COMMUNICATIONS SYSTEMS USED FOR ITS Index Purpose Description Technologies 1 of 5
Purpose The telecommunication system is the main element for the development of telematics in Transport field. It enables on one hand the link between all the components of the architecture and on the other hand it represents the basic support for the operating instrument such as: data exchange, territorial information system, traffic data collection, automatic localisation systems. Description When we speak about telecommunication network, we consider a chain of nodes linked among them and communicating with the system user; three different types of means of communication can be used: copper cables, optic fibre and ether (radio link and satellite link). In relation to the geographical coverage we have: Personal Area Network (PAN): fit for the communication on short distances (few meters); Local Area networks (LAN) or (Wireless LAN): one settlement coverage (few kilo-meters); Metropolitan Area networks (MAN) networks covering an urban areas (few kilo-metres) Wide Area Networks (WAN) very extensive networks able to reach different places in the world. Figure 1 Communication Networks 2 of 5
According to the intrinsic features of the Transport (e.g. speed, environmental contest, etc.) and or specific restrains (e.g. safety and security for Emergency vehicle) different kind of technologies can be used. By way of example bi-directional data or information transmission can be supported by cellular network, satellite systems and mobile-radio (differentiated between : PAMR, Public Access Mobile Radio, and PMR, Private Mobile Radio). In respect to the passenger transport or to safety and security issues it could be important to use radio broadcasting communication technologies e.g. Radio Data Systems (RDS), Digital Audio Broadcasting (DAB) or Digital Video Broadcasting (DVB). Last but not least Dedicated Short range Communication (DSRC) has been exploited as a road side system of data collection from passing vehicle, micro-waves or Bluetooth technologies instead has been used as base principle for detection sensors. Dedicated Short Range Communication System (DSRC): this kind of system uses short range data communication (typically at 5.8GHz) between the road infrastructure and an OBU (onboard unit) installed in authorized vehicles. The technology is non invasive for the user, in the sense that the OBUs are usually small, easy to install and highly reliable with regard to the percentage of errors in the transmission of data. The equipment is often supplied free of charge by the system manager, although sometimes a deposit is requested or a monthly fee. If a tariff is foreseen (for example when the vehicle travels within a charging zone), this may be made on board or off board. In the former case, payment can be by smart card (a prepaid card is inserted in the OBU and can be recharged when the credit falls below a given level). In the latter case, the amount is debited from the user s current account or credit card. The approach does however involve high costs for the equipment on the road infrastructure as it is necessary to set up tolling stations. Increasing automation has made considerable improvements possible by moving from Single Lane systems to Multi Lane Free Flow. Examples of Multi Lane Free Flow DSRC with an open architecture are the road charging system on Austrian motorways, in Australia, Canada and Chile. 3 of 5
Technologies Different from the previous technologies, enabling the communication of a specific vehicle, the technologies presented in this section are referred to a collective way of information transmission. RDS-TMC (Radio Data System Traffic Message Channel) a traffic information dedicated radio channel (RDS), has been used to transmit coded messages (TMC), which are recognized and encoded by on board receivers and communicated to the driver in a visual or vocal form. The standard format for the message id DATEX; DAB (Digital Audio Broadcasting) and DVB (Digital Video Broadcasting): are two digital radiodiffusion systems (TMC) able to completely replace the analogical ones. TETRA: The Terrestrial Trunked Radio (or Trans-European Trunked Radio) is a communication technology based on mobile radio used for professional aim e.g. it is developed for emergency services as police forces, ambulance, etc. The system is based on a Time Division Multiple Access (TDMA): that is the communication can be transferred on four user channels for each dedicated carrier (with a spacing between carriers equal to 25kHz). This means that it is possible both a point-to point communication than a point-to-multipoint one. The system is composed by Mobile Stations (MS) and a Switching and Management Infrastructure (SwMI) made of TETRA Base Stations. Mobile station can communicate directly in Direct Mode Operation or these can use a trunked-mode operation (TMO) using the SwMI (in this case communication is managed by the Base stations). The DMO is often used for communication between two Mobile station, but sometimes, when the network coverage is not sufficient it is possible to use a sequence of direct communication between TETRA terminals used as a relay. In this case we speak about DMO gateway (DMO to TMO) or DMO repeater functionality (DMO to DMO).This functionality is called DMO gateway (from DMO to TMO) or DMO repeater (from DMO to DMO). According to the necessity, the system can provide different services: group calling mode or a one-to-one communication (walkie-talkie without a normal range limitation); in addiction the system can act as a cell phones with direct connection to the other TETRA users or to the Public Switching Telephone Network. In the specific case of emergency communication, Terminals are provided with an emergency button which let the communication override activity taking place at the same time. 4 of 5
GPRS is a cellular phone technology. It represents extension of the GSM (Global System for Mobile Communication) technology and in respect to the latter it is defined as General Packet Radio Service (GPRS) since it enables data transferring by internet network in packet switched cellular mode, using the same TDMA (Time Division Multiple Access) channels that are used for the GSM technology (but in circuit switching mode). The new services that this technology make possible are: Point-to Point internet network connection (IP protocol), Point-to-Multipoint connection (e.g. group call) and Multimedia Messaging Service (MMS). In addition, GPRS technology make possible the selling of service as a part of a bundle as well as pay-as-you-use (the only one possibility with previous generation mobile technologies). 5 of 5