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GNSS and UWB

GNSS and UWB. Joe Newman Interactive Media Systems Group. Contents. GPS How it works Errors Augmentations GLONASS Galileo UWB. GPS. Constellation of 24 satellites 6 orbital planes at 54.8 o Atomic clock Broadcast on two L-band frequencies Pseudo-random code

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GNSS and UWB

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  1. GNSS and UWB Joe Newman Interactive Media Systems Group

  2. Contents • GPS • How it works • Errors • Augmentations • GLONASS • Galileo • UWB

  3. GPS • Constellation of 24 satellites • 6 orbital planes at 54.8o • Atomic clock • Broadcast on two L-band frequencies • Pseudo-random code • Military encrypted code

  4. Ranging • Received signal level less than background • Errors • Clock errors • Atmospheric delay • Pseudorange is range including error • Navigation message • Carrier phase tracking

  5. Triangulation 1 range puts user on the spherical face of the cone. Intersecting with a 2nd range restricts user to the circular arcs. 3rd range constrains user to 1 of the 2 points. Which point is determined by “sanity” – 1 point obviously wrong.

  6. GDOP • Geometric Dilution of Precision • Depends on user-satellite geometry • TDOP • HDOP • VDOP

  7. DGPS • Errors in one location are similar to errors in surrounding error • Corrections broadcast from Reference Station to Mobile Station over Data Link

  8. WAAS/EGNOS/MTSAT • 25 ground reference stations across US • Master ground station broadcasts corrections to geo-stationary satellites

  9. LAAS • Similar to WAAS • Ground reference stations in vicinity of airport • Line-of-sight VHF radio link to plane • Can be augmented with pseudolites

  10. GLONASS • 24 satellite constellation in 3 orbital planes (8 currently active) at 64.8o • Higher inclination of satellite orbits • More availability for higher latitudes (e.g. Sweden and polar regions) • Better accuracy for civilians (pre-SA) • Some devices use GLONASS and GPS together

  11. Galileo • 30 satellite constellation • 27 operational + 3 active spares • 3 MEO orbital planes of 56o inclination • Planned active by 2008 • Safety critical systems • Quality of service guarantees • Business model TBA • Subscriber services • Search and Rescue feature

  12. UWB • Claim - “Communications with precision ranging and positioning ability” • Transmit short discrete pulses instead of modulating code onto carrier signal • Pulses last ~1-2 ns • Distinguish pulses 1-2 ft apart • UWB avoids • Ranging accuracy degradation • Deep fades

  13. Questions & Discussion

  14. UWB revisited (1) • Not sinewave – millions pulses per second • Time coded to make noise-like • Channelization • Anti-jamming • Smooths spectrum • Pulse Polarity modulation

  15. UWB revisited (2) • Time of flight precisely measured by phase shift of code • Receiver locks to coded sequence of transmitter with accuracy < 100 ps

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