Description
The Sidelink Shared Channel (SL-SCH) is a transport channel in the 3GPP LTE and NR protocol stacks dedicated to carrying user data and some control information for direct device-to-device communication, known as sidelink. It operates over the PC5 interface. Functionally analogous to the Downlink Shared Channel (DL-SCH) and Uplink Shared Channel (UL-SCH) used for network-to-device links, the SL-SCH is the workhorse for sidelink data transmission. In the transmitter's protocol stack, data from higher layers (e.g., IP packets for V2X messages) is processed by the Packet Data Convergence Protocol (PDCP), Radio Link Control (RLC), and Medium Access Control (MAC) layers. The MAC layer delivers transport blocks to the physical layer, which maps them onto the SL-SCH. The physical layer then applies channel coding (e.g., Turbo codes in LTE, LDPC in NR), modulation, and maps the coded bits to resource elements within the sidelink resource pool in the time-frequency grid. A key component associated with the SL-SCH is the Sidelink Control Information (SCI), transmitted on the PSCCH (Physical Sidelink Control Channel). The SCI carries the necessary demodulation and decoding information for the corresponding SL-SCH transmission, such as the resource allocation, modulation and coding scheme (MCS), and group destination ID. At the receiver, the process is reversed: the UE decodes the SCI first, then uses the information to locate, demodulate, and decode the SL-SCH transport block. The SL-SCH supports both broadcast and groupcast transmission modes and is designed for dynamic and efficient shared resource usage among multiple UEs in proximity.
Purpose & Motivation
The SL-SCH was created to provide a standardized, efficient, and scalable transport mechanism for user data in direct device-to-device communication, which was a foundational new capability introduced in 3GPP starting with LTE Release 12 for Proximity Services (ProSe). Prior to its introduction, device-to-device communication in cellular networks was non-standardized or relied on short-range technologies like Bluetooth or Wi-Fi Direct, which lacked the wide-area synchronization, quality of service, and seamless integration with cellular networks that 3GPP aimed to provide. The SL-SCH solves the problem of how to efficiently multiplex data from many potential transmitting UEs onto a shared radio resource pool in a controlled manner. It enabled critical use cases like public safety communication when cellular networks are unavailable (e.g., during disasters) and vehicle-to-everything (V2X) communication for automotive safety. Its evolution through subsequent releases has been driven by the need for higher reliability, lower latency, higher data rates, and more sophisticated resource allocation modes (mode 1 network-scheduled and mode 2 autonomous) to support increasingly demanding applications like autonomous driving and advanced industrial IoT.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (26 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-12, normative work from Rel-15.
In Release 15, specific technical corrections and additions were made for V2X sidelink communication, including a correction on the MCS (Modulation and Coding Scheme) for the SL-SCH and the addition of the number of SL (Sidelink) processes for V2X. These changes, detailed in the relevant Technical Specifications, refined the operation of the SL-SCH transport channel, which is mapped to the PSSCH physical channel.
- Clarification on CRC attachment for DL-SCH and PCH transport channels in NB-IoT TS 36.212CR0285
- Correction on V2X sidelink communication in TS 36.300 TS 36.300CR1199
- Correction on MCS for V2X sidelink communication in TS 36.302 TS 36.302CR1196
- Introduction of DL channel quality reporting TS 36.300CR1245
- Addition of the number of SL processes for V2X sidelink communication TS 36.306CR1569
- Introduction of DL Channel Quality reporting TS 36.306CR1611
In Release 16, the SL-SCH (Sidelink Shared Channel) was newly specified for 5G V2X sidelink within the NR framework, introducing it as a defined transport channel mapped to the PSSCH physical channel. The technical specification established that the SL-SCH, like the SL-DCH, uses tail biting convolutional coding with a 1/3 coding rate, formalizing its channel coding and rate-matching procedures.
- Introduction of 5G V2X with NR Sidelink TS 36.300CR1271
- Introduction of 5G V2X sidelink features into TS 38.212 TS 38.212CR0025
- Correction for NR sidelink communication TS 36.300CR1287
- Clarification on LTE DAPS and sidelink on 36.300 TS 36.300CR1338
- Corrections on 5G V2X sidelink features after RAN1#100-e TS 38.212CR0036
- Corrections on 5G V2X sidelink features after RAN1#100bis-e and RAN1#101-e TS 38.212CR0040
+ 4 more changes
In Release 17, the SL-SCH (Sidelink Shared Channel) saw the introduction of NR sidelink enhancement, which included new procedures for channel access type indication in both fallback and non-fallback DCI formats. These enhancements also required corrections for intra-UE multiplexing and semi-static channel occupancy to ensure proper operation.
- Introduction of NR sidelink enhancement TS 38.212CR0094
- Corrections on NR sidelink enhancement in 38.212 TS 38.212CR0100
- CR on ChannelAccess-Cpext in Fallback DCI TS 38.212CR0118
- Correction on NR sidelink enhancement TS 38.212CR0122
- CR on channel access type indication in non-fallback DCI TS 38.212CR0125
- Corrections on intra-UE multiplexing and semi-static channel occupancy TS 38.212CR0136
In Release 18, the primary new development for the SL-SCH was the introduction of NR sidelink evolution, which encompasses enhancements to the sidelink shared channel's functionality and performance. This evolution required subsequent corrections to the technical specifications, particularly within the channel coding and multiplexing procedures detailed in TS 38.212. The foundational technical mapping for SL-SCH to the PSSCH physical channel and its use of turbo coding at a 1/3 rate, as shown in the grounding context, remained the basis for these new evolutionary features.
In Release 19, the specific new changes for the SL-SCH function are not detailed in the provided grounding context, which only contains established technical specifications from earlier releases. The accompanying Change Request title indicates work was done on "Corrections on R19 NES adaptation of common channel/signals," suggesting Release 19 included corrective updates, but the provided text does not specify the new technical content for SL-SCH itself.
- Corrections on R19 NES adaptation of common channel/signals TS 38.212CR0243
Explore further
Broader topics and technologies where SL-SCH plays a role.
Defining Specifications
3GPP specifications that define or reference SL-SCH, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 36.212 vj10 | LTE Multiplexing and Channel Coding | Rel-19 |
| TS 36.300 vj00 | E-UTRAN Radio Interface Protocol Architecture Overview | Rel-19 |
| TS 36.302 vj00 | E-UTRA Physical Layer Services | Rel-19 |
| TS 36.306 vj00 | E-UTRA UE Radio Access Capability Parameters | Rel-19 |
| TS 38.212 vj10 | NR Multiplexing and Channel Coding | Rel-19 |
| TR 38.889 vg00 | NR-based access to unlicensed spectrum study | Rel-16 |