Abstract
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.
Highlights
In recent years, the rapid increase of vehicles around the world has brought about more serious challenges to traffic safety and efficiency
Fully considering the application performance requirements of Vehicular ad hoc networks (VANETs) with unmanned aerial vehicles (UAV)-enabled roadside unit (RSU), the characteristics of hybrid medium access control (MAC) protocols, and the shortcomings of existing protocols, this study proposes a high efficiency contending and adaptive time division multiple access (TDMA) hybrid MAC protocol for VANET to improve throughput, delay, and packets drop rate (PDR)
The proposed protocol PHB-MAC is compared with other protocols such as CB-MAC and NC-PNC MAC in the simulation of MATLAB. e simulation scenario is a 2-kilometer long two-way straight road with a number of moving vehicles. e UAV-enabled RSU (U-RSU) are evenly arranged on the roadside with an interval of 500 meters. e average speed of each vehicle is defined as 60 km/h, with a range of 50 km/s to 70 km/s
Summary
The rapid increase of vehicles around the world has brought about more serious challenges to traffic safety and efficiency. Many contention-free MAC protocols are proposed to improve QoS and efficiency of VANET, especially in a high-density application scenario [8]. E main mechanism of the contention-free protocol is based on time division multiple access (TDMA), frequency division multiple access (FDMA), and some other multiple access methods In this transmission scheme, each node has its own time slot or frequency band to access channel and transmit information [9]. (iii) In the adaptive TDMA-based period of the proposed protocol, time slots are allocated to transmission between OBUs and U-RSU and to the information exchanges between adjacent U-RSUs. e trajectory of the vehicle is along the road and predictable, so it is efficient for a U-RSU to transmit information of vehicles in its transmission range to the U-RSU with which the vehicle will communicate.
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