| The wireless local area network(WLAN)technology has made tremendous progress in the past two decades.Because of its advantages of low cost,flexibility,scalability,and easy deployment,WLAN has shown great vitality in many wireless network scenarios such as home,enterprise,and industry.Industrial WLAN inherits the basic functions and characteristics of WLAN,but the complexity of industrial environment and its inherent insufficiency of WLAN protocol lead to the non-determinism of the network,which makes it difficult for traditional WLAN to be directly applied to industrial communications.Therefore,industrial WLAN research focuses on the determinism of transmission,which is defined as the reliable data communication within a predefined delay bound.This dissertation focuses on the deterministic problem of communication in industrial scenarios for WLAN MAC protocol.The main work and innovations of this dissertation are shown as follows:(1)A deterministic load balancing algorithm for WLAN in industrial real-time scenarios is proposed in this dissertation.The algorithm consists of two parts:metric check process and load distribution process.In the process of metric check,each STA assesses the status of network load according to the deadline miss rate and packet loss rate.In the process of load distribution,the algorithm models the load distribution process as a first-price sealed-bid auction model in the game theory,and solves the model to redistribute the network load.Subsequently,the proposed method is compared with several typical algorithms in industrial scenarios.The simulation results show that this method can effectively reduce the deadline miss rate and packet loss rate of data transmission,which enables the network to support industrial applications with higher deterministic requirements.(2)Aiming at the deterministic access problem in the industrial dense network scenario,this dissertation first analyses the recently proposed standard of IEEE 802.11 ah for the dense scenario,and models one of the restricted access window mechanism defined in the standard.Secondly,in order to avoid the performance degradation caused by heavy traffic in the restricted access window,this paper proposes a contetion window adaption algorithm,which has an interference discrimination function.The algorithm adapts the size of the contention window in real time according to the channel conditions to enhance the determinism of the network.Finally,in order to validate the performance of this algorithm,this dissertation compares this algorithm with other two typical contention window adaption algorithms.The simulation results show that,compared with the other two algorithms,the proposed method can improve the transmission performance of the 802.11 ah protocol under high load,and support industrial applications with higher deterministic requirements.(3)For the industrial applications with both high deterministic and high transmission rate requirements,this dissertation designs and implements a deterministic MAC protocol based on the IEEE 802.11 protocol.The protocol adopts centralized architecture and time division multiple access mechanism,which can ensure the end-to-end determinstic delay of data to the greatest extent,and provide deterministic guarantee for high-speed industrial applications.On the other hand,the implementation process of the protocol is based on commercial off-the-shelf hardware of IEEE 802.11,which only modifies the hardware driver.Therefore,the protocol can be deployed in the actual industrial system more easily and cheaply.In addition,this dissertation builds a test platform and prototype system in the actual industrial environment to validate the performance of this protocol.Comparing the protocol with the existing multi-hop WLAN protocol,the results show that the protocol has better deterministic performance than the existing WLAN protocol,and can support high-speed industrial applications with relatively stringent real-time requirements. |
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