gps “big five” contribution to users needs an update
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GPS “Big Five” contribution to Users Needs AN UPDATE. Showing Dependence of User Measures of Effectiveness ( MOE ) on GPS System Design & Design Decisions. Prof. Brad Parkinson Draft Developed for IRT – August 2008 - PowerPoint PPT PresentationTRANSCRIPT
October 08Interim Report Big 5 and MOEs
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GPS “Big Five” contribution to Users Needs AN UPDATE
Prof. Brad Parkinson
Draft Developed for IRT – August 2008Thanks to Col. Dave Madden and Aerospace for help, Particularly Tom Powell
and Paul Massatt
Also FAA with Sam Pullen and Todd Walter
Showing Dependence of User Measures of Effectiveness (MOE) on GPS System Design & Design Decisions
October 08Interim Report Big 5 and MOEs
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The IRT “Big 5” – Essential GPS PNt Characteristics
A Bridge between User’s MOE and GPS System Design
1. Assured (Geometric) Availability of GPS signals
2. Resistance to (Deliberate or Unintentional) Interference
3. Accuracy of User’s GPS Position (After satisfying #1 and #2)
4. Bounded inaccuracy –Limiting potential for very large
errors (Fratricide or Collateral Damage)
5. Integrity – Identifying and eliminating the non-normal
GPS system or local errors (e.g. extreme user multipath or runaway
clocks).
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Performance EnvelopeConceptual Examples
Current GPS Capabilities
(30+ Sats)
Current GPS Specification
(e.g. 21+3 Sats)
Needs for SDB
(Target Designation in Visibility
Impaired Region)Cat III
Aircraft Landing
(Integrity – Time to Alarmor Availability)
Potential GPS Enhancements
Potential GPSAugmentationsThe
“Envelope”
“Envelope”
Missions
FAA ATCModernization
ADS-B
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Envelope Examples of Uses(Summarize A, B, and D)
Military Uses M1. Use of Small Diameter Bomb
in region where ground target locator has impaired visibility (e.g. mountainous terrain or urban street) (In Mission A)
M2. Delivering weapons close to friendly troops, or close to sensitive “don’t hit” locations (In Mission A)
M3. Operating with impunity in the vicinity of high-power (or multiple, distributed) Enemy Jammers (In Mission A)
M4. Operating in mined land or restrictive sea areas
Civilian Uses C1. Precision Aircraft Approach and
Landing (Up to Cat III) demanding 10-9 integrity (Mission B – includes a military mission)
C2. First Responder PNT in Urban Area (Mission C)
C3. Precision Survey using GPS carrier Phase
C4. Use of GPS ADS-B mandated for future ATC System – improving separation distances (Mission D)
C5. Resistance to inadvertent GPS interference or deliberate sabotage (see military #3)
C6. Obscuration in Open Pit Mining
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Mission Trade AnalysisMission A. Air Dropped Bomb against Ground located
target
Want to show effect of GPS Decision Maker’s Trades
onMeasures of Effectiveness
Note: this is illustrative of the technique and approach
It does not incorporate actual weapons system’s data
Sensitive results are presented in Relative Terms
UPDATE
October 08Interim Report Big 5 and MOEs
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Afghanistan in this Analysis
• Observer is assumed to be part way up Mountain (Red Dot)
• Slope assumed at 45 to 60 degrees (could be steeper)
• Target Building is on other side of Valley
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Constraints and AssumptionsWithin current Availability In Red, the next step
possibilities – also analyzed • Terrain – Valley in Afghanistan
mountains, – Observer on side of 45 (or 60)
degree slope Obscuration ~40%
• Observer Laser Sight: – Gyrocompass North- – Azimuth - 3 mils, – Elevation 3 Mils– Range 3 Meters
• Observer GPS – 2.6 meter multipath-limited
receiver (1 meter multipath narrow tracking correlator)
– 0.75 meter receiver noise• Target
– 1 km away
• GPS Constellation– 18, 21, 24, 27, 30, 33, 36
considered with 1,2, or 3 satellites randomly out
– URE: Block II 0..57m, Block III 0.25m
• Bomb/Weapon– Same Constellations
considered– 3.5m Guidance error
Guidance Error 1.0m– GPS 0.8m noise, negl.
multipath URE as above– Vertical at impact
• Jamming interference– Assume a hostile 10W noise
Jammer
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Buildings on a Mountain RoadTarget is Largest Building
Numbers in Boxes are the number of Hits
Road
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Observer on Slope of 45 Degrees
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99.9% Circle -Only 1 in 1000
exceeds
50% Circle Half in, Half out.
