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A well-functioning transportation system ranges from moving goods and enabling trade to facilitating daily mobility and promoting health and social inclusion (Sochor, 2013). The progress of the transportation industry is an essential factor in the economic and social development of the society. However, the increase in the number of vehicles brings about saturation on the road which exposes more problems such as increase in the number of accidents and human fatalities (Stanica et al., 2012). 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 (World Health Organization. Violence, Injury Prevention, 2013). This challenge has led to the development of the transportation systems known as the Intelligent Transportation System (ITS). ITS is a comprehensive transportation management and service system, which aims to provide innovative services relating to different modes of transportation management (Lin et al., 2017). An important component of an ITS is the vehicular communication network (VANET) that enables information exchange among vehicles.
Vehicular adhoc network (VANET) is a self-organized, multi-purpose, service oriented communication network which enable communication between vehicles and between vehicles and roadside infrastructures for the purpose of exchanging messages. These messages are either periodic (beacons) or event-driven (Sattari et al., 2013). Beacon messages are sent periodically by vehicles to inform their neighbouring vehicles of their condition such as position, direction and speed. 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 (Sattari et al., 2013). These messages are sent and received by nodes by sharing a limited number of wireless channels each with limited bandwidth. Dedicated Short-Range Communications (DSRC) is considered the most promising wireless access technology for vehicular communication. 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 and Bakar, 2013).
VANET is characterized by a dynamic topology and a rapid change in node densities. In a dense traffic scenario the message traffic may generate a load higher than the available capacity of the transmission medium leading to channel congestion problem. Channel congestion leads to degrading of the overall channel quality and a rise in packet loss rates and transmission delay. Controlling the congestion enhances bandwidth utilization, responsiveness, and fairness usage of network resources (Taherkhani, 2015). Some existing congestion control schemes adapt transmission parameters, such as transmission power, rate, contention window and so on and make comparison with neighboring values using classical logic. This method does not consider points between two close parameter values. This work uses fuzzy logic concept to improve the adaptation process of the network contention window parameter.to control channel congestion.
The contributions of this study can be summarized as follows:
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A feedback control mechanism built using a fuzzy logic design which uses the collision probability as feedback parameter.
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A control mechanism which has the ability to adapt the contention windows according to the wireless channel load during vehicle-to-vehicle (V2V) communication.
The remainder of the paper is organized as follows: Section 2 summarizes some of the related works found in the literature. The developed fuzzy logic based congestion control approach is discussed in section 3. Section 4 includes the simulation scenarios of the design and the results of the simulation discussed in section 5. The final section provides the summary about the study with final remarks.