Description
Multi-Radio Dual Connectivity (MR-DC) is an advanced Radio Access Network (RAN) architecture defined by 3GPP, enabling a User Equipment (UE) to maintain concurrent connections with two distinct base stations, typically involving different radio access technologies (RATs) like LTE and New Radio (NR). This is achieved through a master node (MN) and a secondary node (SN), where the MN provides control plane connectivity and the SN adds additional user plane resources. The UE utilizes multiple receivers and transmitters to communicate with both nodes, aggregating data flows to increase throughput and reliability. Key variants include EN-DC (E-UTRA-NR Dual Connectivity) with LTE as master and NR as secondary, NE-DC (NR-E-UTRA Dual Connectivity) with NR as master and LTE as secondary, and NR-DC (NR-NR Dual Connectivity) within 5G. The architecture involves split bearer options where data radio bearers (DRBs) can be terminated at the MN, SN, or both, allowing flexible traffic steering and load balancing.
Operationally, MR-DC relies on tight coordination between the MN and SN via standardized interfaces: the X2 interface for LTE-based nodes or the Xn interface for NR-based nodes. The MN handles core network signaling (e.g., via the S1 or NG interface) and manages UE context, while the SN contributes additional radio resources without direct core network attachment. Procedures include SN addition, modification, and release, driven by measurement reports from the UE to optimize performance. The UE measures signal qualities from both nodes, enabling dynamic resource allocation and mobility events like handovers. This setup supports features like carrier aggregation across RATs, enhanced mobility through make-before-break handovers, and improved coverage by leveraging lower-frequency bands from one RAT and higher-frequency bands from another.
In the network, MR-DC plays a crucial role in facilitating smooth transitions between 4G and 5G, allowing operators to deploy 5G incrementally while reusing existing LTE infrastructure. It boosts user experience by providing higher peak data rates, lower latency for split bearers, and increased reliability through path diversity. For network operators, MR-DC optimizes spectrum utilization and capital expenditure by enabling non-standalone (NSA) 5G deployments, where 5G NR is anchored to an LTE core. The technology is foundational for achieving the performance targets of 5G, such as enhanced mobile broadband (eMBB), and supports advanced use cases like ultra-reliable low-latency communication (URLLC) by leveraging dual connectivity for redundancy.
Purpose & Motivation
MR-DC was created to address the challenges of evolving mobile networks from 4G to 5G, ensuring backward compatibility and efficient resource use during the transition. Prior to MR-DC, dual connectivity existed within a single RAT (e.g., LTE-LTE DC), but it could not leverage the benefits of combining different RATs like LTE and NR. This limitation hindered the ability to deliver the high data rates and low latency promised by 5G without a full standalone deployment. MR-DC solves this by allowing UEs to simultaneously utilize LTE and NR radios, maximizing available spectrum and improving network performance without requiring immediate core network upgrades.
Historically, the motivation for MR-DC stemmed from the industry's need for a cost-effective path to 5G, as building entirely new 5G networks from scratch was prohibitively expensive. By enabling non-standalone 5G architectures, MR-DC allows operators to launch 5G services quickly using existing LTE infrastructure for control plane functions and NR for enhanced capacity. It addresses problems such as coverage gaps in early 5G deployments, where high-frequency NR bands have limited range, by anchoring connections to more pervasive LTE networks. This approach also enhances mobility robustness, as UEs can maintain connectivity through LTE while adding NR for boosted throughput.
Furthermore, MR-DC supports the growing demand for diverse services and network slicing in 5G. By aggregating resources across RATs, it provides flexibility to meet varying quality of service (QoS) requirements, from high-speed data to reliable low-latency communication. The technology fosters innovation in multi-RAT coordination, paving the way for future enhancements like integrated access and backhaul (IAB) and advanced carrier aggregation. Its standardization in 3GPP ensures global interoperability, enabling seamless user experiences and facilitating the co-existence of multiple network generations.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (329 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the foundational framework for Multi-Radio Dual Connectivity (MR-DC) was introduced, defining its two primary categories: MR-DC with the EPC via EN-DC and MR-DC with the 5GC via NGEN-DC, NE-DC, or NR-DC. This release also established specific management requirements for these operations, including support for different user plane connectivity options and the management of the NR node (en-gNB) in EN-DC. Furthermore, it introduced procedures for handling multiple active NAS connections and clarified associated security aspects, such as key activation and user plane security policy.
- Agreements for MR-DC TS 37.340CR0073
- Multiple NAS connections TS 33.501CR0095
- Security Procedures for Dual Connectivity TS 33.501CR0185
- Multiple NAS connections: taking a new security context into use on non-3GPP access TS 33.501CR0334
- Handling of UP security policy in MR-DC TS 33.501CR0380
- Multiple NAS connections: clarification on the action of MAC verification in registration request over non-3gpp access TS 33.501CR0389
+ 85 more changes
In Release 16, MR-DC enhancements introduced support for inter-RAT handover from NR to EN-DC, mobility enhancements, and the introduction of ARPI & SPID for EN-DC. The release also added specific measurements for Secondary Node Addition and RRC connection usage per UE multi-RAT capability, alongside corrections and support for features like RACS and overheating handling in EN-DC and NR-DC scenarios. Furthermore, management requirements were defined for different MR-DC user plane connectivity options and for nodes like the en-gNB in EN-DC operation.