Usually called CEP – a poor measure of
effectiveness
95 % Circle Should approximate Target
size, (for first round effectiveness)
Sometimes called “2d”bldgldg
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Observer on Slope of 60 Degrees
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Selected Civil “Envelope” Missions
• Precision Approach and Landing (Mission “B”)– Representative US Airports
– Desire Availability of >99.5% (99.9% ?)
• Advanced Air Traffic Control System (Mission “D”)– GPS Based
– Uses Automatic Dependent Surveillance Beacon (ADSB)
– Integrity Guaranteed - Issue is Geographic Coverage for 99.5% availability
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Constraints and Assumptions for Mission B – CAT III Precision Landing
• Terrain – Civil Airports and Military Airfields
• Aircraft guided down to 200’ HAT CAT I Decision Height solely by GPS Local Area Augmentation System (LAAS) fielded at airport/airfield where landing takes place
– Vertical guidance is limiting factor
• From 200’ to 100’ HAT, aircraft guided by LAAS with airborne inertial system as backup
• Below 100’ HAT (above runway threshold), aircraft primarily guided by radar altimeter
• GPS Constellation– 21, 24, 27, 30, 33, 36
considered with 1,2, or 3 satellites randomly out (cycle through all outage permutations)
– URE: dictated by LAAS ground and airborne error models
• RF interference– When present, assume
unintentional ground-based RF interference sufficient to make satellites below 10, 15 deg. elevation (TBC) unusable
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Four Measures of Effectiveness (MOEs) for Mission “B” – Cat III Landing
• MOE 1: Long-term probability that CAT III operation is available (without RF
interference)
Trade I – No. of GPS Satellites in Constellation
• MOE 2: Longest interval that CAT III operation is unavailable (without RF
interference)
Trade I – No. of GPS Satellites in Constellation
• MOE 3 : Loss-of-continuity probability when RF interference is suddenly
introduced
Trade II - Techniques to reduce RF interference vulnerability
• MOE 4: Availability probability when RF interference persists
Trades I and II
October 08Interim Report Big 5 and MOEs
2124 23 22 21
0.86
0.88
0.9
0.92
0.94
0.96
0.98
1
Number of Healthy SV's
Ava
ilabi
lity
Results for 12 Airports
Max. Outage Duration (min)
27
67
142
284
Note Min. Avail. on
Plot
99.9 % Availability Threshold
Availability Results for IRT “Baseline” 24-SV Constellation – 1,2, or 3 GPS outages (Slide 1 of 2)
October 08Interim Report Big 5 and MOEs
22MIA ATL MEM IAD JFK MS P ORD DFW S LC LAX S EA ANC
0.86
0.88
0.9
0.92
0.94
0.96
0.98
1
Airport Loca tion
Ava
ilab
ility
Availability Results for IRT “Baseline” 24-SV Constellation (Slide 2)
0
268
19
6
27
0 0
9
0 3 0 0
19
284
272
Max. Outage Duration
(min)
284
244276 272
228
236
264
248
164
110
116
102
106
8294 98
96
142
88
86
80
49
43
35
65
6745
51 46
50
51
33
43
3 SV Out (4-min updates)
2 SV Out (2-min updates)
1 SV Out (1-min updates)
0 SV Out (15-sec
updates)
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2330 29 28 27
0.98
0.982
0.984
0.986
0.988
0.99
0.992
0.994
0.996
0.998
1
Numbe r of He a lthy SV's
Ava
ilab
ility
Availability Results for IRT 30-SV Constellation
Max. Outage Duration (min)
0 26
56
136
Note Min. Avail. on
Plot
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Comparison of CAT III Availability for All Six IRT Constellations (21 – 36 SV’s)
0 SVs Out 1 SV Out 2 SVs Out 3 SVs Out10
-6
10-5
10-4
10-3
10-2
10-1
100
Number of SV’s Unhealthy
Un
-ava
ilab
ilit
y
IRT 21-SV
IRT 24-SV
IRT 27-SV
Desired Availability
99.9%
IRT 33-SV
IRT 36-SV
IRT 30-SV
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• To compare to IRT constellations, a recent GPS
constellation almanac (Week 465, 25 July 2008) was downloaded and simulated.
