# Presentation: 813830

## GPS “Big Five” contribution to Users Needs

- Prof. Brad ParkinsonDraft Developed for IRT - March 2008
- Thanks to Col. Dave Madden and Aerospace for help, Particularly Tom Powell and Paul Massatt

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

- Preliminary Draft

## The IRT “Big 5” - Essential GPS 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).

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## Background

- IRT’s “Big 5” are critical GPS System Characteristics,   _***but:***_
- Relationship to user’s Measures of Effectiveness (MOE) not      well understood and defined
- Impacts on GPS System Design not clear
- Any clarification builds on:
- Explicit CONOPs (with MOE)
- Statement of boundary conditions and constraints
- Attempts to consider all possible missions not feasible       nor desirable
- Instead focus on the challenging, important missions that push the envelope of GPS capabilities (the “Envelope Missions”)

**Explicitly show decision makers the MOE relationship to GPS Design trades**

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## Outline

- Define “Envelope Uses” (or missions)
-  Show Civil/Military Examples  - Relate to MOE
- Analyze one (Mission “A”: Precision Weapon Delivery)
- Summarize the MOE trades for the Study of Mission “A”
- Identify three other “Envelope Missions” Studies
- Conclusions
- Recommendations

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## Envelope GPS Missions and Uses

- Many Missions/Uses have little impact on GPS system design 	(because capability included when other users satisfied)
_*Operational Envelope*__*:*_ Includes all senarios where GPS provides needed P&T to the user.
_*Envelope Missions*__*:*_ Defined as those that have significant impact on the GPS system design – “Pushing the Envelope”, **Examples follow.**

- Focusing on EMs reveals the essential, User-oriented trades between System Design and the user’s Measures of Effectiveness

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## Envelope Mission/Use Examples(Analyzed here will be Mission A.  Next steps B, C, and D.)

**Military**
-   Use of ***Small Diameter Bomb*** in region where ***ground target locator*** has impaired visibility (e.g. mountainous terrain or urban street)  (In Mission A)
-   Delivering weapons ***close to friendly troops***, or close to sensitive “don’t hit” locations (In Mission A)
-   Operating with impunity in the ***vicinity of*** high-power (or multiple, distributed) ***Enemy Jammers  ***(In Mission A)
-   Operating in ***mined land*** or restrictive sea areas*** ***

**Civilian**
-  Precision Civil Aircraft ***Approach and Landing*** (Up to Cat III) demanding 10-9 integrity (mission B)
- First Responder PNT in Urban Area(Mission C)
**Precision Survey** using GPS carrier Phase
- Use of GPS ADS-B mandated for future ATC System – improving separation distances (Mission D)
- Resistance to inadvertent GPS interference or deliberate sabotage
- Obscuration in Open Pit Mining

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## 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)

- Needs for
- Truck Navigation

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

- Potential GPS Enhancements

- Potential GPSAugmentations

**The ****“Envelope”**

**“****Envelope ****Missions**

- A/J for the Ground User

- Potential UE Enhancements

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## Obscured Visibility Problem

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## Relationships

**1.  Availability ****of Geometry**

**2. Resistance to ****Interference **

**5.  Integrity **

**3.  Positioning ****Accuracy**

**4. Bounded ****Inaccuracy**

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## Relationships

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## Decision Maker’s Leverage on Future Capability

| Pivotal GPS Design trades |  |
| --- | --- |
| Trade | Why important to Users |
| T-I.  Number of Satellites | Constrains useable operating region, particularly for visibility impaired user. The Geometric Satellite Configuration is defined by # of satellites (optimal constellation) and the local visibility constraints |
| T-II.  Satellite Ranging Error | Combined with the Geometric Satellite Configuration, determines the user’s Positioning Accuracy and bounds on inaccuracy.   Principally a function of Satellite Block. |
| T-III.  Jamming Resistance Allocations/ Pronav | Insures ability to operate in jammed environment. Combines at least 4 system aspects:
Signal Structure/frequencies and user processing
Degree of integration with Inertial (or zero velocity)
User Antenna and local shielding against jamming 
Satellite Broadcast Power |
| T-IV.  Integrity - Time to Alarm GPS System Problems | Insures against wild position fixes, particularly important when Safety of Life is concerned (aircraft landing or possible fratricide situations for the warfighter). |

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## Decision Makers Trade I.How many GPS Satellites are the “Spec”

