Signal Structures for Satellite-Based Navigation: Past, Present, … · 2013-07-16 · CLASSIFICATION CLASSIFICATION Multiple origins of modern GNSS signal structures – Original

John W. Betz 23 April 2013

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

*Approved for Public Release; Distribution Unlimited. 13-0908. 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.

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Early Satnav Signal Design

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Project 621B Contributions to Structure of Original GPS Signals and Receiver Processing

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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

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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

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© 2012 The MITRE Corporation. All rights reserved.

Project 621B Contributions Not Included in Structure of Original GPS Signals

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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

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Satnav Circa 10 Years Ago

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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

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Satnav Today

Approximately 90 Operational Satellites

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Satnav Circa 10 Years from Now Open: Blue, Encrypted: Red

Frequency (MHz)

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1560 1570 1580 1590 1600 16101160 1170 1180 1190 1200 1210 1220 1230 1240 1250 1260 1270 1280 1290 1300JWBetz

?

GPS: 27 to 36 SVs

GLONASS: 24 to 30 SVs

Galileo: 26 to 30 SVs

BeiDou: 35 SVs

QZSS: 3+ SVs

IRNSS: 5+ SVs

SBAS: 14 to 20 SVs

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Satnav Circa 10 Years from Now Open: Blue, Encrypted: Red

Frequency (MHz)

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1560 1570 1580 1590 1600 16101160 1170 1180 1190 1200 1210 1220 1230 1240 1250 1260 1270 1280 1290 1300JWBetz

?

GPS: 27 to 36 SVs

GLONASS: 24 to 30 SVs

Galileo: 26 to 30 SVs

BeiDou: 35 SVs

QZSS: 3+ SVs

IRNSS: 5+ SVs

SBAS: 14 to 20 SVs

More than 160 Operational Satellites

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Future Signal Occupancy in Upper L Band: GPS, GLONASS, SBAS, QZSS, Galileo, BeiDou Phase 3

1560 1565 1570 1575 1580 1585 1590 1595 1600 1605 1610Frequency (MHz)

Pow

er S

pect

ral D

ensi

ty (

dBW

/Hz)

Betz

GPSM Code

GPSM Code

GPSC/A Code

GPS L1CGalileo E1 OSBeiDou B1-CGalileo

PRSGalileoPRS

BeiDouB1-A

BeiDouB1-A

GLONASS L1OF

GLONASSL1OC

GLONASSL1SC

GPS C/A Code QZSS C/A Code and SAIF

L1 SBAS

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Quantifying the Future Signal Occupancy in Upper L Band

System Number of Signal Types

Number of Satellites

Signal-Satellite Product

GPS 4 36 144 GLONASS 4 27 108

SBAS 1 19 19 Galileo 2 30 60 BeiDou 2 35 70 QZSS 3 7 21

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

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Signal Characteristic Original Civil Signals

Changes In Today’s New and Modernized Signals

Possible Changes In Future Signals

Carrier Frequency L Band, One Civil

Signal Center Frequency

Two or Three Civil Signal Center Frequencies in L

Band

S Band, C Band, Diverse Carrier Frequencies in

Upper L 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 ≤1023 bits; Shift-

Register Generated

4092 to 767,250 bits; Memory and Weil-Based

Data Message Structure Fixed Flexible Message Format,

Intersystem Time Offsets

Digital Signatures or Other Authentication,

Text Messages Data Message Error

Correction and Detection

Hamming Code Parity Bits

Modern Error Control Coding621, CRC-Based

Error Detection

Data Modulation 50 bps, Biphase 25 to 2000 Bits per Second; Code Shift Keying

Pilot and Data Components Only Data Distinct Pilot and Data

Components

Overlay Codes Extensively Used

Multiplexing Carrier Phase Division

Time-Division621, Majority Voting, Interplex, Intervote, Non-Symmetrical AltBOC,

Generalized AltBOC

Optimized M-ary Constant-Envelope

Transmission

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Band






Register Generated








Modern Error Control Coding621, CRC-Based

Error Detection



Components

Overlay Codes Meander Extensively Used


Time-Division621, Majority Voting, Interplex, Intervote, Non-Symmetrical AltBOC,

Generalized AltBOC


Transmission

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Band






Register Generated








Modern Error Control Coding621B, CRC-Based

Error Detection



Components

Overlay Codes Meander Capable and Extensive


Time-Division621B, Majority Voting, Interplex, Intervote,

Symmetrical AltBOC


Transmission

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Band




Spreading Modulation BPSK-R BOC, Symmetrical AltBOC, TMBOC, CBOC Asymmetrical AltBOC


Register Generated




Digital Signatures or Other Authentication, Text

Messages Data Message Error



Modern Error Control Coding621B, CRC-Based

Error Detection



Components

Overlay Codes Meander Capable and Extensive


Time-Division621B, Majority Voting, Interplex, Intervote,

Symmetrical AltBOC

Asymmetrical & Generalized AltBOC,


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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

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System Designers Will Select Degrees of Interoperability and Diversity

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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

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Parting Thoughts

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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?

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Parting Thoughts

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An Analysis of Combined COMPASS/BeiDou-2 and GPS Single- and 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

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GNSS Signal Structures Session

Documents

Signal Structures for Satellite-Based Navigation: Past, Present, … · 2013-07-16 · CLASSIFICATION CLASSIFICATION Multiple origins of modern GNSS signal structures – Original