Objectives

Objective 1: Antenna and XL Array technologies for hybrid-field applications

QUEST-6G aspires to propose various antenna array designs that meet the high-level requirements of 6G networks – especially concentrating on NF beam-focusing techniques.

XL array antennas: According to the main QUEST-6G concept scenario, the objective is the investigation of 6G radio links (communication and sensing) that can deliver remarkable data rates and seamless connectivity, enabling a wide range of applications.

Reconfigurable antenna arrays: The investigated antenna architectures also include novel reconfigurable antenna array systems that can suitably adjust the radiation pattern to track channel dynamics and user mobility and create favourable propagation conditions. Two types can be considered as the best candidates for array implementation: (a) Pixel reconfigurable antenna arrays (employing a switched grid of metallic pixels) that can combine conventional phase-shifting and parasitic beamforming. (b) Dual-band gridded patch arrays (with competitive beamsteering range and compact dimensions). Fabrication and Measurements: Moreover, in the implementation aspects, the antenna arrays should adopt the hybrid RF/digital topology that is able to combine the classical phased arrays with digital processing using commercial of-the-shelf (COTS) components to serve the 6G scope in the mid-band spectrum frequency range. QUEST-6G will not only investigate and propose specific antennas, but at least two designs will be qualified for implementation. Fundamental lab measurements of the realized antenna arrays will be performed in the available RF test facilities that will be made available for the project. Reflection coefficients, coupling, and radiation patterns will be measured and used as an input for other work packages, which investigate the 6G link on a system level.

Objective 2: Design and Fabrication of an FR3 Beamfocusing chip

One of the main technical objectives of QUEST-6G is the design and fabrication of a novel Beam-Forming Integrated Circuit (BFIC) chip operating in the mid-spectrum FR3 band, to be used in the development of the XL-array and enhance the beam-forming/focusing characteristics of the proposed system. The BFIC will be developed using a standard low-cost bulk CMOS technology node, ensuring cost efficiency and long-term sustainability for deployment in large antenna arrays. It will integrate multiple transceiver chains (e.g. eight) operating in the low FR3 frequency band. Each transceiver will incorporate input and output switches to support Time Division Duplex (TDD) operation. The chip will feature two RF ports for horizontal and vertical polarization, enabling it to drive multiple dual-polarized antenna elements.

Objective 3: Channel Measurements and modelling for FR3 ISAC channels

QUEST-6G will perform a series of channel sounding measurements to characterize and model the NF characteristics and the spatial non-stationarity of the channel due to the use of extremely large antenna arrays in the FR3 band. The wideband measurements will be based on sounding equipment with a large number of RF chains and an XL-MIMO array developed in QUEST-6G for dual-polarization operation. Furthermore, an indoor ISAC channel measurement will be performed to acquire target sensing characteristics. Enhanced statistical signal processing of the sounding measurement data will result in the channel characteristics in several domains, i.e., in space-time-frequency or the corresponding spectral domains angle-Doppler-delay. These characteristics will facilitate the development of geometry-based stochastic models (GBSMs) that will support variations of the multi-path angles over the antenna array, instead of considering a single angle per multi-path. Moreover, ISAC specific models will provide the needed target modelling to capture communication and sensing channel characteristics.

Objective 4: Waveform Designs – Modulations / Numerologies – Channel Estimation – Codebooks – Preambles- Random Access and Resource allocation scheduling

6G hybrid NF/FF ISAC must reconcile Orthogonal Frequency Division Multiplexing (OFDM) backward compatibility with new waveforms, operate with XL-MIMO spherical propagation and deliver joint communication–sensing under mobility, aging channels, and tight energy budgets. Accurate yet low-overhead estimation, synchronization, and ranging are needed, alongside secure operation and coexistence across FR1/FR2/FR3. Massive asynchronous access, semantic-level reliability, and AI-native optimization must scale without sacrificing spectral efficiency, latency, or robustness in real deployments.

Objective 5: Beam focusing and Near-field Performance Analysis and Fundamental Limits

NF communications are one of the core pillars of 6G networks. Indeed, the spherical wavefronts now facilitate beamfocusing in the NF enabling beams to be precisely targeted both in angular and Euclidean distances. By leveraging this unique property, Multi – User (MU) communications within the same angular direction can be realized. However, the performance of NF communications dependent heavily on the electromagnetic characteristics of the XL-arrays employed. Moreover, the NF statistical channel models employed for continuous large aperture antennas remain deeply unexplored. This makes the performance evaluation at system-level particularly challenging. QUEST-6G will pave the way for the development of a complete analytical framework to conduct performance evaluation of NF communication networks at system-level and derive analytical expressions for key performance indicators, bounds and fundamental limits.

