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    ADABCAST: ADAptive BroadCAST Approach for Solar Energy Harvesting Wireless Sensor Networks
    (IEEE, 2017-04) Khiati, Mustapha; Djenouri, Djamel
    The problem of message broadcasting from the base station (BS) to sensor nodes (SNs) in solar energy harvesting wireless sensor networks (EHWSN) is considered in this paper. The aim is to ensure fast and reliable broadcasting without interfering with upstream communications (from SNs to BS), whilst taking into account energy harvesting constraints. An adaptive approach is proposed where the BS first selects the broadcast time slots, given a wake-up schedule for the SNs (the time slots where the SN are active and in receiving mode). Hence, the SNs adapt their schedules. This is then iterated seeking optimal selection of the broadcast time slots, so as to minimize broadcast overhead (transmitted messages) and latency. Our approach enables fast broadcast and eliminates the need for adding protocol overhead (redundancy), compared to the existing solutions. Hidden Markov Model (HMM) and Baum-Welch learning algorithm are used for this purpose. Numerical results confirm that our scheme performs the broadcast operation in less time, and by reducing the broadcast overhead, as compared to state-of-the-art approaches.
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    Optimal Placement of Relay Nodes Over Limited Positions in Wireless Sensor Networks
    (IEEE, 2017-04) Bagaa, Miloud; Cheli, Ali; Djenouri, Djamel; Taleb, Tarik; Balasingham, Ilangko; Kansanen, Kimmo
    This paper tackles the challenge of optimally placing relay nodes (RNs) in wireless sensor networks given a limited set of positions. The proposed solution consists of: 1) the usage of a realistic physical layer model based on a Rayleigh blockfading channel; 2) the calculation of the signal-to-interferenceplus- noise ratio (SINR) considering the path loss, fast fading, and interference; and 3) the usage of a weighted communication graph drawn based on outage probabilities determined from the calculated SINR for every communication link. Overall, the proposed solution aims for minimizing the outage probabilities when constructing the routing tree, by adding a minimum number of RNs that guarantee connectivity. In comparison to the state-of-the art solutions, the conducted simulations reveal that the proposed solution exhibits highly encouraging results at a reasonable cost in terms of the number of added RNs. The gain is proved high in terms of extending the network lifetime, reducing the end-to-end- delay, and increasing the goodput.
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    Energy Harvesting Aware Minimum Spanning Tree for Survivable WSN with Minimum Relay Node Addition
    (CERIST, 2016-08-31) Djenouri, Djamel; Bagaa, Miloud; Ali, Chelli; Balasingham, Ilangko
    Survivable wireless sensor networks that take advantage of green energy resources from the environment is considered in this paper. The particular problem of constrained relay nodes (RNs) placement to ensure communication coverage in the single-tiered topology while taking advantage of the energy harvesting potentials of sensor nodes (SNs) is dealt with. The contribution is to consider a realistic energy harvesting model where harvesting potentials may vary from one node to another. Without loss of generality, the energy model used in this paper is appropriate to wireless charging, but the proposed solution can be extended to the use of any energy harvesting technology. Based on this model, we propose a heuristic based on spanning tree calculation in an edge weighted graph model where the traffic routed at every node is proportional to its effective energy. RNs are added to help non-leaf nodes in the tree that cannot meet the defined survivability condition. A lower-bound of the proposed model is derived using integer linear programming. The proposed solution is compared by simulation to the single solution from the literature that treats the problem of RNs placement while considering energy harvesting capacity of SNs. A simplified model is used in the simulation to allow comparison. The performance results show that the proposed solution ensures survivability by adding a lower number of RNs.
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    An Oscillation-Based Algorithm for Reliable Vehicle Detection with Magnetic Sensors
    (CERIST, 2016-02-25) Djenouri, Djamel; Doudou, Messaoud; Kafi, Mohamed Amine
    Vehicle monitoring using a wireless sensor network is considered in this paper, where a new algorithm is proposed for vehicle detection with magnetic sensors. The proposed algorithm is based on processing the magnetic signal and thoroughly analyzing the number/direction of its oscillations. The main feature of the proposed algorithm over the state-of-the-art ones is its capability to detect vehicles with different shapes of signatures, while most state-of-the-art algorithms assume regular shapes of signatures. This makes the algorithm effective with all types of magnetic sensors. The proposed algorithm has been implemented on Micaz sensor motes and tested in real word scenarios. Results show reliability beyond 93% in all samples, and more than 95% in most of them.
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    Implementation of High Precision Synchronization Protocols in Wireless Sensor Networks
    (IEEE, 2014-05) Djenouri, Djamel; Bagaa, Miloud
    Microsecond-level time synchronization is needed in realtime applications of wireless sensor networks. While several synchronization protocols have been proposed, most performance evaluations have been limited to theoretical analysis and simulation, with a high level of abstraction by ignoring several practical aspects, e.g. packet handling jitters, clock drifting, packet loss, etc. Effective implementation in real motes faces several challenges due to motes’ limitations and the unreliable lossy channels. These issues affect the protocol performance and precision. Authors of some pragmatic solutions followed empirical approaches for the evaluation, where the proposed solutions have been implemented on real motes and evaluated in testbed experiments. This article throws light on issues related to the implementation of synchronization protocols in WSN. The challenges related to WSN environment are presented, the importance of real implementation and the testbed evaluation are motivated by some experiments that we conducted. Finally, some relevant implementations of the literature that meet microsecondlevel precision are discussed.
