Part I GPS CONSTELLATION PERFORMANCE AND MODERNIZATION PLAN

1. Part I GPS CONSTELLATION PERFORMANCE AND MODERNIZATION PLAN GALILEO: DESIGN OVERVIEW AND THE DEVELOPMENT PLAN GS894G

2. References • Dave Hook, 2nd Space Operations Squadron: GPS CONSTELLATION STATUS 2002 CGSIC, April 2002 • David Goldstein, GPS JPO: GPS Modernization, Springfield, VA, 17 April 2002 • De Jong, C.D. papers available at: http://www.geo.tudelft.nl/mgp/index.html • The benefits of third carrier frequency to GNSS users • Galileo, Europe’s answer to the American Global Positioning System • Hegarty, C. and A.J. Van Dierendonck: Civil GPS/WAAS Signal Design and Interference Environment at 1176.45 MHz: Results of RTCA SC159 WG1 Activities, ION GPS 1999, CD ROM. • Spilker, J.J., and A.J. Van Dierendonck: Proposed New Civil GPS Signal at 1176.45 MHz, ION GPS 1999, CD ROM. • http://www.schriever.af.mil/gps/ • http://www.navcen.uscg.gov/ • http://www.starlinkdgps.com/gpsstatus.htm • http://www.aero.org/communications/relatedsites.html • http://www.space.com/missionlaunches/launches/launch_schedule.html • http://ravel.esrin.esa.it/docs/galileo_world_paper_Dec_2000.pdf • http://gps.faa.gov/gpsbasics/GPSmodernization.htm

3. GPS is... • Originally a Military Warfighter Support System • Global grid for coordinated position and time synchronization • Navigation, rendezvous, mine warfare, weapon delivery, etc. • Funded, managed, and operated by the DoD since 1973 • Civil access to GPS granted in 1983 by President Reagan • Now a Critical Dual-Use International Asset • More essential to military forces than ever imagined • Current example: precision guided munitions (smart bombs) • Becoming indispensable to civil/commercial users • Transportation, communication, disaster response, etc. • Still funded, managed, and operated by the DoD • Ground system, satellites, and receivers for military users • Ground system and satellites for civil/commercial users

4. Constellation Summary: January 2004 • Recent launches • GPS IIR-8, PRN16/SVN56, was launched on January 29, 2003 • GPS IIR-9 on 31 March 2003 • 20 March 2004, 23 Jun 2004, 6 November 2004 • Scheduled launches • GPS IIR-10 on 18 July 2003 • 29 On-Orbit Satellites • 1 Block II, 16 Block IIA, 12 Block IIR • Age Summary • 6 satellites past updated mean mission duration (MMD) • Oldest satellite: PRN 15 from Block II, Oct. 1, 1990

5. Today Vehicle Age (April 2002) Launch through Mean Mission Duration (MMD) Design Life: 7.5 yrs Block II MMD: 9.60 yrs Block IIA MMD: 10.23 yrs Block IIR MMD: 10.62 yrs 6 SVs past MMD 10 more exceed MMD in 02/03

6. Vehicle Age by Plane D Plane A Plane C Plane E Plane B Plane F Plane

7. Constellation Performance • PDOP Availability: • Requirement - PDOP of 6 or Less, 98% of the time or better • Actual - 99.99 • Horizontal Service Availability • Requirement - 95% threshold of 13 meters, 99% of the time or better • Actual - 4.49 meters • Vertical Service Availability • Requirement - 95% threshold of 22 meters, 99% of the time or better • Actual - 6.43 meters • User Range Error • Requirement - 6 meters or Less, Constellation Average • Actual - 1.47 meters Constellation exceeds all performance requirements

8. 2001 Global Position Error

9. Summary: Performance • Constellation is exceeding all performance requirements • No continuous monitoring of the civilian signal and incomplete monitoring of military signal • Service failure may go undetected for a long time (http://www.ion.org/meetings/past/gps2002/gps2002_sd_thu.pdf) • Acceptance of GPS as global standard may be difficult • GPS is an aging constellation (see the vehicle age chart) • Launches are scheduled to sustain constellation health

10. GPS JPO (GPS Joint Program Office ) Challenges • Maintain Constellation while Adding Capabilities (system modernization) • On-orbit satellite constellation sustainment strategies • Multiple blocks of satellites (II, IIA, IIR now; IIR-M, IIF soon) • Ground system upgrades and modernization • Operational Control System (OCS) • Testing / validating new signals - design and operations • Capturing Future User Needs - Military and Civil • Best way to understand military operational needs • Best way to understand civil “value added” needs • Procurement Strategies to Enable Future Growth • Ability to forecast GPS user requirements through 2030 • Reducing Total Ownership Costs • Weigh costs and benefits to make the right system trade-offs

