# Wireless Communication Technologies for Safe Cooperative Cyber Physical Systems
## 3 Communication Technologies for SafeCOP Co-CPSs
### Vehicular Applications
The supported ad hoc mode reduces delay, as messages do not have to take the detour around the access point or base station. ETSI is responsible for developing the whole protocol stack including vehicle-centric road traffic safety applications, whereas applications orienting towards road traffic efficiency utilizing road infrastructure are under the responsibility of CEN. ETSI has standardized a profile of IEEE 802.11p adapted to the 30 MHz frequency spectrum at the 5.9 GHz band allocated in Europe that today comprises one control channel and two service channels. Non-safety related applications are directed to a 20 MHz band at 5.855-5.875 GHz. The dedicated frequency bands have been divided into 10 MHz frequency channels. Due to the proximity of these bands to the frequency band used for ETC in Europe (5.795-5.805 GHz), ETSI TC ITS must also develop mitigation techniques to avoid to interfere with the ETC systems. There is no cost associated with using this frequency band (it is license free). However, EN 302 571 standard specifies requirements on output power limits, spectrum masks, etc. A MAC protocol for a typical vehicular application has to be flexible enough to cope with high mobility and frequent topology changes. Therefore, the IEEE 802.11p MAC is based on a completely decentralized approach: the CSMA/CA random access MAC method used in IEEE 802.11 WLAN. The IEEE 802.11p MAC includes some enhanced features such as prioritized access to the channel by using queues with different arbitration interframe spaces (AIFS). This will ensure that data traffic with higher priority (e.g., video, IP telephony) has a higher probability of channel access compared to low priority traffic (e.g., background, best effort). However, the different QoS classes will not ensure timely channel access and thus, there will still be problems with collisions, especially during high utilization periods. Regarding the intra-vehicle WSAN-(Wireless Sensor Actuator Network), the IEEE 802.15.4 first published in 2003 targeting low-rate WPANs, is perhaps the most paradigmatic technology supporting WSANs today. The protocol defines the physical and data-link layers and to complement it, several proposals such as the ZigBee, RPL, or 6 loWPAN protocols were presented since its first release. More recently, to satisfy the requirements of emerging IoT applications, particularly in the industrial domain, the IEEE 802.15.4e amendment was proposed to complement the legacy IEEE 802.15.4-2011 standard. The IEEE 802.15.4e defines five MAC behaviors, instead of following a more conservative \"one-size-fits-all\" strategy. Hence, it improves its flexibility in accommodating different kinds of application requirements. In general, these new MAC behaviors are quite different from the ones considered in the legacy IEEE 802.15.4-2011. From the proposed MAC behaviors, the Deterministic Synchronous Multichannel Extension (DSME) is perhaps the closest to the legacy protocol, but nonetheless it brings significant enhancements to the IEEE 802.15.4 beacon-enabled mode by implementing multiple channel frequency hopping and Group Acknowledgments.