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The Radar navigation
system uses a 77GHz-millimetre wave radar to provide reliable and
accurate absolute position to a series of pre-surveyed target reflectors
in the operating environment. These measurements are used in combination
with the signals from wheel-based encoders and steer angle encoders
to provide a continual accurate estimate of vehicle position. In
addition (and unlike GPS) the radar navigation system measures the
vehicle orientation. No other external data is required to navigate.
The encoder
measurements are used to model the vehicles trajectory. This estimate
will become increasingly poor as errors accumulate. To overcome
this problem, measurements to absolute reference points are taken
by the millimetre wave radar system. This sensor is capable of measuring
range and bearing with high accuracy. The reference points are implemented
with radar reflectors with large capture angle and radar cross-section
at surveyed positions within the operating area. The data fusion
between encoder model and absolute measurements is made in a Kalman
filter, tuned to represent the error models of the sensors. The
radar and navigation algorithms then form a navigation package that
can be adapted to different vehicle types.
Automated
Flat Bed Test vehicle
The accuracy
achievable by the Navigation system depends upon the kinematics
of the vehicle to which they are fitted, but +/- 25mm accuracy is
typical, about the same as that of a differential GPS and sufficient
for real time control of the vehicle. Unlike GPS the radar navigation
system is reliable in areas where overhead structures may obscure
the satellite signal; beside tall buildings, underneath gantries
or even underground. The radar measurement is reliable in all weather
and environmental conditions. To compare the accuracy of GPS position
fixes and radar navigation, see test results for a port
vehicle navigation system.
For further
information and a comparison of GPS position fixes and radar navigation
accuracy please follow the link:
Vehicle
Navigation with Navtech 77GHz FMCW Radar (Download .pdf file)
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