A Slotted Multichannel MAC Protocol for Fair Resource Allocation in VANET

1. Introduction

Connecting various physical devices, vehicles, buildings and many other items via internet to transmit and receive data is termed as Internet of Things (IoT). Being one of the most advanced application or rather a constituent part of IoT, Intelligent Transportation System (ITS) is a refined transportation scheme that aims to provide services to various modes of transport and helps different users to make a smarter and superior use of the vehicular networks. To offer comfort and safety, ITS makes use of Vehicular Ad-hoc network (VANET) technology. This technology involves moving cars to create a wireless network to communicate and transfer essential information as and when required. VANETs use dedicated short range communication (DSRC) to carry out communication between vehicles and between vehicle and infrastructure. The U.S. Federal communications commission has allotted a 75 MHz band to DSRC (Ghandour, Felice, Artail, & Bononi, 2012) at 5.9 GHz incorporating seven non-overlapping channels with one control and the remaining as service channels. To efficiently use these channels, a set of procedures are defined by IEEE 802.11p along with the IEEE 1609 family. The combined system is termed as Wireless Access for vehicular environment (WAVE) which defines a multichannel medium access control protocol with the aim to reduce the congestion and allow simultaneous transmissions.

IEEE 1609.4 specifies a split phase mode for the multiple channels that are synchronized by the Multichannel MAC (“Wireless LAN Medium,” 2005; “IEEE Draft Amendments,” 2009). The channel access time is divided into synchronous intervals (SI) of 100 milliseconds (ms) each as depicted in the Figure 1. Further, the SI is divided into two equal intervals of 50ms namely the control channel interval (CCHI) and the service channel interval (SCHI). In the CCHI, all the vehicles must tune to the specified control channel frequency to exchange safety messages and few control messages like beacons that are sent periodically by the vehicle to mark its presence. In the course of SCHI, all the nodes must switch to the specified frequency of the service channel through which the data has to be transferred. Enhanced distributed channel access (EDCA) procedure is responsible for the transmissions taking place through any of the seven channels (Mo & So, & Walrand, 2008).

Figure 1.

Multichannel access process in IEEE 1609.4