System Level Analysis of Non-Terrestrial Networks

Tuesday, 3 June 2025, 14:00 – 17:30, room 1.A
Organisers:
  • Francois Baccelli (INRIA Paris and Telecom Paris, FR)

Motivation and Background

6G will feature the integration of 2D cellular networks and 2D or 3D NTN networks. The latter comprise UAV networks, LEO constellations or LEO, MEO and GEO constellations. The former will comprise several types of cellular organizations (e.g. multi-tier). NTNs already constitute one of the most creative domains of communication networks research and engineering worldwide, in a broad set of domains including data communications, data sensing and harvesting, or Internet routing. There is a clear need for a system level analysis of 3D NTN networks which would extend the 2D framework and even more for an analysis methodology of the network of networks sharing all the same frequency and spatial resources. This is already clear when one tries to assess the impact of NTN on 2D networks. This is also the case when one wants to assess the potential gains of an organized interplay This workshop will be focused on the system level analysis of such networks. The aims are the evaluation and the prediction of the statistical properties of spectral efficiency in such networks, the design of new tools for the design of optimal architectures, and the economic analysis of such networks. The workshop will gather groups, in Europe and Worldwide, involved in the first steps of this type of analysis.

Structure

14:00 – 15:20: Session 1

  • Federated beamforming in Non-Terrestrial Networks, Alessandro Guidotti, National Inter-University Consortium for Telecommunications – CNIT, Italy
    The identification of key technologies for 6G communications has just started in the industrial and scientific communities, but it is already globally recognised tha Non-Terrestrial Networks (NTN) will play a fundamental role allowing to truly achieve global, resilient, and ubiquitous connectivity. To meet the challenging objectives that are being defined for 2030 communications, NTN systems shall be capable of providing very high throughput from the sky. In this presentation, we focus on Cell-Free massive Multiple Input Multiple Output (CF-MIMO) for NTN by discussing: i) high-level architecture design concepts supporting centralised and federated (swarm-based) CF-MIMO in NTN; ii) CF-MIMO algorithms and power normalisations supporting federated solutions; and iii) numerical results for CF-MIMO systems based on channel state information and location information provided by the users.
  • Stochastic Geometry and Dynamical System Analysis of Walker Constellation Networks, Chang-sik Choi, SKKU, South Korea
    In practice, low Earth orbit (LEO) and medium Earth orbit (MEO) satellite networks consist of multiple orbits, each populated with many satellites. A widely used spatial architecture for satellites is the Walker constellation, where the longitudes of orbits are equally spaced and the satellites are periodically distributed along the orbits. In this presentation, we present a new stochastic geometry model for Walker constellations by constructing orbits that are invariant with respect to Earth’s spin and satellites that are invariant to orbit-wise rotation. This model enables an analysis based on dynamical systems, which allows one to address structural properties such as periodicity and ergodicity. It also enables a stochastic geometry analysis where, for a typical user at a given latitude, we show the derivation of the performance of downlink communications as a function of key constellation parameters, including orbit inclination and altitude, the number of orbits, the number of satellites, and the user latitude.
  • Latitudinal Distributions in Stochastic Analysis of Satellite Networks, Taneli Riihonen, Tampere University, Finland
    While basic three-dimensional modelling for satellite networks would be based on uniform point processes on spherical surfaces, the density of any real constellation is inherently non-homogeneous. That is, there are more satellites near the northernmost and southernmost latitudes of the orbits than around the equator. Likewise, terminals on Earth’s surface and atmosphere are certainly not distributed evenly all around the world. The nonsynchronous rotation of Earth with respect to non-geostationary satellites’ orbiting around it makes the longitudinal distributions uniform though. In this presentation, we overview solutions for considering non-uniform latitudinal distributions in stochastic geometry-based modelling and analysis of non-terrestrial networks.
  • System-Level Evaluation of NTN Architectures, Jedrzej Stanczak, Nokia, Finland
    This presentation gives an overview of how Nokia performs system-level nonterrestrial network evaluations via simulations. The focus is on evaluating the impact of satellite antenna gain (i.e., architecture in terms of antenna size) on end-user throughput, and secondly the impact of satellite architecture (e.g., regenerative vs. transparent) and UE HARQ capabilities (e.g., varying number processes) on end-user throughput.

 