- Current “Requirement” – 24 satellites (21 plus three active spares)
- Currently on orbit are 31 or 32 - _***not in optimal orbits***_
- Much improved availability over requirement due to geometry
- Users now expect this performance
- Paired Orbits – not optimal for 30 (Some used as standbys)
- DOD Not committed to this current level of service
- Many studies have suggested the “knee in the curve” for user availability is 30 to 36
- Critical users – those with impaired sky visibility
- Potential 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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## Decision Makers Trade II.  User Range Error Note: the decision is the Satellite GenerationDual Frequency – does not include User Multipath and receiver “Noise”

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## Decision Makers Trade III. Procuring or IncorporatingProven Jamming Resistance Methods

- Smorgasbord of techniques to increase resistance to interference
- The goal of a Hostile jammer is to deny use over an area
- The payoff of Resistance to that jamming (A/J) is the reduction in effective area

| Techniques Available | dB Improvement(ΔJ/So) | Reduction in Jammer effective area up to |
| --- | --- | --- |
| Signal Structure/frequencies and user processing | 3 to 7 | 80.0% |
| Degree of integration with Inertial (or zero velocity) | To 15 | 96.8% |
| User Antenna and local shielding against jamming  | To 20 | To 99.0% |
| Satellite Broadcast Power(IIIA increase of 8 dB – 6.3 times Block II) | 8 | TO  84.2% |

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## Connecting EMs/MOEs and GPS Design Trades

- Select Four “Envelope” Uses or Missions and Show the GPS Trades
- Major National/Warfighter Importance
- Span critical Design Trades to Illustrate Process
- Most other Important Missions are subtended

_**Missions (or uses) Selected for Current or Future Analysis Are**_**:**
_***Mission A***_.  Ground designated Bombing in region where ***ground target locator*** has impaired visibility (e.g. mountainous terrain or urban street), and friendly troops or “don’t hit” areas are nearby, and there is a threat of enemy jamming
_***Mission B.***_  Precision Civil Aircraft ***Approach and Landing*** (Up to Cat III)
_***Mission C***_.  ***First**** ****Responder*** pinpointing urban locations
_***Mission D***__*. *_* **Use* of GPS based ADS-B mandated for future ATC System – improving separation distances

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## 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*

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## A Representative User Need Statement for Mission A:Ground designated Bombing in region where ground target locator has impaired visibility (e.g. mountainous terrain or urban street)Note that this includes 4 significant Measures of Effectiveness (MOE) 

_***Mission***_: Destroy a _*ground-located*_* target* with an air–dropped, GPS-guided bomb 	**(MOE 1: # of Sorties/weapons to deliver bomb within distance, R - 95%)**
_***Where***_: Mountainous Terrain – Will include representative masking angles producing sky obscuration for ground observer (Constraint)
_***When***_: All-weather, 24/7 (Constraint)
_***Enemy countermeasures***_: Ground observer to operate within X km of 10 W GPS noise 	jammer **(MOE 2: Min Operating Range to enemy Jammer)**
_***Collateral Damage***_:  Probability of hitting friendly troops Z meters away less than 	Y% due to GPS **(MOE 3 : P (miss distance > Z m)**
_***Integrity -GPS System Malfunction***_: Notify User of GPS System/single satellite	malfunctions (out of normal Specification) within S seconds 	**(MOE 4 is **_**T**_**ime **_**t**_**o **_**A**_**larm – TTA –S seconds)**

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## Constraints and AssumptionsWithin current Availability In Red, the next step possibilities – also analyzed 

- Terrain – Typical Mountain Valley,
- Observer on side of 45 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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## Reminder:  The Weapon Delivery Double-Right Triangle

- Total Error (TE) due to Three Components:
- Weapon Location (WLE)
- Weapon Guidance (WGE)
- Target Location (TLE)
- For independent errors, square of result equals sum of squares.
- Can be visually depicted with two right triangles
- All three can be affected by GPS Accuracy

**WLE**

**WGE**

**Target Location Error**

**Weapon Error**

**TOTAL Error**

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## Summary: The Measures of Effectiveness (MOEs)  for Mission/Use “A”

