دانلود رایگان مقاله پروتکل چند کاناله کارای MAC برای شبکه های ad hoc بی سیم

Abstract

IEEE 802.11 MAC is designed for single channel and based on Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). The throughput of network is limited by the bandwidth of the single channel and the CSMA-based MAC protocol with omnidirectional antennas can cause the serious unfairness or flow starvation. By exploiting the multiple channels and using the directional antennas, nodes located in each other’s vicinity may communicate simultaneously. This helps to increase the spatial reuse of the wireless channel and thus increase the network performance. In this paper, we propose a Multi-channel MAC protocol with Directional Antennas (MMAC-DA) that adopts IEEE 802.11 Power Saving Mechanism (PSM) and exploits multiple channel resources and directional antennas. Nodes have to exchange control packets during the Announcement Traffic Indication Message (ATIM) window to select data channels and determine the beam directions which are used to exchange data packets during the data window. The simulation results show that MMAC-DA can improve the network performance in terms of aggregate throughput, packet delivery ratio, energy efficiency and fairness index.

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.