A New TDMA-based MAC Protocol to Achieve High Reliability of One-hop Broadcast in Vehicular Ad Hoc Network

Vehicular Ad Hoc Network (VANET) is considered one of the most promising Mobile Ad Hoc Network (MANET). One-hop broadcast which is time-triggered plays a leading basic role in VANET. Since the primary applications in VANET are life-safety related, there is a strong need of high reliability related to packet transmission and reception. Though IEEE 802.11p has been defined as an international standard for VANET, IEEE 802.11p has in practice some limitations in terms of reliability. Then, other MAC protocols such as MS-Aloha have been proposed to achieve higher reliability. MS-Aloha has become recommended by ETSI after evaluation, making it a promising substitute to IEEE 802.11p. However, because of inefficient use of radio channels and the problem of continuous blockings, the reliability of MS-Aloha is still not satisfying especially under very congested traffic conditions. In this thesis, a new MAC protocol named Reliable TDMA-based One-hop Broadcast (RTOB) is proposed. RTOB takes MS-Aloha as groundwork, inheriting all its advantages, which makes it advanced and easy to be applied. Compared with MS-Aloha, RTOB can achieve much higher reliability by two principles – Efficient Timeslot Usage (ETU) and Timeslot Sharing (TSS). Moreover, to evaluate the reliability from the viewpoint of life-safety applications, a novel metric named Cover Ratio (CR) which is more appropriate than the conventional Packet Delivery Ratio (PDR) is proposed too. The definition and advantages of CR are given out. Besides the explanations of the main principles of RTOB, via computer simulation, this thesis quantitatively demonstrates its sufficiently high reliability under congested traffic conditions, no matter in urban, rural or highway scenarios.