_**MOE 1**_: Number of Sorties/weapons to deliver bomb within R meters 	***with 95% probability.***  **Trades I and II – No. of GPS Sats and Ranging Errors**
_**MOE 2**_: Closest Operating Range to enemy Jammer  **Trades III - Techniques to reduce jamming effectiveness**
_**MOE 3**_ : P (miss distance > Z m) Also **Trades I and II – No. of GPS Sats and Ranging Errors**
_**MOE 4**_:  is _T_ime _t_o _A_larm – TTA -Seconds) This is currently about 45 minutes for DOD, **the trades to improve****	****this have been studied, but will not be discussed here**

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## Mountain Valley for Analyses

-   Observer is assumed to be part way up Mountain (Red Dot)
-   Slope assumed at 45 to 60 degrees (could be steeper)
-  Target is on other side of Valley

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## MOE 1: Assured Weapon Accuracy

- Use 95th percentile as more meaningful than “CEP” which is the 50th percentile (only half the time)
- Two Decision Trades:
- Number of GPS Satellites
- Satellite Generation (Ranging Accuracy)
- Major Environmental Variable:	Slope of observer’s mountain side
- Nominally assumed to be 45o also looked at 60o

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## Results:  95th Percentile Radius Achievable with N Sorties normalized to 30 SVs 1 random SV inoperable in constellation –Block II Ranging ErrorMountainous Terrain – Observer on 45o slope

|   | 1 | 2 | 3 |
| --- | --- | --- | --- |
| 18 | 67.57 | 33.78 | 16.89 |
| 21 | 3.38 | 1.69 | 1.18 |
| 24 | 2.03 | 0.97 | 0.66 |
| 27 | 1.53 | 0.70 | 0.55 |
| 30 | 1.00 | 0.64 | 0.51 |
| 33 | 0.88 | 0.60 | 0.49 |
| 36 | 0.84 | 0.57 | 0.47 |

- Number Sorties

- Constellation Size

- meters

- 24 Sats take twice the sorties for assured delivery at Radius R compared to 30 Sats

- 24 Sats take 50% more sorties for assured delivery at 2/3rds R compared to 30 Sats

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## Tradeoff I: Number of Satellites (Block II Ranging Accuracy)MOE:  # of Sorties for 95% Accuracy AssuranceMountainous Terrain, 45o Slope

- Number of Satellites

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## Tradeoff I and II: Number of Satellites + Block IIIA Ranging AccuracyMOE:  # of Sorties for 95% Accuracy Assurance Mountainous Terrain, 45o Slope

- Tradeoff I and II: Number of Satellites + Block IIIA Ranging AccuracyMOE:  # of Sorties for 95% Accuracy Assurance Mountainous Terrain, 45o Slope

- Number of Satellites

- Normalized to 30 Block II Spacecraft

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## Trade II.  Comparing MOE 1 for Block II and Block III with improved Target Locator

- Number of Satellites

- 30 Satellites seems to be the natural “knee”

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## MOE 2: Closest Operating Range to enemy Jammer

- Baseline is a dual-frequency handheld with no “extra” 	enhancements to minimize interference
- Improvements generally cascade and are additive in their dB effects
- Suggested improvement trades are all well demonstrated and 	clearly feasible
- Implementing requires direction and budget
- Capabilities of Jammers is not 1/R2 for ground users – there is 	greater ground attenuation and interference
- The calculations should be viewed as conservative – the effective range of jammers may fall of as 1/R4, giving substantially less effectiveness at longer ranges

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## Trade III.  Effect of Decisions onImproving Dual-Frequency Handheld- Anti-JamMOE 2: Effective Range of 10W Jammer

| Case | Description | J/S Improve-ment (dB) |
| --- | --- | --- |
| A | Upward Beam Antenna | 15 |
| B | Ultra-tight Coupling | 12 |
| C | GPS III  | 8 |
| ALL |  | 35 |

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## Decision Makers Trade III.  Applying the Possible Mitigation Techniques to a Handheld GPS set

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## MOE 3: Probability (miss distance > Z m) 

- Also Called Bounded Inaccuracy (The “normally occurring” Wild Points limited by Good Geometry and bounds on ranging error)
- Estimation of effects similar to MOE 1
-  More strongly affected by weak “satellite geometry” due to local obscuration
-  Also affected by satellite ranging error
- Particularly important for weapon delivery
- Senisitive non-targets (Mosques, Embassies...)
- Working close to friendly troops
- GPS in weapon or used by ground spotter can be critical

