• Unlimited capacity
• Less complexity for ground-based system
• Potential for aircraft based integrity solution
• Potential to leverage use of existing DMEs and
  GBTs
• Potential to uplink data other navigation data to
  aircraft
• Weaknesses
• Minimum of 3 sites required to compute aircraft
  position
• Significant investment in processing facilities
  and terrestrial communications network may be
  required
• Common GPS-independent timing reference needed
• Greatest Impact to Aircraft Avionics
• Least mature concept, no standards exist

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APNT Timing Service
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Ground-to-Ground Time Synchronization
GEO WAAS L5 MEO GNSS
LEO MSS
30 dB of processing gain
DMEs Planned DMEs GBTs
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WAAS L5 for Ground-to-Ground Synch.
STAP
J/S 45 dB
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Summary

• NextGen Operational Improvements enabled by
  performance based navigation capabilities
  increases dependence on GPS and alternate PNT
  services
• GPS vulnerability to radio frequency interference
  needs to be addressed for trajectory based
  operations at some locations
• Alternatives are being studied for further
  consideration

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Questions