A Review of Congestion Control Schemes for Vehicular Ad-Hoc Network (VANET) Communication

Introduction

The progress of the transportation industry is an essential factor in the development of our society. It simply makes the relation between different economic branches possible and efficient. However, the increase in the number of vehicles has also brought an increase in the number of accidents and human fatalities (Stanica, 2011). According to World Health Organization (2013), road traffic accidents lead to about 1.24 million deaths worldwide, and 92% of them occur in middle-income and low-income countries. This challenge has led to the development of new transportation systems such as the Intelligent Transportation System (ITS). Intelligent Transportation Systems (ITS) is the integration of telecommunication and information technologies to improve the safety and efficiency in transportation systems (Jarupan & Ekici, 2011). One of the potential architectures for ITS is vehicular ad hoc network (VANET) (Bouk, Kim, Ahmed, & Kim, 2015).

A VANET is a self-organized, multi-purpose, service oriented communication network enabling vehicle-to-vehicle and vehicle-to-roadside infrastructure communication for the purpose of exchanging messages to ensure an efficient and comfortable traffic system on roads (Biswas, 2012). In VANET, each vehicle equipped with communication devices represents a node and is allowed to send and receive safety messages through wireless communication channels. These messages are either periodic (beacons) or event-driven (Sattari, Noor, & Keshavarz, 2012). Beacon messages are sent periodically by vehicles to inform their neighbour vehicles of their condition such as position, direction and speed. These messages are simply used by the neighbouring vehicles (nodes) to be aware of their environment as well as preventing potential dangers. The event-driven safety messages are generated when an abnormal condition or an imminent danger is detected and are disseminated within a certain range with higher priority. The event-driven safety messages should be delivered to neighbouring node by high reliability and limited time. A single delayed or lost message could result in loss of life (Sattari, Noor, & Keshavarz, 2012).

Dedicated Short-Range Communications (DSRC) is considered the most promising wireless access technology for vehicular communication (Bai, Stancil, & Krishnan, 2010). The DSRC standard provides seven channels of 10MHz of bandwidth each. It consists of six Service Channels (SCHs) and one Control Channel (CCH). The CCH is used for safety messages while SCHs are used for non-safety services (Darus & Bakar, 2011). In dense network, a large number of vehicles can possibly broadcast beacon messages resulting in the congestion of the CCH channel. These periodic messages lead to broadcast storm/blind flooding problem in VANETs. It is very important to keep the CCH channel free from congestion in order to ensure timely and reliable delivery of event-driven safety messages (Vyas & Dandekar, 2014). Several congestion control approaches have been presented to operate within vehicular ad hoc networks. These algorithms are able solve congestion problems in VANET with some tangible contributions. However, some drawbacks of these approaches include overhead under high node density, dissemination delay, long time to converge to efficiency and the exchange of message priorities leading to congestion. This study presents a review of existing congestion control schemes for VANETs with the aim of discussing the contributions and drawbacks of the algorithms.