Empirical Performance Models of MAC Protocols for Cooperative Platooning Applications

Aqsa Aslam,Pedro M Santos,Frederico Santos,Luís Almeida

doi:10.3390/electronics8111334

Abstract

Vehicular ad-hoc networks (VANET) enable vehicles to exchange information on traffic conditions, dynamic status and localization, to enhance road safety and transportation efficiency. A typical VANET application is platooning, which can take advantage of exchanging information on speed, heading and position to allow shorter inter-vehicle distances without compromising safety. However, the platooning performance depends drastically on the quality of the communication channel, which in turn is highly influenced by the medium access control protocol (MAC). Currently, VANETs use the IEEE 802.11p MAC, which follows a carrier sense multiple access with collision avoidance (CSMA/CA) policy that is prone to collisions and degrades significantly with network load. This has led to recent proposals for a time-division multiple access (TDMA)-based MAC that synchronize vehicles’ beacons to prevent or reduce collisions. In this paper, we take CSMA/CA and two TDMA-based overlay protocols, i.e., deployed over CSMA/CA, namely PLEXE-slotted and RA-TDMAp, and carry out extensive simulations with varying platoon sizes, number of occupied lanes and transmit power to deduce empirical models that provide estimates of average number of collisions per second and average busy time ratio. In particular, we show that these estimates can be obtained from observing the number of radio-frequency (RF) neighbours, i.e., number of distinct sources of the packets received by each vehicle per time unit. These estimates can enhance the online adaptation of distributed applications, particularly platooning control, to varying conditions of the communication channel.

Highlights

With the advance of autonomous driving and platooning technologies, it is expected that cooperative platooning will make for a considerable share of highway traffic, as it leads to considerable gains in safety and fuel efficiency
In [19], we presented vehicular simulations to explore the behaviour of relevant network performance metrics, namely the rate of collisions and the ratio of medium accesses during which the medium was busy, with the three aforementioned protocols, i.e., carrier sense multiple access with collision avoidance (CSMA/CA), PLEXE-slotted and RA-TDMAp
We present empirical models that relate the number of RF neighbours that a platoon member, in a highway platoon-only scenario, observes with relevant network performance metrics

Summary

Introduction

With the advance of autonomous driving and platooning technologies, it is expected that cooperative platooning will make for a considerable share of highway traffic, as it leads to considerable gains in safety and fuel efficiency. The performance of these applications, those safety-critical applications such as platooning, depends significantly on the quality of the communication channel. Application designers must rely on models of network performance to predict the reliability, volume and timeliness of data exchanges that can occur and define the adaptation the application should perform in response to the network service quality. Often such models will be defined as a function of contextual parameters, e.g., number of nodes in the system [3,4]

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