, some fundamental modifications to PC5 have been made, including additional reference symbols to support high Doppler frequencies associ- ated with relative speeds of up to 500 km/h and high frequency bands (e.g., 5.9 GHz ITS band being the main target) [1,24]. In order to support distributed scheduling, a sensing mechanism with semi-persistent trans- mission has been introduced. The C-V2V traffic from a device is mostly periodic in nature. This was utilized to sense congestion on a resource and estimate future congestion on that resource. Based on this estimation, the resources are reserved in advance. This technique optimizes the use of the channel by enhancing resource separation between transmitters that are using overlapping resources. The design is scalable for different bandwidths. There are 798 Chapter 7 GNSS Timing GNSS Timing Interface Interface Interface Interface Interface Interface Scenario1: Dedicated carrier and Scenario 2: Dedicated carrier and distributed scheduling V2V centralized scheduling V2I and V2V communications communications Figure 7.3 LTE V2X use cases and scheduling options [1]. two high-level deployment scenarios that are currently defined, as illustrated in Fig. 7.3. Both scenarios use a dedicated carrier for V2V communications, meaning that the target band is only used for PC5-based V2V communications. In both use cases, global navigation satellite system (GNSS) is used for time synchronization. In the first scenario, the schedul- ing and interference management of V2V traffic is supported based on distributed algo- rithms (referred to as mode 4) implemented between the vehicles. As we mentioned earlier, the distributed algorithm is based on sensing with semi-persistent transmission. Furthermore, a new mechanism where resource allocation is dependent on geographical information is introduced. Such a mechanism counters near-far effect arising due to in-band emissions. In the second scenario, the scheduling and interference management of V2V traf- fic is assisted by eNBs (referred to