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.