Site-Specific Channel Modeling and Optimization of RIS-Assisted Multiuser MISO Systems

Abstract

This paper presents a physics-based channel modeling and optimization framework for reconfigurable intelligent surface (RIS)-assisted downlink multi-user multiple-input single-output (MU-MISO) communication systems in site-specific environments. A hybrid ray-tracing (RT) and full-wave electromagnetic analysis approach is developed to construct a deterministic channel model that explicitly captures multipath propagation, RIS scattering behavior, and mutual coupling effects through a non-diagonal load impedance representation. Based on this model, an alternating optimization scheme jointly updates the base-station (BS) beamformer and RIS load impedances to maximize the minimum achievable rate under a total transmit power constraint and practical capacitance limits. The objective of the proposed framework is to provide a reliable initial assessment of the system-level impact of RIS deployment in realistic propagation scenarios. To evaluate this capability, the RIS is operated in a column-paired 1-bit control mode that enables exhaustive evaluation of all realizable configurations in both simulation and measurement. Performance is compared at the distribution level through achievable-rate histograms across all configurations and further examined under small user-location variations. The observed agreement between simulation and measurement demonstrates that the proposed framework reliably captures practical performance trends and provides useful guidance for the design and deployment of RIS-assisted MU-MISO systems in site-specific environments.

Figures (10)

• Figure 1: RIS unit cell topology (obtained from liu2025channel). The design features a Jerusalem cross patterned on an RO3003 substrate with two varactors (red) and two resistors (black) enabling reconfigurable operation at 5.8 GHz.
• Figure 2: Illustration of a MU-MISO communication environment with three linear antennas as Txs, each separated by $\lambda/2$ at an operating frequency of $5.8$ GHz. The RIS is located at (0, 0, 0) with 1D control. The total electric field distribution is shown within the region indicated by orange dots, and the targeted users are located at (1.3, 3.13, 0) m, (1.8, 2.38, 0) m, and (2.3, 1.63, 0) m, marked as red ,blue, and green dots in order. The RIS structure consists with the one designed in liu2025risliu2025channel.
• Figure 3: The comparison between simulation and measurement with and without RIS deployment.
• Figure 4: Comparison of RIS capacitance distributions (column-wise) for continuous and 1-bit configurations shown in red and blue bars, respectively.
• Figure 5: Signal gain distribution (normalized by $30$ dBm/Hz and shown in dB scale) within the receiving region for three target locations: (1.30, 3.13, 0) m, (1.80, 2.38, 0) m, and (2.30, 1.63, 0) m (red circles). Distributions correspond to $|\mathbf{H}_{\omega_k}|^2$ for $k=1,2,3$ and their corresponding continuously tuned RIS capacitance configurations.