Industrial Wireless Local Area Network Research Articles

IEEE 802.11ax Meet Edge Computing: AP Seamless Handover for Multi-Service Communications in Industrial WLAN

IEEE 802.11ax, as a new generation of wireless local area network (WLAN) standard, has great development potential for multi-service access in industrial WLAN with its characteristics of low-cost, quick-deployment and high-efficiency. However, it still faces the problem of quick and efficient access point (AP) seamless handover for multi-service communications due to terminal mobility and channel degradation. To solve the problem, combining the characteristics of orthogonal frequency division multiple access (OFDMA) technology and multi-user multiple-input multiple-output (MU-MIMO) technology, this paper firstly proposes an edge computing based IEEE 802.11ax multi-service bearer mechanism by dynamically allocating channel resource units (RUs). Secondly, a multi-service AP seamless handover mechanism based on edge computing is proposed, which consists of a channel scanning delay optimization method based on virtual AP sentinel, a handover trigger judgment algorithm considering mobility and RU reallocation, a multi-objective optimized AP handover model considering load balancing, transmission rate optimization and handover cost minimization with service attributes. Finally, we propose a multi-service AP seamless handover algorithm based on improved particle swarm optimization (PSO) to get optimized handover making-decision. Simulation results show that the proposed handover mechanism can reduce the handover delay significantly while realizing seamless handover accurately in multi-service industrial WLAN.

Retransmission Diversity with Channel Selectivity for High Reliable and Low Latency Industrial Wireless Control System

The emerging applications in the 5th generation (5G) network, such as industrial control system and Machine-to-Machine (M2M) communication require high reliability and low latency communication at the same time. The retransmission scheme is one of the practical approaches to increase system reliability when other diversity techniques are avoided due to hardware complexity or significant transmission delay. In order to address such problems, in this paper, we propose a fast yet reliable retransmission scheme. The proposed retransmission scheme leverages the frequency diversity through simple channel selectivity. The channel selectivity is carried out by employing low complexity subcarrier allocation for selecting other channels in Orthogonal Frequency Division Multiplexing (OFDM) transmission. The evaluation results show that the proposed retransmission method outperforms the conventional scheme. The proposed method can reduce the number of retransmission by up to 30%, corresponding to a success rate of 0.9999 . In addition, it can be employed in an industrial Wireless Local Area Network (iWLAN) system with a large number of users. The achievable control duration is around 52-63 μs, an improvement of approximately 36% compared to the conventional system.

An efficient genetic algorithm for large-scale transmit power control of dense and robust wireless networks in harsh industrial environments

The industrial wireless local area network (IWLAN) is increasingly dense, due to not only the penetration of wireless applications to shop floors and warehouses, but also the rising need of redundancy for robust wireless coverage. Instead of simply powering on all access points (APs), there is an unavoidable need to dynamically control the transmit power of APs on a large scale, in order to minimize interference and adapt the coverage to the latest shadowing effects of dominant obstacles in an industrial indoor environment. To fulfill this need, this paper formulates a transmit power control (TPC) model that enables both powering on/off APs and transmit power calibration of each AP that is powered on. This TPC model uses an empirical one-slope path loss model considering three-dimensional obstacle shadowing effects, to enable accurate yet simple coverage prediction. An efficient genetic algorithm (GA), named GATPC, is designed to solve this TPC model even on a large scale. To this end, it leverages repair mechanism-based population initialization, crossover and mutation, parallelism as well as dedicated speedup measures. The GATPC was experimentally validated in a small-scale IWLAN that is deployed a real industrial indoor environment. It was further numerically demonstrated and benchmarked on both small- and large-scales, regarding the effectiveness and the scalability of TPC. Moreover, sensitivity analysis was performed to reveal the produced interference and the qualification rate of GATPC in function of varying target coverage percentage as well as number and placement direction of dominant obstacles.

