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Precise Navigation Using GNSS

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									Precise Navigation Using GNSS

    Antonio Rius, Estel Cardellach


 CVA Summer School, Barcelona 2005




          July 28 2005   Precise Navigation Using GNSS   1/20
Overview


  1   Required Navigation Performance

  2   Augmentation Systems

  3   Techniques for mitigation of threats to GPS Signal quality

  4   GPS Formation Flying Vehicles

  5   Further reading ...




                            July 28 2005   Precise Navigation Using GNSS   2/20
            Required Navigation Performance


A few concepts


     Precision is a measure of the dispersion of the
     measurements
     Accuracy is a measure of the deviation from the reality
     Integrity is a measure of the probability of not radiating
     false guidance signals
     Continuity is the likelihood that the signal-in-space
     supports accuracy and integrity
     Availability is the fraction of time that the navegation
     function provides acceptable accuracy, integrity and
     continuity before the approach is initiated




                              July 28 2005    Precise Navigation Using GNSS   3/20
            Required Navigation Performance


Requirements


  Item                           CAT I                 CAT II                 CAT III
  Decision Height                200+ ft               100+ft                 0-100 ft
  Runway visual range            2400 ft               1200 ft                700 ft
  Vertical Accuracy              5m                    2.5 m                  2.5 m
  Continuity                     10^-5                 10^-7                  10^-7/30 sec
  Integrity                      4*10^-8/app           4*10^-8/app            10^-9/app
  Availability                   .999                  .999                   .999
  Vertical Alert Limit           10 m                  5.3 m                  5.3 m
  Time to alarm                  6 sec                 6 sec                  2 secs




                              July 28 2005    Precise Navigation Using GNSS             4/20
                      Augmentation Systems


Augmentation Systems
Wide Area Augmentation Systems




        WAAS: ground network and geostationary satellites
        Wide area reference stations collect and send raw GPS
        data to the master stations to generate corrections and
        integrity information.
        The information is uploaded into geostationary broadcast
        to the WAAS users.
        The WAAS users improves accuracy to 8 meters with
        integrity




                              July 28 2005   Precise Navigation Using GNSS   5/20
                      Augmentation Systems


Augmentation Systems
Local Area Augmentation Systems




        LAAS The space segment includes GPS and WAAS
        satellite.
        In addition a network of receivers creates more precise
        corrections which are sent to the airborne users via a
        dedicated data link.
        The airborne determines its position accurately, and uses it
        to produce deviation signals to conduct the precision
        landing depending on the facilities of the airport and the
        aircraft




                              July 28 2005   Precise Navigation Using GNSS   6/20
                   Augmentation Systems


Augmentation Systems




     Pseudolites Are beacons placed at or near the airport
     transmiting signals similar to the GPS signals.
     An example is the Integrity Beacon Landing System (IBLS)
     Uses two pseudolites so that differential carrier tracking is
     possible.
     Its accuracy is at centimetric level




                           July 28 2005   Precise Navigation Using GNSS   7/20
                  Augmentation Systems


Augmentation Systems


     GPS differential corrections for Space users
     The plan is to use the Tracking and Data Relay Satellite
     System (TDRSS), a fleet of 10 geosyncronous
     communications satellites to distribute GPS information
     according to the following table:
          Information                       Frequency
     GPS Orbit corrections               Every 32 seconds
    GPS Clock corrections                Every 2 seconds
      GPS Integrity flags                   Every second
  Earh Orientation parameters               Every hour
           Solar flux                     Every three hours



                          July 28 2005    Precise Navigation Using GNSS   8/20
             Augmentation Systems


NASA TDRSS




                     July 28 2005   Precise Navigation Using GNSS   9/20
 Techniques for mitigation of threats to GPS Signal quality


Radio frequency interference and jammers


          Aircrafts (missiles) use GPS guidance to the vicinity of the
          airports (targets)
          But GPS are at 20.000 km above the receiver: the signaks
          are very week (below the background radiation)
          a GPS jammer is a radio transmitter designed to broadcast
          signals in the GPS band
          They are easy to build in the simplest versions
          A “can” jammer powered with a lantern battery could
          interfere up to 10 Km.
          To interfere at larger distances (more than 100 Km) it is
          needed a a power source like a towed diesel generator



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  Techniques for mitigation of threats to GPS Signal quality


