An Opportunistic Routing Protocol Based on Position Information for Beam Alignment in Millimeter Wave Vehicular Communications

In millimeter wave (mmWave) vehicular communications, beam scanning is usually used for beam alignment. However, beam scanning takes a long time, which makes it unsuitable in the mmWave vehicular communications with highspeed nodes. Moreover, the existing research on mmWave vehicular communications is usually based on one-hop transmission. However, due to a limited transmission range of mmWave, in many cases, multi-hop transmissions are required to transmit information from a source node to a destination node. To solve these problems, we propose an opportunistic routing protocol based on position information for beam alignment in mmWave vehicular communications. Beam alignment is performed based on the location information of neighbor nodes instead of beam scanning, which avoids the increase of network load and delay caused by beam scanning. In addition, the interference in concurrent transmissions is considered in order to optimize beamwidth and forwarding priorities. When the opportunistic routing is used, even if one candidate forwarder (CF) fails to forward a packet, the other CFs receiving the packet can still forward it, avoiding an increase in the network load and unicast delay caused by a large number of retransmissions. In an experiment, we extend the existing one-hop communication protocols into multi-hop communication protocols. Compared with these protocols, the proposed protocol yields lower end-to-end delay, higher packet delivery ratio and network throughput.