An efficient genetic algorithm for large-scale planning of dense and robust industrial wireless networks

With the penetration of Internet of things in manufacturing industry, it is an unavoidable issue to maintain robust wireless connections among machines and human workers in harsh industrial environments. However, the existing wireless planning tools focus on office environments, which are less harsh than industrial environments regarding shadowing effects of diverse obstacles. To fill this gap, this paper proposes an over-dimensioning (OD) model, which automates the decision making on deploying a robust industrial wireless local area network (IWLAN). This model creates two full coverage layers while minimizing the deployment cost, and guaranteeing a minimal separation distance between two access points (APs) to prevent APs that cover the same region from being simultaneously shadowed by an obstacle. Moreover, an empirical one-slope path loss model, which considers three-dimensional obstacle shadowing effects, is proposed for simple yet precise coverage calculation. To solve this OD model even at a large size, an efficient genetic algorithm based over-dimensioning (GAOD) algorithm is designed. Genetic operators, parallelism, and speedup measures are tailored to enable large-scale optimization. A greedy heuristic based over-dimensioning (GHOD) algorithm is further proposed, as a state-of-the-art heuristic benchmark algorithm. In small- and large-size OD problems based on industrial data, the GAOD was demonstrated to be 20%–25% more economical than benchmark algorithms for OD in the same environment. The effectiveness of GAOD was further experimentally validated with a real deployment system. Though this paper focuses on an IWLAN, the proposed GAOD can serve as a decision making tool for deploying other types of robust industrial wireless networks in terms of coverage, such as wireless sensor networks and radio-frequency identification (RFID) networks.

Performance Analysis of Industrial WLAN Based on EDCA Scheme Defined in IEEE802.11e

In the last few years wireless local area network (WLAN) technology and products have grownunusually. This growth has encouraged many researchers to employ WLAN technology in differentapplication Areas. Recently, using IEEE 802.11 WLAN in industrial automation applications is attractiveand more interesting. However, the currently used medium access mechanism makes WLANs nondeterministicand hence not suitable for industrial real-time traffic. Legacy IEEE 802.11 WLANs wereinitially designed for best effort traffic only and did not provide any QoS support for this kind of traffic.The new amendment IEEE 802.11e standard was introduced and ratified in 2005. It defines the concept ofa Hybrid Co-ordination Function (HCF) at the MAC layer for medium access control. HCF is acombination of HCF Controlled Channel Access (HCCA) with parameterized quality of service (QoS)and Enhanced Distribution Channel Access (EDCA) with prioritized QoS. Enhanced DistributionChannel Access (EDCA) is an enhanced version of Distributed Coordination Function )DCF( mechanismused in the original IEEE 802.11 WLAN. This paper analyze the performance of the EDCA in anindustrial automation network with real-time requirements by means of a simulation with the networksimulator OPNET 11.5 and compares the results with the DCF in terms of latency and throughput invarious scenarios.

A water pumping control system with a programmable logic controller (PLC) and industrial wireless modules for industrial plants—An experimental setup

This paper describes a water pumping control system that is designed for production plants and implemented in an experimental setup in a laboratory. These plants contain harsh environments in which chemicals, vibrations or moving parts exist that could potentially damage the cabling or wires that are part of the control system. Furthermore, the data has to be transferred over paths that are accessible to the public. The control systems that it uses are a programmable logic controller (PLC) and industrial wireless local area network (IWLAN) technologies. It is implemented by a PLC, an communication processor (CP), two IWLAN modules, and a distributed input/output (I/O) module, as well as the water pump and sensors. Our system communication is based on an Industrial Ethernet and uses the standard Transport Control Protocol/Internet Protocol for parameterisation, configuration and diagnostics. The main function of the PLC is to send a digital signal to the water pump to turn it on or off, based on the tank level, using a pressure transmitter and inputs from limit switches that indicate the level of the water in the tank. This paper aims to provide a convenient solution in process plants where cabling is not possible. It also has lower installation and maintenance cost, provides reliable operation, and robust and flexible construction, suitable for industrial applications.