Vehicular ad hoc networks (VANETs) connect vehicles with other network units through wireless communication, thus improving traffic efficiency and safety by interacting with traffic information in networks. Roadside unit (RSU) plays an important role in VANETs in connecting vehicles with the transportation centre. With the rapid development of unmanned aerial vehicles (UAV), UAV-enabled RSU (U-RSU) is an effective way to promote the performance of VANETs. In this paper, a novel medium access control (MAC) layer protocol named PHB-MAC is proposed based on the priority setting of transmitted messages. Firstly, the priority-based contention mechanism is presented to ensure the transmission efficiency of the safety message. Then, the proposed MAC protocol combining contention and adaptive scheduled scheme is described in detail. Finally, the numerical analysis and simulation results of PHB-MAC and other existing protocols are presented. It is revealed that the proposed protocol improves throughput by at least 30%. Meanwhile, it reduces packets drop rate and delay by 21% and 22%, respectively. Finally, the numerical analysis and simulation results are given to prove the advancement of the proposed protocol on throughput, packets drop rate (PDR), and delay.

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Recently, unmanned aerial vehicles (UAVs) have been widely used in various industries. However, the communication links of UAVs are also threatened by eavesdropping. To enhance physical layer security (PLS) for UAV communications, a time-division multiarray beamforming (TDMB) scheme is proposed. Multiple antenna arrays steer their beamforming vectors based on their position relative to the legitimate user (LU). Thus, angle-distance-dependent directional modulation (DM) can be achieved. Time-division means multiple antenna arrays take turns transmitting different symbols from a same packet. The receiver in undesired directions suffers from intersymbol interference (ISI) because of the path differences between the receiver and different antenna arrays. This paper shows the signal-to-interference-plus-noise ratio (SINR) distribution with the proposed method in a 2-dimensional plane. Also, the improvement of the secrecy rate with the proposed method under different total antennas and artificial noise power is studied. Overall, these results indicate that the security rate has improved more with the proposed method, where the numbers of antennas and the power of AN are limited. Therefore, this method is suitable for UAV security communication.

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