Objective 6: Investigation of accelerating and self-healing beams

Self-accelerating (curved) beams, e.g., finite-energy Airy beams, have attracted increasing interest for their potential to provide enhanced capabilities to wireless networks. These beams preserve unique properties, such as self-acceleration, diffraction resistance, and self-healing, enabling novel NF communication strategies that surpass conventional beamforming limits. Therefore, these beams can open up new avenues for communications, WPT, microwave imaging and security in dense and dynamic environments in 6G networks. QUEST-6G will investigate the theoretical issues and limits of the accelerating beams in the FR2 and FR3 bands, will provide design rules and limitations of arrays and EM surfaces that can produce these beams, and finally will experiment with possible designs of arrays and metasurfaces and fabrication alternatives to open up new ways of manipulating the wireless channel.

Objective 7: Hybrid-field, hybrid beam- forming/focusing algorithms

Hybrid in field (near-far) and hybrid in architecture (analog-digital) novel beam- forming/focusing schemes and algorithms will be designed and developed to support MU and multi-functional operation in cell-free 6G networks. QUEST-6G will support users in both the NF and the FF with beams originated by reconfigurable XL-arrays, to allow for spectrally efficient and interference-free cell-free networks. Leveraging upon the modular architecture of the XL-array allowing for the formation and selection of subarrays and coupled with the beam-forming/focusing chip, the project will facilitate the exploration of a wide range of alternatives. Furthermore, QUEST-6G will examine extensive beamforming techniques based on various EM transmitters, i.e., XL-arrays, FA arrays, MA arrays, parasitic arrays, hybrid (active/passive) RIS, and SIM for holographic MIMO.

Objective 8: Multiple functionalities for NF (NF-ISAC, Energy Transfer and Physical Layer Security)

The evolution from massive MIMO to NF XL-MIMO is not simply an increase in the array size, but faces totally new design challenges, in terms of NF channel modelling, performance analysis, channel estimation, and practical implementation. In this context, multiple functionalities and key enabling technologies such as ISAC, power transfer and PLS that 6G will endorse are now required to be smoothly integrated into the NF XL-MIMO systems. Bridging the conceptual, design, and practical challenges between NF XL-MIMO systems and the functionalities of 6G networks is a non-trivial task. Although a few research efforts have been devoted, meaningful results to enable design insights to, have still not been derived.

Objective 9: Intent-based multifunctional RAN for user-centric adaptation

Intents are declarative expressions of requirements that describe what a network or subsystem must achieve, without prescribing how to achieve it. They encapsulate objectives such as performance, availability, latency, or energy efficiency, but also include requirements from new functionalities, like sensing, power transfer or secrecy. By shifting focus from low-level parameter configuration to high-level declarative goals, intents enable a separation of concerns, where autonomous systems take responsibility for translating these requirements into optimal actions. Intent-based RANs autonomously translate service-level intents (for example, “assure 7 Mbps uplink with 40 ms latency for Ultra Reliable Low Latency Communications (URLLC) flows”) into fine-grained RAN functions such as scheduling, beam-focusing/forming, link adaptation, based on network and channel conditions. Through AI-driven closed loops and agentic architectures with Large Language Models (LLMs), these intents are continuously interpreted, contextualized, and mapped into precise RAN configurations. The DoF provided by the XL-arrays and the variability of the NF/FF environment give a difficult scheduling problem that, in QUEST-6G, will benefit from the exploitation of quantum tools. Moreover, the Sensing as a Service (SaaS) concept is integrated at the QUEST-6G intents, where ISAC operation is requested by users or operators on demand and the scheduler redistributes resources to achieve the intended goals.

