Hassan H. Halawa

On the effect of interference on Wi-Fi-based Wireless Networked Control Systems

This study investigates a Wi-Fi-based Wireless Networked Control System. This system is first modified in order to enhance resistance to interference. Then, it is subjected to different types of interference. The system consists of a workcell containing 30 sensors, 30 actuators and 1 controller. All forms of interference modeled focus on the operating frequency band used by the control nodes. All simulations are conducted on OPNET Network Modeler and system performance is measured in terms of packet end-to-end delay and correct packet transmission/reception. All results are subjected to a 95% confidence analysis. The results show that intentional jamming is more damaging than medium congestion, which in turn is more damaging than network congestion.

Sensor actuator Ethernet-based Networked Control Systems

A direct sensor to actuator communication model for Ethernet-based Networked Control Systems (NCSs) is presented in this paper. This model is compared to a previously introduced model including an in-loop controller node. OMNET simulations showed the success of the presented model in meeting system delay and strict zero packet loss (with no over-delayed packets) requirements. The model also showed a reduction in the end-to-end delay of control packets from sensor nodes to actuator nodes in both Fast and Gigabit switched Ethernet-Based. A major improvement is the increase in the amount of additional load the proposed model can accommodate.

Network fabric redundancy in NCS

Fault-tolerance is becoming an increasingly crucial aspect of the design of Networked Control Systems (NCSs) in order to mitigate system downtime. However, the introduction of fault-tolerance is typically associated with significant traffic overhead. In this paper, an optimization to an Ethernet-based network fabric fault-tolerant NCS is proposed. The proposed optimization halves the amount of overhead traffic necessary for fault-tolerance while maintaining the same level of robustness. Moreover, based on the same optimization methodology, an expanded model with two in-line cells is presented and subsequently tested. The expanded two-cell model is designed to provide controller-level in addition to fabric-level fault-tolerance. Simulations using OPNET followed the traffic analysis, and proved the models to be fully reliable in the case of a single failure at a time, for both the single-cell model and the expanded two-cell network.

Analysis of parallel redundant WLAN with timing diversity

Redundancy techniques based on the combination of multiple diverse communication channels are an established countermeasure to improve performance characteristics of wireless communication systems. Besides parallel redundancy in the space and frequency domain, serial redundancy in the time domain can be utilized. It is known that the parallel approaches can significantly improve performance characteristics like jitter and reliability, when applied for wireless packet-based data transmission. In this work, an investigation on the performance impact of additional time diversity on top of the parallel redundancy approaches is performed. An OPNET simulation model is created and analysed for its performance characteristics.

Heterogeneous LTE/Wi-Fi architecture for ITS traffic control and infotainment

Intelligent Transportation Systems (ITS) make use of advanced technologies to enhance road safety and to improve traffic efficiency. In order to assist passengers to travel safely, efficiently and conveniently, several application requirements have to be met simultaneously. For this purpose, this paper proposes a heterogeneous LTE/Wi-Fi vehicular system that supports both infotainment and ITS traffic control data. A performance simulation-based study is conducted to validate the feasibility of the proposed system in an urban vehicular environment. The system performance is evaluated in terms of data loss, data rate, delay and jitter. The results indicate that the proposed system offers acceptable performance that meets the requirements of both infotainment and traffic control.

WSN goodput and energy consumption for various wireless communication standards

This paper proposes a methodology for calculating the energy consumption and the throughput of a Wireless Sensor Network (WSN) taking into account retransmissions and data dropped due to collisions. For various scenarios, simulations are conducted using OPNET and utilizing off-the-shelf wireless communications standards such as ZigBee, Low-Power Wi-Fi and Wi-Fi. A figure of merit is then introduced for a fair comparison between the mentioned standards.

Wi-Fi-based hierarchical Wireless Networked Control Systems

This paper proposes a novel architecture for a hierarchical Wireless Networked Control System (WNCS). It consists of three cascaded workcells each containing 30 sensors, 30 actuators and one controller. The wireless communication protocol used is IEEE 802.11g with multicasting. The hierarchy of the system is such that the lowest level is that of the sensors and actuators, the intermediate level is the controllers, and the highest level is a supervisory node. This supervisor can be either active or passive. System performance is measured using OPNET simulations and the results are confirmed analytically. The system is shown to tolerate all possible controller failure scenarios. The supervisor can handle the entire control load of all three controllers, should the need arise. The system exhibits zero packet drops and delay constraints are met in all scenarios. The effect of interference is then investigated and the maximum interference that can be tolerated by the system is quantified.

TMR sensors for reliable S2A architectures

In this paper, TMR Sensors are applied to a fault-tolerant direct sensor to actuator (S2A) architecture for Ethernet-based Networked Control Systems (NCSs). The architecture is studied using switched Fast and Gigabit Ethernet. It is shown analytically and verified via OMNeT++ simulations that the architecture succeeds in meeting system end-to-end delay and strict zero packet loss (no over-delayed packets) requirements when using Gigabit Ethernet. Reliability modeling is carried out to quantitatively assess the benefits of the TMR sensors architecture when compared to an S2A fault-tolerant controller architecture.

Application of parallel redundancy in a Wi-Fi-based WNCS using OPNET

A powerful approach to improve the performance of wireless communication is the parallel redundant transmission with dual-radio wireless devices. To further verify this approach in this work, an OPNET simulation is performed on a star-topology WNCS workcell with 30 sensor and actuator pairs that are equipped with dual-radios for parallel redundancy. The applied wireless simulation model is based on IEEE 802.11g (Wi-Fi) standard and a quantitative analysis of the effect of interference in an industrial environment, is presented. This study proved that parallel redundancy improves system performance under different interference environments.

Simulation of parallel redundant WLAN with OPNET

Applying multiple redundant and diverse communication channels is an established method to achieve an improved overall communication channel. When applied for packet-based data transmission over channels with strongly nondeterministic behaviour due to environmental influence, such as Wireless Communications, timing performance can be greatly improved by this approach. The central element in such a system is the so called “Combiner” on the receiving side. In this work, a new specific type named “Timing Combiner” is described. The Parallel Redundancy Protocol (PRP) according to IEC 62439-3 realizes such a Timing Combiner on the Ethernet level. In this work, an OPNET simulation model is created and analysed for its performance characteristics. Also a quantitative analysis of the effect of different interference models in an industrial environment is presented.