Abstract: Using directional antennas for both transmission and reception provides many
benefits for Ad Hoc networks such as longer transmission range and lower probability of
being detected. However, applying traditional broadcast mechanisms for network layers
to Ad Hoc networks will cause long delay problem. To deal with this problem, a broadcast
mechanism is proposed, which uses the reservation sub-frame in the D-TDMA MAC
protocol to reduce the time for delivering broadcast packets. Nodes make reservation for
forwarding broadcast packets after exchanging modified handshaking messages with their
neighbors. This can avoid long delay caused by waiting for receiving broadcast packets
from their parent nodes. Simulation shows that, compared to the performance of planting
traditional network layer broadcast mechanism into an Ad Hoc network, broadcast packets
can be transmitted to all nodes more quickly by occupying smaller slots by using the
proposed mechanism.

Key words: directional-TDMA protocol, directional antenna, Ad Hoc network, broadcast