Abstract
The use of multiple channels in wireless networks may provide performance advantages in reducing collisions and enabling more concurrent transmissions. A mobile host that participates in multi-channel transmission may equip with one or more transceivers. A MAC protocol designed for multi-channel wireless networks should deal with the communications among the MHs no matter how many transceivers they use. Moreover, the multi-channel wireless networks should accommodate traditional MHs that support single channel transmission. Channel selection is also a key point to improving the performance of multi-channel wireless networks. A MH should choose proper channels which do not interfere with other MHs’ channels. Furthermore, the whole network throughput and performance should be guaranteed that higher than single channel environment. In this dissertation, we propose a new multi-channel MAC protocol for MHs that are equipped with single transceiver or multi-transceivers in a multi-hop wireless network, which is named Self Adjustable Multi-channel MAC protocol (SAMMAC). The proposed scheme modified the RTS/CTS frames for multi-channel usage, and divides the transmission frame into channel negotiation and data transmission period. SAMMAC can contain different type of MHs (including multi-channel and single channel nodes) and achieve high throughput. Channel assignment is an important issue in the multi-channel wireless networks to achieve high throughput. Previous works on multi-channel assignment can be classified into two categories: the algorithms-based and the negotiation-based schemes. The algorithm-based schemes treat channel assignment as the coloring problem and require complex computations. The negotiation-based schemes usually need a common control channel to negotiate data channels but fewer computations. However, they usually require time synchronization, which is hard to achieve in wireless networks. Moreover, the negotiation-based schemes have larger end-to-end delay in multi-hop communications due to message exchanges. This dissertation proposed an asynchronous scheme, named Hierarchical Clustering Channel Assignment (HCCA), for channel assignment based on clustering nodes into a hierarchy. Channels are allocated from the highest cluster to lower clusters. The HCCA is efficient to mitigate the interference of adjacent MHs. We also design an algorithm to adjust the contention window according to the traffic condition, named Traffic Aware Multi-channel Medium Access Control (TAMMAC), which can exploit multiple channels with smart window increase and decrease rules to adjust the contention window size dynamically and properly according to network traffic condition to maximize the channel utilization. In addition, we design a hop-by-hop congestion control scheme for MANET with multi-channel usage, which is named Efficient Flow Control with Multi-channel (EFCM), to improve the whole network throughput. In this scheme, the intermediate nodes have higher priority than the source (or leaf) nodes to contend for the right of transmission to solve the intraflow contention. In order to solve the interflow contention, congestion control is taken in every node to construct a flow table, which restricts the number of packets of every flow passing by congested nodes. The simulation results show that our schemes can effectively exploit multiple channels to achieve higher throughput than IEEE 802.11 and many existing multi-channel MAC protocols.