Research On Packet Scheduling Mechanism And MAC Protocol In Wireless Mesh Network

Wireless Mesh Network, a combination of WLAN and mobile Ad-hoc network with the characteristics of reliability, self-organization and self-healing, is a new type of distributed multipoint-to-multipoint network with high rate and high capacity for solving the"last mile" access problem. Nowadays, with the development of network technology and multimedia technology, the network application is becoming diversified. Different users require differentiated services, how to distinguish vary network application, ensure the QoS of the high-priority flow is become much more important. The article will improve the protocol from two aspects that are packet scheduling mechanism and MAC protocols.On the aspect of packet scheduling mechanism, firstly, the overview of the packet scheduling mechanism which contain principle, performance indicators is introduced. Secondly, we compare and analyze the strengths and weaknesses of the existing packet scheduling mechanism whick contain DropTail and RED. Thirdly, this article provides a new packet scheduling mechanism P-RED which can support the QoS of the high-priority flow on the base of RED. P-RED can set different queue thresholds for differentiated service, as well, the queue thresholds of the high-priority flow is greater than the low-priority flow so that the drop probability of the high-priority flow is lower. In order to balance the strong dependence on control parameters, a new threshold parameter is introduced in P-RED, it can improve the robustness of the packet scheduling mechanism. Finally, this paper verify the correctness of P-RED based on NS2 simulation.On the aspect of MAC protocol, firstly, the hidden terminal and exposed terminal problems in the wireless network is introduced. Secondly, we compare and analyze the strengths and weaknesses of the existing MAC protocols which contain the single-channel MAC protocol DCF, PCF, the single-transceiver multi-channel MAC protocol MMAC and the dual-transceiver multi-channel MAC protocol DCA. Thirdly, this article provides a new muliple-channel MAC protocol P-MMAC which can support the QoS of the high-priority flow from two aspects that are backoff algorithm and channel allocation. In order to distinguish differentiated services, the P-MMAC set different backoff time range that can ensure the high-priority flow have higher opportunities to access channel and send data. In order to allocate the high-priority flow to different channels, the high-priority flow will first choose the channel whose total weight of priority is lowest, as the result, it can reduce the opportunities that the-high priority flow compete a same data channel. Finally, through the simulation and the elaborate ananysis, we prove that the P-MMAC can increase the throuthput and decrease the packet delay of the high-priority indeed in the wireless communication.