## 1 Introduction
### Application of ADRs in Hostile VLC Environments  
After an in-depth literature review, no direct applications of ADRs in underground mining VLC environments were found. However, a recent work involving angular diversity selection schemes in hostile environments, specifically tunnel construction, is presented in [42]. This paper presents a characterization of the optical channel for tunnels, implementing PDs arrayed with angular diversity to improve the symbol error rate (SER) in reception. Although the tunnel construction environment is similar to the underground mine, the dimensions of the scenarios and the location of the transmission LEDs are different. Besides, the performance analysis in this work is preliminary, without giving greater depth to solutions of angular distributions of PDs or evaluation of other VLC system parameters.  
In this work, we expand the work in [43], extending its application in a VLC underground mining scenario, and considering two typical mining environments: mining roadway and mine working face [9; 16]. Moreover, a new ADR geometric distribution is proposed, called hemi-dodecahedron ADR, to evaluate its performance to mitigate the ICI and compare it with the pyramidal ADR presented in [22]. Three signal combination schemes are included with the ADRs [44]: select best combining (SBC), equal gain combining (EGC), and maximum ratio combining (MRC). To the best of our knowledge, this is the first time that the problem of ICI in VLC underground mining environments has been analyzed, and that ADRs are presented as a solution to mitigate the ICI in these VLC mining scenarios. The contributions of this work are the following.  
1. A detailed underground VLC system model, in which, further to considering LoS and NLoS components with their channel impulse responses and channel direct current (DC) gains, thermal noise, and shot noise are also considered. These parameters affect underground mining environments to a greater extent. Furthermore, a brief analysis of the lighting in the proposed mining scenarios is done.
2. An analytical framework of a pyramidal ADR is performed, based on a regular pyramidal polyhedron, where the PDs are located on the lateral triangular faces, pointing in different directions, which mitigates the ICI and minimizes fluctuations of the SINR.  
A new ADR structure is proposed, it is based on a regular hemi-dodecahedron, which consists of a PD located on its upper pentagonal face and five PDs located on its lateral pentagonal faces. This design acquires the best characteristics of the pyramidal and hemispherical ADRs existing in the state of the art, with the objective of reducing the ICI.
4. The impact of applying the proposed ADRs, in the improvement of the overall system performance, is measured by using the following metrics: the user data rate (UDR), the SINR, shown as a cumulative distribution function (CDF), and the BER, together with the SBC, EGC, and MRC schemes, validating them with Monte-Carlo simulation results. Although few authors have addressed the issue of VLC in underground mines, some of these metrics have not been evaluated in previous studies, these being necessary to verify the ICI mitigation.  
The remainder of this paper is organized as follows. In Section 2, the VLC system model for underground mining is presented in detail. In Section 3, we contextualize the ICI in VLC underground mining environments and describe the analytical frameworks of the ADR solutions presented for this work. In Section 4, the signal combining schemes to be implemented with the ADRs are mathematically described. Section 5 evaluates and compares the solutions presented in the underground VLC mining system, based on several established metrics. Finally, relevant conclusions are presented in Section 6.