Description
Network Controlled Repeater – Mobile Termination (NCR-MT) is a functional component introduced in 3GPP Release 18 as part of the network-controlled repeater (NCR) architecture. It refers to the mobile termination aspect of an NCR, which allows the repeater to establish a connection with the network similar to a user equipment (UE). This enables the repeater to be managed and controlled by the network via standard signaling protocols, rather than operating as a standalone, unmanaged device. NCR-MT facilitates centralized optimization of repeater parameters, such as gain and beamforming, based on network conditions and policies.
Architecturally, an NCR consists of two main parts: the mobile termination (NCR-MT) and the repeater termination (NCR-RT). The NCR-MT handles the control plane connection to the network, including procedures like registration, authentication, and receiving control commands. It uses standard UE protocols, such as RRC and NAS, to communicate with gNBs and the core network. The NCR-RT, on the other hand, manages the amplification and forwarding of user plane traffic between UEs and the network. By separating these functions, NCR-MT allows the network to treat the repeater as a managed node, enabling dynamic configuration and monitoring.
How NCR-MT works involves the repeater initiating a connection to the network using its MT functionality, similar to how a UE camps on a cell. Once connected, the network can send control messages to adjust repeater settings, such as turning specific beams on or off, adjusting amplification levels, or reporting status information. This is achieved through defined signaling procedures, often leveraging existing UE protocols with extensions for repeater-specific commands. The NCR-MT ensures that the repeater operates in alignment with network optimization goals, such as minimizing interference or enhancing coverage in targeted areas.
Key components of NCR-MT include the protocol stack for control plane signaling, interfaces for receiving network commands, and mechanisms for translating these commands into actions on the repeater termination side. It integrates with network management systems to enable automated control loops, where the network adjusts repeater parameters based on real-time feedback. NCR-MT plays a crucial role in making repeaters intelligent and network-aware, moving beyond traditional analog or simple digital repeaters. This enhances the scalability and efficiency of repeater deployments in 5G and beyond.
Purpose & Motivation
NCR-MT was created to address the limitations of traditional repeaters, which often operated independently without network coordination, leading to issues like interference, suboptimal performance, and difficult management. As 5G networks demand higher capacity and coverage, especially in challenging environments, there was a need for repeaters that could be centrally controlled and optimized. NCR-MT solves this by enabling repeaters to connect to the network as managed entities, allowing dynamic adjustment of their behavior based on network conditions.
Historical context includes the evolution of repeater technology from simple amplify-and-forward devices to more intelligent solutions. Earlier repeaters lacked network awareness, making them prone to creating interference or amplifying noise. NCR-MT, as part of the broader NCR framework, introduces standardized control mechanisms, allowing operators to integrate repeaters into their network management ecosystems. This addresses the gap between standalone repeater deployments and network-controlled infrastructure.
Motivations for NCR-MT include the need for flexible coverage extension in 5G, support for beamforming and massive MIMO, and reduction of operational costs through automation. By enabling network control, it solves problems related to repeater configuration, optimization, and troubleshooting, enhancing overall network performance. This is particularly important for dense urban areas, indoor coverage, and rural expansions, where repeaters play a key role in service delivery.
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (71 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the NCR-MT function was introduced to enable network-controlled mobile terminated communication handling for scenarios like mobile base station relays. This allows the network, specifically the AMF, to manage reachability and paging for UEs in CM-IDLE state, even when served by a relay, ensuring mobile terminated data and signaling can be delivered. The mechanisms build upon existing UE reachability procedures, including the use of mobile reachable and implicit deregistration timers, while accounting for specific mobility patterns.
