Signal Structures for Satellite-Based Navigation: Past, Present, and Future*

Transcription

1 Signal Structures for Satellite-Based Navigation: Past, Present, and Future* John W. Betz 23 April 2013 *Approved for Public Release; Distribution Unlimited The contents of this material reflect the views of the author. Neither the Global Positioning Systems Directorate nor the U.S. Air Force makes any warranty or guarantee, or promise, expressed or implied, concerning the content or accuracy of the views expressed herein.

2 2 Early Satnav Signal Design

3 Project 621B Contributions to Structure of Original GPS Signals and Receiver Processing Direct sequence spread spectrum/code division multiple access Clear/Acquisition signal Techniques for Selective Availability (SA) and differential techniques to remove SA Poor crosscorrelation performance of short spreading codes used for GPS C/A code signal Carrier-aided code tracking DLL tracking error model for wideband processing of BPSK-R signals in white noise 6 db lower tracking threshold of coherent phase locked loop carrier tracking over Costas loop tracking Pseudocoherent carrier tracking and data wiping 3

4 Project 621B Contributions Not Included in Structure of Original GPS Signals 4 Powerful error correction codes, both block and convolutional Separate pilot ( unmodulated carrier component ) and data components Phase-multiplexing and time-multiplexing of different signals or components onto the same carrier 2012 The MITRE Corporation. All rights reserved.

5 5 Satnav Circa 10 Years Ago Two global systems: GPS and GLONASS Fewer than 40 total operational satellites Each satellite transmitted three signals, only one for civil use SBAS emerging; none fully operational 2012 The MITRE Corporation. All rights reserved.

6 6 Satnav Today Two operating global systems: GPS and GLONASS Almost 60 total operational satellites Newest satellites transmit five to seven signals, three for civil use on different carrier frequencies One operating regional system: BeiDou Two emerging global systems: BeiDou and Galileo Two emerging regional systems: QZSS and IRNSS Three operational SBASs: WAAS, EGNOS, MSAS Three emerging SBASs: GAGAN, SDCM, BeiDou Approximately 90 Operational Satellites 2012 The MITRE Corporation. All rights reserved.

7 Satnav Circa 10 Years from Now GPS: 27 to 36 SVs 7 Open: Blue, Encrypted: Red GLONASS: 24 to 30 SVs Galileo: 26 to 30 SVs BeiDou: 35 SVs QZSS: 3+ SVs IRNSS: 5+ SVs? SBAS: 14 to 20 SVs Frequency (MHz) JWBetz

8 Satnav Circa 10 Years from Now GPS: 27 to 36 SVs 8 Open: Blue, Encrypted: Red GLONASS: 24 to 30 SVs Galileo: 26 to 30 SVs BeiDou: 35 SVs QZSS: 3+ SVs IRNSS: 5+ SVs? SBAS: 14 to 20 SVs JWBetz Frequency (MHz) More than 160 Operational Satellites

9 Future Signal Occupancy in Upper L Band: GPS, GLONASS, SBAS, QZSS, Galileo, BeiDou Phase 3 9 Power Spectral Density (dbw/hz) Galileo PRS BeiDou B1-A GPS M Code GPS C/A Code QZSS C/A GPS Code and SAIF C/A L1 SBAS Code GPS L1C Galileo E1 OS BeiDou B1-C BeiDou B1-A GPS M Code Galileo PRS GLONASS L1OF GLONASS L1SC GLONASS L1OC Frequency (MHz) Betz 2012 The MITRE Corporation. All rights reserved.

10 Quantifying the Future Signal Occupancy in Upper L Band 10 System Number of Number of Signal-Satellite Signal Types Satellites Product GPS GLONASS SBAS Galileo BeiDou QZSS Total signal-satellite product: 422, or 8.3 per MHz 1559 MHz to 1594 MHz, signal-satellite product: 314, or 9.0 per MHz 1594 MHz to 1610 MHz, signal-satellite product: 108, or 6.8 per MHz 2012 The MITRE Corporation. All rights reserved.

11 2012 The MITRE Corporation. All rights reserved. Signal Characteristic Original Civil Changes In Today s New Signals and Modernized Signals L Band, One Civil Two or Three Civil Signal Carrier Frequency Signal Center Center Frequencies in L Frequency Band Min. Received Power < 160 dbw < 154 dbw Polarization RHCP Multiple Access CDMA and FDMA CDMA Spreading Modulation BPSK-R BOC, Symmetrical AltBOC, TMBOC, CBOC Spreading Code Data Message Structure Data Message Error Correction and Detection Data Modulation Pilot and Data Components Overlay Codes Multiplexing 1023 bits; Shift- Register Generated Fixed Hamming Code Parity Bits 50 bps, Biphase Only Data Carrier Phase Division 4092 to 767,250 bits; Memory and Weil-Based Flexible Message Format, Intersystem Time Offsets Modern Error Control Coding 621, CRC-Based Error Detection 25 to 2000 Bits per Second; Code Shift Keying Distinct Pilot and Data Components Extensively Used Time-Division 621, Majority Voting, Interplex, Intervote, Non-Symmetrical AltBOC, Generalized AltBOC Possible Changes 11 In Future Signals S Band, C Band, Diverse Carrier Frequencies in Upper L Band Digital Signatures or Other Authentication, Text Messages Optimized M-ary Constant-Envelope Transmission

