Positioning, Synchronization, and Communication in 6G: Insights from Massive MIMO, RIS, and NTN
Doctoral thesis, 2025
Sixth-generation (6G) wireless networks aim to transform communication and localization by enabling precise positioning and seamless connectivity for advanced applications like autonomous systems, augmented reality, and smart cities. Technologies like massive multiple input multiple-output (MIMO), reconfigurable intelligent surface (RIS), and non-terrestrial networks (NTNs) play a critical role in achieving these objectives by addressing challenges in capacity, coverage, and synchronization in diverse environments.
This thesis investigates the use of massive MIMO technology to optimize communication architectures by analyzing the interplay between the number of antennas and quantizer resolution. This work identifies massive MIMO configurations that balance performance and complexity across varying signal- to-noise ratios (SNRs). The study contributes to the design of robust and scalable architectures for next-generation communication systems.
Moving on to the localization topic, this thesis also explores a frugal RIS- enabled localization and synchronization setup designed to provide precise positioning in cost-effective deployments. A scenario with one base station (BS) and two RISs is studied to localize a stationary user equipment (UE), despite the presence of an unknown carrier frequency offset (CFO) between the UE and the BS. This work highlights the potential of RIS technology to enhance localization accuracy and reduce infrastructure requirements.
Another emerging direction in localization is the use of NTNs, driven by their potential for large scale deployment. This thesis investigates an integrated LEO-cellular network for NTN-based localization and synchronization. A hybrid system with one BS and one low Earth orbit (LEO) satellite is analyzed to estimate the UE’s position, velocity, clock bias, and CFO under synchronization challenges. The results highlight NTN’s potential for robust localization in areas with limited terrestrial infrastructure.
By tackling key challenges in communication and localization, this thesis contributes to the design of efficient solutions for 6G networks, supporting their practical deployment in next generation wireless systems.
This thesis investigates the use of massive MIMO technology to optimize communication architectures by analyzing the interplay between the number of antennas and quantizer resolution. This work identifies massive MIMO configurations that balance performance and complexity across varying signal- to-noise ratios (SNRs). The study contributes to the design of robust and scalable architectures for next-generation communication systems.
Moving on to the localization topic, this thesis also explores a frugal RIS- enabled localization and synchronization setup designed to provide precise positioning in cost-effective deployments. A scenario with one base station (BS) and two RISs is studied to localize a stationary user equipment (UE), despite the presence of an unknown carrier frequency offset (CFO) between the UE and the BS. This work highlights the potential of RIS technology to enhance localization accuracy and reduce infrastructure requirements.
Another emerging direction in localization is the use of NTNs, driven by their potential for large scale deployment. This thesis investigates an integrated LEO-cellular network for NTN-based localization and synchronization. A hybrid system with one BS and one low Earth orbit (LEO) satellite is analyzed to estimate the UE’s position, velocity, clock bias, and CFO under synchronization challenges. The results highlight NTN’s potential for robust localization in areas with limited terrestrial infrastructure.
By tackling key challenges in communication and localization, this thesis contributes to the design of efficient solutions for 6G networks, supporting their practical deployment in next generation wireless systems.
6G
reconfigurable intelligent surfaces (RIS)
synchronization.
communication
massive multiple-input multiple- output (MIMO)
localization
non-terrestrial networks (NTNs)
EDIT-EA Lecture Hall, Rännvägen 6B, Chalmers
Opponent: Prof. Pierluigi SALVO ROSSI
Author
Yasaman Ettefagh
Chalmers, Electrical Engineering, Communication, Antennas and Optical Networks
Performance of Quantized Massive MIMO with Fronthaul Rate Constraint over Quasi-Static Channels
IEEE Access,;Vol. 11(2023)p. 56935-56950
Journal article
Y. Ettefagh, MF. Keskin, K. Kheykhosravi, G. Seco-Granados, and H. Wymeersch, “Frugal RIS-aided 3D Localization with CFO under LoS and NLoS Conditions”
Y. Ettefagh, S. Saleh, MF. Keskin, H. Chen, G. Seco-Granados, and H. Wymeersch, “Integrated Cellular and LEO-based Positioning and Synchro- nization under User Mobility”
6G networks are set to transform the way we connect and navigate the world. Beyond just faster internet, 6G will combine communication and precise positioning to enable technologies like self-driving cars, delivery drones, and smarter cities. It will provide seamless connectivity and accuracy, even in remote areas or environments where today’s networks fall short.
This work focuses on three technologies that will make this possible. Massive multiple-input multiple-output (MIMO) uses large arrays of antennas to boost network performance and handle thousands of devices efficiently. Smart surfaces, known as reconfigurable intelligent surface (RIS), can direct signals like mirrors for better coverage and pinpoint accuracy, even in crowded or tricky spaces. Satellites, working alongside ground networks, bring connectivity and positioning to places where traditional systems can not, like deep oceans or isolated mountains.
Together, these innovations are shaping a future where connectivity is everywhere, reliable, and perfectly in sync with our increasingly digital lives. With 6G, the world will feel smaller, smarter, and more connected than ever before.
This work focuses on three technologies that will make this possible. Massive multiple-input multiple-output (MIMO) uses large arrays of antennas to boost network performance and handle thousands of devices efficiently. Smart surfaces, known as reconfigurable intelligent surface (RIS), can direct signals like mirrors for better coverage and pinpoint accuracy, even in crowded or tricky spaces. Satellites, working alongside ground networks, bring connectivity and positioning to places where traditional systems can not, like deep oceans or isolated mountains.
Together, these innovations are shaping a future where connectivity is everywhere, reliable, and perfectly in sync with our increasingly digital lives. With 6G, the world will feel smaller, smarter, and more connected than ever before.
Areas of Advance
Information and Communication Technology
Infrastructure
C3SE (-2020, Chalmers Centre for Computational Science and Engineering)
Subject Categories (SSIF 2025)
Electrical Engineering, Electronic Engineering, Information Engineering
ISBN
978-91-8103-202-4
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5660
Publisher
Chalmers
EDIT-EA Lecture Hall, Rännvägen 6B, Chalmers
Opponent: Prof. Pierluigi SALVO ROSSI