Media Access Control Protocol In Hybrid Wireless Ad Hoc Network Based On Directional And Omni-directional Antennas

As one of the important technologies in the 21st century, Wireless Ad Hoc Networks have attracted a great deal of concerns and are widely used. The development of directional antennas brings lots of advantages into Wireless Ad Hoc Networks while makes them face with a lot of challenges, especially the Media Access Control Protocol which is a vital part in the network protocol stack.As compared with traditional MAC protocols based on omni-directional antennas, directional MAC protocol takes full advantage of the direction of the antennas to increase spatial reuse, alleviate the communication interference and improve the whole throughput. In the hybrid Wireless Ad Hoc Networks, directional MAC protocol imposes some new hidden terminal problems and deafness problems. In order to address these problems, we designed a hybrid MAC protocol called NCDMAC which is based on multi-hop RTS/CTS and nested antenna circumrotation mechanism.NCDMAC protocol adopts RTS/Multi-hop CTS + Multi-hop RTS/CTS mechanism to deal with the asymmetric communication problem and alleviate the hidden terminal problem while makes use of nested antenna circumrotation mechanism to decrease the deafness problem. There is a concomitant backoff problem to the transmitting nodes. NCDMAC employs a new backoff mechanism for the different nodes to set correct NAV or DNAV.In order to validate the theoretic performance, we proposed an analytical evaluation with a Markov chain of the saturation throughput, delay and packet-loss rate, in the assumption of ideal channel conditions and computed the distributing of these three parameters in the network with different numbers of nodes. The results showed: the saturation throughput in NCDMAC is almost as high as MMAC and Circular-MAC, the saturation delay is more and the saturation packet loss rate is less.We also implement NCDMAC on NS-2 and compared it with DMAC, MMAC and Circular-MAC. The simulation and evaluation indicate that NCDMAC can resolve the new hidden terminal problem and the deafness problem effectively and improve network performance in hybrid Wireless Ad Hoc Network. However, the communication delay increases sharply. So NCDMAC is suitable for the networks of high throughput and low latency requirements.In summary, we have proposed a MAC protocol-NCDMAC for the Hybrid Wireless Ad Hoc Networks based on directional and omni-directional antennas. Moreover, some in-dept experiments, including analytical experiments and simulation experiments, have been done for NCDMAC. Experiment results are valuable.