Sustainable Metasurface-Assisted Indoor Wireless Communication System Design

QC 20260330

Abstract

The densification of wireless networks toward fifth- and sixth-generation standards has intensified the demand for reliable high-throughput connectivity in indoor deployment scenarios (IDS), such as aircraft cabins, metro wagons, and stadiums. Although millimeter-wave (mmWave) communication offers the spectral resources needed to meet this demand, its sensitivity to propagation loss and blockages severely limits its performance, particularly in IDS. Metasurfaces have emerged as a promising means of extending mmWave coverage through manipulating the propagation environment. Advanced investigations have been conducted on metasurface-featured system performance enhancement. However, the operating cost, which is a practical and critical concern of metasurface deployment, has received insufficient attention in the literature. Deploying a reconfigurable metasurface in practice requires cabling, power supply, and control infrastructure, costs that represent a real barrier to scalable deployment, particularly in indoor environments like IDS, where infrastructure installation is physically limited or tightly regulated.

This thesis investigates the design of sustainable metasurface-assisted indoor wireless communication systems, placing operating cost alongside performance as a primary design criterion. The work examines different types of metasurfaces that differ in the metasurface gain they provide and the operating cost they incur. By identifying and verifying an optimal design choice among these alternatives, this thesis advances a sustainable metasurface-assisted system that addresses the performance-cost dilemma inherent to IDS deployments.

The first contribution studies the trade-off between operating cost and performance enhancement by optimizing a mixed static metasurface (SMS) and reconfigurable intelligent surface (RIS) deployment in an mmWave IDS. Using a fractional programming penalty-based successive convex approximation (FPPSCA)-based iterative algorithm, the results reveal a diminishing-returns relationship. While replacing two SMSs with RISs already yields a 13 Mbps gain, increasing the RIS count beyond 16 out of 22 surfaces produces less than 1 Mbps of additional gain, confirming that full reconfigurability is unnecessary and motivating a more cost-effective middle-ground solution. The second contribution proposes and evaluates a self-sustainable RIS (ssRIS)-assisted mmWave system for IDS, where ssRIS achieves self-sustainability through power harvesting via a codebook-based element splitting scheme, eliminating the need for cabling and external power. A two-stage iterative algorithm jointly optimizes phase shifts, user equipment (UE)-to-ssRIS associations, and time allocation. The results show that ssRIS outperforms SMS by up to 19.8 Mbps in compact environments, confirming a favorable position within the gain-cost trade-off, with coverage advantages diminishing as deployment distances grow. The third contribution conducts a feasibility study of ssRIS across diverse scenarios, analyzing how element count scales with transmit power, data rate demands, and outage constraints under element splitting (ES) and time switching (TS) schemes. TS benefits from stronger channel hardening under moderate conditions, but scales exponentially with harvesting difficulty, whereas ES scales only linearly, offering greater robustness in challenging environments. Together, these findings provide actionable guidance for practical ssRIS deployment.

Link to DiVA