11. New Civil Signals • Some Consider as 2nd/3rd Steps of Modernization • Many civil users consider setting SA = 0 as the 1st step • May 2000 • Civil Users Currently Limited to One GPS Signal • C/A-code at L1 frequency (1575.42 MHz) • Low power signal, not intended for precision navigation • C/A = "Coarse/Acquisition" (c.f. P-code; P = "Precise") • Adding a Second Civil Signal • C/A-type code at L2 frequency (1227.60 MHz) • Low power signal, not intended for precision navigation • Adding a Third Civil Signal • P-type codes at L5 frequency (1176.45 MHz) • Higher power signal, intended for precision navigation

15. Current GPS Signals L2 L1 Present Signals • Coarse Acquisition (C/A) • Biphase shift keying, BPSK(1) - 1.023 MHz chipping rate (1540 carriers per chip on L1) • 1023 bit PRN code length (repeats every millisecond) • Not encrypted • Used by authorized users to initiate satellite tracking • Open to all users • Precise (P) • BPSK(10) - 10.23 MHz chipping rate (very long code – resets each week) • Encrypted to become Y code -- Anti-Spoofing (A/S) • Roughly ½ (-3dB) the power of C/A code

16. GPS Signal Evolution L2 L1 Present Signals • L2C – BPSK(1) • C/A or Time Division Data Modulation (TDDM) Long and Medium Codes • Next generation navigation message? • M Code - BOC(10,5) – Military Signal for the next 30 years! • Next generation navigation message Block IIR-M 2nd Civil Signal (L2C) and Military (M) Code

17. GPS Signal Evolution L2 L1 Present Signals Block IIR-M 2nd Civil Signal and M Code Block IIF 3rd Civil Signal L5 BPSK(10) New Nav Message

18. L5 L2 L1 C/A P(Y) P(Y) Present Signal C/A C/A P(Y) P(Y) New Civil General Utility Signal C/A C/A Civil Safety of Life Applications and New Military Signals M M P(Y) P(Y) 1176 MHz 1227 MHz 1575 MHz

19. The first phase of the modernization of the Block II system will provide two additional signals, designated as code, on L1 and L2 for military use. The M code signals are designed to use the edges of the band with only minor signal overlap with the preexisting C/A and P(Y) signals. A second dedicated civil signal on L2 will be added to give civil users full dual-frequency service. In the next phase of modernization, another frequency (L5) with a new modulation type will be dedicated to high-accuracy use, fundamentally for aviation.

20. The current GPS constellation has signals on two frequencies (L1 and L2) with P(Y) code modulation dedicated to military use. L1 also has the C/A coded signal that is the primary signal for civil GPS users. Among the facts considered in selecting the optimal frequency and bandwidth for a space-to-Earth signal suitable for high-accuracy ranging are attenuation through the ionosphere, rain attenuation, code rate for accuracy, and of digital circuitry and radio-frequency components. As part of the GPS modernization efforts, Aerospace reexamined these tradeoffs and found that the current C/A and P(Y) codes at the L1 and L2 frequencies are fact optimal choices.

21. Block IIR – Modified Satellites

22. Block IIF – Modified Satellites

23. GPS L5 Signal: Summary • The GPS L5 signal will be comprised of a pair of carriers (in-phase and quadrature) at 1176.45 MHz (~25.5 cm wavelength) that are Binary Phase Shift Keying (BPSK) modulated by: • 10.23 MHz spreading sequences – The in-phase and quadrature carrier channels are BPSK modulated by different sequences. Length 10230 sequences will be employed, resulting in a 1 ms repetition period • The in-phase signal is BPSK modulated by data (navigation message). The data rate is 50 bps • Thus the code epoch period is the same 1 ms period as for the present C/A code. However it has a period 10 times longer when measured in chips in order to provide improved cross-correlation isolation between codes from different satellites.

24. GPS L5 Signal: Summary • The L5 navigation data will have the same navigation data format as the present GPS satellites, navigation data words in 24 bit blocks. • However the navigation data will be coded with a more powerful block error detection code for improved error detection capability. • The resulting bit stream at 50 bps is then coded with a rate ½ forward error correction convolutional code (FEC) for improved error rate performance. The output of the rate ½ coded data stream is then 100 bps. • The receiver can decode this signal with approximately 5 dB less signal-to-noise ratio while achieving the same error rate.

