TV-GPS Enhancing Global Positioning Systems Using Television Signals By Chris Lehnert

Overview  Introduction  Dissecting the Signal  Positioning  Conclusions  Resources

Introduction  What is TV-GPS?  Positioning using synchronization signals that are broadcast by VHF and UHF frequencies  Why use TV transmitters?  Higher power transmitters  Lower broadcast frequency  Number of different signals  Higher bandwidth

Introduction  Benefits  Compliments conventional GPS  Not affected by: transmitter Dopplertransmitter Doppler ionospheric propagation delaysionospheric propagation delays data that is modulated into other signalsdata that is modulated into other signals  Low Horizontal Dilution of Precision (HDOP)  Superior triangulation of lateral positions  More accurate, reliable and rapid positioning

Dissecting the Signal  Focus on American Standards Television Committee (ASTC)  Frame: 626 segments, 832 symbols each  Segment: 4 symbols for synchronization  Segment types: Field Synchronization, Data

Dissecting the Signal  Downconverting TV signal process:  Assume nominal offset frequency  Sample the frequency  Create complex code signal  Compute Fourier Transform

Positioning  Device acquires signal  Triangulates latitude and longitude  Pseudoranges  Monitor unit tracks signals  No common clocks  Location server does computations  Sends data to chips

Positioning

Positioning  Message flow diagram

Conclusions  Positive:  Excellent positioning system when paired with conventional GPS  Robust, high speed, large coverage  Many practical uses  Negative:  Location privacy

Resources  A New Positioning System Using Television Synchronization Signals. Matthew Rabinowitz, James Spilker. ROSUM           