**6. Conclusion**

An overview of co-operative systems and their importance in future transportation systems has been presented in this chapter. The chapter started with a short introduction about the historical background and the purpose of co-operative systems. Emphasis was given to the communication architecture, including its components, which is mainly the outcome of the efforts carried out so far in Europe. Also the importance of the definition of a common architecture for further deployment of co-operative systems was stressed.

In the following, the focus was on the wireless technologies used within the co-operative systems framework which are divided into two categories: general and vehicular specific communication technologies. These technologies are the cornerstone of co-operative systems and their objective is the continuous communication among different road users (vehicles, motorbikes, trucks, roadside units, infrastructure etc.). To achieve this continuous and seamless communication a mixture of general and vehicular specific technologies is needed. Some of these technologies are already in use, while some others are still under development.

Additionally, some co-operative applications were described which are categorized into three main groups: safety, efficiency and infotainment. The applications addressing safety and efficiency are of great importance today because the minimization of accidents and their consequences as well as the reduction of CO2 emissions are the primary targets worldwide. Finally, emphasis was given on hot research topics concerning co-operative systems such as data fusion, routing, security and privacy. A general description highlighting each of these topics, the research challenges as well as some solutions were indicated.

Although many problems are not yet solved, the general feeling is that vehicles could benefit from evolving wireless communications in the near future, making "talking vehicles" a reality. Co-operative systems will not only provide lifesaving and environmental friendly applications, but they will become a powerful communication tool for their users.
