5G & beyond cellular networks for industrial IoT: a cross-layer perspective

5G networks are transforming telecommunications by serving both human and machine communications, enabling new use cases across various industries. As a key enabler for Internet of Things (IoT), 5G provides connectivity to devices that collect and act on data. Within this context, Industrial IoT (IIoT) supports Industry 4.0, improving efficiency and safety of industries by enabling communication between industrial devices. However, this progress introduces significant challenges, as networks must meet the performance, reliability, and scalability requirements dictated by the served applications. To overcome these challenges, this thesis provides solutions based on the industrial applications, the cellular network, and their interplay, including cross-layer approaches. The arguments span the whole protocol stack and focus on the mutual dependence between applications and the supporting network. Novel solutions and methodologies are provided, addressing the challenges of industrial communications to advance future cellular IIoT systems. First, an analysis of cellular networks and IIoT is provided. Next, it is performed a joint analysis of a safety-critical industrial application and the 5G network serving it, highlighting their interplay, and how this affects scalability and reliability. Subsequently, we leverage application-layer data to optimize the Radio Access Network (RAN), enhancing the performance of the served industrial application. Following, to address the growing demand for throughput and reliability in IIoT, Orthogonal Chirp Division Multiplexing (OCDM), a promising waveform for beyond-5G communication, is evaluated. Additionally, Industrial Ethernet protocols and their integration with 5G networks are examined. The findings, derived mainly from simulations and experiments, provide valuable insights on cellular IIoT networks and show improvements over current solutions. These results highlight the importance of adopting a cross-layer approach to meet IIoT requirements and offer guidelines for designing future cellular networks, laying the groundwork for more efficient and reliable industrial systems.