Infinite and finite blocklength analysis of RIS assisted communication with spectrally efficient signaling techniques

Abstract

Reconfigurable intelligent surfaces (RISs) emerged as a pivotal technology for the upcoming sixth generation (6G) wireless communication because of its characteristics of controlling propagation environment, increasing signal strength and extending coverage with sufficient energy efficiency (EE). On the other hand, to support the massive connectivity of devices with various quality-of-service (QoS) requirements and offer significant spectral efficiency (SE) and EE improvements, non-orthogonal multiple access (NOMA), cognitive radio (CR), and full-duplex (FD) systems have been considered as the potential technologies in the communication systems, such as cellular network, relaying networks, and wireless sensor networks. This thesis focuses on the performance analysis of RIS-assisted communications with spectrally efficient signaling techniques like NOMA, CR, and FD by using infinite blocklength (IBL) and finite blocklength (FBL) codes. Firstly, we design a novel paradigm of RIS-assisted NOMA system by formulating a phase shift matrix that provides coherent phase shift across both users of a NOMA pair. The performance of the considered system is analyzed by deriving the closed-form expression of outage probability (OP) and system throughput. Furthermore, ultra-reliable and low-latency communication (URLLC) is one of the pillars for 6G networks to satisfy the rigorous conditions of internet of things (IoT) applications (e.g., industrial automation, remote surgery, virtual/augmented reality, tactile internet, and vehicle-to-everything communications) subjecting to extremely high reliability (99.999%) and ultralow latency (≤ 1 ms). For such conditions, the conventional analysis approaches based on the Shannon capacity with the assumption of IBL wireless transmission are no longer suitable. To this end, a new transmission method, short-packet communication (SPC) with finite FBL codes, has been used to reduce the physical-layer transmission latency for URLLCs. Therefore, secondly, we have considered the IBL and FBL analysis of RIS-assisted CR-NOMA system with energy harvesting mechanism to deploy IoT devices by considering practical constraints of hardware impairments (HIs). For the IBL regime, we derived the analytical expression of OP and system throughput. For the FBL regime, we derived the novel analytical expression of average block error rate (ABLER), goodput, latency and reliability. Thirdly, we have investigated the performance of active RIS (ARIS) with two FD users communicating with each other using FBL codes by considering HIs at the FD transceiver nodes. We derived the analytical and asymptotic expressions of ABLER and ergodic capacity. Additionally system throughput, goodput and latency parameters are also analyzed. Finally, the FBL analysis of simultaneously transmitting and reflecting RIS (STAR-RIS) assisted NOMA system by considering imperfect channel state information (CSI) is analyzed. We derived the novel analytical expressions of ABLER, system throughput, goodput, latency and reliability. All the analytical results presented in this thesis are validated through extensive Monte-Carlo simulations.