The growth of road traffic and the increasing inconvenience and environmental damage
caused by road congestion require better use of the infrastructure for physical transport.
Over the last few years it has become clear that Advanced Traffic and Transportation
Management and Information Systems (ATM/IS), Commercial Vehicle Operations
(CVO) and Automated Vehicle Control Systems (AVCS) will require a
communications infrastructure for vehicles communicating with roadside base stations
and vice versa and with other (nearby) vehicles. This will require extensive use of
mobile radio communication, in addition to the present desire to extend conventional
services, such as cellular telephony and wireless data services, to mobile subscribers. Efficient use of the available radio spectrum and effective management of
the tele-traffic appears essential.
Applications and Services
Electronic Toll Collection
Traffic Information Datacasting
In Europe, the Radio Data System (RDS) uses
digital
data signals which are inaudibly inserted into the FM-program on the same subcarrier
frequency
as ARI, but now pan-European, and the Radio Data System-Traffic Message Channel (RDS-
TMC), that will use RDS capacity for transmitting digitally coded traffic messages to vehicles,
requiring a dedicated TMC receiver to language-independently decode the messages.
Furthermore, in Britain CARFAX is being used, while in German speaking countries from
around 1974 we find the Autofahrer Rundfunk Information (ARI), that alerts drivers for an
upcoming traffic information broadcast, and ARI aufgrund Aktueller Messdaten (ARIAM),
which
uses automatic incident detection devices to reduce the elapsed time between observing and
reporting traffic disturbances.
In the USA, Highway Advisory Radio (HAR) is operational,
which is a special short-ranged radio that spatially localizes traffic information messages,
using
dedicated amplitude modulation (AM) transmitters located at the roadside, and
Advanced Highway Advisory Radio (AHAR), which is a more advanced version of HAR,
which provides an automatic interrupt when an advisory message is available.
Future Systems
The European road authorities collaborate within the European Conference
of the Ministers of Transport (ECMT), in the Sub Working
Group on Road Vehicle Communication.
This group cooperates with
broadcasters and manufacturers to
coordinate the development of systems for traffic information distribution, such as RDS-TMC.
The ECMT Sub Working Group
works on standardizing European communication protocols
for the message distribution or exchange, and the coding
of location references.
One objective of the road authorities is to
optimize of the use of existing road networks and to
mitigate congestion.
Interestingly, a system-optimum use of the road infrastructure,
as desired by the road authority, may differ from
advising the shortest and fastest route for each individual motorist.
The "ALERT C" protocol uses messages standardized as
an extension of the EBU "Catalogue of Events". It was developed
under the DRIVE I programme. It provides among other things,
- Information on typical road traffic event and status messages,
- parking
information, and
- route planning data.
A traffic advisory system involves
- Collection of traffic data, e.g. from probe vehicles.
- Data fusion and processing
- Traffic Information datacasting, e.g., through the FM Radio Data System (RDS-TMC),
DAB-TMC, GSM packet data services,
and Highway Advisory Radio (HAR). HAR uses low-power AM or FM radio transmitters.
- In-vehicle data processing by navigation systems
Migration to a Dedicated Communication Architecture
The network architecture and transmission standard for Intelligent Vehicle Highway
Systems are topic of current discussions. One approach is to use existing
technologies, preferably even existing communication services. Some other approaches
aim at a dedicated infrastructure for IVHS, with its own frequency allocation. As an
IVHS application for a spectrum allocation will compete with similar requests from
many other new services, it is unlikely that a new band can be allocated to IVHS
without a detailed plan for the services and applications to be supported, an architecture
for the network and estimates of the teletraffic loads.
Whether the lower-layer
communication services are best provided by a single, uniform
radio access technique, suitable for any propagation environment and for any set of
services, or, alternatively through multiple radio networks, each developed to offer only
a selected set of data transport services is not a problem unique to IVHS. It is unclear
whether multiplexing different categories of teletraffic onto the same spectrum resources
leads to a substantial trunking gain in wireless networks. This is in contrast to the
situation in cable or fiber-optic backbone (ISDN) links, where installation and
maintenance cost is the essential motivation for integration. Nonetheless, there is clear
need for wireless systems that can offer integrated services, even though hybrid, non-
uniform radio access techniques might be used. Nonetheless, a dedicated IVHS
communication infrastructure has several advantages over a hybrid communication
architecture using existing systems.
- Spectrum conservation
Piggybacking IVHS on existing wireless communication
services does not imply that IVHS communication does not consume spectrum; it only
does not require a new allocation for the new service. Initial (experimental) IVHS
services may very well be offered through RDS FM subcarrier transmission or through
modems attached to circuit-switched cellular telephone links, but these solutions appear
not very spectrum efficient. FM subcarrier transmission reduces the coverage of the
audio entertainment program to an extent which is significantly more costly, in terms of
MHz.km.sec. than 30 kHz of dedicated IVHS bandwidth.
- ElectroMagnetic Compatibility (EMC).
European car manufacturers have
complained that GSM cellular phones interfere with some Anti-Lock Brakes (ABS)
systems. Airlines attempt to make their passengers aware of the EMC problems in
aviation equipment caused by walkman radio receivers, notebook computers and
cellular phones. Similar problems are likely to occur when more advanced, more
complicated vehicle electronics systems are subjected to radio transmissions in many
different bands.
- Manufacturing costs may become excessive if IVHS requires communication
through a hybrid architecture involving multiple communication receivers and
transmitters. Cartoons of cars with twenty antennas and sensors already appeared years
ago.
- Flexibility of design is a fourth reason to adopt a common radio interface for
IVHS services.
- Safety requirements in more advanced IVHS applications provide the fifth
argument. Current research and development programs experiment with Automatic
Vehicle Control Systems (AVCS). Communication appears to be crucial to the safety of
these systems. This implies the need for active enforcement of interference protection.
Further Reading
Printable Documents
- J. Walker (Ed.), "Mobile Information systems", Artech House, London, 1990.
- M.P. Ristenblatt, "Communication architectures for the Intelligent Vehicle Highway
Systems are available", IEEE Veh. Soc. Newsletter, Vol. 39, No. 1, Feb. 1992, pp. 8-
19.
- A. Polydoros et al., "Vehicle-to-roadside communication study", USC, Los Angeles,
1992.
- More
In the USA, Highway Advisory Radio (HAR) is operational,
which is a special short-ranged radio that spatially localizes traffic information messages,
using
dedicated amplitude modulation (AM) transmitters located at the roadside, and
Advanced Highway Advisory Radio (AHAR), which is a more advanced version of HAR,
which provides an automatic interrupt when an advisory message is available.
Literature