**3.1.1 Cellular networks**

450 Wireless Communications and Networks – Recent Advances

The central component is a public authority or a road operator who manages the cooperative applications or services. An example of such component is a traffic management center which uses roadside units to inform the drivers about traffic status or accidents in a specific road network and suggests alternative routes. The central component can receive

Each one of the above components contains an ITS station which in turn comprises a number of ITS specific functions and a set of devices implementing these functions. From a communication's point of view an ITS station is based on the reference protocol stack depicted in Figure 3. This protocol stack follows the ISO/OSI reference model and consists of four horizontal layers and two vertical ones that flank the horizontal stack. Access, networking and transport, facilities and applications layers are the horizontal ones, whereas

The wireless technologies used for the continuous communication among different vehicles and between vehicles and the road infrastructure are the cornerstone of co-operative systems. These technologies concern the *networking & transport* and *access* layers of the reference protocol stack of an ITS station (Figure 3) and can be divided into two main

Therefore, for the connection among vehicles and the road infrastructure a mixture of general and vehicular specific technologies is needed. Some of these technologies are

This category comprises well known wireless communication technologies such as cellular networks, WiMAX, WiFi, infrared, bluetooth, DVB/DAB etc. which are not specifically developed for vehicular networks but play a significant role for future deployment of cooperative systems. Currently, in ITS the main focus is on cellular networks and WiMAX and

categories: general and vehicular specific communication technologies.

already in use, while some others are still under development.

information from vehicles or roadside units and in turn send information to them.

**2.4 Central component** 

**2.5 Reference protocol stack** 

management and security are the vertical ones.

Fig. 3. Reference protocol stack of an ITS station.

**3.1 General communication technologies** 

for this reason only those two will be analyzed below.

**3. Wireless technologies** 

Cellular networks are evolving rapidly to support the increasing demands of mobile networking. Although these networks are designed for voice data exchange they can be applied also to vehicular networks especially for information and entertainment applications. Nowadays, cellular networks migrate from GPRS, to UMTS, to LTE standards, increasing bandwidth and reducing delay times making these networks appropriate also for other kind of applications such as efficiency and trip planning.

Cellular networks have several characteristics suitable for co-operative systems like large scale usage and long range communication. However, some drawbacks of cellular networks which are relevant to vehicular connectivity are summarized below:


However, despite all the above disadvantages, cellular networks can be used for ITS applications which require moderate delay, long range communication, and low data rate. With the migration from 3G towards 4G (such as LTE) the focus remains on technologies that can serve a circular area with Internet connectivity, with no special provision for following the road infrastructure and optimising for connected car services.