- Add measurements related to Secondary Node Addition for E-UTRA-NR Dual Connectivity TS 32.425CR0184
- Add measurement on RRC connection usage per UE multi RAT capability TS 32.425CR0188
- Support of inter-RAT handover from NR to EN-DC in TS 36.331 TS 36.331CR4232
- Introduce of alternative cell reselection priority for EN-DC TS 36.331CR4229
- Stage2 Introduction of ARPI&SPID for EN-DC TS 37.340CR0173
- Stage 2 CR for Inter-RAT HO between NR to EN-DC in Rel-16 TS 37.340CR0185
+ 72 more changes
In Release 17, MR-DC enhancements included specific support for higher uplink power limit capabilities in inter-band EN-DC and updated UE capabilities for EN-DC band combinations within FR1. Furthermore, the release introduced management system requirements to ensure OAM connectivity continuity for WAB-gNBs and provided clarifications for IAB within the EN-DC architecture.
- Introduction of further multi-RAT dual-connectivity enhancements TS 36.331CR4774
- Introduction of further multi-RAT dual-connectivity enhancements TS 37.340CR0309
- Introduction of further multi-RAT dual-connectivity enhancements TS 38.331CR2954
- Clarification to IAB in EN-DC architecture TS 33.501CR1323
- Clarifications on the multicast security context handling in session creation procedure TS 33.501CR1379
- Overheating assistance info for FR2-2 in (NG)EN-DC - RIL E801 TS 36.331CR4820
+ 65 more changes
In Release 18, the MR-DC function introduced new capabilities including support for intra-band EN-DC with non-collocated cells and specific channel spacing, alongside enhancements for multi-carrier operations. It also added signaling for UE preference regarding multi-receive operation and integrated Release 18 positioning features into the MR-DC framework. Furthermore, corrections and clarifications were made for handover procedures and capability descriptions related to these enhancements.
- Lower MSD capability for EN-DC TS 36.331CR4991
- Introduction of R18 positioning to MR-DC TS 37.340CR0371
- Introduction of new capability for intra-band EN-DC channel spacing [Intra-Band_EN-DC_Channelspacing] TS 38.306CR1174
- Introduction of UE preference for multi-Rx operation in UAI TS 38.331CR4380
- Signaling support for intra-band non-collocated NR-CA, EN-DC TS 38.331CR4396
- PTM retransmission reception for multicast DRX with HARQ feedback disabled [PTM_ReTx_Mcast_HARQ_Disb] TS 38.331CR4504
+ 57 more changes
In Release 19, the MR-DC enhancements primarily focused on expanding UE capability reporting and test specifications for EN-DC configurations, including the addition of capabilities for Release 15, Release 16, and Release 19 EN-DC combos within FR1. The release also introduced new RF baseline implementation capabilities for PC2 EN-DC combinations and added Protocol Implementation Conformance Statement (PICS) provisions for several new EN-DC and CA configurations. Furthermore, corrections were made to the management system descriptions for MR-DC within the NRM definitions.
- Rel-19 CR TS 28.540 corrections for MR-DC related description TS 28.540CR0026
- Rel-19 CR TS 28.540 Add new requirements to support broadcast multiple TACs for NTN TS 28.540CR0040
- Introduction of Multi-path Relay Enhancement [N3C_M_Relay] TS 38.306CR1296
- Introduction of Multi-path Relay Enhancement [N3C_M_Relay] TS 38.331CR5373
- Introduction of Rel-19 Multi-carrier enhancements TS 38.331CR5400
- Introduction of NR sidelink multi-hop relay TS 38.331CR5429
+ 20 more changes
Explore further
Broader topics and technologies where MR-DC plays a role.
Defining Specifications
3GPP specifications that define or reference MR-DC, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 28.540 vk10 | 5G Network Resource Model (NRM) Management | Rel-20 |
| TS 32.425 vj00 | E-UTRAN Performance Measurements | Rel-19 |
| TS 33.501 vk00 | 5G Security Architecture and Procedures | Rel-20 |
| TS 36.331 vj00 | LTE RRC Protocol Specification | Rel-19 |
| TS 37.340 vj00 | Multi-Connectivity Operation Overview | Rel-19 |
| TS 38.133 vj20 | 5G UE Radio Requirements for RRC_IDLE Mobility | 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 |
| TS 38.425 vj10 | NR User Plane Protocol Specification | Rel-19 |
| TS 38.508 vj11 | 5G NR UE Radio Transmission & Reception | Rel-19 |
| TS 38.521 vj20 | NR Physical Layer UE Conformance Testing | Rel-19 |
| TR 38.846 vi10 | Technical Report | Rel-18 |