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## MOE 3: Bounds on inaccuracy (Probability of Large Error) - 1 GPS Satellite not operatingMountainous Terrain, 45o slope, Block II Ranging error

- 30 Satellites will not exceed 40 meter error more than 1 % of cases

- 24 Satellites have _**>15%**_ chance of exceeding 100 m error

- MOE 3: Bounds on inaccuracy (Probability of Large Error) - 1 GPS Satellite not operatingMountainous Terrain, 45o slope, Block II Ranging error

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## MOE 3: Bounds on inaccuracy (Probability of Large Error) - 2 GPS Satellites not operatingMountainous Terrain, 45o slope, Block II Ranging error

- 30 Satellites will not exceed 70 meter error more than 3 % of cases

- 24 Satellites have _**>25%**_ chance of exceeding 100 m error

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## MOE 3: Bounds on inaccuracy (Probability of Large Error) - 1 GPS Satellites not operatingMountains of Afghanistan, 45o slope, Block III Ranging error

- MOE 3: Bounds on inaccuracy (Probability of Large Error) - 1 GPS Satellites not operatingMountains of Afghanistan, 45o slope, **Block III Ranging error**

- 30 Satellites will not exceed 20 meter error more than 1 % of cases

- 24 Satellites have _**>10%**_ chance of exceeding 100 m error

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## MOE 3: Bounds on inaccuracy  (Probability of Large Error) - 1 GPS Satellites not operatingMountainous Terrain, 60o slope, Block III Ranging error- More restricted user case- similar to urban streets

- MOE 3: Bounds on inaccuracy  (Probability of Large Error) - 1 GPS Satellites not operatingMountainous Terrain, 60o slope, **Block III Ranging error****- ***More restricted user* case- similar to urban streets

- 30 Satellites will not exceed 40 meter error more than 10 % of cases

- 24 Satellites have _**>40%**_ chance of exceeding 100 m error

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## 	MOE 4 is Time to Alarm – TTA –S secondsNotify User of GPS System/single satellite malfunctions (out of normal Specification) within S seconds 

- Sometimes Called Integrity Assurance
- Identifying and eliminating the non-normal GPS system errors that would cause Hazardous/Misleading information
- Examples include:
-  Satellite Runaway clock
- Extreme Local Multipath
-  Evil Waveforms (distortion that leads to erroneous ranging 	measurement)
-  Discontinuities in Ionosphere
- Methods for eliminating include:
- Satellite self checking (FAA would have limitations)
- Direct external measurement and notification (WAAS)
- Notification through GPS message (may be a time to alarm issue)
- User Self Checking Using Satellite Redundancy (_***RAIM***_ – Receiver Autonomous Integrity Monitoring)
- Current Military Technique – TTA about 45 minutes

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## Comments

- RAIM is perhaps the simplest to implement, but requires sufficient satellites to have Geometric leverage
- Two Cases
- Alert that there is a problem
- Identification of the offending satellite and elimination from the users solution

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## MOE Summary for Mission APrecision Bomb Delivery with Ground Observer in Mountainous Terrain

|  | 24 Sats Blk II | 30 Sats Blk. II | 30 Sats
Blk III Improved Locator |
| --- | --- | --- | --- |
| MOE 1 1 sortie 95% Accuracy* | 2.0 | 1.0 | 0.4 |
| MOE 3
Bounds on Miss | >100m, >15% of time | >40m,<1% of time | >20M,<1% of time |

|  | Current | Available Improvements |  |  |  |
| --- | --- | --- | --- | --- | --- |
|  |  | Ant | Tight Couple | IIIA | All |
| MOE 2:10WJammer Range (nm) | 31.5 | 5.1 | 7.9 | 12.0 | 0.6 |

|  | Current | FAA’s WAAS | RAIM |
| --- | --- | --- | --- |
| MOE 4Time to Alarm | 45 Min. | 10 sec | 3 sec? |

- * MOE 1 results have been normalized

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## Next Steps:  Repeat Analysis for other Uses/Missions

_**Other Envelope Missions/Uses**_**:**
_***Mission B.***_  Precision Civil Aircraft ***Approach and Landing*** (Up to Cat III)
_***Mission C***_.  ***First**** ****Responder*** pinpointing urban locations
_***Mission D***__*. *_* **Use* of GPS based ADS-B mandated for future ATC System – improving separation distances

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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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