RIS-Assisted UAV-Enabled Cell-Free MIMO Systems for 6G Communications

Abstract

The exponential surge in global mobile data traffic and the stringent requirements of emerging applications such as extended reality, holographic telepresence, and advanced industrial automation expose fundamental limitations in 5G networks, particularly in achieving ultra-reliable low-latency communication (URLLC) and massive connectivity in challenging environments. This thesis investigates the performance enhancements provided by four pivotal 6G enabling technologies: conventional massive MIMO, cell-free massive MIMO, Reconfgurable Intelligent Surfaces (RIS), and UAV-assisted communication, with a focus on their ability to deliver superior coverage probability in high signal-to-interference-plus-noise ratio (SINR) regimes essential for future wireless systems, including Industry 4.0 deployments. Despite extensive theoretical and simulation-based research demonstrating individual benefits of these technologies, a notable research gap persists in the absence of unified, comparative evaluations conducted under consistent modelling assumptions and realistic propagation conditions. To address this gap, this study employs large-scale Monte Carlo simulations (10,000 independent drops per scenario) to systematically quantify coverage probability across SINR thresholds ranging from 0 to 20 dB. The primary objectives are to: (1) model and evaluate the SINR coverage performance of each technology against its respective baseline; (2) assess implications and limitations for 6G network design. Key findings indicate that cell-free massive MIMO achieves near-perfect coverage (100 %) even at 20 dB SINR, outperforming all others due to macro-diversity and cell-edge elimination. RIS delivers substantial passive gains, pushing coverage close to 100% in obstructed scenarios. Conventional massive MIMO provides reliable and consistent array gain improvements, while UAV-assisted communication offers modest but valuable line-of-sight enhancements under favourable conditions. Overall, the technologies rank as cell-free MIMO > RIS > conventional MIMO > UAV for high-reliability applications. These results highlight the critical role of technology integration in realising robust, energy-efficient 6G networks capable of supporting extreme reliability demands in industrial settings.