Low Cost and Portable GPS Jammer
www.phrack.org/60/p60-0x0d.txt

   1 - Project Overview
   2 - Why?
   3 - Technical Description
   3.1 - Phase Locked Loop
   3.2 - Noise Generator
   3.3 - RF Amplifiers
   3.4 - Voltage Regulation
   3.5 - Antenna
   4 - Construction Notes
   4.1 - Component Purchasing
   4.2 - Layout
   5 - Operation
   6 - References
   Appendix A: Links to Datasheets
   Appendix B: Schematic Diagram
                                              July 28 2005     Precise Navigation Using GNSS   11/20
 Techniques for mitigation of threats to GPS Signal quality


Antenna

                                                                                                                                              Wireless
                                                                                                                                              NAVIGATION


                                                                                                                                              DM N100-1 GPS ANTENNA

Antenna                                                                                                                                     The newly introduced DM N100-1 GPS antenna has
                                                                                                                                            been designed to provide a reduced size aperture
                                                                                                                                            for Antijam GPS reception over the full military GPS
                                                                                                                                            bandwidth. While fully compliant with GAS-1N
                                                                                                                                            requirements, the DM N100-1 footprint is a mere

    Antenna gain patterns are                                                                                                               7.0” x 7.0” x 1.0”. The antenna assembly is a four-
                                                                                                                                            element antenna aperture which is designed to
                                                                                                                                            receive right-hand circularly polarized (RHCP) radiated
                                                                                                                                            signals from NAVSTAR GPS satellites and couple the
                                                                                                                                            radio frequency (RF) signal to the antenna electronics


    shaped to attenuate                                                                                                                     (not supplied by AIL/DM) via four coaxial cables. The
                                                                                                                                            antenna assembly contains the antenna elements,
                                                                                                                                            radome, housing, SMA female bulkhead connectors,
                                                                                                                                            and 10” removable coax cables that interconnect
                                                                                                                                            the antenna assembly to the antenna electronics.


    reflected signals                                                                                                                        Microstrip patch type radiators provide a low-profile
                                                                                                                                            package while a hybrid feed incorporated in each
                                                                                                                                            element allows operation over a wide temperature
                                                                                                                                            band without the temperature induced detuning
                                                                                                                                            often associated with microstrip patch elements, and
                                                                                                                                            provides for operation over the full military


      Multiple antennas can steer                                                                                                           bandwidth without any pattern degradation. The
                                                                                                                                            four-element array is used to adaptively steer nulls
                                                                                                                                            in the presence of interfering jamming signals, when
                                                                                                                                            used in conjunction with interference cancellation
                                                                                                                                            hardware.


      nulls in the direction of the                                                SPECIFICATIONS
                                                                                      Frequency Range                                 1227.6 ± 10.23 MHz



      multipath and increase the
                                                                                                                                      1575.42 ±10.23 MHz
                                                                                      VSWR                                            2.0:1




                                                                      ELECTRICAL
                                                                                      Gain                                            -3.5 dBic over 160° cone
                                                                                      Polarization                                    RHCP
                                                                                      Null Depth                                      >20 dB


      gain in the direction of the                                                    TX Power
                                                                                      Radiation Pattern
                                                                                                                                      Receive Only
                                                                                                                                      Hemispherical




      emitting GPS
                                                                      MECHANICAL
                                                                                      Weight                                          1.5 lbs
                                                                                      Military                                        MIL-E-5400
                                                                                                                                      MIL-STD-202
                                                                                                                                      MIL-STD-810


                                                                                   Specifications subject to change without notice.                                                      1099-267(M20)




                                             July 28 2005     Precise Navigation Using GNSS                                                                                                              12/20
 Techniques for mitigation of threats to GPS Signal quality


Receivers

  Receivers
     The receiver correlates the received GPS signal with a
     replica computed with models for the delay and the delay
     rate
          The simple receivers compute this correlation at two
          different delays.Basically the receiver assumes that the
          correlation function is symettrical
          These values are used to correct the delay and delay rate
          modules
          More sophisticated receivers computes the
          cross-correlation at more points
          The estimation of the corrections is more robust and less
          affected by the multipath and jamming.

