Dynamic reallocation based window access scheme for enhancing QOS of vehicular ADHOC networks

Abstract

Vehicular Ad-hoc Networks (VANETs) technology has now been established as a reliable network that provides communication between vehicles aiming to provide efficient and safe transportation. The applications devised for VANETs can be divided into the following three service categories: Safety Services, Traffic Management and User-Oriented Services. Among these services, safety services usually require bounded transmission delays as well as low access delays. For this reason, an efficient transmission slot management is very crucial for medium access control (MAC) protocols in VANETs. Additionally, VANETs, which have very dynamic topology, are very much prone to allocating a time slot in overlapping areas. In this case, two types of collisions may occur: access collision between vehicles trying to access the same available time slots, and merging collisions between vehicles using the same time slots. In this thesis, three new TDMA based MAC protocols are presented for V2I (Vehicle-to-Infrastructure) communication, to ensure fairness and reusability of TDMA slots in the control channel (CCH) of road traffic networks. By maintaining a balanced waiting time, the proposed TDMA based scheduling protocols allocate CCH's TDMA slots to the vehicles uniformly and continuously monitor the network for free slots. Presented protocols ensure reusability of free slots by using “capture effect” and “time slot reassignment” mechanisms. The proposed scheme uses strategies to avoid one-hop neighboring collision for boundary vehicles and to minimize merging collision for vehicles that will be passing over a RSU's broadcasting area and entering another RSU’s broadcasting area in the middle of a frame. These protocols also improved quality of service (QoS) of CCH traffic. We have ensured fairness on slot distribution by providing each vehicle almost equal number of slots in initial distribution and by providing balanced waiting time for participating vehicles. As all the data on control channel have unique priorities, we have proved QoS enhancement by comparing results using parameters such as throughput, average delay, data loss ratio and number of collisions. We have verified our proposed protocols by simulation in OMNeT++. Simulation results show that the proposed protocols outperform the conventional systems in terms of successfully transmitted data packets, throughput, average delay, data loss ratio and number of collisions.