title: Investigating the data rate in reconfigurable intelligent surfaces assisted wireless communication
Creators: name: Hassouna, Saber I.H.
Publisher: name: University of Glasgow
Year: 2024

description: In the realm of wireless communications, reconfigurable intelligent surfaces (RIS) offer network providers the capability to manage the behaviour of electromagnetic signals, encompassing their scattering, reflection, and refraction properties. Numerous research findings have underscored RIS’s effectiveness in controlling wireless wave attributes, such as amplitude and phase, without necessitating intricate equalization and decoding at the receiver’s end. However, it’s crucial to note that configuring the surface in practical scenarios with frequency-selective fading channels should be carefully addressed across the entire bandwidth. This entails considering a wideband orthogonal frequency division multiplexing (OFDM) communication system that is based on a practical RIS configuration, involving distinct phase shifts for each element on the surface.

In this thesis, we propose a communication setup to investigate the user data rate enhancement with the aid of RIS surface using practical phase shift model for multi-bit RIS phase resolutions. It is observed that the achievable data rate enhances with higher bit resolutions but the cost of hardware complexity. The effects of mutual coupling (MC) due to the large RIS surface and the electromagnetic interference (EMI) due to the unavoidable signals from external sources are well investigated on the performance data rate. The MC and EMI degrade the achievable rate so, the RIS must be aware of such signal impairment parameters.

Furthermore, we have extended the study of the performance of the achievable data rate for multi-users in single-input-single-output (SISO) wideband based-RIS system with single antenna at the access point (AP) and each user. The propagation environment was assumed to have both line-of-sight (LoS) and non-line-of-sight (NLoS) channels so, it is more realistic and practical. Different RIS algorithms are studied in both LoS and NLoS channels scenarios taking into considerations the computational complexity and run time. The semidefinite relaxation scheme shows higher performance than the other schems but at the cost of computational complexity and run time consequently, the thesis proposes low complex with comparable performance iterative power method that adopts codebook approach.

The RIS demonstrated significant performance data rate not only in communication but also in localization. The RIS-enabled localization has been investigated in the near and far-field regimes using realistic RIS phase shift model that considers the phase and amplitude variations. We introduced an analysis of Fisher information using a straightforward expression for the Fisher information matrix (FIM), illustrating how the position error bound (PEB) is influenced by the phase profiles of RIS. We employed three types of RIS phase profiles—random, directional, and positional configurations—to showcase the impact of RIS on localization and communication within the near-field range. These profiles were designed considering both the amplitude and phase responses of the RIS, utilizing a practical phase-dependent amplitude model. The random profile ensures a uniform signal-to-noise ratio (SNR) across the deployment area, while the directional and positional profiles enhance SNR towards the user’s location. Additionally, we devised a straightforward localization scheme to simplify the maximum likelihood (ML) estimator’s complexity. In the near-field region, the achievable data rate diminishes with distance, mirroring the gradual increase in localization error as distance from the RIS grows. Both the achievable data rate and localization error exhibit subpar performance when employing the RIS phase-dependent amplitude model with amplitude values less than one. Consequently, the widespread assumption of unity amplitude in the RIS phase shift model, as commonly seen in literature, leads to overly optimistic and inaccurate results in localization and communication performance.

Simulation results have shown the importance of utilizing RIS technology in both communication and localization. Finally, we have carried out RIS measurements field in the mast lab to configure the test bed hardware of 64×64 RIS elements in order to show the capability of such new technology in improving the signal strength and coverage.