ess are identical to the corresponding PSSCH/PSCCH/ PSDCH/PSBCH transmission. As shown in Fig. 7.26, for sidelink transmission modes 3 and 4 on PSSCH and PSCCH, the mapping uses symbols l = 2,5 for the first slot in the Synchronization subframe 1 ms 6 PRBs N subchannels PSCCH PSBCH First slot Second slot Figure 7.26 C-V2X frame structure and location of various physical channels and signals [3]. 830 Chapter 7 subframe and symbols l = 1, 4 for the second slot in the subframe. For sidelink transmission modes 3 and 4 on PSBCH, the mapping uses symbols l = 4, 6 for the first slot in the sub- frame and symbol l = 2 for the second slot in the subframe. For sidelink transmission modes 1 and 2, the pseudo-random sequence generator used for scrambling is initialized at the start of each slot where PSSCH = 0, whereas for sidelink transmission modes 3 and 4, the pseudo-random sequence generator is initialized at the start of each slot where PSSCH mod2 = 0. For sidelink transmission modes 3 and 4, the quantity nx is equal to the decimal representation of the CRC on PSCCH transmitted in the same subframe as PSSCH according to nx = --- with parameters p and L defined in [3]. 7.4.3.2 Synchronization Signals Time and frequency synchronization are important aspects of cellular communication for interference management and mitigation, which are further extended to V2X communica- tion. A V2X-enabled device first needs to determine if it is in coverage of the network. A device is defined to be in-coverage based on signal quality measurement using the RSRP measurement performed on the downlink synchronization signals. When the measured RSRP values are above a specific threshold, the device considers itself in coverage and uses the base station downlink synchronization signals for timing and frequency alignment. This threshold is defined as part of broadcast system information. If the received signal quality measurement falls below the threshold, the device would start transmission of sidelink syn- chronization signals (SLSS) and the 