GPSBased Location Determination

1
GPS-Based Location Determination
J. Walker / A. Zhang / B. Azimi-Sadjadi / P.S.
Krishnaprasad
Control Algorithm
Simulated Results
Introduction

• 24 GPS satellites spaced around Earth in 6
  orbital planes transmit an amplitude-modulated
  clock signal and navigation message that includes
  the time the message was sent and other error
  information
• GPS receiver determines the time taken for the
  signal to travel from satellite to receiver and
  calculates a pseudorange by multiplying by the
  speed of light.
• GPS receiver calculates position relative to
  Earth knowing at least four pseudoranges with
  satellite positions and error information
• Differential GPS determines accurate position by
  broadcasting range errors from a base receiver
  with fixed known location to one or more rover
  receivers
• ISL has previously developed a radio-controlled
  vehicle built on a commercial platform that can
  navigate using differential DGPS

• Simulated vehicle was successful in traversing
  predefined paths such as straight lines, grid
  paths, star paths, irregular paths, and
  elliptical paths.

• Use flag e to tell whether in turning state or
  in straight-line state
• Calculate initial turning point (p1x, p1y) of
  circle inscribed within corner
• Determine Length, distance from turning point to
  vertex corner
• Start turning when distance from vehicle to
  vertex is less than or equal to Length
• Determine chord length D of inscribed circle
• Stop turning once distance from vehicle to
  initial turning point is greater than or equal to
  D
• Reset flags e and d to regain a straight line
  state

Increasing Path Complexity
Experimental Results
DGPS Setup

• Vehicle was able to steer in real-time with
  simulated paths described above
• Steering was controlled by the software while
  throttle was controlled by pulling the vehicle
  using two strings tightened at front. This
  method made it easy to maintain and reduce the
  speed of the vehicle, thus reaching better
  accuracy than a gas powered vehicle.
• Real-time DGPS controlled experiment could not
  be performed due to a malfunctioning GPS receiver

Turning Stage Diagram
Differential GPS Setup

• Base and Rover antennas connect to commercial
  DGPS receivers
• Receivers communicate correction data using
  radio modems
• Base receiver sends positioning information to
  laptop through Comm port
• Laptop makes control decisions, sends digital
  control signal to D/A card
• D/A card sends analog signal to input of remote
  control
• Remote control sends radio wave signal to
  vehicle
• Vehicle receives radio wave signal for control
  of servos associated with steering and
  throttling, navigates to a new position

Interior steering unit
Meter-long RC Car
Applications
Inscribed Turning Circle
GPS Application

• Self-navigation of
• Farming machines which follow irregular-shaped
  paths for long distances.
• Wheeled robots used as ticketing authority in a
  parking lot.
• Wheeled robots used as outdoor tour guides or
  security guards.

Control View
What We Did

• Create new child frame class, create sizeable
  grid with axes
• Associate left and right mouse clicks with
  functions to record points on grid
• On left click, store points in local array
• On right click, map points from Control View
  grid to Global Map grid

• Test differential GPS system from previous year
• Modify control algorithm so that vehicle may
  turn and follow predefined paths that include
  both angled corners and straight lines
• Create a Control View window to help simplify
  path input
• Test software with various paths in simulation
  and real-time mode

Control View Window