The Blind Side: Latency Challenges in Millimeter Wave Networks for Connected Vehicle Applications

Millimeter-wave (mmWave) is a promising network access technology to enable the high data rates, high reliability and ultra-low latency required by connected vehicle services in future vehicular networks. However, mmWave links are prone to blockages due to high penetration loss, which can cause frequent service interruptions and degrade the system performance in terms of reliability and latency. In this study, we analyze the latency and reliability performance of mmWave communications between vehicles and roadside units (RSUs) in a highway scenario, where the line-of-sight (LOS) links can be blocked by vehicles. First, we establish a continuous-time Markov chain model of the blockage events. By using the steady-state solution of this model, we explicitly derive the blockage probability and average blockage duration, which can be used to characterize the reliability and latency performance. We validate the accuracy of the analytical model by comparing it with simulations using real-world traffic data and vehicle distributions. We demonstrate that reducing the duration of long-lasting blockage events is more challenging than reducing the frequency of blockages. We consider three approaches to control the blockage probability and distribution of blockage durations: (i) increasing RSU density, (ii) increasing RSU heights and (iii) managing the vehicular speed limits. We show that the first two approaches are effective in reducing the blockage probability, whereas the third approach can be used to eliminate long blockages and improve latency performance. We discuss the implications of our results in terms of the benefits and challenges associated with these approaches.