Alternate Position, Navigation & TimeAPNT for Civil Aviation

For Working Group B of the International GNSS Committee

Shanghai, May 2011by Per Enge & Leo Eldredge

Work supported by the Federal Aviation Administration under CRDA 08-G-007.

This briefing is NOT intended to convey a US Government position; rather, it is provided to facilitate a

working-level discussion and exchange of ideas.

Danger of Radio Frequency Interference

Danger of Radio Frequency Interference

… and a few more “Personal Privacy Devices”

$55 Ebay

$110 Ebay $335 Ebay$92 Ebay

$152 Ebay$40 GPS&GSM

$83 GPS&GSM

Why APNT?• GPS radio frequency interference (RFI) requires mitigation

– Waiting the interference source to be turned off is unacceptable– Continuity of operations must be assured at high density airports

• NextGen capabilities establish greater demand for precise PNT services, provided by GPS– 2X traffic is more than a controller can handle using radar vectors– Trajectory-based operations (TBO) will be used to improve capacity– Automation will sequence aircraft performing TBOs– 3 nm separation will be based on precise RNAV/RNP paths– Surveillance used for “conformance monitoring”– Controllers intercede to provide “control by exception”– DME/DME/IRU is not accurate enough to enable 3 nm separation

• FAA would like to avoid $1B cost to replace aging VORs– VORs are not compatible with RNAV and RNP

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

APNT Performance Zones

5 SM of Airport

Zone- 1Enroute High

CONUS

FL-600

FL-180

5000’ AGL

Zone- 2Enroute Low

CONUS Zone-3 TerminalOEPs + Next 100 Busiest Airports

2° Slope from 500’ AGL

27 SM89 SM

8

Combined Network of DMEs and GBTs

1090 DMEs

646 GBTs

9

Bay Area Coverage from Terrestrial Radio

1010

DMEs + New Terminal Area DMEs + GBTs

GEO: WAAS L5

MEO: GPS

LEO: Iridium

Ground-to-Ground Synchronization

11

Ground-to-Air Synchronization

request/reply(aka two-way ranging

or true range)

one-way ranging(aka pseudo-range)

DMEs + Planned DMEs + GBTs

12

Coverage at 500’ AGLTrue Ranging to DMEs + GBTs

from R. Niles at Mitre & S. Lo

εFTE = .0625 NMεR = 328 m

Longitude (deg)

Latit

ude

(deg

)

SFO

OAK

SJC

-123 -122.8 -122.6 -122.4 -122.2 -122 -121.8

37.2

37.3

37.4

37.5

37.6

37.7

37.8

37.9

38

38.1

RNP 0.3 0.5 1 2 5 10

13

Longitude (deg)

Latit

ude

(deg

)

SFO

OAK

SJC

-123 -122.8 -122.6 -122.4 -122.2 -122 -121.8

37.2

37.3

37.4

37.5

37.6

37.7

37.8

37.9

38

38.1

RNP 0.3 0.5 1 2 5 10

Coverage at 500’ AGLTrue Ranging to DMEs + GBTs

from R. Niles at Mitre & S. Lo

εFTE = .0625 NMεR = 160 m

14

Coverage at 500’ AGLTrue Ranging to DMEs + GBTs + New DMEs

from R. Niles at Mitre & S. Lo

εFTE = .0625 NMεR = 160 m

Longitude (deg)

Latit

ude

(deg

)

SFO

OAK

SJC

-123 -122.8 -122.6 -122.4 -122.2 -122 -121.8

37.2

37.3

37.4

37.5

37.6

37.7

37.8

37.9

38

38.1

RNP 0.3 0.5 1 2 5 10

15

Signal Design Objectives

• Ranging accuracy !– Present DME is not precise enough for approach operations– Wider bandwidth than DME ?

• Better coverage ?• New avionics would require new benefits• Data capacity to support new benefits

– Authentication, time, identification & location +– Wide area GBAS (ΔΦ) for Category II & III– AGPS for GPS anti-jam– WAAS & ISM for LPV

• Transportability to VHF ?

16

APNT Signals in the DME Band

• Any new signal in the DME band should be pulsed to minimize impact on legacy users.• Bench tests needed to verify non-interference with 4 ms pulses.

950 1000 1050 1100 1150 1200 12500

5

10

15

20

25

30

35

40

45DME all histogram (X & Y) 1522 sta

Freq (MHz)

Coun

t

DMEJTIDSTransponder

1030

1090

978

GPS

L5

1717

UAT

FMS

TR

VOR

R

VHF CommT

GNSS

ADS-B Positionout

Aviation Signals of Opportunity GuidanceINS

RR

DMET

L bandV

HF band

1818

UAT

FMS

TR APNT

VOR

R

VHF CommT

GNSS

ADS-B Positionout

Aviation Signals of Opportunity GuidanceINS

RR

DMET

L bandV

HF band

19

Pulse Position Modulation (PPM) orPulse Pair Position Modulation (PPPM)

15 -10 -5 0 5 10 15

time (µsec)15 -10 -5 0 5 10 15

time (µsec)

15 -10 -5 0 5 10 15

time (µsec)15 -10 -5 0 5 10 15

time (µsec)

PPPM data capacity of 300 to 1200 bps

20

Universal Access Transceiver (UAT)

21

Summary

• 200,000 civil aircraft rely on GPS• With NextGen, our reliance is increasing• Consolidate & re-purpose ground navigation aids• Backup GPS RNAV & RNP to ensure NextGen

success