                                             July 28 2005     Precise Navigation Using GNSS   13/20
               GPS Formation Flying Vehicles


Motivation

Methods
    A formation is a group of
    vehicles working togheter in
    a coordinated manner
    To use GPS (or similar
    systems) as a part of a
    sensor for a formation flying
    cluster
    We need to know a coarse
    cluster absolute position
    and a precise relative
    position of its elements
    We need also the
    orientation with high
    precision
                               July 28 2005    Precise Navigation Using GNSS   14/20
               GPS Formation Flying Vehicles


Motivation

Methods
    A formation is a group of
    vehicles working togheter in
    a coordinated manner
    To use GPS (or similar
    systems) as a part of a
    sensor for a formation flying
    cluster
    We need to know a coarse
    cluster absolute position
    and a precise relative
    position of its elements
    We need also the
    orientation with high
    precision
                               July 28 2005    Precise Navigation Using GNSS   14/20
               GPS Formation Flying Vehicles


Motivation

Methods
    A formation is a group of
    vehicles working togheter in
    a coordinated manner
    To use GPS (or similar
    systems) as a part of a
    sensor for a formation flying
    cluster
    We need to know a coarse
    cluster absolute position
    and a precise relative
    position of its elements
    We need also the
    orientation with high
    precision
                               July 28 2005    Precise Navigation Using GNSS   14/20
                       GPS Formation Flying Vehicles


Cost savings



    Spacecraft System         Potential savings         Achieved trough          Other Improvements
    Operational Savings
    Ground Operations         $M per year               Autonomous vehicle       Hand-off operation,
                                                        operations               formation flight
    Navigation tracking       $100 k’s per year         On-orbit navigation      Better accuracy, real
                                                                                 time positioning
    Design savings
    Precision Timing          $1M                       Replaces on-board        Syncronization
                                                        atomic clocks            across         multiple
                                                                                 spacecraft
    Attitude determinati-     $100 k’s                  Replaces other attitu-   Improved reliability,
    on                                                  de sensors               reduced power and
                                                                                 mass
    Spececraft    Design      $100k’$                   Reduces interfaces,      Quicker design time,
    and Testing                                         COTS hardware            less project risk




                                         July 28 2005      Precise Navigation Using GNSS                   15/20
              GPS Formation Flying Vehicles


Other applications




     air-to-air refueling
     Unmanned air vehicles
     Ground based formation of farming equipment
     See Enabling Spacraft Formation Flying trough
     Spaceborne GPS and Enhanced Automation Technologies




                              July 28 2005    Precise Navigation Using GNSS   16/20
               GPS Formation Flying Vehicles


Simple model

     Each transmitter (GPS and/or pseudolites) sends signals,
     which phases are recorded at the different antennas
     placed in different vehicles:

                                        Ltransmitter
                                         antennavehicle

     These phases are modelled as:


         Ltransmitter
          antennavehicle   =   (transmitter ; antennavehicle ) + other

     where
                           (transmitter ; antennavehicle )
     is the distance between the transmitter and the antennas

                               July 28 2005    Precise Navigation Using GNSS   17/20
             GPS Formation Flying Vehicles


Simple model


     and the other terms are instrumental bias or they could be
     calibrated or removed using the differences already
     discussed
     an apriori survey provide the positions of each antenna un
     each vehicle body frame
     The kinematic state of each vehicle could be characterized
     (we assume that the vehicles are rigid) by a position and a
     rotation.
     Each vehicle could be described using a position and a
     rotation (6 unknowns)




                             July 28 2005    Precise Navigation Using GNSS   18/20
              GPS Formation Flying Vehicles


Simple model



     In principle we could use the model equation to solve for
     the state of the array of N vehicles using the all phases [

                                       Ltransmitter
                                        antennavehicle

     The work is facilitated using differences between the
     antennas at each vehicle to estimate the rotations and
     using differences between antennas at different vehicles to
     estimate to positions of each element of the cluster




                              July 28 2005    Precise Navigation Using GNSS   19/20
                Further reading ...




Leitner, J. (2002), Distributed Spacecraft Systems Develop
New GPS Capabilities,GPS World, 2002 Feb 1, 2002
Omerbashich, M (2002), Integrated INS/GPS Navigation
from a Popular Perspective, Journal of Air Transportation,
Vol. 7, No. 1-2002
Yoaz Bar-Sever, et al(2004), NASA’s Global Diferential
GPS System and the TDRSS Augmentation Service for
Satellites, NAVITEC, ESTEC,December 2004
ESA NAVIGATION
http://www.esa.int/esaNA/SEME0V1DU8E index 0.html
Precision Landing Tests with Improved Integrity Beacon
Pseudolites
Cobb H.,et al. (1995) Precision Landing Tests with
Improved Integrity Beacon Pseudolites,Institute of
Navigation GPS-95, Palm Springs, California

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