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GPS “Big Five” contribution to Users Needs

This draft explores the relationship between the "Big Five" characteristics of GPS systems and user measures of effectiveness (MOE). It highlights the importance of considering user needs in GPS system design and provides examples of envelope missions that have significant impacts on system design. The draft concludes with recommendations for future GPS system design.

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GPS “Big Five” contribution to Users Needs

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  1. GPS “Big Five” contribution to Users Needs Showing Dependence of User Measures of Effectiveness (MOE) on GPS System Design Prof. Brad ParkinsonDraft Developed for IRT - March 2008 Thanks to Col. Dave Madden and Aerospace for help, Particularly Tom Powell and Paul Massatt Draft-For Comment

  2. The IRT “Big 5” - Essential GPS CharacteristicsA Bridge between User’s MOE and GPS System Design • Assured(Geometric)Availability of GPS signals • Resistanceto(Deliberate or Unintentional)Interference • Accuracyof User’s GPS Position(After satisfying #1 and #2) • Boundedinaccuracy –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). Draft-For Comment

  3. 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 Draft-For Comment

  4. 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 Draft-For Comment

  5. 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 Draft-For Comment

  6. 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 Envelope Mission/Use Examples(Analyzed here will be Mission A. Next steps B, C, and D.) Draft-For Comment

  7. 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. 21+3 Sats) Cat III Aircraft Landing(Integrity – Time to Alarmor Availability) Potential GPSAugmentations A/J for the Ground User The “Envelope” Needs for Truck Navigation Potential UE Enhancements Draft-For Comment

  8. Obscured Visibility Problem Draft-For Comment

  9. Mission Parameters Big Five System Characteristics Probability of Mission Accuracy When and Where- (Masking Angles) Resistance to Enemy Countermeasures Avoidance of CollateralDamage GPS Malfunction Alerts Relationships 1. Availability of Geometry 3. Positioning Accuracy 2. Resistance to Interference 4. Bounded Inaccuracy 5. Integrity Draft-For Comment

  10. Mission Parameters System Design Probability of Mission Accuracy Satellite Numbers and Distribution When and Where- (Masking Angles) User Ranging Accuracy Resistance to Enemy Countermeasures A/J & A/S User Integration Receiver Countermeasures Satellite Power Signal structure Avoidance of CollateralDamage GPS NotificationTechniques or RAIM GPS Malfunction Alerts Relationships Draft-For Comment

  11. Decision Maker’s Leverage on Future Capability Draft-For Comment

  12. 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 Draft-For Comment

  13. Currently Avg ~ 0.9 Decision Makers Trade II.User Range ErrorNote: the decision is the Satellite GenerationDual Frequency – does not include User Multipath and receiver “Noise” Draft-For Comment

  14. Decision Makers Trade III. Procuring or IncorporatingProven 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 Draft-For Comment

  15. 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. FirstResponder pinpointing urban locations Mission D. Use of GPS based ADS-B mandated for future ATC System – improving separation distances Draft-For Comment

  16. Mission Trade AnalysisMission 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 Draft-For Comment

  17. 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 Time to Alarm – TTA –S seconds) Draft-For Comment

  18. 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 Constraints and AssumptionsWithin current Availability In Red, the next step possibilities – also analyzed Draft-For Comment

  19. 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 Target Location Error TOTAL Error Weapon Error WGE WLE Draft-For Comment

  20. 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 JammerTrades 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 Time to Alarm – TTA -Seconds) This is currently about 45 minutes for DOD, the trades to improve this have been studied, but will not be discussed here Draft-For Comment

  21. 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 Draft-For Comment

  22. 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 Draft-For Comment

  23. Results: 95th Percentile Radius Achievable with N Sorties normalized to 30 SVs1 random SV inoperable in constellation –Block II Ranging ErrorMountainous Terrain – Observer on 45o slope Number Sorties 24 Sats take twice the sorties for assured delivery at Radius R compared to 30 Sats Constellation Size 24 Sats take 50% more sorties for assured delivery at 2/3rds R compared to 30 Sats meters Draft-For Comment

  24. Normalized to 30 Block II Spacecraft Tradeoff I: Number of Satellites (Block II Ranging Accuracy)MOE: # of Sorties for 95% Accuracy AssuranceMountainous Terrain, 45o Slope Number of Satellites Draft-For Comment

  25. 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 Draft-For Comment

  26. Normalized to 30 Block II Spacecraft 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” Draft-For Comment

  27. 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 Draft-For Comment

  28. Trade III. Effect of Decisions onImproving Dual-Frequency Handheld- Anti-JamMOE 2: Effective Range of 10W Jammer Draft-For Comment

  29. Effect of Jamming Mitigation TechniquesCombination reduces effective Jammer Area to less than 1/1000th of original 0.000001 Ultra-tight 0.00001 Coupling 0.0001 Combination of Techniques 0.001 Area Ratio of Jamming Effectiveness Simple Beam 0.01 Antenna 0.1 GPS III 1 0 10 20 30 40 50 60 Improvement in dB Decision Makers Trade III. Applying the Possible Mitigation Techniques to a Handheld GPS set Draft-For Comment

  30. 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 Draft-For Comment

  31. MOE 3: Bounds on inaccuracy(Probability of Large Error) - 1 GPS Satellite not operatingMountainous Terrain, 45o slope, Block II Ranging error 24 Satellites have >15% chance of exceeding 100 m error 30 Satellites will not exceed 40 meter error more than 1 % of cases Draft-For Comment

  32. MOE 3: Bounds on inaccuracy(Probability of Large Error) - 2 GPS Satellites not operatingMountainous Terrain, 45o slope, Block II Ranging error 24 Satellites have >25% chance of exceeding 100 m error 30 Satellites will not exceed 70 meter error more than 3 % of cases Draft-For Comment

  33. MOE 3: Bounds on inaccuracy(Probability of Large Error) - 1 GPS Satellites not operatingMountains of Afghanistan, 45o slope, Block III Ranging error 24 Satellites have >10% chance of exceeding 100 m error 30 Satellites will not exceed 20 meter error more than 1 % of cases Draft-For Comment

  34. 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 24 Satellites have >40% chance of exceeding 100 m error 30 Satellites will not exceed 40 meter error more than 10 % of cases Draft-For Comment

  35. MOE 4 is Time to Alarm – TTA –S secondsNotify 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 Draft-For Comment

  36. 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 Draft-For Comment

  37. MOE Summary for Mission APrecision Bomb Delivery with Ground Observer in Mountainous Terrain * MOE 1 results have been normalized Draft-For Comment

  38. 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. FirstResponder pinpointing urban locations • Mission D. Use of GPS based ADS-B mandated for future ATC System – improving separation distances Draft-For Comment

  39. 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 Draft-For Comment

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