title: Reconfigurable intelligent surface for future wireless communication
Creators: name: Kazim, Jalil ur Rehman
Publisher: name: University of Glasgow
Year: 2023

description: In the current era of wireless communication, there is a constant demand for higher data rates to support the increasing use of data-intensive applications such as streaming video, online gaming, and high-definition video conferencing. These applications require a fast and reliable wireless connection to function properly. The demand for wireless services is constantly increasing, but the amount of available spectrum is finite. This means that network operators must find ways to use the available spectrum efficiently in order to support a large number of users and data-intensive applications. A more straightforward choice is to utilise higher frequencies which provide more bandwidth, but this, on the other hand, reduces the coverage area. Consequently, this would require a smaller cell size with more base stations raising deployment costs. Overall, meeting the demands of users in the current era of wireless communication requires a comprehensive and strategic approach to addressing the various challenges faced by network operators. Lately, the concept of Reconfigurable Intelligent Surface (RIS) has been introduced, which is a technology that consists of nearly passive elements, i.e., active only when voltage is applied, with no Radio Frequency (RF) chain. Instead of tuning the network endpoints, the RIS is utilized to manipulate the propagation channel environment. It is envisioned that RIS will provide numerous benefits by 1) expanding the coverage area, 2) reducing the network deployment cost, 3) improving the energy efficiency of the network and 4) increasing the network capacity. The thesis presents the world’s first in-house developed RIS prototype consisting of ‘4096 elements’ at Sub-6 GHz. The operation frequency of the RIS is kept around 3.75 GHz, which is compatible with the existing 5G operating bands. The elements are controlled via PositiveIntrinsic-Negative (PIN) diodes which switch between two-phase states. Furthermore, every unit element is individually controlled, which makes it usable to operate in the near field and perform channel estimation. The operational power consumption of the proposed RIS is observed to be 12-15 watts with beam switching speed reaching 15 ms. Two distinct application areas have been explored, i.e., RIS-assisted wireless communication and RIS-assisted health care for vitals detection. In the communication scenario, the RIS is able to focus the beam at different angles and perform conventional beam steering in real time. Additionally, a demonstration of the Orthogonal Frequency Division Multiplexing (OFDM) communication setup shows the channel manipulation by the RIS with transmitter and receiver in the non-line-of-sight (NLoS). Experiments reveal improved signal conditions attained in the presence of RIS. In the context of health care, the benefit of RIS is investigated for vitals detection, including heartbeat and breathing rate. It is shown that RIS can assist in detecting the heartbeat and breathing rate in the NLoS. Alongside, the E-field exposure around the human head (Phantom model) is investigated in the presence of RIS. Measurement results show that the RIS can reduce the E-field exposure around the head by dynamically changing its electrical aperture, thereby resulting in a reduction of the uplink energy at the user’s terminal. Hence, the overall motivation of the thesis is to explore and investigate the efficacy of RIS both in communication and healthcare scenarios.