Page 416 - Understanding Automotive Electronics

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FUTURE AUTOMOTIVE ELECTRONIC SYSTEMS 11

in the car and decoded. If there is a code match, a signal is sent to the door lock
actuator, which can be solenoids or motors.
The vehicle-to-roadside communication (VRC) system provides a means
of transmitting messages from a road information system (via radio). The latter
requires an infrastructure of low-power transmitters and receivers located
adjacent to highways at strategic locations, as well as a message-generating
system. The latter can be an internal preprogrammed fixed message (e.g.,
specific road closure) or it can be a digital data link to a computer-controlled
master controller capable of generating variable messages (e.g., warning of
congested traffic on a given route at a specific time). The infrastructure can also
be used to automatically interrogate passing vehicles via an on-board
transponder. The transponder is a special transceiver that receives coded
messages from a master controller requesting that certain data be transmitted
back to the master. Transponders are commonly used in aircraft to report
position and altitude to an air traffic control radar interrogator. In the VRC
system, data can be collected from moving vehicles. A form of VRC is in use
today for automatic toll collection as well as to read truck weights while the
truck is in motion.
The VRC concept includes a transponder on board the vehicle that has an
output for relaying messages to the driver. These messages are routed along the
data bus to either the HUD display or to an audio warning message system, or
both. Message complexity is limited by the system’s maximum data rate and by
the time interval in which the moving vehicle is within the limited range of the
roadside transmitter. The message is repetitively transmitted by the roadside
transmitter at intervals sufficient for all passing vehicles to receive the entire
message. In an experimental implementation developed by Delco, the data rate
is roughly 50 kbits/sec for a 5-second repetition period. Uses of the VRC
system can include roadsign-type information to warn drivers of hazardous
road conditions, speed limit changes (e.g., for work crews), services available,
weighing of commercial vehicles while in motion, and, as indicated above, toll
collections from vehicles traveling at highway speed without requiring stops at
toll collection booths.
The digital audio broadcast system (DBS) is a radio broadcast
entertainment system that has the potential to achieve CD-quality audio and
reliable data services over a broadcast radio channel. The nonaudio message
should have a capacity of the order of 10 kbits/sec. An experimental system has
been tested that operates with a carrier frequency of 1.5 GHz and uses a form
of phase-shift keying modulation.
The radio data system (RDS) utilizes an auxiliary channel (subcarrier) on
a commercial FM radio signal. A special receiver is required to obtain the data
from the auxiliary data channel. Uses of RDS include paging, traffic congestion
messages, and warnings of hazardous conditions (rock slides, icy bridges, etc.).
An interesting potential use for RDS is to relay corrections to GPS signals
appropriate for a local receiving area. These corrections provide greatly

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