Embodiments are presented herein of apparatuses, systems, and methods for a vehicle-to-everything (V2X) capable wireless device configured to perform sidelink cellular communications. The wireless device performs sidelink communications using a two-stage sidelink control information (SCI) protocol including Stage 1 SCI messaging carried on a physical sidelink control channel (PSCCH), and Stage 2 SCI messaging carried on a physical sidelink shared channel (PSSCH). The SCI messaging may be encoded using polar codes. Channel interleaving is utilized on the SCI to interleave the SCI between two or more layers of a MIMO transmission system. Scrambling for Stage 2 SCI messaging is performed based on the result of a cyclic redundancy check (CRC) performed on Stage 1 SCI messaging. Collisions between sidelink HARQ feedback to be transmitted to a base station and other transmissions are avoided based on a priority analysis of the sidelink HARQ feedback.