GPS Modernization Legacy User Equipment Compatibility Tests

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L2 and L5 Civil Signal Industry Day 2 May
2001 LCDR Richard Fontana GPS Deputy Program
Manager, DOT
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GPS L2 Civil Signal Industry Day Agenda

• ITEM BRIEFER TIME
• Welcome and Introductions LCDR Fontana 0900-0910
• Overview of GPS Modernization Paul
  Novak 0910-0920
• Advantages of a New L2 CS LCDR Fontana 0920-0945
• BREAK 0945-1000
• Technical Description of L2CS Tom
  Stansell 1000-1100
• Laboratory and Simulation Dr Dafesh 1100-1130
• Results
• Almanac Karl Kovach 1130-1200
• Question and Answer Session LCDR
  Fontana 1200-1215
• LUNCH 1215-1330

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GPS L5 Civil Signal Industry Day Agenda

• ITEM BRIEFER TIME
• Welcome and Introductions Lt Victoria 1330-1340
• L5 Design Background Dr Hegarty 1340-1400
• L5 Design Background Dr Van Dierendonck 1400-144
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• L5 Environmental Studies Dr Hegarty 1445-1500
• BREAK 1500-1515
• ICD-GPS-705 Organization Dr Slattery 1515-1540
• ICD-GPS-705 Review Process Lt Victoria 1540-1600
• Question and Answer Lt Victoria 1600-1630

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L2 and L5 Civil Signal Industry Day 2 May
2001 Paul Novak SMC/CZC (SAIC)
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Civil Use of GPS
The nations reliance on GPS has become an issue
of national security -- national security in its
broadest sense, that goes beyond merely national
defense. -- Dr. James Schlesinger, March 1997
Power Grid Interfaces
Personal Navigation
Surveying Mapping
Trucking Shipping
Aviation
Communications
Railroads
Recreation
Fishing Boating
Off shore Drilling
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GPS Space Systems
24-satellite (nominal) constellation Six orbital
planes, four satellites per plane Semi-synchronous
, circular orbits (11,000 mi)
Block IIF
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Civil GPS, Summary of Key Events

• 1978 - First Global Positioning System satellite
  launch
• 1983 - President Reagan offers GPS to the world
  free of charge
• 1993 - GPS Standard Positioning Service available
• 1994 - FAA approves GPS for use in National
  Airspace System
• 1996 - Presidential Decision Directive, first
  National GPS policy
• 1998 - Two new GPS civil signals (L2 and L5)
  announced
• 1999 - Third civil signal (L5) at 1176.45 MHz
  announced
• 2000 - Congress funds GPS Modernization in DoD
  budget
• 2000 - Selective Availability set to zero
• 2000 - GPS JPO begins modifications to IIR-M and
  IIF satellites
• 2000 - JPO awards Boeing and Lockheed Martin GPS
  III contracts

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GPS Modernization Mission
Current Mission
Additional Modernization Mission
Anti-Jam/Anti-Spoof Protection, Civilian Safety
of Life Signals, Upgraded Redundant Control,
and demonstrate Legacy and Upgraded Military
Receivers.
Precise Continuous, 3-D Position, Velocity and
Timing Information to an unlimited number of
military and civil users
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GPS Users Wants
Civil User

• Accuracy
• Availability
• Coverage
• Integrity
• Robustness
• Redundant signals
• More power

• More jam resistance
• More security
• Anti-spoof
• User discrimination
• Shorter time to first fix
• Backward compatibility

Military User

• Selective Availability (SA) to zero
• Second civil signal
• Ionospheric correction
• Redundancy
• Third civil signal
• High accuracy
• real-time applications
• Spectrum protection for
• safety of life applications

L2 Civil Signal
Military code L1 / L2

• Higher power
• New military signal
• Spectral separation
• from civil signals
• Faster signal acquisition
• Improved security codes

L5
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Why Modernize GPS?The Civil GPS Perspective

• Better support to civil GPS customers worldwide
• New civil signals for improved accuracy,
  integrity and continuity of service robustness
• Global utility economic enabler
• Optimize GPS PVT and augmentation systems in a
  overall national network architecture

Presidential Decision Directive - Mar 96 Vice
Presidential Announcements - Mar 98 and Jan 99
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GPS ModernizationBlock II Space Vehicles
Block IIR-M
Block IIF

• L1 Enhancements
• New developmental Military code (M-code)
• L2 Enhancements
• New L2 civil signal
• New developmental M-code

