Terahertz Signal Coverage Enhancement in Hall Scenarios Based on Single-Hop and Dual-Hop Reconfigurable Intelligent Surfaces

Terahertz (THz) communication offers ultra-high data rates and has emerged as a promising technology for future wireless networks. However, the inherently high free-space path loss of THz waves significantly limits the coverage range of THz communication systems. Therefore, extending the effective coverage area is a key challenge for the practical deployment of THz networks. Reconfigurable intelligent surfaces (RIS), which can dynamically manipulate electromagnetic wave propagation, provide a solution to enhance THz coverage. To investigate multi-RIS deployment scenarios, this work integrates an antenna array-based RIS model into the ray-tracing simulation platform. Using an indoor hall as a representative case study, the enhancement effects of single-hop and dual-hop RIS configurations on indoor signal coverage are evaluated under various deployment schemes. The developed framework offers valuable insights and design references for optimizing RIS-assisted indoor THz communication and coverage estimation.

💡 Research Summary

This paper addresses the severe free‑space path loss that limits the coverage of terahertz (THz) communication, especially in indoor environments where line‑of‑sight (LOS) paths are often blocked by walls, pillars, or other obstacles. To mitigate this limitation, the authors propose the use of reconfigurable intelligent surfaces (RIS) that can dynamically steer incident electromagnetic waves toward desired directions, thereby creating additional high‑gain propagation paths.

A three‑dimensional (3 × 45 × 3 m) hall model is first built in SketchUp, with realistic material parameters (ceiling board, granite floor, concrete walls and pillars) defined at a carrier frequency of 332 GHz. The transmitter (Tx) is placed at (5, 28, 1.5) m and initially both Tx and receivers (Rxs) use omni‑directional antennas. Ray‑tracing simulations performed with the CloudRT platform reveal three typical regions: (A) pillar‑blocked zones with weak signals, (B) wall‑blocked zones near openings with modest reflected/scattered contributions, and (C) deep shadow zones where only second‑order reflections or sparse scattering are present, resulting in extremely low received power.

To evaluate RIS‑assisted coverage, an antenna‑array‑based RIS model is integrated into CloudRT. Each RIS consists of a 100 × 100 microstrip patch array (half‑wavelength spacing) whose element phases are controlled according to a quantized phase‑shift formula that accounts for incident angle, element position, and the number of quantization bits. The RIS radiation pattern is generated by extending MATLAB’s array antenna toolbox. The received power for a single‑hop RIS link is expressed as

P = Pt · GTx · (1/4πL1²) · cosθ1 · S1 · F1 · (1/4πL2²) · GRx · λ²/(4π)

and for a dual‑hop configuration as

P = Pt · GTx · (1/4πL1²) · cosθ1 · S1 · F1 · (1/4πL2²) · cosθ2 · S2 · F2 · (1/4πL3²) · GRx · λ²/(4π).

These equations explicitly incorporate the effective illuminated area (cosθ·S) and the RIS gain (F) for each hop, allowing a precise quantification of the additional loss introduced by the extra hop.

Three deployment schemes are examined. In Scheme 1, RIS 1 is placed at (2.5, 2.5, 1.5) m and RIS 2 at (43, 34, 1.5) m. Deploying RIS 1 alone raises the average received power in Region 1 from –152.9 dBm to –132.6 dBm, a 20.3 dB gain. Adding RIS 2 further improves Region 2, achieving –166.6 dBm where no LOS or strong scattered paths exist without RIS.

Scheme 2 moves RIS 1 to (14.68, 6.1, 1.5) m while keeping RIS 2 at the same location as Scheme 1. Here RIS 1 alone provides 7.2 dB and 10.0 dB gains in Regions 1 and 3, respectively, and the combined RIS 1 + RIS 2 configuration yields –162.2 dBm in Region 2.

Scheme 3 positions RIS 1 at (2.5, 2.5, 1.5) m and RIS 2 at (32.61, 17.67, 1.5) m to target shadowed zones created by pillars. RIS 1 alone improves Regions 1 and 3 by 6.8 dB and 13.9 dB, while RIS 2 adds a modest 4.9 dB increase in Region 4.

Across all scenarios, the results demonstrate that a well‑placed single‑hop RIS can deliver substantial power boosts (up to 20 dB) in areas lacking LOS, especially when the RIS is located where first‑order scattering points are dense. The second‑hop RIS, despite its weaker contribution, still provides measurable improvements (≈4–6 dB) in deep‑shadow regions where the first hop alone cannot reach. Moreover, when two weak‑signal regions are aligned along a straight line, a single RIS can sometimes serve both, reducing system complexity.

The paper’s contributions are threefold: (1) development of a high‑fidelity RIS‑enabled ray‑tracing framework by integrating an antenna‑array RIS model into CloudRT, (2) quantitative assessment of single‑ and dual‑hop RIS deployments in a realistic indoor hall, and (3) provision of practical design guidelines—such as placing the first‑hop RIS near dense first‑order scatterers and using dual‑hop configurations to bridge isolated shadow zones. The authors suggest future work on optimal multi‑RIS placement algorithms, dynamic beam‑steering strategies, and experimental validation with hardware prototypes to bridge the gap between simulation and real‑world deployment.