Abderrazak Abdaoui

Structural Health Monitoring Using Wireless Sensor Networks: A Comprehensive Survey

Structural health monitoring (SHM) using wireless sensor networks (WSNs) has gained research interest due to its ability to reduce the costs associated with the installation and maintenance of SHM systems. SHM systems have been used to monitor critical infrastructure such as bridges, high-rise buildings, and stadiums and has the potential to improve structure lifespan and improve public safety. The high data collection rate of WSNs for SHM pose unique network design challenges. This paper presents a comprehensive survey of SHM using WSNs outlining the algorithms used in damage detection and localization, outlining network design challenges, and future research directions. Solutions to network design problems such as scalability, time synchronization, sensor placement, and data processing are compared and discussed. This survey also provides an overview of testbeds and real-world deployments of WSNs for SH.

On the effects of combined atmospheric fading and misalignment on the hybrid FSO/RF transmission

Free-space optical (FSO) communication is known for its various impairments such as atmospheric turbulence and misalignment fading. In this paper, we study the performance of an FSO link operating under combined path loss and atmospheric and misalignment fadings. We derive a closed-form expression for the bit error rate (BER) of the FSO link in such conditions when the on-off keying (OOK) modulation is employed and when the fluctuations of the received signal are modeled by Gamma- Gamma distribution. In addition, we evaluate the effects of the combined fadings on the outage probability of the FSO link for different strengths of turbulence and pointing errors. Furthermore, we investigate the advantages of combining radio frequency (RF) with FSO to form hybrid FSO/ RF systems. The RF link is based on 16 quadrature amplitude modulation (16-QAM) and on Rician channel fading. We study the performance of the hybrid FSO/RF system in terms of outage probability and BER and find that the hybrid FSO/RF system can overcome the weaknesses of FSO links, which are sensitive to atmospheric variations and misalignment fading.

A Modular IoT Platform for Real-Time Indoor Air Quality Monitoring

The impact of air quality on health and on life comfort is well established. In many societies, vulnerable elderly and young populations spend most of their time indoors. Therefore, indoor air quality monitoring (IAQM) is of great importance to human health. Engineers and researchers are increasingly focusing their efforts on the design of real-time IAQM systems using wireless sensor networks. This paper presents an end-to-end IAQM system enabling measurement of CO2, CO, SO2, NO2, O3, Cl2, ambient temperature, and relative humidity. In IAQM systems, remote users usually use a local gateway to connect wireless sensor nodes in a given monitoring site to the external world for ubiquitous access of data. In this work, the role of the gateway in processing collected air quality data and its reliable dissemination to end-users through a web-server is emphasized. A mechanism for the backup and the restoration of the collected data in the case of Internet outage is presented. The system is adapted to an open-source Internet-of-Things (IoT) web-server platform, called Emoncms, for live monitoring and long-term storage of the collected IAQM data. A modular IAQM architecture is adopted, which results in a smart scalable system that allows seamless integration of various sensing technologies, wireless sensor networks (WSNs) and smart mobile standards. The paper gives full hardware and software details of the proposed solution. Sample IAQM results collected in various locations are also presented to demonstrate the abilities of the system.

Multi-objective sensor placement using the effective independence model (SPEM) for wireless sensor networks in structural health monitoring

This paper studies the optimal placement problem in structural health monitoring (SHM) using wireless sensor networks (WSN). This problem is formulated as a refined multi-objective optimization problem with various constraints of connectivity and flow conservation conditions, while minimizing the energy consumption and maximizing the information quality are the objectives. To perform the multi-objective optimization, we modify the heuristic single objective power-aware sensor placement using the effective independence model (p-SPEM) algorithm introduced in [1]. In this paper, we design and analyze a multi-objective p-SPEM (mop-SPEM) algorithm for sensor node placement. The multi-objective formulation adds more flexibility because the energy consumption and the information quality can be easily traded-off. The mop-SPEM is simulated and compared with p-SPEM for a nine-storey building. Results show that mop-SPEM is able to trade-off the energy with the information quality by adjusting the relative weights of the objective functions.

On the Effects of Temperature on the Performances of FSO Transmission under Qatar's Climate

Strong atmospheric turbulence can highly affect the free space optical (FSO) link. In fact, the strength of turbulence is depending on weather factors where the temperature is considered as the main parameter increasing these turbulences. In this work, an experimental investigation of the effect of Qatars harsh climate on FSO link in term of packet ratio delivery (PDR) is carried out. Two FSO transceivers, operating June at 1550 nm for 600 m link distance, have been used. Based on Bendersky, Kopeika and Blaunstein (BKB) model and on the measured weather factors we tried to characterise the strength of turbulences under Qatar climate.

