Study On The MAC Protocols For Ad Hoc Network Using Smart Antennas And Power Control

Ad hoc network is a multi-hop, packet forwarding and temporary autonoumous system of mobile terminals that consists of wireless transceiver. Due to the sharing characterisitis of the wireless medium, MAC protocol becomes the key technology for the development of ad hoc network. Currently, the study in this field is still an open issue and many problems are still waiting for solution. Using smart antennas and power control technology in the study for MAC protocols for ad hoc network will greatly reduce interference, enhance transmission quality and improve network performance. However, two major problems remain unsolved on the application of smart antennas. Firstly, the directional beam of smart antennas worsens the hidden terminal, and it even introduces new problem of node deafness. Secondly, directional beam and omni-directional beam are assumed to have the same transmission gain. This limits the benefit of the enhanced transmission range of the directional communication. Many power control protocols are based on CSMA/CA mechanism. With the single channel, the RTS-CTS handshake cannot prevent the hidden terminal problem caused by different power level. They cannot realize the target of both saving the power and improving the network capacity. Thus, it is theorically and pratically significative for us to conduct effective research in this field.The SDA-MAC protocol employs switch beam antennas based on CSMA/CA mechanism. The SDA-MAC protocol combines the RTS/CTS handshake, TDMA and directional beam. It uses RTS/CTS handshake to exchange the position of sender and receiver. The SDA-MAC protocol is suitable for single-hop envirnment, and multiple transmissions of different direction can exist in the same space at the same time without interfering with each other. The SDA-MAC protocol sloves the problems of hidden terminal and node deafness and considerabely improve the network performance. The maximum throughput of the SDA-MAC protocol is 119% of D-MAC and 307% of IEEE 802.11.The DMH-MAC protocol improves the SDA-MAC protcol, and uses beam-steering antennas. The O-O mode is used for idle status and channel contention, while D-D mode is used for data packet transmission. The DMH-MAC protocol makes full use of the benefit of directional communication of smart antennns in the multi-hop senarios. It transmits the packets to destination node using lesser hops and improves the performance. The main characteristic of the DMH-MAC protocol is that it does not need the entire route, and it is simple to realize directional communication. The maximum throughput of the DMH-MAC protocol is 121% of D-MAC and 312% of IEEE 802.11.The SPC-MAC protocol negotiates the transmit power of DATA and ACK using RTS-CTS handshake. It has two main characteristics. Firstly, the sender node decides the maximum transmitting power PMax. The sender node may be a hidden terminal, it must limit the transmit power according to the overheard CTS, thus avoid interfering with other nodes. Secondly, the receiver node decides the minimum transmitting power PMin for successful decoding. In the multi-hop environment, the routing packeting is transmitted with the maximum power level to make it heard by all the nodes in one-hop range. The SPC-MAC protocol eliminates the interference of the periodical transmission with the maximal power of PCM protocol, and does not need the extra channel of PCMA protocol. The maximum throughput of the SPC-MAC protocol is 120% of PCM and 272% of IEEE 802.11.We design the node model, smart antennas model and power control model under the same simulation platform in OPNET environment, and realize the MAC protocol using smart antennas and power control in the same templete. We conduct the simulation of the SDA-MAC protocol, the DMH-MAC protocol and the SPC-MAC protocol under different scenarios. The simulation results validate the main purpose of this dissertation that the SDA-MAC protocol, the DMH-MAC protocol and the SPC-MAC protocol can effectively realize the spacial reuse, and greatly improve the performance of ad hoc network in terms of throughput and end-to-end delay.