25. GPS L5 Signal: Summary • Federal Aviation Administration (FAA) also plans to eventually implement a WAAS (Wide Are Augmentation System) signal at L5 • GPS L5 minimum received signal power at or near the surface of the earth will be –154 dBW. This level is 6 dB higher than the specified minimum power for the C/A code on L1 and facilitates coexistence of the L5 signal with existing systems

26. GPS L5 Signal: Cycle Slip Performance • Cycle Slip Performance of L5 with PLL Compared to Cycle Slip Performance of L1 C/A Code as a function of signal-to-noise density, S/No • To achieve a cycle slip probability of 10-5 per second, roughly 3.5 dB less signal-to-noise is required for the GPS L5 signal as compared to the standard BPSK signal (C/A Code )

27. GPS L5 Signal: Ranging Precision • GPS L5 signal structure will provide improved ranging precision in the presence of multipath, as compared to the L1 C/A code • The higher chipping rate also improves ranging precision in the presence of noise and interference • In the presence of additive white Gaussian noise, the GPS L5 signal structure provides an approximate factor of three improvement in root mean square (rms) tracking errors over the L1 C/A code (assuming both signals are limited to bandwidth of 24 MHz). • This improvement is due to the roughly three-fold larger rms bandwidth of the GPS L5 signal, as compared to the L1 C/A code.

28. New Civil Signal Roll-Out (original plan) • Second Civil Signal (L2C) - Block IIR-M Satellites • First launch in 2003, then every satellite thereafter* • Provides a redundant signal for civil users • Improved continuity in case L1 signal reception is lost • Improved accuracy via dual-frequency ionosphere correction • Wide-lane for extremely-precise local area differential GPS • Third Civil Signal (L5) - Block IIF Satellites • First launch in 2005, then subsequent satellites thereafter • Provides redundant dual-frequency capability for civil users • Improved continuity in case L1 or L2 signal reception is lost • Improved accuracy via triple-frequency ionosphere correction • Tri-lane for ultra-precise local area differential GPS • Provides an interference-resistant signal for civil users *1 IIR saved for after first IIR-M

29. http://www.oosa.unvienna.org/SAP/act2002/gnss1/presentations/session01/speaker01/sld033.htmhttp://www.oosa.unvienna.org/SAP/act2002/gnss1/presentations/session01/speaker01/sld033.htm

32. GPS IIF and III Effects on Precise Positioning • Better ionosphere removal (see GS609 notes on second order iono-free combination) • Faster and more reliable ambiguity resolution Dual frequency float solution Dual frequency fixed solution

33. GPS IIF and III Effects on Precise Positioning • Faster and more reliable ambiguity resolution • probability of correct integer ambiguity estimation, referred to as success-rate, is increased • This probability mass function can be constructed from the probability density function of the real-valued ambiguity estimates resulting from the ‘float’ solution, and the integer mapping applied in the second step (ambiguity fixing) • The characteristics of the probability density function are captured in the covariance matrix of the real-valued ambiguities. This covariance matrix is a function of the a priori stochastic model of the observations and of the relative receiver-satellite geometry.

34. GPS IIF and III Effects on Precise Positioning

35. GPS IIF and III Effects on Precise Positioning • Faster and more reliable ambiguity resolution • The geometry-free model is the simplest possible functional model for the adjustment of GNSS observations that allows the estimation of integer carrier ambiguities • The model consists of the double differenced code and carrier observations, parameterized in terms of the unknown double difference satellite-receiver range, carrier ambiguities and, if they cannot be ignored, ionospheric delays (four-measurement filter, see GS609 notes) • The success-rates shown below are based on a standard deviation of the undifferenced carrier observations of 3 mm, and is provided as a function of pseudorange standard deviation • Geometry-free combination for a baseline is used

36. GPS IIF and III Effects on Precise Positioning Geometry-free (ionosphere fixed) success-rates for a single epoch as a function of the standard deviation of the code observations.

37. GPS IIF and III Effects on Precise Positioning Geometry-free (ionosphere float) success-rates for a single epoch as a function of the standard deviation of the code observations.

