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Ad Hoc network is a special form of wireless mobile network, at any time, any place does not rely on a fixed network infrastructure, therefore, Ad Hoc network has free wiring, mobility, flexible networking, invulnerability, the investment cost low characteristics, widely used in operational command, project supervision, and implementation of emergency rescue and disaster relief missions occasions. Ad Hoc networks because of its particularity makes it networking network environment with time-varying characteristics, which makes the copy in a very good application of traditional wired networks TCP / IP layered protocol is no longer viable, so this article for Ad Hoc network protocols used a cross-layer design approach, that is, from a global perspective, multi-layer design makes the joint between the layers of the protocol stack have more information sharing and interaction in order to achieve comprehensive network performance optimization, thus improving network resource utilization and system performance. To maximize network throughput as the goal, this paper focuses on the IEEE 802.11-based protocol for Ad Hoc network MAC layer and physical layer channel access mechanism and rate selection mechanism, detailing the current classic rate adaptive mechanisms: ARF, RBAR and OAR. But the vast majority of the data rate adaptation algorithm for adaptive frame rate, while for the control frame rate adaptive algorithm is still very rare. This selection of the data frame rate OAR classical adaptive algorithm, and the control-frame proposed a rate adaptive algorithm by modifying the virtual carrier sense, and with the extended interframe spacing EIFS and physical carrier sensing to achieve control frame rate adaptation. By NS2 network simulation tool for controlling the frame rate adaptive algorithm used five kinds of data packets of different sizes in three different environments (single-hop single-stream, single-hop multi-stream, multi-hop multi-stream) simulation. The results showed that: in different contexts with different sizes of data packets through the control frame rate adaptation can effectively reduce system overhead, to varying degrees, to improve network throughput. Data packet size and the scenes of these two important parameters of the specific relationship with the network throughput is: one, the data packet greater network throughput greater; two, with single-hop single-stream and multi-stream environments compared to the single-hop, in a multi- hop multi-stream environments, the most obvious improvement in network throughput, this environment is also closest to the real environment, and therefore proposed to control the frame rate adaptive algorithm has good practical value.
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