An experimental performance evaluation of the hybrid FSO/RF

This paper is a first attempt to study the effects of atmospheric turbulences on hybrid free space optics/ radio frequency (FSO/RF) transmission system in Doha, Qatar. The state of Qatar is characterized by a Mediterranean climate with hot and dry summers with modest cloud coverage highly affected by airborne dust. Due to its sensitivity to atmospheric turbulences, throughout this study, we try to demonstrate the working capabilities of FSO technology as well as to promote an understanding of this technology amongst the countries of the gulf cooperation council (GCC). Moreover, we studied the behavior of RF link during the same period. In order to analyze the transport media, two transmitting subsystems are employed and installed at Qatar University (QU) at two different buildings separated by a distance of 600 m. Each system is composed of a FSO and RF terminal. We have ported an Embedded Linux kernel on Micro-blaze processor build in Field Programmable Gate Array (FPGA). Then, we have designed a network sniffer application that can run on the FPGA board. The measurements from the network sniffer applications were carried out during summer season from June up to September 2015. The relation between the measurements and the atmospheric factors, taken from a weather station installed at QU, were also found.

Indoor test of the fog's effect on FSO link

In order to distinguish the most rigorous model, we made a comparison between measurements data and the mostly used empirical models. These models use the visibility as a basic parameter to predict the fog attenuation. In order to measure the visibility, we used a laser lamp of 532 nm and two light sensors. The experimental set up is composed of a fog machine and two KORUZA terminals operating at 1310 nm and 1550 nm, respectively. Every one minute, the measured attenuation is averaged to one value then compared to the attenuation calculated based on measured visibility and according to the empirical models cited previously.

Impact of time synchronization error on the mode-shape identification and damage detection/localization in WSNs for structural health monitoring

Time synchronization in wireless sensor networks (WSNs) is a critical challenge for any distributed system such as WSNs for structural health monitoring (SHM). In SHM, mode shape identification, damage detection and damage localization are sensitive to time synchronization errors (TSEs). Indeed, the errors, due to the time shift between the incoming raw data from each sensor node, may hugely affect the data integrity and then the mode shape identification of the structure under analysis. In this paper, we characterize the impact of TSE on the modal analysis, damage detection and damage localization using frequency domain decomposition (FDD) implemented in a semi-local manner. In order to decrease the size of the transmitted data by the sensor nodes and reduce the processing load and the needed storage capacity on the central unit, we adopt a semi-local processing approach where each sensor node partially processed data and transmit it to a central unit for further processing such as mode shape identification, damage detection and damage localization. We adopt the model where each sensor node performs the Fast Fourier Transform (FFT) of the measured vibration signal and the transmission of the FFT values to a central unit or to a cluster head for further processing. The results show that TSE has a strong impact on the mode shape identification, damage detection and damage localization. Furthermore, results show that semi-local processing is more sensitive to TSE compared to centralized processing.

Impact of time synchronization error on the mode-shape calculation in wireless sensor networks for structural health monitoring

For structural health monitoring (SHM), mode shape calculation is an important task that needs to be performed accurately and reliably. The use of wireless sensor networks (WSNs) for SHM is a very effective and a promising solution. However, WSNs experience synchronization errors among the sensor nodes, which can affect the accuracy of the mode shape calculation. In this paper, we study the impact of time synchronization error (TSE) on the mode shape calculation in a semi-local manner using frequency domain decomposition (FDD) implemented in a semi-local manner. In order to decrease the size of the transmitted data by the sensor nodes and reduce the processing load and needed storage capacity on the central unit, we adopt a semi-local processing approach where each node partially processes the measured data. Then, sensor nodes send the partially-processed data to a central unit for further processing and mode shape calculation. Numerical results prove that the time synchronization error has a significant impact on the accuracy of the mode shape calculation. Furthermore, results show that semi-local processing is more sensitive to TSE compared with centralized processing.

On the Capacity of Mid-latitude High Frequency Ionospheric Channel

In this paper we consider the theoretical characterization of the ionospheric transmission. More accurately, we derive a closed form expression of the average capacity for Mid-latitude High Frequency (HF) ionospheric channels. Heretofore, this problem has been studied for Rayleigh channels when each tap of the impulse response has a Rayleigh distribution without characterizing the variance of this distribution. In this paper, we extend these works to HF ionospheric channels by evaluating the variance of the amplitude attenuation versus the Doppler spread and then the channel capacity. For a multipath HF ionospheric channel, we model the Doppler phenomenon as a Gaussian profile which is suggested for HF environments. Finally, we derive a closed form expression of the average channel capacity using the probability density function (pdf) of the instantaneous impulse response. Numerical results on both simulated and real measured data are derived at the end of the paper.