SAFE-MAC: Speed Aware Fairness Enabled MAC Protocol for Vehicular Ad-hoc Networks

Abstract

Highly dynamic geographical topology, two-direction mobility, and varying traffic density can lead to fairness issues in Vehicular Ad-hoc Networks (VANETs). The Medium Access Control (MAC) protocol plays a vital role in sharing the common wireless channel efficiently between vehicles in a VANET system. However, ensuring fairness between vehicles can be a challenge in designing MAC protocols for VANET systems. The existing protocol, IEEE 802.11 DCF, ensures that the packet transmission rate for a particular vehicle is directly proportional to the amount of time a vehicle spends within a service area, but it does not guarantee that faster vehicles will be able to send the minimum number of packets. Other existing MAC protocols based on IEEE 802.11 are able to provide a minimum amount of data transmission regardless of velocity, but are unable to provide an amount of data transmission that is more proportionate to the time a vehicle spends in the service area. To address the above limitations, we propose a Speed Aware Fairness Enabled MAC (SAFE-MAC) protocol that calculates the residence time of a vehicle in a service area by using mobility metrics such as position, direction, and speed to synthesize the transmission probability of each individual vehicle with respect to its residence time. This is achieved by dynamically altering the values of parameters such as minimum contention window, maximum backoff stage, and retransmission limit in the MAC protocol. We then develop an analytical model to compare the performance of our proposed protocol with contemporary MAC protocols. Numerical analysis results show that our proposed protocol significantly improves fairness among the speed-varying vehicles in VANET.

Review of MAC Protocols for Vehicular Ad Hoc Networks

“…Speed-aware fairness-enabled MAC (SAFE-MAC) is different from the traditional IEEE 802.11p, which uses CSMA/CA mechanism to access the channel with dynamic MAC parameters, such as the minimum CW, maximum back-off stage, and retransmission limit [ 59 ]. It uses mobility metrics of vehicles, including location, direction, and speed, to calculate their residence time in the service area.…”

An Adaptive Multi-Channel Cooperative Data Transmission Scheduling in VANETs

“…Karabulut et al [ 14 ] proposed a novel orthogonal frequency division multiple access-based efficient cooperative MAC protocol for VANETs. Siddik et al [ 15 ] propose a speed aware fairness-enabled MAC protocol that calculates the residence time of a vehicle in a service area by using mobility metrics such as position and speed to synthesize the transmission probability of each vehicle concerning its residence time.…”

Mobility Aware Co-operative MAC Protocol for Reliable Transmission in VANET

“…In SAFE-MAC [3], the vehicles are grouped into batches based on their residence time and then assigned priorities. But in case of V2V communication, if the target vehicle is not reachable, then packets may not be transmitted correctly.…”

“…Because of the usage of a distinct radio channel, the MAC procedure is of supreme reputation in VANET schemes. [3]. The IEEE 802.11p pile also services the typical CSMA/CA MAC which rapidly displays its incapability to put up augmented system traffic due to the absence of ACKs [4].…”