| Mobile Ad Hoc Networks (MANET) is such a kind of networks that has no fixed infrastructure, and can be organized fast and flexibly. It is fully constituted by mobile terminals, which is different from the ordinary Mobile IP networks. All the nodes in the Ad Hoc networks have equal status and have abilities of routing and forwarding, which can form small region communications systems at any time. This network can be set up fast, flexibly, and without bound by cable, which can be widely used in such scenarios as military communications, disaster relief, communication in remote areas without wired network, or some temporary networks that if it is set up using cables the cost will be too high. So it has wide application fields, and obtains attention and research. The MAC (Medium Access Control) protocol determines the way that nodes access to shared wireless channel and channel resources that are available. The performance of MAC protocol directly impacts on the overall performance of Ad Hoc network. It has been more and more concerned recent years, and become a hotspot in academic research.Routing and channel access control in Ad Hoc networks are two main research directions currently. IETF's MANET working group of the Ad Hoc has put forward some drafts about routing and three formal RFC documents-AODV, OLSR, TBRPF. On channel access control, both single-channel access protocol and multi-channel access protocol have related works so far. And IEEE802.11 has become the most widely used component of the Ad Hoc network physical layer and MAC layer technology.Based on IEEE802.11 standards and analysis of the existing improved channel access protocol, this paper proposes an improved scheme on IEEE802.11 protocol in order to improve the Ad Hoc Network MAC Protocol performance and network survivability. The main idea of proposed scheme is extending single-channel MAC protocol to multi-channel. According simulation results, the scheme can improve the performance of the entire wireless system and ensure the network survivability, which can provide reference value for application. The main research works include the following.(1) On analysis and design of multi-channel perception strategy, a multi-channel channel list maintenance algorithm is proposed by defining key data structure and introducing virtual MAC address. The data stream transmition process is analyzed using queue theory. Two multi-channel perception mechanisms, active perception and passive perception, are analyzed respectly. Different perception frames for the two mechanisms are designed, and corresponding network costs are calculated.(2) On analysis and design of multi-channel allocation strategy, a channels allocation algorithm is proposed based on the basic idea of greedy algorithm according to statistical characteristics of channels. After analyzing two types of allocation, the method of setting data stream with different priorities is made to guarantee QoS of the important business.(3) On analysis and design of multi-channel aggregation strategy, several physical channels are aggregated into a high-bindwidth logical channel for high-priority, high real-time demand, large scale data transmitting or forwarding. From the perspective of queuing theory, the multi-channel aggregation strategy can be proved to improve network performance. At the same time, in order to solve the erroneous reservation problem, corresponding mechanism suitable for multi-channel communication is put forward to ensure higher network survivability.(4) Simulation is made by using the Network Simulator 2 (NS2). The result which is obtained by camparing with former protocol shows that, multi-channel scheme can meet the needs of Ad Hoc networks survivability and improve wireless network performance.Based on the existing protocol IEEE802.11DCF access problems, this paper proposes a number of improvements to extend it to multi-channel MAC protocol. These works can provide some idea to applications. |
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