Hybrid MAC Protocol For Ad Hoc Networks

Ad hoc network requires no infrastructure and nodes are free to enter, leave, or move inside the network without prior configuration. Therefore, ad hoc network has gained a lot of attention and its research content is abroad. As we know, the media access control (MAC) protocol controls how the nodes access the wireless channel and influences the performance of the ad hoc network greatly.Consequently, this dissertation focuses the mind on how to improve the performance of the MAC protocol. According to the requirement of the wireless communications and the characters of the ad hoc network, some novel methods to research and improve the performance of the hybrid MAC protocols that offer scalable and efficient performance across some ranges of ad hoc network operating conditions are presented. The main research production of this dissertation is as follows:1. We study the backoff algorithm of the hybrid MAC protocol and propose a node-degree-based BEB-M (NBEB-M) backoff algorithm. According to the number of competing nodes estimated from the information of the one hop neighboring nodes, the proposed NBEB-M backoff algorithm can dynamically adjust the initial contention window to suit the current network environment. Consequently, our proposed NBEB-M backoff algorithm can improve the performance of the contention scheme included in the hybrid MAC protocol.2. In order to utilize the limited wireless bandwidth efficiently, we study the slot assignment problem of the ad hoc network and propose a topology-dependent hybrid MAC protocol (TDHM) which adopts a dynamic slot assignment policy and a hybrid channel access strategy. Our proposed TDHM protocol does not need to estimate the information of the network topology accurately in advance and can assign a suitable frame length and assigned slot to the node based on the information of its neighboring nodes up to two hops away provided it has data to transmit. Moreover, the TDHM protocol can release the assigned slots when they are no more used by the nodes, utilize the idle slots and solve the contention between the assigned slots effectively. Consequently, the TDHM protocol can adapt to the variations of the network topology and traffic load. The simulation results show that the performance of our proposed TDHM protocol is much better than the existing conventional hybrid MAC protocols which adopt a fixed slot assignment policy.3. In order to overcome the shortages of the topology-transparent MAC protocol under certain conditions, we introduce a topology-transparent hybrid MAC protocol (TTHM) which combines the topology-transparent slot assignment policy and the TDHM protocol. In the proposed TDHM protocol, nodes which have data to transmit can utilize the assigned slots and idle slots effectively. Consequently, the TTHM protocol can adapt to the variations of the network topology and traffic load better. Moreover, we analyze the performance of the proposed TTHM protocol and testify our analysis by simulations. The simulation results show that the performance of our proposed TTHM protocol is better than the existing conventional topology-transparent MAC protocols.4. Multiple input multiple output (MIMO) technique is known to provide extremely high spectral efficiency in the multi-path channel by simultaneously transmitting multiple independent data streams in the same channel. In order to exploit the unique characteristics of MIMO ad hoc networks, we present a MIMO-based topology-transparent hybrid MAC protocol (MIMO-TTHM) for MIMO ad hoc networks with the combination of the topology-transparent character and the MIMO technique character. By exploiting the anti-interference ability over MIMO technique, the proposed MIMO-TTHM protocol can control each node to utilize its assigned slots and the idle slots effectively. Simulation results show that our proposed MIMO-TTHM protocol can improve the performance of the MIMO ad hoc networks as compared with the TTHM protocol.