Research Of Inter-cluster Link Scheduling Strategy For Industrial Wireless Network

In recent years, industrial wireless network has become a hotspot in the research of automation field. Industrial wireless network is based on the traditional wireless sensor network (WSN), the technology not only has the advantage of WSN, such as ubiquitous sensing, low cost, low power, eased use and eased maintenance, but also anti-interference, high reliability and real-time communication. So it can be widely used in industrial process automation for monitoring and controlling.WIA-PA (Wireless Networks for Industrial Automation-Process Automation) project with independent intellectual property rights is researched and developed by around 10 organizations including the Shenyang Institute of Automation, Southwest University and Chongqing University of Posts and Telecommunications. It is a technical specification of industrial wireless network for process automation. WIA-PA uses wireless communication technology into industrial process control field, which main focus on how to solve the high reliability, real-time, low power consumption communication and other key issues in harsh industrial environments.Link scheduling is for a reliable point to point or multipoint communication link, and the purpose is to achieve efficient and equitable sharing of communication resources. WIA-PA has a double-layer network topology, star network and mesh network. Each star network forms a cluster. In the WIA-PA communication protocols, it uses super-frame to organize communication resources, the star networks corresponding to the cluster communication of the super-frame, and the mesh networks corresponding to the inter-cluster communication. WIA-PA mesh network communications plays a vital role in the entire wireless network; a reasonable inter-cluster link scheduling is one of the key technologies to ensure the reliable and real-time communication.The inter-cluster communication of WIA-PA adopts TDMA link scheduling, which divided the time into cyclical frame, then divided the frame into small time slots. The nodes in mesh network get the communication slot from appropriate scheduling mechanism to receive and send packets. TDMA-based link scheduling mechanism for wireless networks allocates the slots to the communication links. During the participation of WIA-PA project, after deeply analyzing the features of inter-cluster link scheduling in WIA-PA, This paper proposes the Spatial ruse and Centralized TDMA inter-cluster link scheduling strategy based on graph vertex Coloring algorithm, that is SCC-TDMA.This paper main studies the scheduling model and algorithms of WIA-PA mesh network. Firstly, we analyze three key problems of the link scheduling:How to avoid the existence of two types of wireless network communication conflicts; how to solve the uneven flow problems for each link caused by convergecast communication; how to improve the channel utilization issues. This paper also gives the formulation description of the scheduling problem, and proves the scheduling problem which is NP-Hard. Then, we build the scheduling model, which is to find the minimum frame period length under meeting the needs of communication conflict and demand constraints of time slots for each link. Secondly, we translate the scheduling problem into the minimum graph vertex coloring problem using conflict graph. Graph coloring is a well-known NP-Hard problem. This article designs the algorithm based on an independent set of graph vertex coloring algorithm to strike an approximate solution, which low complexity, high efficiency, suitable for WIA-PA mesh network link scheduling. This paper also describes the flow diagram of SCC-TDMA algorithm used in WIA-PA inter-cluster link scheduling.To verify the SCC-TDMA scheduling algorithm performance, this paper selects two typical TDMA link scheduling algorithm,the greedy algorithm and the hybrid intelligent algorithm for comparing algorithms, which selects the color number, algorithm running time, network throughput and network delay as four comparison parameters. Simulation results show that the number of colors for coloring algorithm and running time are two conflicting arguments, SCC-TDMA algorithm achieves a better compromise. We build ten typical network topology for experiment, both the number of required slots and algorithm running time can well meet the needs of WIA-PA. Finally, this paper also simulates the data collection process of the gateway for WIA-PA, the results show that, the network throughput and data collection delay of SCC-TDMA algorithm are better than the greedy algorithm and the hybrid intelligent algorithm. And with the network size increasing, the advantage is more obvious.In the network size of 121 nodes, the network throughput is increased by 19.2% compared with the greedy algorithm, and 12.8% compared with the hybrid intelligent algorithm; the data acquisition delay is increased by 33.6% and 22.0%, which proves that SCC-TDMA algorithm is effective to apply to WIA-PA.