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    Energy Harvesting Aware Relay Node Addition for Power-Efficient Coverage in Wireless Sensor Networks
    (CERIST, 2015-01-11) Djenouri, Djamel; Bagaa, Miloud
    This paper deals with power-efficient coverage in wireless sensor networks (WSN) by taking advantage of energyharvesting capabilities. A general scenario is considered for deployed networks with two types of sensor nodes, harvesting enabled nodes (HNs), and none-harvesting nodes (NHNs). The aim is to use only the HNs for relaying packets, while NHNs use will be limited to sensing and transmitting their own readings. The problem is modeled using graph theory and reduced to finding the minimum weighted connected dominating set in a vertex weighted graph. A limited number of relay nodes is added at the positions close to the NHNs in the resulted set. The weight function ensures minimizing the number of NHNs in the set, and thus reducing the relay nodes to be added. Our contribution is to consider relay node placement (addition) in energy harvesting WSN, where only HNs are used to forward packets. This is to preserve the limited energy of NHNs. Extensive simulation results show that the proposed relay node addition strategy prolongs the network lifetime, from the double, to factors of several tens of times. This is at a reasonable cost in terms of the number of relay nodes added, which is compared to a lower-bound derived in the paper.
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    Implementation of High Precision Synchronization Protocols in Wireless Sensor Networks
    (CERIST, 2014-03-17) Djenouri, Djamel; Bagaa, Miloud
    Microsecond-level time synchronization is needed in realtime applications of wireless sensor networks. While several synchronization protocols have been proposed, most performance evaluations have been limited to theoretical analysis and simulation, with a high level of abstraction by ignoring several practical aspects, e.g. packet handling jitters, clock drifting, packet loss, etc. Effective implementation in real motes faces several challenges due to motes' limitations and the unreliable lossy channels. These issues affect the protocol performance and precision. Authors of some pragmatic solutions followed empirical approaches for the evaluation, where the proposed solutions have been implemented on real motes and evaluated in testbed experiments. While there are several survey articles presenting the protocols from the conception perspectives, and others dealing with mathematical and signal processing issues of the estimators, a survey on aspects related to the practical implementation is missing. This article throws light on issues related to the implementation of synchronization protocols in WSN. The challenges related to WSN environment are presented, the importance of real implementation and the testbed evaluation are motivated by some experiments that we conducted. Finally, some relevant implementations of the literature that meet microsecond-level precision are discussed.
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    MLE for Receiver-to-Receiver Time Synchronization in Wireless Networks with Exponential Distributed Delays
    (CERIST, 2014-01-30) Djenouri, Djamel
    Receiver-to-receivertimesynchronizationinwirelessnetworksisconsidered,andappropriatemaximum-likelihoodestimators(MLE)forenvironmentswithexponentialdistrustedreceptiondelaysareproposed.Inthereceiver-to-receiversyn-chronizationapproach,timeatreceiversshouldbedirectlyrelatedtooneanotherwithoutrefereingtothesender(reference),whichpermitstoeliminatethesender’suncertaintyfromthevariabledelays(timecritical-path).Themodelsandestimatorsproposedforthesender-to-receiverapproacharethusinappro-priateforthereceiver-to-receiverone.Amodelthataccuratelyreflectstherelativefeatureoftheconsideredapproachandeliminatesthesenders’suncertaintyisused,wheretimestampsatthereceiversaredirectlyrelatedwithoutrefereingtothesender’stimeortimestamps.Bydirectlyrelatingtimeattworeceiverswithidenticalexponentialreceptiondelay,,ityieldsadistributionasthedifferencebetweenthetwodelays.TheyusetheloglikelihoodfunctionofthelatterandtheMLmethod,theoffsetestimatorhasbeenanalyticallyderived,wherealinearprogramisgivenforthejointoffset/skewmodel.Theaccuracyoftheproposedestimatorshasbeennumericallyanalyzedbysimulation.Resultsshowhighprecisionoftheproposedestimators,whichcanbeintegratedwithanyreceiver-to-receiversynchronizationprotocol.
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    Efficient Multi-Path Data Aggregation Scheduling in Wireless Sensor Networks
    (CERIST, 2013) Bagaa, Miloud; Badache, Nadjib; Ouadjaout, Abdelraouf; Younis, Mohamed
    In wireless sensor networks, in-network data aggregation filters out redundant sensor readings in order to reduce the energy and bandwidth consumed in disseminating the data to the base-station. In this paper, we investigate the problem of reliable collection of aggregated data with minimal latency. The aim is to form an aggregation tree such that there are k disjoint paths from each node to the basestation and find a collision-free schedule for node transmissions so that the aggregated data reaches the base-station in minimal time. We propose a novel algorithm for Reliable and Timely dissemination of Aggregated Data (RTAD). RTAD intertwines the formation of the aggregation tree and the allocation of time slots to nodes, and assigns parents to the individual nodes in order to maximize time slot reuse. The simulation results show that RTAD outperforms competing algorithms in the literature.
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    Preventing vehicle crashes through a wireless vehicular sensor network
    (IEEE Communications Society, 2008-06) Djenouri, Djamel
    In this manuscript we propose a wireless sensor network (WSN) based solution allowing vehicles with merely onboard sensors to avoid frontal collisions in rural highways. Unlike the current solutions that rely on heavy infrastructure, in our vehicular traffic safety solution only tiny low-cost sensors are employed. It can thus replace the infrastructure-based systems in rural and suburban areas, where the deployment of such infrastructure is constrained. It can also serve as an alternative solution for unsophisticated vehicles that are not equipped with aboard computers and cannot take advantage of the current intelligent transportation systems and services.