### Related Work  
Due to the relative hostility of mines compared to classical indoor environments, various channel models have been proposed for UM-VLC systems. In Ref. [15], the authors propose a geometric-based deterministic model (GBDM) considering the LOS and NLOS components for a coal mine's workforce with hydraulic support metal columns along its footpath. The authors considered the reflections of the metal columns, roof, and floor. Additionally, they also derive the optimal TX location that maximizes the coupled energy of the light signals blocked by the metal columns. The authors also studied the degrading effect of coal dust on the optical signal, employing Mie theory for modeling light scattering and absorption. The authors of [16] have proposed a recursive UM-VLC channel model that considers light scattering and absorption due to particles and shadowing caused by people. They simulate both a mining roadway and a workforce scenario containing multiple transmitters modeled as ideal Lambertian sources and obtain the path loss and RMS delay for the LOS and NLOS links, considering multiple link ranges. Mie theory is used to model light attenuation caused by dust, and a bimodal Gaussian distribution (BGD) is used to model shadowing phenomena. In Ref. [17], the authors present a VLC channel model for underground tunnels in general. They focus their attention on the relative orientation of LEDs and PDs and their effect on the irradiance and incidence angles, proposing a Lambertian VLC channel model that considers an LOS component dependent on the azimuthal (tilt) and polar (rotation) angles of LEDs and PDs and a diffuse NLOS component independent of the PD's incident angle. They provide simulation results in a tunnel scenario in terms of the symbol error rate (SER) for a VLC link based on pulse amplitude modulation (PAM). In Refs. [7; 18; 19], the authors propose a ray-tracing-based UM-VLC channel considering a Lambertian light source, arbitrary LED and PD tilt and rotation angles, reflections on non-flat irregular walls, scattering due to dust particles, and shadowing due to large machinery. The LED/PD tilt and rotation modeling is taken from [17]. The irregularity of the walls is modeled by discretizing the walls into a grid with small wall segments, each with nondeterministic azimuthal and polar angles. The shadowing effect is modeled as a weighting parameter in the LOS and NLOS links and is calculated as the expected value of a Poisson process which describes the random entry of light-blocking objects into the simulation scenario. The light scattering is modeled as a combination of Rayleigh and Mie regimes, with dust particles randomly distributed around the PD in a two-dimensional disk in [7] and in a hemispheric three-dimensional region in [18]. The light-degrading effects of scattering are not factored into the LOS and reflection-induced NLOS links; instead, another NLOS channel link is modeled, induced by the scattered light, in what could be called a scattering-induced NLOS link. Scattering-induced NLOS links are common in optical communication channels where TX and RX are blocked by obstacles or the LOS link cannot be guaranteed [20], whereas it is not common in VLC channels since the LOS link is usually available. In Ref. [7], the proposed channel model was evaluated in a simulated UM tunnel. The resulting CIR, received optical power, and RMS delay were presented and compared with a referential classical indoor VLC channel model. In Ref. [18], the same simulated environment was used, with CIR, received optical power, SNR, RMS delay, and BER being presented for different amounts of modeled dust particles, and compared to the proposed channel model in [7], considering on-off keying (OOK) modulation. In Ref. [5], the authors propose a UM-VLC channel based on ray tracing for coal mines, considering a Lambertian light source, scattering, and absorption of light and shadowing. Mie theory is used to model the scattering and absorption due to coal dust, while shadowing is modeled using a BGD.