- Controlled support of (AF) session binding for Ethernet PDU Session Type TS 23.501CR0067
- Mobile Terminated SMS over NAS: 5GS Access Selection TS 23.501CR0201
- Network controlled NSSAI for SR-related Access Stratum connection establishment TS 23.501CR0656
- Avoiding security risk for RLC UM bearers during termination point change TS 38.331CR0570
In Release 16, the NCR-MT function introduced the capability for the network to handle mobile terminated communication via the Intermediate SMF (I-SMF), which controls User Plane Functions for local data networks. This enables the CN-based mobile terminated (MT) communication handling, allowing for paging and data delivery to a UE in CM-IDLE state even when it is served by an I-SMF in a different service area. The release also addressed specific UE reachability procedures, ensuring MT traffic could be managed effectively for UEs in various mobility and power-saving modes.
In Release 17, the NCR-MT function introduced the "Termination on UE assistance mode" procedure, which allows the network to manage mobile-terminated communications based on the UE's power-saving state. This builds upon the existing mobile termination handling framework by incorporating specific UE assistance information to control reachability.
- Update of Credentials Holder controlled prioritized lists of preferred SNPNs and GINs using SoR TS 23.501CR2999
- Termination on UE assistance mode TS 23.501CR3111
- CR to 38.106: Output power definitions for NR repeaters TS 38.106CR0004
- CR to TS38.106: clarification on the supported operating bands for NR repeater TS 38.106CR0009
- CR to TS 38.106 with corrections to repeater core specification TS 38.106CR0011
- CR to 38.106: NR repeater ACLR requirements TS 38.106CR0013
+ 8 more changes
In Release 18, the new NCR-MT (Network Controlled Repeater – Mobile Termination) function introduced specific performance and radio resource management (RRM) requirements for these mobile devices acting as relays. This included defining conducted performance requirements and clarifying propagation conditions for the NCR-MT, as detailed in updates to TS 38.106 and TS 38.115-1. Furthermore, the release provided corrections and core maintenance for the NCR-MT requirements, solidifying its support within the 5G system architecture.
- Introduction of Mobile Base Station Relay TS 23.501CR3813
- Support of graceful/gradual termination of PDU sessions during network slice decommissioning TS 23.501CR4078
- Update to Support Network Controlled Repeater TS 23.501CR5273
- Big CR to TS 38.106 on RRM core requirements for NR network-controlled repeaters TS 38.106CR0049
- Draft CR for TS38.106 on conducted performance requirements for NCR-MT TS 38.106CR0065
- BigCR for introduction of performance requirements for NCR-MT in TS 38.115-1 TS 38.115CR0029
+ 40 more changes
In Release 19, the new NCR-MT (Network Controlled Repeater – Mobile Termination) function introduced support for a Mobile Base Station Relay within the 5G system, utilizing the IAB-architecture with mobility. This enables a mobile repeater, such as one mounted on a vehicle, to act as a relay for UEs and requires the network to handle mobile terminated communications for the relay itself, including reachability and paging procedures while in CM-IDLE state, as defined for other mobile terminations.
Explore further
Broader topics and technologies where NCR-MT plays a role.
Defining Specifications
3GPP specifications that define or reference NCR-MT, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.501 vk00 | 5G System Architecture Stage 2 | Rel-20 |
| TS 38.106 vj20 | NR Repeater Radio Transmission and Reception | Rel-19 |
| TS 38.114 vj00 | EMC Requirements for NR Repeaters and NCR | Rel-19 |
| TS 38.115 vj20 | NR Repeater RF Conformance Testing Part 1 | Rel-19 |
| TS 38.211 vj10 | NR Physical Channels and Modulation | Rel-19 |
| TS 38.213 vj10 | NR Physical Layer Control Procedures | Rel-19 |
| TS 38.214 vj10 | NR Physical Layer Procedures for Data | Rel-19 |
| TS 38.304 vj00 | UE RRC_IDLE and RRC_INACTIVE Procedures | Rel-19 |
| TS 38.306 vj00 | NR UE Radio Access Capability Parameters | Rel-19 |
| TS 38.331 vj00 | NR Radio Resource Control (RRC) Protocol Specification | Rel-19 |
| TR 38.867 vi00 | Technical Report | Rel-18 |