Real - Time Analysis And Improvement Of Industrial Wireless Control Protocol Based On 802.11DCF

With the rapid development of computer, microelectronics and other fields of science, industrial control network is moving in the direction of intelligent and network. In the industrial production scale has been expanding at the same time, the industrial field environment has become more complicated. Industrial field nodes are widely distributed, some places laying difficult route or the cost is too high, and the presence of moving objects and so on, the emergence of the new situation, making the traditional control bus and the Ethernet control network, becomes more and more not very flexible. The wireless transmission technology (802.11 standard) is more and more used in the field of industrial production because of its advantages of more flexible wiring, more convenient maintenance and lower installation cost.Wireless network control protocol (802.11 standard) was originally developed for commercial use of a protocol, the medium access control (MAC) default to using the carrier sense multiple/collision avoidance (CSMA/CA) mechanism, in essence, is a communication time and communication behavior can not be measured pre competition mechanism. But the industrial control network is a kind of special network which requires high real-time and high reliability. It requires that the data frame transmitted on the local area network can have certain time delay, so as to ensure the stability of the network. Therefore, it is necessary to improve the MAC working mechanism of the 802.11 protocol in order to be used in the field of industrial control.The paper analyzed thoroughly the 802.11 MAC protocol mechanism, and drawing on the domestic and foreign researchers a lot of achievements essence, simultaneously in the industrial control network data frame, proposed the "ack piggybacking""hidden polling" working mechanism, to enhance the transmission of data frames and predictability.Using OPNET simulation platform, the article is divided into three steps, the MAC layer DCF function optimization and comparison. Firstly, the initial environment modeling of the 802.11 protocol is firstly carried out. Second, in view of the particularity of the industry control and the data points for the three priority, from high to low in order:bursty real-time data, periodic real-time data and non real time data, and workstation of different transmission period, the introduction of piecewise backoff window concept of priority classification.In accordance with the data type, the area is divided into three types of workstations, in the same step of the same environment simulation. Third, at last, the paper put forward "ack piggybacking""hidden polling" working mechanism, by the bursty real-time data return ACK signal expansion, to achieve short death data transmission priority. The periodic cycle of data returned to ACK for sending piggyback optimization. Through the simulation of OPNET platform, the results of the three steps are compared and analyzed, and the design scheme is evaluated.