ALIX: 5G Network Simulator

Protocol-Level 5G TN/NTN Simulator

ALIX is a system-level 5G network simulator used for detailed protocol-level evaluation of end-to-end network performance in terrestrial, non-terrestrial, and hybrid architectures.

Operating on a packet level resolution, ALIX enables unbiased, reproducible comparisons across communication technologies (e.g. 5G NR-NTN, DVB-S2X & DVB-RCS2). This supports standardization, benchmarking, and next-generation network and technology development, such as 6G.

✓ Aligned with 3GPP TR 38.811 & TR 38.821

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Stay Aligned with Evolving 3GPP 5G TN/NTN Work

Use standards-aligned simulation scenarios to evaluate new features early and ensure compatibility with 3GPP specifications – including 5G NR-NTN, 6G TN/NTN, and emerging 6G.

Compare Technologies with Reproducible Evidence

Compare communication technologies – such as DVB standards and 5G NR – using transparent, objective, and reproducible protocol-level evaluations.

Prototype & Derisk Future Designs

Test ideas early, accelerate R&D, and identify bottlenecks before costly hardware or field trials.

Key Use Cases for Protocol-Level Network Simulation

Standards-Aligned Validation (3GPP)
- Validate system behavior based on TR 38.811 (NTN channel modeling) and TR 38.821 (NTN scenarios/parameterization)
- Ensure compatibility with 5G NR, 5G‑Advanced, and 6G NTN developments
- Evaluate new protocol features early, before hardware or field testing
Technology Evaluation
- Compare DVB-S2X / DVB-RCS2 and 5G NR-NTN using consistent assumptions and scenarios
- Analyze scheduling performance, HARQ details, and link-to-system mapping
- Evaluate PDCP Multi-Connectivity and protocol trade-offs
- Assess hybrid 5G TN/NTN system coexistence and interference
Focused Constellation Subset Analysis
- Zoom into selected constellation segments and regions
- Evaluate performance for specific constellation subsets
- Compare coverage and performance variations under realistic assumptions
End-to-End Performance Evaluation
- Simulate the complete communications chain
- Evaluate the protocol stack from MAC layer scheduling to application services
- Track SINR, throughput, error rates, Quality of Service mechanisms, and priority routing
- Support objective decision-making for design choices
Virtual Prototyping for Cost-Effective R&D
- Accelerate innovation cycles
- Reduce unnecessary hardware costs
- Verify system performance before physical prototype development
- Identify issues early

Validated Through ESA, EU Horizon & Industry Projects

ALIX has been developed, validated, and continuously advanced through projects with the European Space Agency, the European Union, and industry partners. This work demonstrates ALIX’s technical credibility, standards alignment, and relevance for system-level evaluation of 5G TN/NTN and future network architectures.

ALIX has been used & advanced in key collaborative projects, including:

ALIX – Core development of the 5G TN/NTN simulator and contributions supporting 3GPP standardization

SAIRCC – Integrating satellite communications into future railway mobile communication systems

HELENA – Advancing NTN capabilities with a focus on 5G NTN mobility optimization

DYNASAT – Dynamic spectrum sharing and NTN system optimization

MARINA – Fair comparison of DVB-S2X and 5G NR technologies

EAGER – Exploration of 5G-Advanced and 6G NTN technologies

Research Papers Featuring ALIX

3GPP 5G NR NTN Technologies in a Geostationary Satellite Scenario / Best Paper Award ASMS/SPSC 2025

3GPP 5G NR NTN Technologies in a Geostationary Satellite Scenario / Lauri Sormunen, Tuomas Huikko, Verneri Rönty, Erno Seppänen, Sami Rantanen, Frans Laakso, Vesa Hytönen, Mikko Majamaa, Jani Puttonen

Best Paper Award / Industrial Relevance, the 12th Advanced Satellite Multimedia Systems Conference and the 18th Signal Processing for Space Communications Workshop 2025

This article presents a thorough performance comparison between DVB Second Generation Satellite Extensions (DVBS2X) and Return Channel via Satellite 2nd Generation (DVBRCS2), and NR NTN in a Geostationary Orbit (GEO) satellite scenario, using system-level simulators (SLS) for evaluation, namely Satellite Network Simulator 3 (SNS3) and ALIX 5G (TN-)NTN SLS, built on the same Network Simulator 3 (ns-3) platform.

Co-existence of Terrestrial and Non-Terrestrial Networks on Adjacent Frequency Bands

Co-existence of Terrestrial and Non-Terrestrial Networks on Adjacent Frequency Bands/ Lauri Sormunen, Henrik Martikainen, Jani Puttonen, Dorin Panaitopol, The 11th Advanced Satellite Multimedia Conference and the 17th Signal Processing for Space Communications Workshop (ASMS/SPSC), 6–8 September 2022.

This paper presents the latest achievements concerning 3GPP Release-17 adjacent band coexistence simulation work on 5G new radio non-terrestrial networks (NTNs) for satellite communications.

The main conclusions can be summarized as follows: (1) NTN UE can reuse the current requirements of the TN UE, (2) the satellite connectivity does not require a dedicated satellite waveform, and (3) TN can co-exist with NTN on adjacent channels with relaxed ACIR requirements for the tested simulation scenario.

Multi-Connectivity in 5G and Beyond Non-Terrestrial Networks

Multi-Connectivity in 5G and Beyond Non-Terrestrial Networks / Mikko Majamaa, Henrik Martikainen, Lauri Sormunen, and Jani Puttonen, Journal of Communications Software and Systems, 2022.

In this paper, an adaptive MC activation scheme for throughput enhancement in 5G and beyond Non-Terrestrial Networks (NTNs) is presented. The algorithm is evaluated by system simulations using different traffic split algorithms, namely, even split, data request per connection and per gNB algorithms. In the considered simulation scenario, the maximum throughput enhancement of 9.1%, compared to when MC is turned off, is experienced when using the adaptive Secondary Node (SN) addition algorithm with the combination of the data request algorithms.

A System Simulator for 5G Non-Terrestrial Network Evaluations

A System Simulator for 5G Non-Terrestrial Network Evaluations / Jani Puttonen, Lauri Sormunen, Henrik Martikainen, Sami Rantanen, Janne Kurjenniemi, IEEE International Symposium on a World of Wireless, Mobile and Multimedia Networks (WoWMoM), Non-Terrestrial Networks in 6G Wireless workshop, June 7-11, 2021.

This article presents a 5G NTN extension to an open-source Network Simulator 3 (ns-3) and its 5G extension (5G LENA). The objective is to use the resulting System Level Simulator (SLS) in 3GPP standardization to evaluate different system concepts and parameterizations.

5G Simulator Based on 3GPP Specifications

3GPP Specification-Based Modeling

ALIX implements 3GPP specifications to ensure accurate, standards‑aligned results:

TR 38.811: NTN channel modeling
TR 38.821: NTN scenarios and parameterization

Support for 5G TN/NTN

Supports non-terrestrial, terrestrial & integrated TN/NTN scenarios

Application-Level Traffic & Higher Layers

Realistic application-level traffic modeling (UDP, TCP, traffic generators)
Simplified core network
End-to-end user experience indicators: throughput , latency, jitter, QoS

Protocol Stack Simulation

PHY: Link-to-system mapping, NTN-relevant channel models, adaptive Modulation and Coding Schemes (MCS), SNR/SINR, power control
MAC: 5G NR-NTN scheduling, HARQ operation, resource allocation
RLC: Unacknowledged / Acknowledged Modes (UM/AM), Reliable radio link data transmission