-90.4 dBm and a maximum input level of - 22 dBm [17]. Vehicle-to-Everything (V2X) Communications Adjacent PSCCH+PSSCH Non-adjacent scheme PSCCH+PSSCH scheme Subchannel in RBs SCI or TB (PSCCH or PSSCH) TB Only (PSSCH) TB Transmission SCI Transmission SCI Only (PSCCH) Subframe 1 ms Figure 7.17 C-V2X frame structure and resource allocation schemes 17]. Vehicles communicate using sidelink or V2V communications in mode 4 and autonomously select their radio resources, independent of cellular coverage. When the vehicles are under cellular coverage, the network decides how to configure the V2X channel and informs the vehicles through the sidelink V2X configurable parameters. The message includes the car- rier frequency of the V2X channel, the V2X resource pool, synchronization references, the subchannelization scheme, the number of subchannels per subframe, and the number of RBs per subchannel. When the vehicles are not within the cellular coverage, they utilize a preconfigured set of parameters to replace the sidelink V2X configurable parameters. However, the standard does not specify a specific value for each parameter. The V2X resource pool indicates which subframes of a channel are utilized for V2X. The rest of the subframes can be utilized by other services. The standard includes the option to divide the V2X resource pool based on geographical areas. In this case, vehicles in an area can only utilize the pool of resources that have been assigned to those areas (see Table 7.3). Sidelink transmissions use the same basic transmission scheme as the uplink; however, side- link is limited to single-cluster transmission for all sidelink physical channels. Furthermore, sidelink uses one symbol gap at the end of each sidelink subframe. For V2X sidelink com- munication, PSCCH and PSSCH are transmitted in the same subframe (see Fig. 7.18). The Chapter 7 Table 7.3: Characteristics of LTE V2X transmission schemes [20]. Transmission Characteristics Uu Interface PC5 Interface Operating frequency All bands specified in 3GPP TS 36.