12 2012 The MITRE Corporation. All rights reserved. Signal Characteristic Original Civil Changes In Today s New Signals and Modernized Signals L Band, One Civil Two or Three Civil Signal Carrier Frequency Signal Center Center Frequencies in L Frequency Band Min. Received Power < 160 dbw < 154 dbw Polarization RHCP Multiple Access CDMA and FDMA CDMA Spreading Modulation BPSK-R BOC, Symmetrical AltBOC, TMBOC, CBOC Spreading Code Data Message Structure Data Message Error Correction and Detection 1023 bits; Shift- Register Generated Fixed Hamming Code Parity Bits 4092 to 767,250 bits; Memory and Weil-Based Flexible Message Format, Intersystem Time Offsets Modern Error Control Coding 621, CRC-Based Error Detection 25 to 2000 Bits per Second; Data Modulation 50 bps, Biphase Code Shift Keying Pilot and Data Distinct Pilot and Data Only Data Components Components Overlay Codes Meander Extensively Used Time-Division 621, Majority Multiplexing Carrier Phase Voting, Interplex, Intervote, Division Non-Symmetrical AltBOC, Generalized AltBOC Possible Changes 12 In Future Signals S Band, C Band, Diverse Carrier Frequencies in Upper L Band Digital Signatures or Other Authentication, Text Messages Optimized M-ary Constant-Envelope Transmission

13 2012 The MITRE Corporation. All rights reserved. Signal Characteristic Original Civil Changes In Today s New Signals and Modernized Signals L Band, One Civil Two or Three Civil Signal Carrier Frequency Signal Center Center Frequencies in L Frequency Band Min. Received Power < 160 dbw < 154 dbw Polarization RHCP Multiple Access CDMA and FDMA CDMA Spreading Modulation BPSK-R BOC, Symmetrical AltBOC, TMBOC, CBOC Spreading Code Data Message Structure Data Message Error Correction and Detection 1023 bits; Shift- Register Generated Fixed Hamming Code Parity Bits 4092 to 767,250 bits; Memory and Weil-Based Flexible Message Format, Intersystem Time Offsets Modern Error Control Coding 621B, CRC-Based Error Detection 25 to 2000 Bits per Second; Data Modulation 50 bps, Biphase Code Shift Keying Pilot and Data Distinct Pilot and Data Only Data Components Components Overlay Codes Meander Capable and Extensive Time-Division 621B, Majority Multiplexing Carrier Phase Voting, Interplex, Intervote, Division Symmetrical AltBOC Possible Changes 13 In Future Signals S Band, C Band, Diverse Carrier Frequencies in Upper L Band Digital Signatures or Other Authentication, Text Messages Optimized M-ary Constant-Envelope Transmission

14 2012 The MITRE Corporation. All rights reserved. Signal Characteristic Original Civil Changes In Today s New Signals and Modernized Signals L Band, One Civil Two or Three Civil Signal Carrier Frequency Signal Center Center Frequencies in L Frequency Band Min. Received Power < 160 dbw < 154 dbw Polarization RHCP Multiple Access CDMA and FDMA CDMA Spreading Modulation BPSK-R BOC, Symmetrical AltBOC, TMBOC, CBOC Spreading Code Data Message Structure Data Message Error Correction and Detection 1023 bits; Shift- Register Generated Fixed Hamming Code Parity Bits 4092 to 767,250 bits; Memory and Weil-Based Flexible Message Format, Intersystem Time Offsets Modern Error Control Coding 621B, CRC-Based Error Detection 25 to 2000 Bits per Data Modulation 50 bps, Biphase Second; Code Shift Keying Pilot and Data Distinct Pilot and Data Only Data Components Components Overlay Codes Meander Capable and Extensive Multiplexing Carrier Phase Division Time-Division 621B, Majority Voting, Interplex, Intervote, Symmetrical AltBOC Possible Changes 14 In Future Signals S Band, C Band, Diverse Carrier Frequencies in Upper L Band Asymmetrical AltBOC Digital Signatures or Other Authentication, Text Messages Asymmetrical & Generalized AltBOC, Optimized M-ary Constant-Envelope

15 System Designers Will Select Degrees of Interoperability and Diversity 15 Common signal characteristics make multisystem receivers simpler Reference frames Center frequencies Spectra Spreading modulations Spreading code family Data message structure and encoding Signals with diverse frequencies also have advantages Greater compatibility More robust multisystem receivers 2012 The MITRE Corporation. All rights reserved.

16 16 Parting Thoughts Multiple origins of modern GNSS signal structures Original designs Originally identified concepts not included in original designs More recent innovations Improvements in receiver processing techniques and technologies enable and drive more advanced signal designs 2012 The MITRE Corporation. All rights reserved.

17 17 Parting Thoughts Multiple origins of modern GNSS signal structures Original designs Originally identified concepts not included in original designs More recent innovations Improvements in receiver processing techniques and technologies enable and drive more advanced signal designs Are we approaching the limits of what new signal designs can offer, or do more revolutionary advances lie ahead? 2012 The MITRE Corporation. All rights reserved.

18 GNSS Signal Structures Session 18 An Analysis of Combined COMPASS/BeiDou-2 and GPS Singleand Multiple-frequency RTK Positioning Interoperability and Compatibility Analysis of GNSS L1/B1/E1 Open Signals Semi-Coherent and Differentially Coherent Integration for GPS L1C Acquisition Real-Time Validation of BeiDou Observations in a Stand-alone Mode Research on GNSS Interoperable Parameters 2012 The MITRE Corporation. All rights reserved.