GPS

1
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 ParkinsonDraft Developed for IRT
  August 2008
• Thanks to Col. Dave Madden and Aerospace for
  help, Particularly Tom Powell and Paul Massatt
• Also FAA with Sam Pullen and Todd Walter

2
The IRT Big 5 Essential GPS PNt
CharacteristicsA Bridge between Users MOE and
GPS System Design

1. Assured (Geometric) Availability of GPS signals
2. Resistance to (Deliberate or Unintentional)
   Interference
3. Accuracy of Users 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).

3
Performance EnvelopeConceptual Examples
Envelope Missions
Current GPS Capabilities(30 Sats)
Needs for SDB (Target Designation in
VisibilityImpaired Region)
Potential GPS Enhancements
Current GPS Specification(e.g. 213 Sats)
Cat III Aircraft Landing(Integrity Time to
Alarmor Availability)
Potential GPSAugmentations
The Envelope
FAA ATCModernizationADS-B
4
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 dont 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

5
Mission Trade AnalysisMission A. Air Dropped
Bomb against Ground located target

• Want to show effect of GPS Decision Makers
  TradesonMeasures of Effectiveness

UPDATE
Note this is illustrative of the technique and
approach It does not incorporate actual weapons
systems data Sensitive results are presented in
Relative Terms
6
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

7
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

8
Buildings on a Mountain RoadTarget is Largest
Building
Numbers in Boxes are the number of Hits
Road
9
Observer on Slope of 45 Degrees
10
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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14
Observer on Slope of 60 Degrees
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18
Selected Civil Envelope Missions

• Precision Approach and Landing (Mission B)
• Representative US Airports
• Desire Availability of gt99.5 (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

19
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

20
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

21
Availability Results for IRT Baseline 24-SV
Constellation 1,2, or 3 GPS outages (Slide 1 of
2)
27
99.9 Availability Threshold
Results for 12 Airports
67
142
Max. Outage Duration (min)
284
Note Min. Avail. on Plot
22
Availability Results for IRT Baseline 24-SV
Constellation (Slide 2)
Max. Outage Duration (min)
0
0
0
0
0
0
3
6
9
67
33
35
19
45
0 SV Out (15-sec updates)
19
49
46
51
51
27
50
43
86
43
65
82
102
1 SV Out (1-min updates)
94
98
110
96
88
80
106
116
248
142
2 SV Out (2-min updates)
244
272
272
276
268
264
228
164
284
284
3 SV Out (4-min updates)
236
23
Availability Results for IRT 30-SV Constellation
0
26
56
Max. Outage Duration (min)
136
Note Min. Avail. on Plot
24
Comparison of CAT III Availability for All Six
IRT Constellations (21 36 SVs)
0
10
IRT 21-SV
-1
10
IRT 24-SV
IRT 27-SV
Desired Availability 99.9
-2
10
IRT 30-SV
Un-availability
IRT 33-SV
-3
10
IRT 36-SV
-4
10
-5
10
-6
10
0 SVs Out
1 SV Out
2 SVs Out
3 SVs Out
Number of SVs Unhealthy
25

Simulations with Current GPS Constellation

• 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)

26
Comparison of CAT III Availability for IRT and
Current Constellations
0
10
Current/Realistic (26-SV)
Current/Optimistic (31-SV)
IRT 21-SV
-1
10
IRT 24-SV
IRT 27-SV
Desired Availability 99.9
-2
10
IRT 30-SV
Current/Optimistic (31-SV)
IRT 33-SV
-3
10
Un-availability
IRT 36-SV
-4
10
-5
10
-6
10
0 SVs Out
1 SV Out
2 SVs Out
3 SVs Out
Number of SV's Unhealthy
27

Status of CAT III Analysis

• 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

28
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

ADS-B PVT
ADS-B PVT
ADS-B PVT
ADS-B PVT
ATC Tower
ATC Tower
ATC Tower
FAA ARTCC
Airport B
Airport A
Airport C
29
Perfect Constellation Comparison of GIC (WAAS)
and RAIM Integrity Techniques(Table with
Numerical Values)
Fraction of Airspace (inside 70 deg. Latitude)
with 99.5 availability of support for
Precision Approach to 200 Height Above Terrain
(Like CAT I)
Satellite Constellation Satellite Constellation 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
30
Realistic Constellation Comparison of GIC (WAAS)
and Self-Integrity (RAIM) Techniques(Table with
Numerical Values)
Fraction of Airspace (inside 70 deg. Latitude)
with 99.5 availability of support for
Precision Approach to 200 Height Above Terrain
(Like CAT I)
Satellite Constellation Satellite Constellation 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
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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

32
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

33
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

34
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

35
Comment on MOE 1The 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