• L1 Enhancements
• Similar to IIR-M
• Operational M-code
• L2 Enhancements
• Similar to IIR-M
• Operational M-code
• L5
• New civil signal at 1176MHz

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Modernized GPS Signal Evolution
L2
L1
L5
C/A
P(Y)
P(Y)
Present Signal (Block II/IIA/IIR)
M
M
C/A
L2CS
Next Generation Of Capability (Block IIR-M)
P(Y)
P(Y)
M
M
C/A
L2CS
Civil Safety of Life Applications (Block IIF and
beyond)
P(Y)
P(Y)
1227.60 MHz
1575.42 MHz
1176.45 MHz
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GPS III Architecture Studies

• Military missions
• Precision bombing
• Mine clearing
• Situational awareness
• Civilian missions
• Precision farming
• Building/ urban canyon personnel tracking
• Global Air Traffic Management (GATM)
• Time synchronization for utilities/
• telecommunications

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GPS Modernization Program Summary
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L2 Civil Signal
LCDR Richard Fontana GPS Deputy Program Manager,
DOT May 2, 2001
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Overview

• Background
• Advantages of New Signal
• Design Considerations

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Background

• Option to implement a new signal
• Did not want to limit future GPS by what is
  implemented on IIR/IIF
• Overcome some limitations of C/A coded signals
• Can make significant improvements with new
  technology signal
• C/A code designed as an acquisition signal
• 1070s technology

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Advantages of a New Signal

• Improved Cross Correlation Properties
• Improves ability to transmit more signals
  (SBAS,Pseudolytes)
• Improves the tolerance to interference
• Improves susceptibility to self interference
• Improves the dynamic rage of receivers
• Can receive weaker signals without self
  interference
• Enables operation in more stressful environments
  (wooded area, buildings, urban canyons)
• Enables ability for higher power signals on
  future satellites

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Advantages of a New Signal

• Improved Tracking capability
• Enables operation in more stressful environments
  (wooded area, buildings, urban canyons)
• Improved Data Demodulation
• Want equivalent to tracking threshold
• Again, enables operation in more stressful
  environments
• Acquisition Capability
• Dependent on user equipment
• Design trade with code length
• Not limited by code. With right UE, can acquire
  signal in more stressful environments than C/A
  code

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Design Considerations

• Enhance existing professional/commercial dual
  frequency applications
• Provide more robust iono correction signal
• Provide a more effective single frequency
  navigation signal
• Drives need for data
• Simple to implement in the SV and UE
• Schedule and Cost (both SV and UE)
• Replacement for C/A signal

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Design Considerations (continued)

• Compatible with L2 M-code
• Spectral Separation
• Ensure no detriment to Codeless/Semi Codeless L2
  P(Y) receivers
• As a result of two earlier objectives
• Same power level and spectral shape as C/A
  codeno additional testing required
• Risk Mitigation
• Design schedule short, IIR implementation
  schedule short, coordination process short
• C/A code switch

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Design Considerations (continued)

• What is optimum in the future (GPS III) to
  determine the best step now.
• Did not want to artificially constrain thinking
  due to possible IIR/IIF perceived limitations.
• Perceived cost/schedule limitations.
• Design for future, provide natural migration path
• Then determine what portion could be implemented
  on IIR and IIF
• L2 C/A code compatibility
• Assess impact on both military and civilian
  receivers
• Not a design driver but have C/A switch as risk
  mitigation

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Signal Characteristics

• Two codes one with one without data
• Serves single and dual frequency users
• Signal characteristics
• Codes longer than C/A to minimize cross
  correlation
• Separated by time Time Division Multiplexed
  (TDM)
• Narrow band signal Spectral separation
• Improved data structure Enhanced Data
  demodulation
• Enhance cross correlation, tacking threshold,
  data demodulation threshold.

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Signal Comparison

• L2 splits power 50/50 between data and data-less
  channels
• Medium Code with Data, Long code no data
• Higher effective L2 channel for tracking
• 3db higher than C/A on L2
• Approximately 3dB better Data demodulation
  capability
• Enhanced data structure

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Signal Comparison

• 24dB better cross-correlation protection.
• C/A code cross correlation protection is 21
  dB. The L2CS signal is 45dB protection
• Dynamic range improvement.
• Better capability to receive both weak and strong
  signals
• Acquisition threshold
• Given assumptions of improved UE, not harmed
• Under stressful conditions improved

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L2CS Summary

• TDM service for both single and dual frequency
• Significant improvements in
• Cross correlation performance
• Tracking threshold
• Data recovery threshold
• Acquisition Capability
• Modern signal for future GPS

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