Description
Non-Coherent Joint Transmission (NCJT) is an advanced multi-Transmission/Reception Point (multi-TRP) physical layer technology introduced in 3GPP Release 17 for 5G-NR. It operates under the framework of multi-TRP and multi-panel user equipment (UE) enhancements. Unlike Coherent Joint Transmission (CJT), which requires precise phase synchronization and channel state information (CSI) sharing among TRPs to form a coherent beam, NCJT allows multiple, geographically separated TRPs (or panels within a TRP) to transmit independent data streams to the same UE simultaneously on the same time-frequency resources. These transmissions are not phase-aligned; they are treated as separate spatial layers or transmission occasions. The UE receives these multiple streams and must separate them using advanced receiver processing, such as interference suppression combining or successive interference cancellation, leveraging the spatial characteristics and potentially different quasi-co-location (QCL) assumptions of the channels from each TRP.
Architecturally, NCJT relies on network coordination, typically managed by a central unit (CU) or a coordinating node, which schedules the transmissions from the participating TRPs. The TRPs may be connected via ideal (e.g., fronthaul) or non-ideal backhaul (Xn interface). Key components include the scheduling entity, the participating TRPs (which can be gNBs or remote radio heads), and a UE capable of multi-panel reception or advanced multi-stream decoding. The physical downlink shared channel (PDSCH) is the primary channel for NCJT, where multiple PDSCHs can be transmitted from different TRPs. The network configures the UE via RRC signaling and dynamic scheduling (DCI) with parameters like transmission configuration indicator (TCI) states, each associated with a specific TRP, to indicate the QCL reference signals for each stream.
NCJT's role is to improve spectral efficiency, reliability, and user experience, especially for medium to high mobility users and at cell boundaries. It is a key enabler for ultra-reliable low-latency communication (URLLC) and enhanced mobile broadband (eMBB) scenarios. By not requiring tight phase coherence, it reduces the stringent synchronization and CSI feedback requirements compared to CJT, making it more practical for deployments with non-ideal backhaul. The technology is specified in detail in 3GPP TS 38.214 for physical layer procedures and TS 38.306 for UE radio access capabilities.
Purpose & Motivation
NCJT was created to address the growing demand for higher data rates, improved coverage, and ultra-reliable communications in 5G-Advanced networks, particularly in challenging radio environments. Prior to Release 17, multi-TRP operation primarily focused on schemes like coordinated multipoint (CoMP) with joint transmission requiring coherent combining, which imposed significant overhead for channel estimation, feedback, and tight synchronization between TRPs. This limited its practicality, especially in deployments with non-ideal backhaul links typical in heterogeneous networks.
The motivation for NCJT stems from the need for a more robust and implementable multi-TRP solution that sacrifices some beamforming gain for reduced coordination complexity and enhanced diversity gain. It solves problems like coverage holes, inter-cell interference at edges, and the reliability requirements of industrial IoT and URLLC services. By allowing non-coherent transmission, it enables networks to exploit spatial diversity from multiple TRPs without the need for perfect channel knowledge alignment, thus improving resilience against blockages and fast fading. This evolution reflects a shift towards leveraging multiple, possibly less coordinated, transmission points to boost system performance in real-world deployment scenarios.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (99 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, NCJT (Non-Coherent Joint Transmission) was newly introduced as part of the PDSCH enhancement for multi-TRP operation. The specification defined specific UE procedures for receiving PDSCH with multiple TCI states, including schemes such as 'fdmSchemeA', 'fdmSchemeB', and 'tdmSchemeA' for handling non-overlapping frequency or time domain resource allocations per transmission occasion. This enabled the reception of two PDSCH transmission occasions of the same transport block, each associated with a different TCI state.
- CR to 38.214 capturing the RAN1#92bis and RAN1#93 meeting agreements related to URLLC TS 38.214CR0003
- Change Request for alignment of frequency domain resource allocation with 38.213 for a PUSCH transmission scheduled by a RAR UL grant TS 38.214CR0013
- CR on sequential PDSCH and PUSCH scheduling TS 38.214CR0014
- CR on PDSCH beam indication TS 38.214CR0017
- Correction on TCI indication for multi-slot PDSCH TS 38.214CR0018
- CR on QCL assumption for receiving PDSCH for RAR TS 38.214CR0025
+ 12 more changes
In Release 16, NCJT (Non-Coherent Joint Transmission) was enhanced to support multi-TRP (Transmission Reception Point) operations with schemes like 'fdmSchemeA', 'fdmSchemeB', and 'tdmSchemeA' for transmitting the same transport block from different TCI states. This included corrections to handle collisions between PDCCH and PDSCH in multi-TRP scenarios and clarifications on PDSCH rate-matching capabilities for these schemes. The release also defined procedures for receiving multiple PDSCH transmission occasions, each associated with a different TCI state, within a single slot.
