In recent years, communication between vehicles (V2V) and between vehicles and infrastructure (V2I), cumulatively indicated as V2X, has been investigated as a means to support basic automotive applications, like cruise control, blind spot detection, parking assistance and so on. Currently, the V2V communication protocol is the so-called dedicated short-range communication (DSRC), which provides a nominal coverage range of about 1 km, with achievable data rates in the order of 2-6 Mbps. V2I communication, instead, makes use of the 4G-LTE connectivity below 6 GHz, enabling a data rate of up to 100 Mbps in high mobility scenarios. These technologies, however, will not be able to support the massive demand for high data rates that is expected to be required by the next generation of automotive applications, which will include advanced services based on a number of sophisticated sensors (e.g., radars, cameras, LIDARS), to support higher layers of automated driving (e.g., object recognition,object classification, obstacle avoidance).
A possible answer to this growing demand for ultra-high transmission speeds in vehicular networks can be found in the millimeter wave bands which, however, are subject to high signal attenuation and challenging propagation characteristics.
Therefore, in our works, we started investigating the limits that prevent the direct employment of the existing V2X communication protocols on mmWave links, including:
- Overhead: In current V2X communication technologies, transmissions are mostly omnidirectional while mmWave links are typically directional, to overcome the isotropic pathloss experienced at high frequencies. However, directional links may require precise alignment of the transmitter and receiver beams, an operation which may increase the latency of the communication.
- High mobility: A suitable beam pair may not last long enough to allow the completion of a data exchange, due to the high speed of the nodes, thus resulting in transmission errors. Moreover, the increased Doppler effect could make the assumption of channel reciprocity not valid and could impair the feedback over mmWave links, which is a potential point of failure for beam sweeping.
- Blockage: While signals at lower frequencies can penetrate more easily through buildings, mmWave signals do not penetrate most solid materials. As a result, an obstacle can jeopardize a successful communication even if the automotive nodes are perfectly
- Channel model: Available measurements at mmWaves in the V2X context are still very limited, and realistic scenarios are indeed hard to simulate. In fact, the increased reflectivity and scattering from common objects and the poor diffraction and penetration capabilities of mmWaves are the main factors preventing the existing lower frequency channel models from being used for an automotive mmWave scenario. Moreover, current models for mmWave cellular systems present many limitations for their applicability to a V2X context, due to the more challenging propagation characteristics of highly mobile vehicular nodes.
We also highlighted possible solutions at the PHY and MAC layers to enable automotive networks to operate at mmWaves and, through a preliminary connectivity and throughput analysis, we showed that the performance of the automotive nodes in highly mobile mmWave scenarios strictly depends on the specific environment in which the vehicles are deployed, and must account for several automotive-specific features such as the vehicle’s speed, the beam tracking periodicity, the node density and the MIMO antenna configuration.
|M. Giordani, A. Zanella, and M. Zorzi, "Technical Report -- MillimeterWave Communication in Vehicular Networks: Coverage and Connectivity Analysis"||2017/05||Vehicular|
|M. Giordani, A. Zanella, M. Zorzi, “Millimeter Wave Communication in Vehicular Networks: Challenges and Opportunities”, to appear on IEEE International Conference on Modern Circuits and Systems Technologies (MOCAST)||2017/05||Vehicular|