| With the rapid development of information technology, industrial wireless network technology has became the new hotspot in the field of automation. Evolved from the wireless sensor networks,the industrial wireless networking technology is a wireless communication technology for device-oriented information exchange, and it is not only ubiquitous sensing, ease of use, low-power, but also has the anti-interference and real-time features. It can get the important control parameters and real-time datas of industrial field to monitor and manage the industrial control process at a lower cost of investment.Industrial wireless network technical specification for industrial process automation-WIA-PA (Wireless Networks for Industrial Automation-Process Automation) is researched and developed by more than 10 units in China with support of National High Technology Research and Development Program of China(863 Program), such as Chinese Academy of Sciences, Southwest University, Chongqing University of Posts and Telecommunications and so on. Due to the harsh environment of industrial applications, it needs to solve a series of challenging technical problems such as high reliability, real-time communication, low power consumption, high security and the compatibility with other networks, and the high reliability is extremely important to ensure the quality of service and safety of industrial production, it is also a essencail prerequisite for the normal operations of industrial wireless control system. WIA-PA has a double-layer network topology which is consisted of Mesh and Star to realize the control of distributed and centralized communication of the network. Star network is composed of a router and field devices, the router which is known as the cluster head is on the duty of the allocation of communication resource,the management of field devices, the data processing and transmiting and so on in star network,so it plays a decisive role to ensure the normal operation of the network. Cluster head is once spent, and the communication in the cluster will be paralysis that results in the data of all the field devices in the cluster can not be real-time processed and transmitted and and it may even affect the information sending of other router to cause some communication links unavailable, thereby it will reduce the availability, reliability and safty of the entire network.To solve the single point failure of cluster head in WIA-PA star network, this paper researched on the redundancy mechanism and heartbeat protocol, because the classical accelerated heartbeat protocol has some deficiencies such as the delay of fault detection,the unreversible fault state and so on, this paper designs a adaptive heartbeat protocol-AHB based on using the work load of networks and states of devices to automatically adjust the heartbeat cycle.The AHB can adjust heartbeat cycle using redundant slot according the health status of the nodes and the current communications pressure, monitor the real-time states of cluster heads,detect faults in times to ensure the redundancy mechanism works normally.Based on the AHB,this paper designs a warm standby mechanism with two cluster heads combined with sleep. frequency hopping technologies and Virtual IP to achieve low power consumption and efficient fault detection,and it also optimized the method of entering a cluster of field device to ensure the the continuity and reliability of network services.Markov model is used to modle and analyse the redundancy mechanism of WIA-PA networks based on the AHB to theoretically verify its reliability,and its feasibility and reliability are also verified on the industrial wireless network in WIA-PA.The results show that the warm standby mechanism with two cluster heads based on AHB can discover faults and carry out smooth switching with low switching delay and high switching rate, which can effectively solve the single point failure of cluster head in WIA-PA star network and improve reliability of the network. |
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