Latency-Optimal mmWave Radio Access for V2X Supporting Next Generation Driving Use Cases

With the facilitation of the fifth generation new radio, vehicle-to-everything applications have entered a brand new era to sustain the next generation driving use cases of advanced driving, vehicle platooning, extended sensors, and remote driving. To deploy these driving use cases, the service requirements, however, include low latency, high reliability, and high data rates, which thus render utilizing millimeter wave (mmWave) carriers (spectrum above 6 GHz) as a remedy to empower the next generation driving use cases. However, suffering from severe signal attenuation, the transmission range of mmWave carriers may be very limited, which is unfavorable in mobile network deployment to offer seamless services, and compel directional transmission/reception using beamforming mandatory. For this purpose, both a transmitter and a receiver should sweep their beams toward different directions over time, and a communication link can be established only if a transmitter and a receiver arrange their beam directions toward each other at the same time (known as beam alignment). Unfortunately, the latency of performing beam sweeping to achieve beam alignment turns out to be a dominating challenge to exploit mmWave, especially for the next generation driving use cases. In this paper, we consequently derive essential principles and designs for beam sweeping at the transmitter side and receiver side, which not only guarantee the occurrence of beam alignment but also optimize the latency to achieve beam alignment. Based on the availabilities of a common geographic reference and the knowledge of beam sweeping scheme at the transmitter side, we derive corresponding performance bounds in terms of latency to achieve beam alignment, and the device corresponding latency-optimal beam sweeping schemes. The provided engineering insights, therefore, pave inevitable foundations to practice the next generation driving use cases using mmWave carriers.