Research On The Key Technologies Of 802.11 Wireless MAC Protocol

WLAN has been available everywhere and into our lives, study, work and entertainment. IEEE 802.11 media access control protocol, which is widely used in the international standard of WLAN, naturally becomes the research focus to research scholars. Media access control protocol is used to control the devices to contend for the shared media. In order to meet the needs of users, such as a faster speed, a more stable environment and lower latency, etc., the original 802.11 MAC protocol proposed the CSMA/CA and the binary exponential backoff mechanisms to decrease collisions in the network and keep the transmission stable. However, these mechanisms cannot achieve the best performance of the network for various application scenarios of WLAN all the time, especially its collision and throughput have much space to be improved. Therefore, how to further implement the protocol on the basis of the 802.11 MAC protocol is also of great practical significance. This thesis achieved some relevant improvements which are based on 802.11 MAC protocol, the new implemented protocols mainly concentrate on the reducing collisions and increasing throughput. Specific research contents and innovations are as follows:1)A hybrid MAC protocol, the combination of TDMA and CSMA/CA, is studied in the distributed network. We proposed a compressing slot with collision-free MAC protocol to improve the channel utilization and throughput by compressing idle slot in the TDMA circle and avoiding collisions. The backoff mechanism in proposed protocol is totally different from the traditional Binary Exponential Backoff scheme. Each node is provided a fixed slot to contend for the channel, and the network can achieve collision-free state when all the nodes selected a specific slot. We have theoretically proved that the collision-free state can be reached when the proposed protocol is applied to a single hop network as well as the relationship between a given number of nodes and the number of TDMA circles which is needed to reach collision-free state. Simulation results not only validated the theoretical analysis on convergence circle under saturated load mode, but also demonstrated that the proposed protocol can achieve higher throughput and channel utilization than the state-of-the-art protocols under saturated load and unsaturated load modes.2)By researching on the multi-interface multi-channel protocol, an implemented 802.11 MAC protocol is proposed to adapt the environment of nodes with multi-interface, named multi-interface cooperating(MIC) MAC. MIC uses one successful handshake of one single interface to establish the transmission connection of the other interfaces, which can greatly improve the efficiency of cooperative multi-interface to gain high throughput. Besides, a lower duration of accessing channel benefits from that all interfaces simultaneously contend for the channel. Furthermore, nodes choose the current channel set as decision-making channels of the next transmission after a successful transmission, which can effectively reduce the impact of hidden terminal. In single hop network, the simulation results of MIC protocol show that MIC outperforms the state-of-art protocols in collisions and throughput.