C-ITS systems and services are being deployed mainly on motorways, roads and urban roads and they are designated especially for car drivers, passengers, public transport drivers, emergency vehicles crew, road maintenance workers, road network operators etc.
Currently, the so-called hybrid communication is used for communication between vehicles themselves and between vehicles and equipment on road infrastructure. This communication is based on ITS-G5 technology (“WiFi for vehicles”) and already existing LTE (high-speed data transmission within mobile networks). The 5.9 GHz frequency band is designated for the ITS-G5 technology (DSRC, Dedicated Short Range Communication).
The use of specific technology to a specific section of the transport network may depend on results of cost-effectiveness analysis. In this context, both technologies might complement each other, not be in competition in the sense either just ITS-G5 or LTE will be deployed.
The great emphasis is put on protection of current and future applications against interfering signals (such as jamming or spoofing). Telecommunication operators supporting C-ITS services will also adequately manage network load for C-ITS services with regard to key aspects: road safety and personal data protection.
There are basically three types of C-ITS units. The one situated in vehicle is called OBU
(On-Board Unit). It ensures the communication with units deployed on infrastructure or with other OBU units in range via ITS-G5 or it can also communicate directly with C-ITS back office via data network of mobile operators. OBU can be connected to vehicle systems, thus it can collect the relevant data and distribute it to C-ITS elements which are on higher level in whole system. It can also be used (in combination with suitable SW tool) for interpretation of received C-ITS messages.
In the first stage of C-Roads project, the aftermarket solution was assumed, that means there were additionally installed units in vehicles. These units could also be connected to CAN/OBD-II bus as well as to device with display, appropriate operating system and SW equipment in order to interpret C-ITS messages. However, it is expected that vehicles will be equipped with OBU units by car manufacturers in the future (i.e. embedded solution), which has already been the case since the beginning of 2020 (the latest VW Golf for example).
A mobile application is also ready. This application will display some specific C-ITS messages directly in driver’s cell phone transmitted via LTE network without the need to possess the OBU unit.
Road Side Unit
A stationary communication unit deployed on road infrastructure (e.g. street lighting or traffic sign) is called RSU
(Road Side Unit). This unit allows two-way communication with other C-ITS units in range (both OBU and RSU) as well as with C-ITS back office. Some data is immediately pre-processed in the unit before distribution to C-ITS back office. Data transmission between RSU and C-ITS back office is ensured by mobile networks.
Road Vehicle Unit
The unit located in a maintenance vehicle or a mobile trailer of road infrastructure operator is called RVU
(Road Vehicle Unit). This unit also allows two-way communication with other C-ITS units in range via ITS-G5 as well as with C-ITS back office via mobile networks.
This type of unit is a kind of hybrid between OBU and RSU units, as it ensures the communication with the equipment on infrastructure or other RVU as OBU unit, but it can also become the infrastructure equipment and partially fulfill the function of RSU. For instance, mobile trailer with RVU could also provide the drivers with the information related to road works warning.
C-ITS back office
Back office is the central element of the whole C-ITS system
. Most important data is gathered in back office and further distributed to elements on lower levels (RSU, RVU, OBU, mobile applications) or to traffic information centres (e.g. National Traffic Information Centre). There is a two-way communication between C-ITS back office and all other elements within C-ITS system. In addition to cooperative functions, C-ITS back office provides the basis for visualizations, maps, management, archiving etc.
Integration platform within C-Roads Czech Republic
Central systems enable reception, processing, generation and distribution of C-ITS messages. In addition to the C-TS back office, central systems also include National Traffic Information Centre or the Integration platform. The main objective of the Integration platform within C-Roads Czech Republic is to integrate individual C-ITS back offices in order to ensure fast and reliable data exchange between these back offices as well as National Traffic Information Centre.
The list of C-ITS services is provided in the C-Roads section. All of them are Day 1 and Day 1.5 categories. The additional C-ITS services which belong to Day 2 and Day 3+ categories are subject to research and development.
Message types and communication protocols
The specific types of messages (so-called communication protocols) are used for various C-ITS services. Some information within individual services can be transmitted by different types of messages. Below, there is the list of several standardized message formats:
- CAM (Cooperative Awareness Message) – for transmission of basic information related to vehicle position, speed, direction etc.
- DENM (Decentralized Environmental Notification Message) – for transmission of information about occurred situations (traffic accident, traffic jam, road works etc.)
- IVI (In-Vehicle Information) – for transmission of information about traffic signs and symbols directly to vehicle
- SPaT (Signal Phase and Time) – for transmission of information about traffic light signal plans
- MAP (Map Data) – for transmission of information about topology and geometry of various locations (e.g. intersection)
C-ITS messages within C-Roads project are guaranteed to be secured and not spoofed nor modified. Each C-ITS unit belonging to C-Roads project is connected to the system that delivers a set of certificates to that unit at regular intervals. These certificates are then used for digital signature of all C-ITS messages. The unit which receives the message is able to verify whether the message is signed by valid certificate and whether it comes from a unit belonging to the system.