Objective 10: Reformulating RAN optimization problems into Quantum Optimization problems

A major QUEST-6G objective focuses on developing systematic methodologies for reformulating XL-MIMO optimization problems into “QUBO form”, which represents the native problem formulation for quantum annealers and Ising machines. This transformation process involves several technically challenging aspects that require innovative algorithmic solutions. Constraint handling represents a fundamental challenge, since QUBO formulations inherently lack explicit constraint mechanisms, necessitating the development of penalty function approaches that embed equality and inequality constraints into the objective function while maintaining solution feasibility and optimization efficiency. The transformation of Higher-Order Binary Optimization (HOBO) problems into QUBO form through quadratization techniques, presents another significant technical challenge. Many wireless optimization problems naturally involve polynomial terms of degree 3 or higher, particularly in applications involving product constraints or multi-linear objective functions. The quadratization process requires introducing auxiliary variables to reduce polynomial degree, but this expansion must be minimized to avoid exceeding the variable limits of current quantum hardware. Problem decomposition strategies become essential for large-scale systems that exceed current quantum hardware limitations, requiring the development of hierarchical decomposition approaches that maintain optimization quality while enabling solution on near-term quantum devices. Outcome of the objective is the definition of quantum and quantum-inspired algorithms specifically tailored to the characteristics of XL-MIMO optimization problems. Hybrid precoding optimization (in conjunction with Obj 7) requires algorithms that can efficiently handle the mixed analog-digital nature of the precoding architecture while respecting hardware constraints such as constant modulus requirements for analog precoders. Joint power allocation and beamforming for mixed NF/FF scenarios introduces unique challenges related to the different propagation characteristics and optimization objectives in these regions. Positioning optimization for MAs and FAs represents a particularly complex combinatorial problem where the search space grows exponentially with the number of reconfigurable elements. The development of quantum algorithms for these problems requires careful consideration of the discrete nature of the optimization variables and the coupling between spatial configuration and communication performance. Additionally, this objective encompasses the investigation of non-linear precoding methods such as vector perturbation techniques, which were traditionally considered computationally prohibitive but may be feasible through quantum-enhanced optimization approaches.

Objective 11: QML applications designed for wireless communication challenges

The objective is to investigate QML applications specifically designed for wireless communication challenges. Channel State Information (CSI) prediction and channel modeling represent fundamental problems where QML may provide advantages through enhanced pattern recognition capabilities and improved prediction accuracy for high-dimensional channel data. Adaptive resource allocation based on traffic patterns requires real-time learning and optimization capabilities that may benefit from the parallel processing capabilities inherent in quantum systems. Intelligent beam management and user scheduling in XL-MIMO systems involve complex decision-making processes that must account for interference patterns, user mobility, and quality of service requirements. QML approaches may enable more sophisticated decision-making algorithms that can process multiple factors simultaneously through quantum superposition. Anomaly detection for ISAC applications represents another promising area where quantum pattern recognition may enable the identification of subtle anomalies in high-dimensional sensor data that would be challenging for classical ML approaches.

Objective 12: Definition of use-cases and PoCs

QUEST-6G aims to validate its technical innovations—such as NF/FF hybrid beamforming, XL-MIMO, ISAC, and quantum-assisted radio access control—through simulation, lab testing, and real-world PoCs. This objective aims to design, implement, and validate representative use cases and PoCs that demonstrate the disruptive capabilities of XL-array and cell-free MIMO systems in 6G. An identified use case and major demonstration component is a full-body pose estimation system using FR2/FR3 cell-free MIMO, showcasing integrated RF sensing, edge AI inference, and XR interaction. The project will combine RF data, motion capture ground truth, and AI models to evaluate performance across multiple environments. The focus is on immersive XR, telepresence and auxiliary services that span among verticals like: entertainment, healthcare and rehabilitation, and industrial control, monitoring and training scenarios – where NF and hybrid NF/FF beam- focusing/forming unlock extreme spatial multiplexing and ISAC functionality. By merging distributed ISAC setups with AI/quantum-inspired optimization, the project will validate real-time, privacy-preserving sensing and communication with stringent service requirements. To this end, three PoCs are planned. PoC-0 will focus on radio and PHY designs validating the achievement in XL-array/BFIC fabrication, waveform designs and beam- focusing/forming algorithms (in controlled environment – provided by IMST). PoC-1 and PoC-2 will be hosted in testbeds provided by ORO and IMEC, validating real-time processing, low-latency transmission, and end-to-end (E2E) integration with B5G/6G infrastructure. These demonstrators will establish XL-array supported 6G systems as enablers of scalable, low-latency, EMF-compliant, and socially relevant services. QUEST-6G PoCs come as a follow-up to the PoCs conducted in the course of iSEE-6G and 6G-MUSICAL SNS JU projects.