mm-Wave on wheels: Practical 60 GHz vehicular communication without beam training

At vehicular speeds, the contact time during which a mobile node is in range of a fixed road side unit (RSU) is short. While this is not an issue if the RSU only needs to deliver textual information such as traffic updates, short contact times become problematic when transmitting a large amount of information. For instance, an RSU may need to deliver high volumes of local navigation data for an augmented reality application, or video material regarding tourist information of a nearby town. Millimeter-wave (mm-Wave) communication is highly promising for such scenarios since it provides order-of-magnitude larger throughput than the existing technologies operating at lower frequencies. However, the contact time in mm-Wave vehicular scenarios becomes even shorter due to the directional nature of the communication. This raises a fundamental question: can the high throughput of mm-Wave make up for the reduction in the contact time? In this paper, we analyze this trade-off and design a first-of-its-kind practical mm-Wave vehicular testbed to evaluate the resulting performance. Specifically, we consider alternative locations for the RSU other than at the side of the road, such as on top of a bridge or inside a roundabout. Moreover, we leverage that the road implicitly determines the direction in which the RSU expects a car to be located. This allows us to use fixed beam-steering at both the car and the RSU, thus avoiding costly beam-training. We validate our approach in real-world vehicular scenarios with actual traffic in a mid-sized town in Spain. The results show that our fixed beam-steering approach enables the RSU to transmit large amounts of data in a very short amount of time for a wide range of speeds. This allows us to provide detailed insights into the aforementioned fundamental question regarding the use of mm-Wave in vehicular scenarios.