Abstract
Timely and reliable inter-vehicle communications is a critical requirement to support traffic safety applications, such as vehicle platooning. Furthermore, low-delay communications allow the platoon to react quickly to unexpected events. In this scope, having a predictable and highly effective medium access control (MAC) method is of utmost importance. However, the currently available IEEE 802.11p technology is unable to adequately address these challenges. In this paper, we propose a MAC method especially adapted to platoons, able to transmit beacons within the required time constraints, but with a higher reliability level than IEEE 802.11p, while concurrently enabling efficient dissemination of event-driven messages. The protocol circulates the token within the platoon not in a round-robin fashion, but based on beacon data age, i.e., the time that has passed since the previous collection of status information, thereby automatically offering repeated beacon transmission opportunities for increased reliability. In addition, we propose three different methods for supporting event-driven messages co-existing with beacons. Analysis and simulation results in single and multi-hop scenarios showed that, by providing non-competitive channel access and frequent retransmission opportunities, our protocol can offer beacon delivery within one beacon generation interval while fulfilling the requirements on low-delay dissemination of event-driven messages for traffic safety applications.
Highlights
Safety, comfort and efficiency of both roads and vehicles have improved considerably over the last decade
The rest of this paper is organized as follows: in Section 2, we briefly explain the basic principles of the IEEE 802.11p medium access control (MAC) protocol and, in order to motivate this paper, we review the work related to the design of MAC protocols for platooning applications
Delayed channel access due to contention leads to beacon Inter-Reception Time (IRT) that are longer or shorter than exactly one period, as shown in the graph for IEEE 802.11p
Summary
Comfort and efficiency of both roads and vehicles have improved considerably over the last decade. As shown in several papers published in the area, e.g., [2,3,4], CSMA is not able to provide guaranteed delay bounds with sufficient reliability for vehicular scenarios, especially under high channel usage This problem is serious when implementing a (semi-) automated driving application such as platooning, where inter-vehicle spacing is drastically reduced and the control loop that manages and maintains the platoon requires a frequent, timely and reliable exchange of status information (beacons). Since heavy vehicles benefit greatly from platooning in terms of reduced fuel consumption, the benefits outweigh the extra cost of an additional transceiver This separation enables us to deviate from the standard restrictions on, e.g., beacon update rates, message types and channel access method, to focus on the timely and reliable delivery of platoon control data.
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