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Inertial
Sensors Support GPS and GNSS for Improved Navigation
GPS receivers are specified for conditions with a clear
view of the sky, no obstructions and all satellites in
view. In automotive applications these conditions are
present only part of the time. In mountainous terrain,
under dense foliage and around high rise buildings, GPS
reception is compromised. In dense urban canyons, GPS
radio signals bounce off buildings creating "multipath"
reception, sometimes fooling the GPS receiver into supplying
a position with a large error.
Adding inertial sensors and processing using a Kalman
Filter provides a dead reckoning (DR) position solution.
Combining the DR with GPS gives more consistent navigation. |
Dead
Reckoning Assists GPS Under Severe Multipath Signal Reception
GPS signals originate about 12,000 miles above the Earth.
They are very weak when they reach ground level so are
easily shielded. Buildings, passing vehicles, RF absorbent
material and dense foliage can interfere with signals
from some satellites. At the same time a bounced GPS signal
due to multipath gives a false distance reading to the
satellite, throwing off the position calculation (at the
speed of light, a 3.3 ns delay is approximately equal
to a position error of 1 meter).
Adding inertial sensors and sophisticated dead reckoning
calculations provide a method of keeping the navigation
and positioning system on track. The combination of DR
with GPS increases availability of positioning solutions
in mines, tunnels, under dense foliage, in urban canyons,
in mountains and under bridges or overpasses. |
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