A Location-Aware RF-Assisted MAC Protocol for Sectorized Vehicular Visible Light Communications

Vehicular Visible Light Communications (V-VLC) has emerged as a viable technology complementing RF-based communication in automotive scenarios. This is mainly due to properties such as the large unlicensed spectrum and the intrinsic security due to the Line Of Sight (LOS) requirement. In this context, one aspect of V-VLC needs further attention given the current state of the art, namely medium access under multi-user interference. In this paper, we extensively study interference in typical vehicular scenarios. Based on the findings from this study, we propose a novel approach for medium access. We follow a location-aware cross-layer approach that exploits the Space Division Multiple Access (SDMA) feature of modern matrix lighting modules to avoid interference and thus collisions. Making use of heterogeneous communication concepts, in which vehicles share their positions via the Radio Frequency (RF) channel, V-VLC transmissions can be scheduled accordingly. In an extensive simulation study using a realistic urban scenario, we first identify critical interference scenarios and then assess the efficacy of our proposed solution. We also investigate the impact of position uncertainty due to, e.g., GPS errors. Our results clearly indicate the benefits of a location-aware protocol that exploits the space-division features of the matrix lights.