Description
The Physical Reader-to-Device Channel (PRDCH) is a downlink physical channel defined in the 5G New Radio (NR) sidelink (SL) interface, standardized from 3GPP Release 19 onwards. It is a key component of the NR sidelink communication framework, which supports direct device-to-device (D2D) connectivity. The PRDCH is specifically used by a device acting as a 'reader' or initiating side to transmit data and control information to a target 'device' within a sidelink communication session. This channel operates on the PC5 interface, the reference point for direct communication between user equipments (UEs), and is designed to work in both in-coverage and out-of-coverage scenarios, with or without network scheduling assistance.
In terms of physical layer structure, the PRDCH is mapped to specific physical resources within the NR sidelink resource grid. It utilizes the NR flexible numerology, supporting various subcarrier spacings and cyclic prefix lengths to adapt to different frequency bands (including FR1 and FR2) and service requirements (e.g., high reliability, low latency). The channel carries a transport block which includes user data for sidelink communication. Its transmission involves typical NR physical layer procedures: channel coding (likely using LDPC codes for data), modulation (QPSK, 16QAM, 64QAM, 256QAM), layer mapping, and precoding. The resources for PRDCH can be autonomously selected by the transmitting UE (Mode 2) or scheduled via sidelink control information (SCI) received from the network or another UE.
The role of PRDCH is central to enabling efficient sidelink services such as public safety communications, vehicle-to-everything (V2X) messaging, and commercial proximity services. It works in conjunction with other sidelink channels: the Physical Sidelink Control Channel (PSCCH) carries the associated SCI that schedules and describes the PRDCH transmission (e.g., resource allocation, modulation and coding scheme), and the Physical Sidelink Feedback Channel (PSFCH) may carry hybrid automatic repeat request (HARQ) feedback. The PRDCH supports advanced features integral to NR, including beamforming and MIMO for enhanced coverage and capacity in higher frequencies, and is designed to meet stringent requirements for ultra-reliable low-latency communication (URLLC) and enhanced mobile broadband (eMBB) over sidelink. Its design ensures spectral efficiency and reliable direct communication, forming a foundational data pipe for NR D2D.
Purpose & Motivation
The PRDCH was created to fulfill the need for a high-performance, native NR physical data channel for sidelink communication, as previous D2D standards in LTE (based on the PSSCH) were not optimized for the full capabilities of 5G. The motivation stems from expanding use cases for direct device communication beyond traditional public safety, including advanced V2X applications (like cooperative sensing and autonomous driving), industrial IoT, and immersive extended reality (XR) experiences that require high data rates, very low latency, and high reliability between devices.
It addresses limitations of the LTE sidelink, which was primarily designed for lower data rates and less dynamic resource allocation. The NR sidelink, with channels like PRDCH, leverages the full 5G NR physical layer advancements such as flexible numerology, advanced channel coding, and beam-based operation to support a wider range of spectrum (including mmWave), improve spectral efficiency, and reduce latency. The creation of a dedicated 'reader-to-device' channel nomenclature also helps clarify the directional nature of communication in more complex sidelink scenarios involving discovery, groupcast, and unicast, providing a standardized and efficient mechanism for data transfer in the evolving landscape of proximity-based services.
Key Features
- NR-based physical data channel for sidelink (PC5) communication
- Supports flexible numerology for diverse band and service needs
- Utilizes advanced NR techniques like LDPC coding and MIMO/beamforming
- Can operate in network-scheduled (Mode 1) or autonomous (Mode 2) resource allocation
- Designed for high reliability and low latency required by V2X and URLLC
- Works in conjunction with PSCCH for control and PSFCH for feedback
Evolution Across Releases
Introduced as a new physical channel within the NR sidelink architecture. Defined its basic structure, resource mapping, and association with sidelink control information. Established it as the primary physical channel for carrying user data from a transmitting (reader) UE to a receiving UE in NR-based device-to-device and V2X communications.
Defining Specifications
| Specification | Title |
|---|---|
| TS 38.191 | 3GPP TR 38.191 |
| TS 38.291 | 3GPP TR 38.291 |
| TS 38.300 | 3GPP TR 38.300 |
| TS 38.391 | 3GPP TR 38.391 |
| TS 38.769 | 3GPP TR 38.769 |