JPL's Wireless Communication Reference Website

Chapter: Network Concepts and Standards
Section: DSRC


Vehicle-Roadside Communications Systems for Traffic Management

Design Requirements and Implementation Scenarios

Contributed by Christian Wietfeld  

In order to increase the efficiency and safety of the traffic, new concepts and technologies for a future Integrated Road Transport Environment (IRTE) are currently developed and implemented in various national and international Research & Development Programmes (e.g. Telematics Application Programme/Europe and ITS/North America). Both wide-range (e.g. based on RDS/TMC and GSM) as well as short-range vehicle-roadside communications are investigated with regard to their capability to support various RTTT services [10]. Many ITS- applications require an extremely high system reliability, especially those having an impact on safety (such as automatic cruise control) and those related to financial transactions (Automatic Fee Collection). Due to the influence of the constantly changing environment and the harsh real-time requirements, the development a reliable wireless communications subsystem is an important task in the design process for ITS systems.

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Figure 1:   Possible implementation scenarios for DSRC systems

Vehicle-roadside communication systems as part of the IRTE [2] are very well suited to support a decentralized system approach, where data is distributed and collected in a local environment. They are able to provide a reliable, mobile communication link between vehicles and a roadside infrastructure in free traffic flow using low-cost on-board equipment (OBE). Due to the short communication zones, the exact position of the vehicles can be determined. Typical RTTT services, which require communication between vehicles and the roadside together with accurate localisation information, are: Automatic Fee Collection (AFC), Traveller & Traffic Information, Dynamic Route Guidance (DRG), Fleet Management, Access Control and Parking Management. Figure 1 shows a possible implementation scenario with installations on motorways as well as in urban environments.

For the development of high-performance communication protocols and the optimal selection of system components a number of requirements and constraints resulting from different applications and system environments have to be taken into account: e.g. the amounts of data to be transmitted (data packets from 50 bits up to several hundred kbits) and the required reliability (for automatic fee collection a transaction error rate of 10^-6 is required) vary considerably for different applications. The system environment has a strong influence on the characteristics of the traffic flow (intensities, headway and speed distributions) as well as on the quality of the physical channel: an automatic fee collection system on a motor-way has to cope with high traffic intensities and sometimes extremely high speeds, whereas in an urban environment the vehicle speeds are relatively low, but multi-path fading effects due to reflections of buildings, traffic signs, parking vehicles etc. may lead to a considerable reduction of the channel quality.

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JPL's Wireless Communication Reference Website © Christian Wietfeld (author) and Jean-Paul M.G. Linnartz (Ed.), 1996.