# Presentation: 661106

## GPS “Big Five” contribution to Users Needs AN UPDATE

- 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

- Showing Dependence of User Measures of Effectiveness (_*MOE*_) on GPS _*System Design & *__***Design Decisions***_

## The IRT “Big 5” – Essential GPS PNt CharacteristicsA Bridge between User’s MOE and GPS System Design

- _Assured__ _(Geometric)_ __Availability_ of GPS signals
- _Resistance__ __to__ _(Deliberate or Unintentional)_ __Interference_
- _Accuracy__ _of *User’s GPS Position* (After satisfying #1 and #2)
- _Bounded_ _*inaccuracy*_ –Limiting potential for very large errors (*Fratricide or Collateral Damage)*
- _Integrity_ – Identifying and eliminating the _***non-normal***_ GPS _**system**_ or _**local**_ errors (e.g. extreme user multipath or runaway clocks).

## Performance EnvelopeConceptual Examples

- Performance EnvelopeConceptual Examples

- Current GPS
-  Capabilities(30+ Sats)

- Current GPS
-  _***Specification***_(e.g. 21+3 Sats)

- Needs for
- SDB
- (Target Designation in VisibilityImpaired Region)

- Cat III
- Aircraft Landing(Integrity – Time to Alarmor Availability)

- Potential GPS Enhancements

- Potential GPSAugmentations

**The ****“Envelope”**

**“****Envelope” ****Missions**

- FAA ATCModernizationADS-B

## 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

## Mission Trade AnalysisMission A.  Air Dropped Bomb against Ground located target

- Want to show effect of GPS Decision Maker’s TradesonMeasures 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

## 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

## Constraints and AssumptionsWithin 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

## Buildings on a Mountain RoadTarget is Largest Building

- Numbers in Boxes are the number of Hits

- Road

## Observer on Slope of 45 Degrees

## 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**

## Slide 11

## Slide 12

## Slide 13

## Observer on Slope of 60 Degrees

## Slide 15

## Slide 16

## Slide 17

## 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

## 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

## 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**

## Availability Results for IRT “Baseline”  24-SV Constellation – 1,2, or 3 GPS outages (Slide 1 of 2)

**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)**

## Availability Results for IRT “Baseline”  24-SV Constellation (Slide 2)

**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**

**244**

**276**

**272**

**228**

**236**

**264**

**248**

**164**

**110**

**116**

**102**

**106**

**82**

**94**

**98**

**96**

**142**

**88**

**86**

**80**

**49**

**43**

**35**

**65**

**67**

**45**

**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)***

## Availability Results for IRT 30-SV Constellation

**Availability Results for IRT 30-SV Constellation**

**Max. Outage Duration (min)**

**0**

**26**

**56**

**136**

**Note Min. Avail. on Plot**

## 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 Out

- 10

- -6

- 10

- -5

- 10

- -4

- 10

- -3

- 10

- -2

- 10

- -1

- 10

- 0

- Number of SV’s Unhealthy

**Un-availability**

**IRT 21-SV**

**IRT 24-SV**

**IRT 27-SV**

**Desired**
** ****Availability**
** ****99.9%**

**IRT 33-SV**

**IRT 36-SV**

**IRT 30-SV**

**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**

## Comparison of CAT III Availability for IRT and Current Constellations

- 0 SVs Out

- 1 SV Out

- 2 SVs Out

- 3 SVs Out

- 10

- -6

- 10

- -5

- 10

- -4

- 10

- -3

- 10

- -2

- 10

- -1

- 10

- 0

- Number of SV's Unhealthy

- Un-availability

**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)***

**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**

## 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***

## 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)***

## 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)***

## 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**

## Decision # I.The Number of GPS Satellites

- Current “Requirement” – 24   (21 plus three active spares)
- On orbit are 31_*but 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

## 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

## 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

## 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**