Reliable MAC broadcast protocol in directional and omni-directional transmissions for vehicular ad hoc networks

This paper presents the design, implementation and simulation results of a reliable Medium Access Control (MAC) broadcast protocol for Vehicular Ad hoc Networks for omni-directional and directional transmissions. The IEEE 802.11 MAC protocol uses control frames for handshaking to reliably communicate unicast data. In contrast, the broadcast data is transmitted without any control frames. This results in increased collisions due to hidden terminal problem, which in turn reduces the reliability of the broadcast service. This problem also exists in MAC protocols based on directional transmissions. To overcome this problem in Directional MAC (DMAC), we adapted Batch Mode Multicast MAC (BMMM) protocol, which uses control frames for broadcast transmissions. We implemented BMMM in NS-2 for omni-directional and Directional MAC protocols. Simulations are run for city traffic scenarios and the results are compared with IEEE 802.11 unreliable broadcast support. The simulations and comparison are done for two variants of BMMM protocol implementation integrated with DMAC.