Technical analysis and engineering reference.
In 3GPP Release 14 and 16, Cellular V2X (C-V2X) focused predominantly on automotive vehicular safety (vehicle-to-vehicle collision warnings). With Release 17 and 18, the PC5 Sidelink air interface was fundamentally generalized into a universal device-to-device (D2D) protocol supporting pedestrian smartphones, smart wearables, industrial robotics, and drone swarms.
NR Sidelink operates on flexible numerologies inherited from 5G New Radio: - Subcarrier spacings from 15 kHz up to 120 kHz for millimeter-wave operation. - Physical Sidelink Control Channel (PSCCH) and Physical Sidelink Shared Channel (PSSCH) multiplexed in time and frequency. - Advanced Hybrid Automatic Repeat Request (HARQ) feedback over the Physical Sidelink Feedback Channel (PSFCH), enabling reliable groupcast and unicast communications.
Unlike cars with heavy alternators, smartphones cannot run continuous blind sensing receivers without draining batteries in an hour. Release 17 introduced Discontinuous Reception (DRX) and partial sensing for Sidelink, allowing handsets to sleep for 95% of each frame and waking only for pre-scheduled discovery windows.