Page 409 - Understanding Automotive Electronics

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11 FUTURE AUTOMOTIVE ELECTRONIC SYSTEMS

100 meters is quoted. In experiments, absolute accuracies of 30 meters have
been achieved.
There are a number of problems associated with GPS-based navigation
systems, including cost, time to fix position, and propagation considerations.
The cost of a GPS receiver is determined partly by its precise clock. However,
produced in sufficient quantities, the receiver cost could be brought into a
commercially viable range. The time to fix initial position is on the order of two
to three minutes, which is inconvenient but possibly acceptable. Once initial
position is fixed, updated position is available in about two-second intervals. In
addition, it is necessary to maintain a direct line of sight. This can be a problem
in areas of tall buildings or in mountainous terrain. Nevertheless, GPS is
potentially viable for future automotive navigation and has many advocates.
Signpost Navigation
In signpost navigation, a number of information stations (signposts) are
located throughout the road network. In one scheme, the signpost
continuously transmits data concerning its geographic location. The on-board
navigation system converts this data to map coordinates, which are displayed.
Figure 11.21 is a block diagram of a typical signpost navigation system.
This system requires an augmented database to convert the transmitted data to
map coordinates. This system has the capability to provide position to an
accuracy of a few meters.
There are drawbacks to the signpost system, however, including an
inability to determine position between signposts, inability to show a turn until

Figure 11.21
Signpost
Navigation System

FPO

396 UNDERSTANDING AUTOMOTIVE ELECTRONICS