• Results for two cases shown on the following slide:
– Optimistic – use all 31 satellites listed in almanac (24 “primary” 7 “spare” orbit slots)
– Realistic: remove 5 satellites in “spare” orbit slots that are older than 15 years of age
» Retain use of 2 satellites in “primary” orbit slots that exceed 15 years of age
» 26 satellites are used (24 “primary” 2 “spare” orbit slots)
Simulations with Current GPS Constellation
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Comparison of CAT III Availability for IRT and Current Constellations
0 SVs Out 1 SV Out 2 SVs Out 3 SVs Out10
-6
10-5
10-4
10-3
10-2
10-1
100
Number of SV's Unhealthy
Un-
avai
labi
lity
IRT 36-SV
IRT 30-SV
IRT 21-SV
IRT 24-SV
IRT 27-SV
Current/Optimistic (31-SV)
Desired Availability
99.9%IRT 33-SV
Current/Realistic (26-SV)
Current/Optimistic (31-SV)
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• More availability results to follow…
• Results now available for all SV constellations for no-RFI case
• Now experimenting with best ways to plot these results
Status of CAT III Analysis
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Mission D – GPS-Based ADS-B Support of Air Traffic Control
Many aircraft in flight• Each equipped with
GPS/SPS and/or WAAS• Each equipped with ADS-B
transponder to share GPS-based “PVT” information
Airport C
ATC Tower
ATC Tower
Airport B
FAA ARTCC
Airport A
ATC Tower
ADS-B PVT
ADS-B PVT
ADS-B PVT
ADS-B PVT
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Perfect Constellation: Comparison of GIC (WAAS) and RAIM Integrity Techniques
(Table with Numerical Values)
Satellite Constellation
Architecture 24 27 30
WAAS Integrity 100% 100% 100%
RRAIM (300-sec coasting)
76.1% 99.6% 100%
ARAIM 44.7% 94.1% 100%
Fraction of Airspace (inside ± 70 deg. Latitude) with ≥99.5% availability of support
for Precision Approach to 200’ Height Above Terrain (Like CAT I)
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Realistic Constellation Comparison of GIC (WAAS) and Self-Integrity (RAIM) Techniques
(Table with Numerical Values)
Satellite Constellation
Architecture 24 minus significant
SV
27 minus significant
SV
30 minus significant
SV
WAAS Integrity 86.6% 97.8% 100%RRAIM (300-sec
coasting) 28.0% 52.3% 93.9%
Absolute RAIM 7.8% 30.6% 90.5%
Fraction of Airspace (inside ± 70 deg. Latitude) with ≥99.5% availability of support
for Precision Approach to 200’ Height Above Terrain (Like CAT I)
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Summary and Path Forward
• Evaluation of civil missions/uses B and D (CAT III precision landing and ADS-B support of ATC) will be conducted using common simulation approach
– CAT III application is more clear-cut (based on use of already-defined single-frequency LAAS)
– ADS-B application has more options and trades
• The simulation needed to evaluate Mission B has been built and run for IRT constellations and for two variations of recent GPS Week 465 broadcast almanac
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Decision # I.The Number of GPS Satellites
• Current “Requirement” – 24 (21 plus three active spares)
• On orbit are 31but not optimal– Much improved geometric availability - Users now expect this
performance– Paired Orbits – not optimal for 30 (ready for Failure)
• Many studies have suggested the “knee in the curve” for user availability is 30 to 36– Critical users – those with impaired sky visibility or extreme integrity req.
• A key to increasing commitment to 30 + X is on-orbit cost of Satellites– Major driver Additional Payloads (reduce size, weight, power and complexity)
– Cost savings opportunity - dual launch
• Decision: A National commitment to increased number of SVs– Civil users could have significantly improved availability
– Military Users more effective in impaired situations
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Conclusions• The concept of “Envelope” missions places
focus on those missions that really drive GPS system design and illuminate trades for the decision makers
• We have shown a Process :– relates GPS System Design Trades to Measures of
Effectiveness (MOE)– Closely related to the “Big 5 GPS Characteristics” but
adds the advantage of quantification• MOEs are very mission specific
– relate to particular use and/or users• Additional “Envelope” missions are suggested as
worthy of further MOE analysis
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PL Fundamental Issues – Operations
• Most impaired users are in “harms way”– Placing PLs in the Afghan Mountains not plausible
• One PL usually only benefits a narrow geographic area
• Support for PL requires monitoring• GPS receivers must be specially configured to
handle PL signal– Near-Far problem
• Airborne PLs suffer degraded accuracy, and complex support architecture
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Comment on MOE 1:The Accuracy Payoff
• Reducing error by 3 improves PK by up to 9
• CNN wars dictate reduced collateral damage – the stray bomb is important
• Improve 1st round effectiveness = less US attrition.
• Sorties to destroy = ~ 1/ PR
Issue: Need both TLE and WLE accuracy