Research On The Key Techniques Of MAC Protocol In Wireless Ad Hoc Network

To improve the throughput of wireless Ad hoc network becomes one of important research areas in the design of MAC protocols due to the serious interference in multi-hop transmission. But currently, most of MAC protocols use simplified interference mode, which does not consider the interference range is changing dynamically in the real world. Thus these protocols cannot solve the hidden/exposed terminal problems existing in RTS/CTS handshake mechanism. Meanwhile, with the usage of new technologies, new issues are brought into the design of MAC protocols. The earlier MAC protocols use single channel. In order to increase the throughput, multi-channel and directional antenna technologies have been used in wireless communication.The purpose of this study is to solve these problems, including 1) improving the performance of Ad hoc MAC protocol 2) designing a new multi-channel MAC protocol and 3) designing a new directional MAC protocols using directional antenna. Major contributions and the originalities of this dissertation are as follows:(1) A novel MAC protocol is proposed, which can solve the hidden and exposed terminal problem simultaneously.IEEE 802.11 MAC protocol can not solve the hidden and exposed terminal problems because it regards the transmission range and the interference range as same while the interference range is actually a dynamic value. Many protocols have been proposed to solve these problems. But most of these protocols only focus on one aspect of the interference problem, hence, an interference-aware busy tone based MAC protocol (IABT) is proposed to improve the throughput of the network. Encoding the interference information in the frequency, a busy tone will reserve the space necessary for the ongoing transmission. IABT protocol can solve both the hidden and exposed terminal problem simultaneously.(2) A new deafness problem in simple multi-channel MAC protocol and a new type of hidden terminal problem when using RTS/CTS handshake to reserve the channel are put forward and figured out; A novel mutli-channel MAC protocol is proposed to avoid the deafness problem,hidden and exposed terminal problems simultaneously.The deafness problem will cause the sender sends the RTS repeatedly while the receiver is busy. The consequences of the deafness problem can propagate throughout the entire Ad hoc network and cause low performance and unfairness. Meanwhile the RTS/CTS based handshake cannot solve the hidden terminal problem, which would cause channel selection error in multi-channnel protocol. Currently, most of multi-channel protocols do not deal with the difference between the transmission range and interference range. To solve these problems, a new tone-based multi-channel MAC protocol is proposed, which can improve the throughput of the network.(3) A tone based MAC protocol using directional antennas is proposed to solve the deafness problem, hidden terminal and exposed terminal problems simultaneously.Directional transmission can reduce the interference, increasing the transmission range and the spatial reuse. But it also brings deafness problem in directional MAC protocol, which would lead to the situation that the sender continually backs off, resending RTS. Some protocols can alleviate the deafness problem, but cannot solve it completely. By using two pairs of flip-flop tones, a new directional MAC protocols is proposed to solve the deafness problem, hidden terminal and exposed terminal problems simultaneously, which would greatly increase the throughput of the Ad hoc network using directional antenna.