  A node equipped with a multi-beam antenna can achieve a throughput of up to m
times as compared to a single-beam antenna, by simultaneously communicating on
its m non-interfering beams. However, the existing multi-beam medium access
control (MAC) schemes can achieve concurrent data communication only when the
transmitter nodes are locally synchronized. Asynchronous packet arrival at a
multi-beam receiver node would increase the node deafness and MAC layer capture
problems, and thereby limit the data throughput. This paper presents an
asynchronous multi-beam MAC protocol for multi-hop wireless networks, which
makes the following enhancements to the existing multi-beam MAC schemes (i) A
windowing mechanism to achieve concurrent communication when the packet arrival
is asynchronous, (ii) A smart packet processing mechanism which reduces the
node deafness, hidden terminals and MAC-layer capture problems, and (iii) A
channel access mechanism which decreases resource wastage and node starvation.
Our proposed protocol also works in heterogeneous networks that deploy the
nodes equipped with single-beam as well as multi-beam antennas. Simulation
results demonstrate a superior performance of our proposed protocol.
