Mitigating the Impact of Blockages in Millimeter-Wave Vehicular Networks Through Vehicular Relays

With the high data rates and ultra-low latency it provides, millimeter-wave (mmWave) communications will be a key enabler for future vehicular networks. However, due to high penetration losses and high mobility, mmWave links experience frequent blockages. We present an analytical framework to evaluate the performance of vehicular relaying, where vehicles on a highway exchange data with the network, either over direct vehicle-to-infrastructure (V2I) links with roadside units or a combination of a vehicle-to-vehicle (V2V) sidelink and a V2I link. Both V2V and V2I line-of-sight links can be blocked by other vehicles. We establish continuous-time Markov chain models of the blockage events that V2I links and vehicular relays experience, and use their steady-state solution to obtain analytical expressions for the blockage probability, average blockage duration and the SINR distribution. We demonstrate through numerical examples that relays are helpful, especially when the traffic density is high, since they can provide intermittent but more frequent connection opportunities and reduce the blockage duration. We show that relays that are far from a vehicle only have a marginal benefit since they are blocked with higher probability, compared to the closer relays. The proposed analytical framework enables fast and accurate assessment of a given deployment scenario, which will benefit researchers exploring mmWave-enabled vehicular networks.