| Using directional antennas in wireless ad hoc networks can greatly improve the spatial reuse and the transmission range. Vaidya et al. propose DMAC to utilize these advanteges. However, Using directional antennas will cause the deafness problem, which greatly impairs the network performance. Korakis et al. propose Circular DMAC to address the deafness problem, which has a great constant overhead and the neighboring nodes of the receiver still suffer from deafness problem. Choudhury and Vaidya propose a tone-based MAC protocol, which can achieve a better performance with the cost of an increased complexity of the protocol.
This paper proposes a new MAC protocol to address the deafness problem. In this protocol, the sender and receiver send out directional RTS and CTS (DRTS/DCTS) respectively to inform their neighboring nodes of the forthcoming transmission. A distributed algorithm is also implemented, such that the sender and the receiver can negotiate on spending a much less time to send DRTS/DCTS simultaneously with no collision. By keeping a table which contains the deafness nodes and their corresponding deaf periods, the nodes in the network will not transmit to those deaf nodes, but they can still transmit to other nodes in the same direction as that of the deaf nodes. Thus we can greatly alleviate the deafness problem and maintain a high space reuse at the same time. This paper also uses a different method to set the directional NAV, which can greatly reduce the interference to the ongoing transmission. Simulation results show that our protocol can achieve a better performance than the existing MAC protocols using directional antennas. |