Visible Light and mmWave Propagation Channel Comparison for Vehicular Communications

Future connected vehicles are expected to require fast and reliable exchange of road information to increase safety and enable cooperative driving. Currently, standardized vehicular communication technologies aim to enable basic safety message exchanges with limited bandwidth. Recently, alternative technologies, based on millimeter-wave (mmWave) and visible light spectrum are proposed as complementary vehicle-to-everything (V2X) communication schemes, provisioned to support future connected vehicles with high bandwidth and increased security. However, the understanding of channel propagation characteristics is the key to achieve reliability, due to higher path loss compared to 5.8 GHz band. In this work, we compare channel path loss characteristics of mmWave and vehicular visible light communication (VVLC) schemes to provide an overview regarding technology selection in an indoor parking garage. Path loss measurements are conducted with respect to various inter-vehicular distances, receiver angles, nearby vehicle existence, and lane occupation scenarios. Measurement results indicated path loss of 21.47 dB for VVLC from 3 m to 20 m distances. Moreover, path loss for mmWave 26.5 GHz and 38.5 GHz channels increased 12.5 dB, and 12.7 dB, respectively. Nearby vehicles are shown to decrease path loss of 26.5 GHz and 38.5 GHz signals up to 9.78 dB, and 9.56 dB, respectively, whereas VVLC channel path loss decreases 0.4 dB at the same scenario. Channel frequency response (CFR) measurements indicated frequency flat behavior of VVLC channels while mmWave channel exhibits frequency selectivity induced dispersion due to parking garage structure. Obstructed line-of-sight (OLoS) measurements further reveal that blocking vehicle interrupts VVLC signals while selecting a favorable antenna location leads up to 30 dB less path loss for mmWave signals.