Ad Hoc Networks Cross-layer Rate Adaptation Mechanism

Ad Hoc network is a special form of wireless data communications network, it does not need to rely on any fixed network infrastructure, and have several advantages, such as flexible, robust, less investment, it was used widely in battle field, emergency incidents and sudden disaster, but Ad Hoc network facing some problems, such as dynamic topology changes, variable-time quality of wireless channel, limited bandwidth, limited power, etc. the traditional protocol stack have poor performance on these problems.In order to maintain the independence of layers, Traditional network protocol layer are transparent however, time-varying of wireless communications leads to wireless channel capacity and bit error rate of the time-varying characteristics of the traditional Network design methods can not guarantee the best use of resources and QoS of user Therefore, cross-layer design achieve an overall optimization, rather than local layer optimization in traditional protocol stack because of information sharing and interaction between the network layers.The paper will focus on analysis and study of MAC layer and physical layer rate mechanism in Ad Hoc networks.Firstly, introduced several cross-layer protocol stack and some method of cross-layer design, gave an detailed analysis on some issues of cross-layer design; Secondly, gave an different performance analysis in different fixed data-rate, proposed rate adaptive mechanism for wireless physical channel ,the purpose is to find an appropriate rate adapted to channel quality changes of physical layer; Finally, did research on the principles of some multi-rate mechanism. These different multi-rate lies in different channel quality evaluation, and estimated information of wireless channel include received power, BER, ACK statistics. etc. These estimated information have some defect in some degrees.Aiming at solving this problem, this paper did research on relationship between link of wireless communication and rate-adaptation scheme .through analysis of several rate-adaptation algorithm, did some improvement on the basis of RBAR, this solution improve accuracy of channel estimation and improve the time efficiency.In certain cases, this solution can improve the system throughput and get a big utilization of the bandwidth.