PAGE CONTENTS
Objectives
The objective of the NTN-CPD project is to define the control plane of the 5G New Radio (NR) standard for non-terrestrial networks (NTN) and demonstrate its performance in a software demonstrator.
To be more specific, the project aims to fulfil the following objectives:
- Define a reference NTN architecture based on Non-Geo Stationary Orbits (NGSO);
- Review of the 5G NR control plane procedures and signaling;
- Identify possible strategies for satellite networks to implement a control plane as close as possible to the current 3rd Generation Partnership Project (3GPP) 5G specifications;
- Identify required modifications to the current 3GPP specifications for having an efficient control plane fit to be deployed on NTN;
- Demonstrate such architectures and control plane design in a software demonstrator (e.g. network simulator).
The objective for CCN1 is to study satellite payload options close, especially RLC-PDCP split, to implement the RLC-PDCP split and then study the effects of this split. The CCN1 is natural continuation of the project, complementing the simulator features, and extending the NTN control plane functionality studies.
Benefits
The developed (extended) Alix simulator is designed to enable the evaluation of 5G control plane procedures with flexible NGSO constellations, allowing the discovery of possible issues and optimisation targets for standardization and industrial purposes. The simulator will be capable of modelling relevant control plane features that may impact the 5G NTN performance in high-speed satellite scenarios, including but not limited to cell access, User Equipment (UE) measurements and mobility management.
Key benefits of the project include highly dynamic satellite constellation deployments and assessment of such systems and relevant protocols in high detail from both end-user and network perspectives. The research is complemented by visualisation and demonstration of the simulations via Magister SimLab.
The CCN1 complements the simulator features and extends the NTN control plane functionality of the Alix simulator.
Features
The Alix simulator introduces features in three different software versions.
The implementation Version 1 of the control plane demonstrator introduces a selection of NR-NTN Release 17 features and functionality:
- Radio Resource Control (RRC) signalling
- RRC messages
- Random Access
- Time and frequency synchronisation
- Mobility
- Feeder link
- Synchronisation Signal Block (SSB), synchronisation signals, and system information
- UE measurements
- Radio link failure
- RRC idle/inactive
Version 2 of the software focuses on 3GPP Release 18 and Release 19 control plane features, especially on VSAT UE operability and regenerative satellite payload:
- VSAT
- RACH-less handover
- Conditional HO enhancements
- Satellite switch with re-sync
- Regenerative satellite payload
- gNB CU-DU split
- Inter-satellite links
Version 3 does not contain the implementation of major new features but focuses more on improvements and bug fixes of the code base and parameter optimization of the simulations.
In addition to the RLC-PDCP split in CCN1 is considering the following features:
- 20×20 cm antenna;
- Sat switch with resync for regenerative sat;
- AMF as part of regenerative satellite;
- Overlapping beams;
- Beam-hopping;
- Updated Quasi-Error-Free (QEF) algorithm.
Challenges
The key challenges in the project are to:
- Implement a simulation tool, where the NR control plane is simulated with sufficient level of detail across a variety of different simulation scenarios;
- Implement the simulation tool with a high-level of performance, such that it can be used to effectively simulate and demonstrate complex NGSO scenarios;
- Create a reference NGSO satellite system architecture that can be used to evaluate the NR control plane in NGSO environments and identify possible improvements to the 3GPP specifications.
In CCN1, the challenge is to choose the most relevant and benefitting satellite payload options to be implemented.
System Architecture
The developed (extended) Alix simulation tool enables the evaluation of the control plane of different NGSO satellite constellations, supporting 3GPP specified NTN system architectures, with support for both transparent and regenerative satellite systems. Satellite constellations within one type of orbit are the focus of the simulator, with multi-orbit constellations being supported mostly for providing the serving satellites access to ground via ISLs and feeder links.
The architecture supports simple Inter-satellite Links (ISLs) and functional splitting of the gNB in regenerative satellite systems. The system architecture reflects the project objectives, with greater focus placed on the control plane rather than the user plane. The architecture focuses on the radio access network, while the core network and backhaul connections are largely simplified. The simulator is designed to accurately simulate subsets of the whole constellation, where the subset of satellites can be dynamically selected, based on the area of interest.
In CCN1, the architecture is refined to support split between RLC and PDCP, the prior to be placed in the satellite, and the latter to the ground. Also, other improvements like AMF on satellite are being considered.
Plan
The project started in May 2024 and estimated to end in March 2026. The work has been divided into the following work packages:
- WP1.0: System Scenarios
- WP2.0: Technical Specification
- WP3.0: Technical Baseline
- WP4.0: Demonstrator Design
- WP5.0: Demonstrator Implementation
- WP6.0: Technology Assessment and Development Plan
- WP7.0: Project Management
CCN1 project is started in March 2026 and scheduled to end in September 2026. The CCN1 work is divided into the following work packages:
- WP8.1 Split Payload Architecture and Design
- WP8.2 Split Payload Implementation
- WP8.3 Split Payload Evaluation
Current Status
The project started officially on 18.4.2024 and an official kick-off meeting was held on 23 April 2024. The System Requirements Review (SRR) milestone was achieved on 24 September 2024, the Preliminary Design Review (PDR) was completed on 4 December 2024, the System Design Review (SDR) was completed on 16 June 2025, the Test Acceptance Review (TAR) was finished on 24 October 2025 and the Final Review (FR) was finished on 25 March 2026.
The work is continued in the scope of CCN1 to extend originally planned features of the Alix simulator.
