smission of PSCCH. The latter frequency-first resource mapping must avoid resources that are designated to transmission 826 Chapter 7 of reference signals, starting with the first slot in the subframe. Resource elements in the last SC-FDMA symbol within a subframe are considered in the mapping process but are not used for transmission. The radio resources for direct communication can be selected by the device autonomously or will be scheduled by the network. In case the device has acquired SIB18 and has further a passive connection with the network in RRC_IDLE, the device would select radio resource from the broadcast resource pool in SIB18. Similar to direct discovery case, a UE would have to transit to the RRC_CONNECTED state when no valid (transmit) resource pool are provided by SIB18. In this case, a ProSe UE information indication is sent by the terminal to the network, indicating the intent to use the direct communication capability. In response, the network will assign a sidelink radio network temporary identifier (SL-RNTI) to the device. The network then uses the SL-RNTI and the downlink control channel to assign a transmission grant to the device with the new defined DCI format 5. The DCI for- mat 5 is used for scheduling of PSCCH and contains some SCI format 0 fields that are used for scheduling of PSSCH. The DCI format 5 information fields include 6-bit resource indi- cation for PSCCH; and 1-bit transmit power control command for PSCCH and PSSCH, as well as SCI format 0 fields including frequency hopping flag; RB assignment and hopping resource allocation; and time resource pattern [5]. Similarly, the DCI format 5A is used for scheduling of PSCCH, containing some SCI format 1 fields to schedule PSSCH. The DCI format 5A information fields include 3-bit carrier indicator; the lowest index of the sub- channel allocation to the initial transmission bits as well as SCI format 1 information fields including frequency resource location of initial transmission and retrans- mission; time gap between initial tra