TAR channel access mechanism for VANET safety-critical situations

Abstract

Vehicular Ad-hoc Network (VANET) is among the most relevant forms of mobile ad-hoc networks. VANET helps improving traffic safety and efficiency. By exchanging information between each others, vehicles can warn drivers or even prepare for dangerous situation. These warnings can be about critical situations like vehicles merging in a highway. Detecting and warning about such situations require a reliable communication between vehicles increasing thus the need for an efficient medium access control (MAC) protocol. In this paper, we propose to apply Transmit And Reserve (TAR), an adhoc medium access protocol, to vehicular communications. We integrated TAR into NS-3 simulator and evaluated its performance compared to IEEE 802.11 DCF in a vehicular network context. The evaluation results show that TAR is an efficient medium access protocol for VANET critical situations as it increases the throughput reduces the medium access delays and provides close to optimal short term fairness.

A modified backoff algorithm for safety message delivery in IEEE 802.11p/WAVE networks

“…For a vehicular node, the unique reference in [10] is related to its own geographical location, while the one in [6] is its MAC address of wireless interface. On the other hand, Khoufi et al [11] proposed their TAR (Transmit And Reserve) channel access mechanism, in which a vehicle can select a free backoff value for the next packet waiting for transmission and to piggyback the selected backoff value in the current packet ready to transmit. Without considering the increasing amount of vehicular nodes, the dimension of the TAR cycle may grow up drastically and bring about unbounded delay so that the dropping probability of safety packets becomes worse.…”

“…Without considering the increasing amount of vehicular nodes, the dimension of the TAR cycle may grow up drastically and bring about unbounded delay so that the dropping probability of safety packets becomes worse. Although the schemes presented in [6,[10][11] can reduce the collision probability by preventing two nodes from selecting the same backoff slot number, exact time synchronization to a slot level is quite difficult in such a highly mobile vehicular environment.…”

“…On the other hand, the authors in [11][12] presented a novel protocol for accessing the control channel instead of using the DCF (Distributed Coordination Function) scheme of 802.11p. Aiming to improve the MAC performance for safety message delivery in 802.11p/WAVE networks, this paper presents a modified backoff algorithm (MBA), which consists of two phases: to decide the size of contention window and to generate a nonuniformly distributed backoff timer.…”

TDMA-Based MAC Protocols for Vehicular Ad Hoc Networks: A Survey, Qualitative Analysis, and Open Research Issues

“…These mechanisms consist in adaptively adjusting the most important parameters of the IEEE 802.11p standard, namely the physical carrier sense threshold, the minimum contention window, and the transmission power control. Khoufi et al in [60], [61] have applied the Transmit And Reserve (TAR) 3 channel access protocol, to vehicular communications, especially for safety critical situations.…”

TAR Channel Access Mechanism: A Study of a Highway Ramp Car Merge Case

“…The main target of such networks is to keep drivers informed about safety risks and provide better awareness of traffic conditions as well. We distinguish between emergency safety situations and critical safety situations [11]. The first ones are situations with an extremely high risk of collision due to the presence of a stationary obstacle that blocks the road (e.g.…”