- Introduction of NR URLLC support TS 38.214CR0054
- Corrections on NR URLLC support TS 38.214CR0071
- Corrections on NR URLLC support TS 38.214CR0087
- Corrections to PDSCH PRB bundling notation (Rel-15 origin) TS 38.214CR0116
- Corrections on NR URLLC support TS 38.214CR0130
- Corrections for the issue of PDCCH and PDSCH colliding in multi-TRP TS 38.214CR0135
+ 16 more changes
In Release 17, the NCJT (Non-Coherent Joint Transmission) function was enhanced with a specific correction regarding the "RI restriction description" in the physical layer specifications. This update provided necessary clarifications and corrections to the existing multi-TRP (Transmission Reception Point) transmission schemes, including 'fdmSchemeA', 'fdmSchemeB', and 'tdmSchemeA', which define how a UE receives PDSCH transmission occasions from different TCI states. The changes ensured more reliable and clear operation for NCJT, particularly in scenarios involving multi-PDSCH scheduling via a single DCI.
- Introduction of enhanced Industrial Internet of Things (IoT) and ultra-reliable and low latency communication (URLLC) support for NR TS 38.214CR0229
- Introduction of NR small data transmissions in INACTIVE state TS 38.214CR0237
- 38.306 CR for introduction of MBS PDSCH FDM capabilities TS 38.306CR0805
- Corrections on enhanced Industrial Internet of Things (IoT) and ultra-reliable and low latency communication (URLLC) support for NR TS 38.214CR0255
- Simultaneous transmission of SRS and other channels for intra-band non-contiguous carrier aggregation TS 38.214CR0279
- Corrections on enhanced Industrial Internet of Things (IoT) and ultra-reliable and low latency communication (URLLC) support for NR TS 38.214CR0282
+ 19 more changes
In Release 18, key enhancements for Non-Coherent Joint Transmission (NCJT) included clarifications for the CSI-RS transmission occasion used for NCJT Channel State Information (CSI) and further clarification on restrictions for NCJT CSI Interference Measurement (CSI-IM). These updates built upon the foundational multi-cell scheduling framework to refine the measurement and reporting procedures essential for multi-TRP NCJT operations.
- Introduction of multi-cell PDSCH / PUSCH scheduling TS 38.214CR0442
- Corrections on multi-cell PDSCH / PUSCH scheduling TS 38.214CR0493
- CR on FDM reception of unicast and multicast PDSCH in RRC_INACTIVE state TS 38.214CR0517
- CR on PDSCH resource mapping for dedicated spectrum less than 5 MHz TS 38.214CR0518
- Correction on CPE starting position determination and transmission for PSSCH/PSCCH TS 38.214CR0563
- CR on SRS transmission for NCB PUSCH in STxMP SDM/SFN scheme TS 38.214CR0597
+ 23 more changes
In Release 19, specific UE procedures and capabilities for receiving PDSCH transmissions in Non-Coherent Joint Transmission (NCJT) scenarios were clarified and enhanced. This included defining detailed UE behavior for schemes like 'fdmSchemeA', 'fdmSchemeB', and 'tdmSchemeA' where the UE receives multiple PDSCH transmission occasions of the same transport block with different TCI states. Furthermore, corrections and clarifications were introduced for related multi-PDSCH scheduling and HARQ process handling to ensure proper operation under these NCJT schemes.
- Correction on HPN determination for multi-PDSCH and multi-PUSCH scheduling TS 38.214CR0747
- Correction on TBS determination for SPS PDSCH TS 38.214CR0748
- Msg4 PDSCH repetition and retransmission TS 38.214CR0749
- Clarification on simultaneous transmission capabilities in inter-band CA TS 38.306CR1403
- Clarification on NR uplink transmission duty cycle TS 38.306CR1407
Explore further
Broader topics and technologies where NCJT plays a role.
Defining Specifications
3GPP specifications that define or reference NCJT, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 38.214 vj10 | NR Physical Layer Procedures for Data | Rel-19 |
| TS 38.306 vj00 | NR UE Radio Access Capability Parameters | Rel-19 |