an associated reception resource pool in order to enable bidirectional communication. However, within a cell, there may be more reception resource pools than transmission resource pools, allowing reception from the UEs in the neighboring cells or from the UEs that are out-of-coverage. Fig. 7.23 illustrates the LTE V2X resource pool structure. A sidelink direct communication resource pool is configured semi-statically using layer-3 signaling. The physical resources (subframes and RBs) associated with the pool are parti- tioned into a sequence of repeating hyper frames known as PSCCH periods or alternatively referred to as the scheduling assignment period or sidelink control period. Within a PSCCH period, there are separate subframe pools and RB pools for control (PSCCH) and data (PSSCH). The PSCCH subframes always precede those for PSSCH transmission. This is analogous to the symbol layout of the physical downlink control channel and physical downlink shared channel OFDM symbols within a single downlink subframe, where the control region precedes the data subchannel. The PSCCH carries SCI messages, which describe the dynamic transmission properties of the PSSCH that follows. The receiving UE Vehicle-to-Everything (V2X) Communications 823 Time division resource multiplexing between scheduling and data to frequency division resource multiplexing Rel-12 D2D Resource pool structure Rel-14 LTE V2V Resource pool structure Scheduling assignment pool subchannel Scheduling/data Data pool subchannel Minimum periodicity 40 ms Non-adjacent Adjacent scheduling/ PSCCH PSSCH (Different colors indicate scheduling and data belonging to different UEs) scheduling/data data allocation Resource pool Resource pool allocation Figure 7.23 LTE V2X resource pool structure [13,14]. searches all configured PSCCH resource pools for SCI transmissions of interest. A UE can be a member of more than one sidelink communications group. For PSSCH, the number of current slot in the subframe pool nPSSCH = 2n PSSCH where ie {0,1} is the number of curre