7.2. Simulation results
Fig. 15 shows the performance comparison of different protocols in terms of aggregate throughput, packet delivery ratio and average delay. The network load increases as the packet arrival rate increases. As shown in Fig. 15(a), the aggregate throughput of different protocols are similar when the packet arrival rate is low. However, when the network goes near saturation, MMAC-DA provides higher aggregate throughput than the others. Since MMAC, HMMAC and MMAC-DA exploit multiple channel resources, they provides more concurrent transmissions than IEEE 802.11 which supports single channel. H-MMAC can utilize the multiple channels efficiently, but it does not have high spatial reuse as well as support collision-free transmissions on data channel. By using the directional antennas as well as exploiting multiple channel resources in data transmissions, MMAC-DA allows more nodes to transmit data packets simultaneously. Moreover, after nodes perform the ATIM handshake successfully to select data channel with determined beam direction, nodes can transmit multiple data packets without any collision during the data window. In other words, MMAC-DA reduces the overhead of control packets in data transmissions on the data channels during the data window. That is why MMAC-DA has higher aggregate throughput than the multi-channel MAC MMAC and H-MMAC protocols and the single channel MAC IEEE 802.11 protocol.