Coffee break

15:50 – 17:30: Session 2

  • Constellation Technologies & Operations: providing global connectivity through space, Pierre Popineau, Constellation Technologies, France
    Constellation Technologies & Operations (CT&O) is a French start-up funded in early 2022 with the goal to provide global connectivity thanks to the deployment of a constellation of satellites in very-low Earth orbit (VLEO). CT&O’s network consist of several shells of VLEO satellites, user terminals and gateway stations operating in mmWave bands, with the objective to offer a 5G non-terrestrial network (NTN). This groundbreaking constellation will allow telecom operators to enhance the connectivity services they offer to their clients by delivering highperformance, affordable, sustainable connectivity in areas underserved by terrestrial infrastructure. In this session, we will start by sharing a general overview of our system design and the main key points of the constellation, from the satellites and user terminals to the software architecture we plan to use. We will also provide more details on the hypotheses we made for sizing the system. We will then dig a bit deeper into some technical points and how we solved them. During this session, we will talk about some of the tools we have developed to simulate and estimate our end system including a full-scale Digital Twin of the constellation, and a technical demonstration of some of these tools. Currently, CT&O is in the process of launching its first orbital payload (launch date mid-June 2025), and aims at deploying its first self-designed satellite 2027. The deployment of the full constellation is planned to start in 2028.
  • Timing advance and Doppler shift estimation in 5G NTN satellite networks, Philippe Martins, Telecom Paris, France – A joint work with Ashutosh Balakrishnan, Telecom Paris, France, Pierre Popineau, Constellation Technologies, France
    Accurate timing advance (TA) computation is critical in 5G non-terrestrial networks (NTN). It is necessary to compute it accurately to avoid inter user interference in the uplink at the satellite (BS) level.
    Estimating TA in low earth orbit (LEO) satellite networks is more challenging than in classical terrestrial deployments due to the larger path loss and high-speed movement of non-stationary LEO satellites. Capturing the doppler shift also becomes very pertinent in such scenarios. The problem becomes more challenging in the event of the UE being mobile itself.
    In this work, we propose an extended Kalman filter (EKF) based recursive Bayesian framework to accurately estimate the TA and Doppler shift in the presence of LEO satellite-UE joint motion dynamics. The framework first accurately models the joint motion dynamics and then constructs a Jacobian to linearize the inherent non-linearities present in the motion process. Probabilistic insights are also provided.
    The proposed framework is also useful when the satellite and UE clocks are not in sync, with the corresponding clock drift a function of the measured time difference of arrivals. Our results showcase the efficacy and robustness of the proposed EKF framework to estimate the TA and Doppler shift, even at very high UE speeds. The work is expected to be extremely useful in realizing LEO satellite based non-terrestrial networks.
  • Handover frequency in dynamic terrestrial communication network, Sanjoy Kumar Jhawar, Télécom Paris & Inria, France – A joint work with François Baccelli, Télécom Paris & Inria, France
    In modern architecture of communication network using LEO and MEO satellite constellation, it is crucial to know how frequently an user is performing handover. As a key performance metric of the system, handover frequency essentially reflects onto the cost of quality service. In this talk we consider a far more simplified model of the same flavor of LEO and MEO satellite constellation using stochastic geometry. In this dynamic communication model on the Euclidean plane we consider an user located at origin and it is served by the mobile base stations with initial locations given by a homogeneous Poisson point process. The base stations are moving at an identical speed in a random direction. The user stays connected to the nearest base station at any given point of time. Since the base stations are moving, the user disconnects and connects with different base stations over time, which ever base station is the closest. We determine the handover frequency first in the single-speed setting and use it as a inspiration to the multi-speed scenario. The model explored in this work have several important variants which are linked to these motivations. These variants include the finite visibility case, the case when the initial locations of the base stations are given by Poisson or Manhattan line Cox point processes. Their motion is along the underlying lines. The final variant is of course the spherical case. We shall briefly discuss about the steps towards relaxing these simplifications from the planar to spherical geometry.
  • Stochastic Geometry-Based Routing in LEO Satellite Networks: Analytical Framework, Routing Design, and Performance Analysis, Mustafa Kishk, Maynooth University, Ireland
    Current satellite routing strategies are mainly categorized into graph theory-based and stochastic algorithm-based approaches. The former relies on deterministic topologies, making it unsuitable for dynamic satellite networks. The latter involves stochastic behaviours and is analytically intractable, requiring extensive simulations to evaluate average performance, thus increasing computational complexity. To address these limitations, we propose routing strategies based on spherical stochastic geometry (SSG), which balance dynamic topology modeling with low analytical complexity. First, we develop a topological analytical framework for multi-hop communications by introducing the conditional contact angle, a concept that replaces distance with central angles to simplify analysis. Second, we design the closest relay association strategy, which optimizes relay locations and selects the nearest nodes from a point process. This enables analytical evaluation of key metrics such as availability, coverage probability, latency, and energy efficiency. The strategy performs close to the theoretical upper bound under ideal conditions and significantly outperforms other stochastic geometry-based methods. Finally, we extend the strategy to multi-layer networks by introducing a Markov framework for routing availability optimization. We also design inter-satellite and bent-pipe satellite-to-ground routing schemes to maximize energy efficiency, and compare their performance.
  • How Much Can Reconfigurable Intelligent Surfaces Augment NTN Connectivity: A Stochastic Geometry Approach, François Baccelli, Télécom Paris & Inria – A joint work with Junse Lee, Sungshin University, Seoul, South Korea
    The theory of point processes and stochastic geometry can be used to quantify the sky visibility experienced by users located in an urban environment. The general idea is to represent the buildings of this environment as a stationary marked point process, where the points represent the building locations and marks their heights. The point process framework is first used to characterize the distribution of the blockage angle, which limits the visibility of a typical user into the sky due to the obstruction by buildings. In the context of communications, this distribution is useful when users try to connect to the nodes of a non-terrestrial network in a Line-of-Sight way. Within this context, the point process framework can also be used to investigate the gain of connectivity obtained thanks to Reconfigurable Intelligent Surfaces. Assuming that such surfaces are installed on the top of buildings to extend the user’s sky visibility, this point process approach allows one to quantify the gain in visibility and hence the gain in connectivity obtained by the typical user. The distributional properties of visibility-related metrics are cross-validated by comparison to simulation results.