Achieving low latency and high packet reception ratio in media access control layer in VANET

Vehicular ad hoc networks (VANETs) or inter-vehicle communication (IVC) makes possible the development of a number of innovative and powerful transportation system applications. VANET technology proves an important extension of both cellular and wireless local area networks (WLANs) currently used in the transportation industry. It is widely recognized that the transportation industry serves as an ideal platform for a large number of existing and future wireless applications, many of which have yet to be developed for commercial use.;Safety messaging is one of the most critical uses for VANET, supporting a number of potential safety applications, e.g. emergency electronic brake lights, lane change and pre-crash warning, among others. Many applications require extremely low latency (less than 100ms) and highly reliable (over 99% packet delivery ratio) communication services. In order to satisfy these critical requirements, an efficient media access control (MAC) layer is necessary. At the time of this writing, a de facto standard of VANET MAC is being developed.;Extensive VANET MAC research with regard to safety applications has yet to be done. The proposed base for the VANET future standard uses an 802.11a media access layer whose performance-although studied-is known to contain deficiencies and was accomplished outside the VANET context. These factors motivated the author to initiate the study of VANET and MAC.;In this work, MAC for VANET MAC is extensively researched, and a history of MAC is initially reviewed. The special and critical requirements of VANET MAC are presented and four major categories were investigated and analyzed. Because the under-development of 802.11p is based on the IEEE 802.11a, special consideration is given with regard to the performance of 802.11a MAC and associated requirements. Extensive research enhancements centering on safety applications of the 802.11 MAC are conducted. The author's research generated a platform in which VANET performance can be quantitatively evaluated, analyzed, and verified. The quantitative behavior of the current protocols/algorithms, which include delay and packet delivery ratio, are presented on this platform. Furthermore, the future protocol and algorithm proposals can be added into this platform so that a faster research cycle can be achieved. Through theoretical analysis and simulation, this investigation shows that current proposed VANET MAC and 802.11a MAC enhancements have yet met the critical requirements of VANET. The future work may focus on how to use this theoretical model and simulation tool to assist MAC layer protocol design. Meanwhile, when new algorithms are proposed or accepted by the standard, this model and tool can serve as a fast and convenient platform, where the new algorithm can be easily added for the sake of evaluation and verification. The feasibility of relaxing some assumptions included therein, such as the hidden node problem in a two dimensional space, may also be studied to make the platform closer to a real system.