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PAR-MAC: Reliable MAC Broadcast for Ad Hoc Networks with High Dynamicity
Zhaokun Qin, Weigang Wu, Yajuan Tang and Jiebin Zhang

Almost all ad hoc networks, including VANETs, adopt IEEE 802.11 based MAC protocols, but IEEE 802.11 is known for its inefficiency and unreliability in broadcasting due to lack of channel reservation and data retransmission mechanisms. Although quite a number of efforts have been put to design reliable and efficient IEEE 802.11 based MAC broadcast protocols, existing solutions are usually complex and incompatible with the IEEE 802.11 standard. More importantly, existing works mostly rely on knowledge of neighborhood to achieve reliability, which is not suitable for high dynamic environments like VANETs. To address these problems, we propose PAR-MAC, a novel reliable MAC broadcast protocol with probabilistic ACK mechanism to detect data loss and trigger retransmission. To avoid ACK collision, the time window for ACK is divided into multiple minislots, and each receiver randomly decides on whether and when to send ACK, based on given probabilities. The optimality of ACK sending probability is analyzed and the optimal value is calculated. Comparisons with similar work and standard IEEE 802.11 via simulations show that PAR-MAC is reliable and efficient in terms of packet loss and system throughput.

Keywords: MAC broadcast; IEEE 802.11; ad hoc network; reliability; VANET.

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