layer (ProSe protocol). The IP layer is not used for transmitting the discovery message. The MAC layer determines the radio resource to be used for announcing the reception of the discovery message from upper layer and further generating the MAC PDU carrying the discovery message and sending the MAC PDU with no MAC header to the physical layer for transmission in the predetermined radio resources [7]. The content of discovery message is transparent to the access stratum, over which no distinction is made for sidelink discovery models and types; however, higher layer protocols detect whether the sidelink discovery notification is related to public safety. A UE can participate in announcing and monitoring of discovery message in both RRC_IDLE and RRC_CONNECTED states following eNB configuration, where the UE announces and monitors its discovery message subject to the half-duplex constraint. In order to perform synchronization, the UE(s) participating in announcing of discovery messages may act as a synchronization source by transmitting SBCCH and a synchronization signal based on the resource information allocated for synchronization signals provided in SIB19. There are three range classes. The upper layer authorization provides applicable range class of the UE. The maximum allowed transmission power for each range class is signaled in SIB19. The UE uses the applicable maximum allowed transmission power corresponding to its authorized range class. This sets an upper limit on the configured transmit power based on open-loop power control parameters. 7.4 Physical Layer Aspects V2X communications enable information exchange between vehicles and between vehicles and the infrastructures and/or pedestrians. The information exchange will provide the Public safety ProSe carrier is the carrier frequency used for public safety sidelink communication and public safety sidelink discovery. 812 Chapter 7 vehicles with more accurate knowledge of their surroundings, resulting in improved traffic safety. Some efforts were made in r