Research And Implementation A Delay-Guaranteed Channel Access Technology In WiFi

Due to the advantages of mobility,wide coverage and easy deployment,wireless communication technology is widely used in Industrial Internet of Things(IIoT).With the development of IIoT,there are many potential application scenarios,such as machine vision detection,industrial augmented reality technology,etc.,which require timedelayed and high-throughput data transmission services.Existing industrial wireless communication technologies are still dominated by low rate and cannot meet throughput requirement.WiFi based on the IEEE 802.11 protocol has a high throughput characteristic.However,due to the DCF channel contention access mechanism,the transmission delay cannot be guaranteed.Aiming at the above problems,the thesis designs and implements a wireless channel access protocol for delay guarantee based on the existing WiFi network protocol stack.The protocol adopts the Time Division Multiple Access(TDMA)polling mechanism.By dividing the polling time slice and the centralized scheduling,the protocol could control the data transmission timing of the entire network and ensure the delay limit.The thesis designs an adaptive hierarchical polling scheduling algorithm to solve the empty polling problem,which caused by node traffic changes.The bitmap selection retransmission method is adopted as the basic retransmission method of TDMA polling protocol.By dividing the retransmission dedicated time slice,the protocol could enhance retransmission efficiency.The control unit of the protocol consists of three modules.The node scheduling module is responsible for centralized management and scheduling of the data transmission time slice of the node.The transmission management module is responsible for managing transmission parameters,controlling data reception and transmission behavior.The timer module is responsible for node time synchronization,manage time slots.Finally,by implementing the protocol on the common WiFi hardware platform,a real-time high-speed wireless network prototype system for industrial applications is established.The thesis builds a test platform,and carrys out the delay and throughput tests using the ordinary WiFi as references.The results show that the channel access protocol we designed can provide end-to-end transmission delay of less than 10 ms,delay jitter is less than 3ms,total throughput is not less than 46 Mbps.The expected target of this protocol is achieved.The TDMA polling protocol can provide high-speed data transmission while ensuring transmission stability and delay limits,providing a practical technical solution for applications of IIoT,which require real-time high-speed wireless communication technology.