38. GPS IIF and III Effects on Precise Positioning • Faster and more reliable ambiguity resolution • Three GPS frequencies provide better performance • GPS (3 frequencies) performs better than Galileo (GNSS-2), primarily due to the larger frequency spacing of the three GPS frequencies. • Although adding a third frequency helps in improving the success-rate, all success-rates are very low for ionosphere float solution (long baseline). • indicates that it is not possible to reliably resolve the ambiguities using only a single epoch of data for long baselines (?!) • Figure 5: Success-rates for the geometry-free, ionosphere-fixed • model, as function of the standard deviation of the code

39. GPS IIF and III Effects on Precise Positioning • number of epochs, required for the ionosphere-float model to attain a pre-defined success-rate for two different values of the standard deviation of the code observations.Figure Success-rates for the geometry-free, ionosphere-fixed • model, as function of the standard deviation of the code

40. FIX FOM 1 N 42* 01” 46.12” W 091* 38’ 54.36” EL + 00862 ft 3 menu 1 ON 2 4 5 6 7 WPT 8 POS 9 NAV CLR MARK 0 OFF NUM LOCK ZEROIZE Rockwell GPS III System Description The GPS III System Second Civil Signal Third Civil Signal • Relook at Entire GPS Architecture to: • Achieve long term GPS performance goals • Reduce long term total ownership costs • Ensure GPS III is Synergized with: • Military and Civil Needs/Systems • Possible augmentation opportunities • Build Best GPS for the Next 30 Years

41. GPS III Integrated Approach • GPS Originally Designed without benefit of an Established User Base • Civil Users Previously Solicited for Suggested Changes to Existing System to Meet their Needs • GPS III has Novel Approach for Integrating Needs of the DoD, DOT, FAA… • Just completed System Architecture and Requirements Definition phase gathered and identified future requirements • Interagency Forum for Operation Requirements created to identify and assemble new requirements for GPS • Civil and military requirements to be approved in totality by joint committee • Coast Guard Navigation Center soliciting requirements via website

42. GPS III Increased Capability • Assured Delivery of GPS Signals • Higher Power Military & Civil Signals • Higher Accuracy Service for All Users • Increased Integrity1 Inherent in GPS 1the ability of a system to provide timely detection and warning of the system faults

43. GPS III Assured Delivery • Dual-Use GPS is more than just Adding Civil Signals • Assuring availability and continuity of signals • Realization that GPS is considered a Critical Part of Worldwide Infrastructure • Availability/Continuity Key Factors in GPS III Design • Crosslink architecture • Number of orbital planes • Number of satellites • Sparing strategy • Replacement strategy • Control segment

44. GPS III Higher-Power Signals • Military has Needed Better A-J (anti-jamming) for Long Time • GPS likely candidate for electronic attack during wartime • Transmitting signals with higher power is part of solution • Another one of the key aspects of assured delivery • Military-only M-code allows transmitting with higher power • Backwards compatibility a mandatory requirement • Civil Users Starting to Recognize Need for A-J • Volpe Vulnerability Assessment • Accidental interference • Intentional jamming and/or spoofing • Third civil signal at L5 is step in right direction for A-J • Other GPS III opportunities for regulated "public safety" users

45. GPS III Increased Accuracy • Augmented and standalone missions identified that require more accuracy than modernized GPS • Signal-in-space improvements must keep pace with those in users equipment • Advanced technology clocks and inter-satellite ranging - more accurate signal-in-space • More timely updates and improved models

46. GPS III Increased Integrity • Aviation applications one of key drivers • Other safety-of-life uses also considered • Important military need for integrity is to reduce collateral damage • GPS III architectural changes • Improved monitoring and reporting • Planned interfaces between GPS and augmentations • Potential for meeting broad array of civil and military needs via GPS alone

47. GPS III Sufficient Means of Navigation • Sufficient to be used anywhere, anytime • Without precluding use of other systems or augmentations • Without requiring use of other systems or augmentations • Except for most demanding applications (JPALS/LAAS) • With assured delivery • Availability and continuity (and higher power) • With high accuracy • With high integrity Joint Precision Approach and Landing Systems, JPALS, system is being developed to meet the DoD’s need for an anti-jam, secure, all weather Category I/II/III aircraft landing system that will be fully interoperable with planned civil systems utilizing the same technology LAAS –Local Area Augmentation System

49. Projected Launch • Block IIR with L2 C/A and M-code first launch 2003 • Block IIF with L5 first launch 2005 • GPS III (with M-code) first operational satellite ~2010

50. Summary • GPS Modernization activities well underway • GPS Modernization offers superb opportunity to satisfy both military requirements and civil needs • GPS III exploring complementary DoD/civil augmentation opportunities • Working through challenges • GPS III Architecture – Working hard toward a robust, supportable, flexible, international capability for the next 30 years