Abstract—Broadcast/multicast is a key service for mobile ad hoc networks. A great number of applications rely on a reliable and efficient MAC layer broadcast. The IEEE 802.11 broadcast protocol, which is based on Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), does not offer any MAC layer recovery on broadcast frames. Consequently, the increasing probability of lost frames may deteriorate the quality of broadcast/multicast services offered at upper layers. Previous protocols extended Request-To-Send (RTS), Clear-To-Send (CTS) and Acknowledgement (ACK) to enhance the broadcast reliability. However, they brought about the hidden terminal problem and the excessive retransmission problem at the same time. In this paper, we first formulate the broadcast problem as an optimization problem and show that it is NP-hard even if the upper layer service is periodical beacons. An approximation algorithm with a guaranteed approximation ratio is also suggested. Then a reliable and efficient MAC layer broadcast protocol, named Broadcast Protocol with Busy Tone (BPBT), is proposed. BPBT applies a busy tone to solve the hidden terminal problem. Finally, BPBT is compared with previous protocols for performance evaluation by simulation. Keywords-Ad hoc network; approximation algorithm; broadcast; busy tone; MAC I
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