Description
Conditional PSCell Addition (CPA) is a feature within the 5G NR mobility framework, specifically enhancing Dual Connectivity (DC) and Multi-Radio Dual Connectivity (MR-DC) operations. In DC, a User Equipment (UE) is connected to a Master Node (MN, e.g., an LTE eNB or 5G gNB) and a Secondary Node (SN, e.g., a 5G gNB). The Primary SCG Cell (PSCell) is the primary cell of the Secondary Cell Group provided by the SN. CPA allows the network to configure a UE with a conditional execution command: the UE should add a PSCell (i.e., establish or modify an SCG) when certain measurement-based conditions (e.g., signal strength/threshold of a candidate SN cell) are fulfilled, without needing further real-time signaling from the network at the moment of execution.
The architecture involves the UE, the Master Node (MN), the candidate Secondary Node (SN), and core network functions. The MN initiates the procedure based on its radio resource management strategy. It sends a *RRCReconfiguration* message to the UE containing a *CondPSCellAddition* configuration. This configuration includes the identity of the candidate PSCell, the measurement identity (linking to a configured measurement object), and the execution condition (e.g., A3 event: neighbor cell becomes offset better than source PSCell). The UE then continuously evaluates the specified measurement against the condition while connected to the MN.
When the condition is met, the UE autonomously executes the PSCell addition. It applies the stored configuration, performs random access to the candidate PSCell, and completes the SCG establishment/modification. The UE then confirms the successful execution to the MN via an RRC reconfiguration complete message. This process decouples the decision-making (network-configured condition) from the execution (UE-autonomous), which is crucial in scenarios with rapid signal quality fluctuations or high latency on backhaul links. CPA reduces the probability of handover failure and minimizes data interruption time compared to conventional network-controlled handovers, leading to more robust mobility, especially at cell edges or in high-speed scenarios.
Purpose & Motivation
CPA was created to address the limitations of traditional network-controlled handover and PSCell addition procedures in dynamic radio environments. In conventional mobility, the network makes a handover decision based on UE measurement reports, then issues a handover command. This multi-step process introduces latency and can fail if radio conditions deteriorate rapidly between the measurement report and command reception. For adding a secondary node in Dual Connectivity, this latency can lead to dropped connections or suboptimal user experience.
The motivation for CPA stems from the need for ultra-reliable low-latency communication (URLLC) and enhanced mobile broadband (eMBB) in 5G. By pre-configuring the UE with conditions, the handover decision is effectively brought closer to the radio interface, eliminating the network decision latency. This is particularly valuable in high-speed train scenarios, dense urban canyons, or industrial IoT settings where signal quality can change abruptly. CPA, along with Conditional Handover (CHO), represents a paradigm shift towards UE-executed conditional mobility, improving success rates and seamlessness, which are key requirements for 5G Advanced and 6G evolution.
What changed in its specifications
The latest release-to-release comparison of specifications that define CPA. Each summary describes the whole specification, not only this term.
Rel-19 TS 33.501 adds roaming and inter-PLMN indirect communication authorization, fast re-authentication for non-3GPP mobility, and AI/ML security clauses for positioning and federated learning. It also adds NPN security, NRF access token key retrieval, LTM security, and monitoring-of-signalling-traffic protection.
Full comparison in TS 33.501 →Rel-19 adds NTN-for-IoT Phase 3 and inter-RAT mobility from E-UTRAN to NR NTN, plus LTE-based 5G Broadcast Phase 2 changes. It also adds IMS disaster-roaming access barring, NTN-for-NR Phase 3 fields, and NR RRM Phase 5 items.
Full comparison in TS 36.331 →Release Timeline
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (2 CRs across 1 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Defining Specifications
3GPP specifications that define or reference CPA, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 28.886 vk00 | MDA Phase 4 Management Analytics | Rel-20 read |
| TS 33.501 vk30 | 5G Security Architecture | Rel-20 read |
| TR 33.916 vk00 | Security Assurance Methodology (SECAM) Evaluation Process | Rel-20 read |
| TS 36.331 vj40 | E-UTRA Radio Resource Control (RRC) Protocol | Rel-19 read |
| TS 36.423 vj10 | X2 Application Protocol (X2AP) Specification | Rel-19 read |
| TS 37.340 vj30 | Overview of Multi-Connectivity Operation using E-UTRA and NR | Rel-19 read |
| TS 37.483 vj40 | E1 Application Protocol (E1AP) | Rel-19 read |
| TS 38.300 vj40 | NR and NG-RAN Overall Description | Rel-19 read |
| TS 38.331 vj40 | NR Radio Resource Control (RRC) | Rel-19 read |
| TS 38.401 vj30 | NG-RAN Architecture Description | Rel-19 read |
| TS 38.423 vj40 | NG-RAN Xn Application Protocol | Rel-19 read |
| TS 38.473 vj40 | F1 Application Protocol (F1AP) | Rel-19 read |