František Vejražka, Pavel Kovář, Libor Seidl, Petr Kačmařík, Josef Špaček, Pavel Puričer


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PRESENT SATELLITE RADIO NAVIGATION SYSTEMS, THEIR PERFORMANCE AND USER RECEIVER CONCEPTS

  • František Vejražka,

  • Pavel Kovář, Libor Seidl, Petr Kačmařík, Josef Špaček, Pavel Puričer

  • Department of Radio Engineering

  • Czech Technical University in Prague

  • Czech Republic


Abstract

  • This contribution gives an overview of present and future navigation systems and their augmentations such as GPS, GLONASS, GALILEO, WAAS, EGNOS, MSAT, QZSS, BEIDOU, GAGAN. Performance of the systems depends on their technical parameters. We will try to evaluate these and to present our opinion on their advantages for different applications and in various situations (reception of weak signals suffering from great attenuation under vegetation canopy, in urban canyons, influence of reflections and multipath).

  • The last part of the contribution deals with an application of software radio technology for user receiver design and results obtained from experiments with different algorithms of processing the satellite navigation systems signals.



Terminology



Satellite Navigation Systems

  • Historical Satellite Navigation Systems (not realized)

  • 601

  • TIMATION

  • ...

  • GEOSTAR

  • REXSTAR



Satellite Navigation Systems

  • Past Satellite Navigation Systems

  • NNSS - Transit

  • Tsikad



Satellite Navigation Systems

  • GLONASS



Satellite Navigation Systems



Principles of Satellite Navigation Systems

  • Doppler systems

  • Ranging systems



Principles of Satellite Navigation Systems – Doppler Systems



Principles of Satellite Navigation Systems – Ranging Systems





GPS DELAY DISCRIMINATOR



GPS EARLY-LATE DISCRIMINATOR



Receiver Principle



Systems Parameters (Properties)

  • We will deal with systems:

  • GPS – NAVSTAR

  • GLONASS

  • GALILEO



GPS - NAVSTAR



GPS Constellation



GPS Present Signal Structure (1/3)

  • Signal in time domain:

  • L1: s(t)=ACCC/A(t).D(t)cos(2πf1t)+APP(t).D(t)sin(2πf1t)

  • L2: s(t)=APP(t).D(t)sin(2πf1t)

  • Code multiplex - each satellite has own range codes CC/A(t) and P(t)

  • Signal in frequency domain:



GPS Parameters Signal Structure (2/3)

  • Navigation Message (Data) Content:

  • transmitting satellite Kepler parameters

  • almanac – Kepler parameters of others satellites

  • satellite „health“

  • corrections of

    • satellite clock frequency
    • troposphere refraction


GPS Parameters Signal Structure (3/3)

  • Navigation Message FEC Hamming Coding



GPS Services

  • SPS – Standard Positioning Service only C/A code accessible

  • PPS – Precision Positioning Service for authorized users P(Y) code accessible



GLONASS



GLONASS Constellation

  • 24 satellites (8 satellites in each of 3 planes)

  • e ~ 0 (circular orbit)

  • inclination 64.8°

  • altitude 19 100 km,

  • orbit period 11h 15m

  • angular spacing between orbits 120°



GLONASS Signal Structure

  • Frequencies:

    • L1: fj = 1602 + 9j/16
    • L2: fi = 1246 + 7i/16 [MHz]
  • Modulation:

    • Navigation message
    • Pseudorandom ranging code
      • Sequence of maximum length
      • Period 1 msec
      • Bit rate 511 kb/s
    • 100 Hz auxiliary meander sequence – Manchester code


GLONASS Signal Structure

  • Data

    • Hamming code (84,8)
    • 50 b/s in strings
    • 15 strings ~frame
    • 5 frames ~navigation message ~2.5 min


GLONASS Constellation history



GALILEO



GALILEO Constellation



GALILEO Architecture



GALILEO Services

  • OS – Open Service free of charge, positioning, navigation, timing services

  • CS – Commercial Service added value to OS, garanteed services

  • SoL – Safety of Life integrity message

  • PRS – Public Regulated Service police, customs, ... dedicated signal, under governmental control

  • SAR – Search and Rescue coordinated with COSPAS – SARSAT



GALILEO Signals and Spectra



GALILEO Signals and Spectra – BOC(m,n)

  • s(t) = carrier x subcarier x (ranging)code

  • subcarrier –

  • code – PRN



GALILEO BOC Spectrum



GALILEO BOC Correlation Function



GALILEO BOC modulation



GALILEO Signals, Services and Spectra



GALILEO Signals, Services and Spectra



GALILEO Spectrum, Services and Spectra



GALILEO Signal, Services and Spectra



GALILEO Service Parameters



BEIDOU



BEIDOU

  • „China‘s „Beidou“ navigation system is a regional positioning system mainly covering the country and its neighbouring areas, thus making vertical positioning impossible and limiting the number of users.“

  • 3 geostationary satellites

  • circular orbits



BEIDOU Constellation (Beidou 1B orbit)



Augmentations



Augmentation Differential GPS (DGPS)



Augmentation Differential GPS (DGPS)



Augmentations

  • Many systems

    • NDGPS
    • maritime systems
  • Systems with satellite channel for corrections transmission

    • WADGPS
    • SBAS (ICAO) – Satellite Based Augmentation Systems
      • WAAS
      • MSAS
      • EGNOS → future part of GALILEO


Augmentations SBAS - Constellation



Augmentations SBAS - signals

  • Similar to SATNAV systems signals



Augmentation QZSS



Augmentation QZSS - Constellation



Augmentation QZSS



MODERNISATION

  • GPS



Spectrum of Future GPS





Comparison of Systems



Comparison of Systems

  • What is an advantage of modernized or new systems ???



Comparison of Systems



Comparison of Systems Multipath Mitigation



Comparison of Systems



RECEIVER ARCHITECTURE Requirements

  • Processing of all known and planned SATNAV signals:

    • GPS L1, L2, L5
    • GLONASS
    • GALILEO
    • Augmentations
      • EGNOS
      • WAAS
  • Flexible design and development of powerful algorithms of signal processing

  • Easy implementation of them

  • Rapid and simple prototyping and testing

  •  Software Defined Radio 



RECEIVER ARCHITECTURE Requirements

  • Software Defined Radio 

  • What processor to use ???

  • DSP

  • FPGA



RECEIVER ARCHITECTURE DSP Concept

  • Loops in algorithms – lower computational power



RECEIVER ARCHITECTURE FPGA Concept

  • No loops in algorithms

  • parallel processing → higher computational power



RESULTS at CZECH TECHNICAL UNIVERSITY

  • Experimental receiver



Experimental Receiver CTU (first version)

  • Two-channel RF unit

  • DSP unit – Virtex II FPGA PCI card

  • PC Workstation – Windows 2000



High Frequency Part of the Receiver



Receiver Programming in Simulink



Processor Programming in EDK





Conclusions

  • Software Radio is prospective technology for multi-systems GNSS receivers, as well as FPGA technology

  • This technology make possible design of receivers for hard receptions conditions (leaves canopy, urban environment, etc.)








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