Dynamic Pilot Design for Multicast in the Internet of Vehicles Running at Different Speeds

High mobility of vehicles causes time-frequency selective fading over physical channels within the Internet of vehicles (IoV). To improve the resource utilisation efficiency, a novel transmission strategy, based on dynamic pilot design, is proposed in this paper to reduce the pilot consumption in doubly selective channel estimation for the multicast to vehicles running at different speeds. As the channel coherence time is mainly influenced by the receiver mobility in the multicast from a base station to vehicles, we define a multicast block as the channel coherence time of the slowest vehicle in the multicast group, where common pilot symbols are shared. Then, the multicast data destined for different vehicles are loaded into the block according to their own channel coherence times. To evaluate the performance and resource utilisation of our dynamic pilot design, the metrics of overhead rate, spectral efficiency, and energy efficiency are formulated for the IoV multicast using multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) transmissions. In terms of these three metrics, illustrative numerical results on the comparisons between our dynamic pilot design and the conventional counterpart are provided, which not only substantiate that the former outperforms the latter but also present useful tools and specifications for the pilot design in the IoV multicast using MIMO-OFDM transmissions over doubly selective channels.