## 4 Conclusions  
We have proposed a novel wavelength-dependent SISO UM-VLC channel model. Using the ray tracing method and considering a Lambertian light source, the LOS and NLOS components of the channel were modeled taking into account the spectral characteristics of the UM-VLC channel, the relative tilt, and the rotation angle between the LP and PD, the irregular walls of the UM tunnel, shadowing by large objects, light scattering, and absorption due to dust particles.  
Moreover, a novel wavelength-dependent CSK-based UM-VLC channel model was proposed on the basis of the wavelength-dependent SISO UM-VLC channel model. The CSK-based model considered three LEDs and three PDs, whose pairing forms red, green, and blue channels that interfere with each other. A simulation scenario was defined based on a mining roadway, where the TX was fixed, and the RX could move throughout the scenario. The average received optical power, the SNR, the CIR, and the RMS delay were obtained for the proposed CSK-based model and compared with a referential monochromatic state-of-the-art UM-VLC channel model in multiple LOS-dominant and NLOS-dominant RX positions of the simulated scenario. The SIR between the color  
Figure 10: Bit error ratio curves for the proposed and reference models. Shadowed refers to RX position \(\mathbf{R}_{1}=(2,1,1.8)\) m, while non-shadowed refers to RX position \(\mathbf{R}_{2}=(4,1,1.8)\) m. (**a**) 4-CSK. (**b**) 8-CSK. (**c**) 16-CSK.  
channels was also analyzed for the proposed CSK-based model, demonstrating how color interference changes between the NLOS and LOS regimes.  
Finally, the BER of the proposed CSK-based UM-VLC system was obtained for two positions in the simulation scenario, and compared to a monochromatic CSK-based UM-VLC system, where color distortion was modeled as a linear transformation. It was found that the BER is significantly worse when considering the wavelength-dependent channel, as it induces non-linear color distortion that the color calibration algorithm defined by the IEEE 802.15.7 standard cannot revert effectively. With these results, we believe that we have shown that accounting for wavelength dependency has a big impact on the channel modeling of color-based VLC systems such as CSK-based VLC systems, calling for its consideration in future research.  
To fully validate the proposed channel model, either on-site or test-bed experiments are to be performed in future works. On-site refers to implementing the VLC system in an actual underground mine, while test-bed refers to the implementation of an experimental setup that simulates the physical conditions of the UM-VLC channel. Furthermore, other noise models (e.g., non-Gaussian, colored, etc.) should be analyzed and experimentally verified.  
Conceptualization, R.B., C.A.-M., M.I. and I.S.; methodology, R.B., P.P.J., C.A.-M. and I.S.; software, R.B.; validation, R.B., C.A.-M., I.S., P.P.J., D.F.C., M.I. and J.S.; formal analysis, R.B.; investigation, R.B., C.A.A.-M. and I.S.; resources, C.A.A.-M.; data curation, R.B.; writing--original draft preparation, R.B.; writing--review and editing, R.B., P.P.J., C.A.-M., I.S., J.S., M.I. and D.F.C.; supervision, C.A.A.-M.; project administration, C.A.A.-M. and I.S.; funding acquisition, C.A.A.-M. and I.S. All authors have read and agreed to the published version of the manuscript.  
This research was funded by ANID FONDECYT Regular No. 1211132 and ANID PFCHA/Beca de Doctorado Nacional/2019 21190489.  
The data presented in this study are available on request from the corresponding author.  
This work was supported by Project FONDECYT Regular 1211132. This work was partially supported by CODELCO: Concuso Piersa Mineria 2021; SENESCYT \"Convocatoria abierta 2014-primera fase, Acta CIBAE-023-2014\"; FONDEF ID2110191; and STIC-AmSud 22-STIC-01.  
The authors declare no conflict of interest.