See and Beam: Leveraging LiDAR Sensing and Specular Surfaces for Indoor mmWave Connectivity

TL;DR

Indoor mmWave links suffer from blockage and high path loss, limiting reliability. See and Beam combines low-cost LiDAR sensing with passive specular reflectors to map NLoS environments and steer mmWave beams toward co-reflective paths, leveraging surface properties. Experiments at 60 GHz show LiDAR-guided reflection can improve the minimum RSS by over 20 dB in deep NLoS regions, with LiDAR-derived angle-of-departure steering approaching exhaustive search performance; mirror-type reflectors offer broad coverage, while some surfaces limit LiDAR sensing. This approach provides a low-cost, scalable alternative to active reflectors for enhancing 6G+ indoor connectivity using existing infrastructure.

Abstract

Millimeter-wave (mmWave) communication enables multi-gigabit-per-second data rates but is highly susceptible to path loss and blockage, especially indoors. Many indoor settings, however, include naturally occurring specular surfaces such as glass, glossy metal panels, and signage, that reflect both light and mmWave signals. Exploiting this dual reflectivity, we propose See and Beam, a low-cost framework that combines LiDAR sensing with passive specular reflectors to enhance mmWave connectivity under non-line-of-sight (NLoS) conditions. In this paper, as a proof of concept, we deploy three types of reflectors, glossy, smooth, and matte (non-specular), to evaluate joint LiDAR/mmWave reflection in an indoor scenario. We demonstrate that using LiDAR-mmWave co-reflective surfaces enables a co-located LiDAR sensor to map the NLoS environment, localize NLoS users, and identify viable communication reflection points. Experimental results at 60 GHz show that LiDAR-guided beam steering with co-reflective surfaces improves the minimum received signal strength by over 20 dB in deep NLoS regions. Moreover, LiDAR-derived angle-of-departure steering achieves performance comparable to exhaustive NLoS beam search. This low cost, and scalable framework serves as an effective alternative to configurable reflecting surfaces and enables robust mmWave connectivity in future 6G and beyond networks.

Figures (9)

• Figure 1: Indoor surface types with specular or semi-specular reflection properties relevant to mmWave and LiDAR sensing. These materials can serve as passive mmWave reflectors and optical relays for joint sensing and NLoS communication.
• Figure 2: Simulated reflectance versus incidence angle at 60 GHz for selected indoor materials using their complex dielectric constants obtained from Correia1994, and Balanis2012.
• Figure 3: Flat reflector surfaces of size 0.3 × 0.9 $m^2$ mounted on a foam board at an azimuth angle of $45^o$ with respect to the transmitter.
• Figure 4: Left: L-shaped corridor featuring 102 grid points for RSS measurements. Right: image of the co-located mm-wave transmitter and LiDAR at the end of the corridor.
• Figure 5: Beyond LoS LiDAR tracking of a user (1.8 m tall) in an L-shaped corridor using a glossy silver sheet reflector (Fig. \ref{['fig:UTsurfaces1']}) of size $0.3 \times 0.9 m^2$.