CRISTAL Laboratory

Manouba, Tunisia

CRISTAL Laboratory

Manouba, Tunisia

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Ayoub Z.T.,CRISTAL Laboratory | Ouni S.,CRISTAL Laboratory | Kamoun F.,CRISTAL Laboratory
Proceedings of 2011 4th Joint IFIP Wireless and Mobile Networking Conference, WMNC 2011 | Year: 2011

Technology of wireless sensor networks has grown thanks to technological developments in different areas related to microelectronics. However, to become truly ubiquitous, these networks must overcome a number of challenges such as resource constraints (energy, memory, etc.), quality of service (bounded transmission delays), etc. It follows that the energy conservation and latency minimization are critical functions for sensor networks. The ZigBee standard, combined with IEEE 802.15.4 offers the features that best meet the needs of wireless sensor networks. This standard defines the association procedure that allows the sensors to self-organize into a topology through which data can be routed to their destination. In this paper, we propose new approaches of association designed to optimize the topology formation of IEEE 802.15.4/ZigBee network. Then, we use simulation to validate their efficiency in terms of energy saving and optimization of latency for IEEE 802.15.4/ZigBee sensor networks. © 2011 IEEE.


Azzaz S.,CRISTAL Laboratory | Saidane L.A.,CRISTAL Laboratory | Minet P.,French Institute for Research in Computer Science and Automation
PE-WASUN'11 - Proceedings of the 8th ACM Symposium on Performance Evaluation of Wireless Ad Hoc, Sensor, and Ubiquitous Networks | Year: 2011

Fault-tolerance is one of the main issues in Wireless Sensor Networks (WSNs) where applications require a continuous service. In this paper, we show how to use a small number of mobile robots to handle failures that may occur in the WSN. We study two strategies: Centralized Manager Strategy (CMS) and CMS with anticipation noted by CMS* to detect, report sensor failures and coordinate the movement of robots. The goal is to minimize the dysfunction time and avoid the coverage and connectivity degradation of the network upon a failure. The CMS is based on the Centralized Manager Algorithm [1] that we improve to ensure that the central manager robot receives a report upon an occurred failure. This manager robot selects a maintainer robot to replace the failed sensor. However, in the CMS* we propose, the manager robot anticipates the sensor failure and reacts before it happens using an energy state model representing the behavior of a sensor based on a discrete time Markov chain. Copyright 2011 ACM.


Ouni S.,CRISTAL laboratory | Gherairi S.,CRISTAL laboratory | Kamoun F.,CRISTAL laboratory
International Journal of Ad Hoc and Ubiquitous Computing | Year: 2013

Critical applications in real-time wireless sensor networks require bounded service latency and energy consumption optimisation. This motivates us to design a novel scheduling approach, which integrates communications with pipelining and data aggregation. The aim of our aggregation technique is to reduce the number of messages, which consequently reduces energy consumption. However, our pipelining technique is defined to minimise communication latency. Our approach is applied on tree wireless sensor networks and in a real-time context, which requires communications without interference. Thus, we use TDMA and a multi-frequency access method based on parent relationship clustering. In this context, we made the necessary mathematical formulation to determine communication response time and to predict the impact of real-time constraints, particularly deadlines, on communication delay. Our simulations outperform the efficiency of our approach to comprise between communication delay and energy consumption constraints. Copyright © 2012 Inderscience Enterprises Ltd.


Sebai D.,Cristal Laboratory | Chaieb F.,Cristal Laboratory | Ghorbel F.,Cristal Laboratory
3D Research | Year: 2016

The multi-view video plus depth (MVD) video format consists of two components: texture and depth map, where a combination of these components enables a receiver to generate arbitrary virtual views. However, MVD presents a very voluminous video format that requires a compression process for storage and especially for transmission. Conventional codecs are perfectly efficient for texture images compression but not for intrinsic depth maps properties. Depth images indeed are characterized by areas of smoothly varying grey levels separated by sharp discontinuities at the position of object boundaries. Preserving these characteristics is important to enable high quality view synthesis at the receiver side. In this paper, sparse representation of depth maps is discussed. It is shown that a significant gain in sparsity is achieved when particular mixed dictionaries are used for approximating these types of images with greedy selection strategies. Experiments are conducted to confirm the effectiveness at producing sparse representations, and competitiveness, with respect to candidate state-of-art dictionaries. Finally, the resulting method is shown to be effective for depth maps compression and represents an advantage over the ongoing 3D high efficiency video coding compression standard, particularly at medium and high bitrates. © 2016, 3D Research Center, Kwangwoon University and Springer-Verlag Berlin Heidelberg.


Ouni S.,CRISTAL Laboratory | Ayoub Z.T.,CRISTAL Laboratory
Wireless Personal Communications | Year: 2013

The major challenge of real-time Wireless Sensor Networks stills the optimization of both constraints: energy consumption, to get long network lifetime and the communication delay, to meet real-time requirements. In the context of IEEE 802.15.4/ZigBee networks, the association procedure has a direct effect on building paths optimizing those constraints. In this paper, we are interested on the definition of an ideal approach of load balancing to fairly distribute energy consumption among nodes in IEEE 802.15.4/ZigBee WSNs. This approach leads to conserve energy of each node in order to extend the network lifetime. To be closer to this ideal, we propose new dynamic association/re-association approaches allowing path alternation relative to association criteria and their threshold parameters. The implementation of those approaches in NS2 simulator highlights the efficiency of cooperative and dynamic association criteria particularly the one based on the sum of the inverses of remaining energy. Indeed, this approach gives better results with regard to energy distribution according to ideal approach which leads to a longer lifetime. It also performs lower latency for real time communication. © 2013 Springer Science+Business Media New York.


Ayoub Z.T.,CRISTAL Laboratory | Ouni S.,CRISTAL Laboratory
Lecture Notes of the Institute for Computer Sciences, Social-Informatics and Telecommunications Engineering, LNICST | Year: 2015

Recent technological progress in microelectronics has allowed a considerable development of Wireless Sensor Networks. These networks are deployed in several relevant applications such as healthcare and wildlife which require the support of sensor nodes mobility. However, this mobility is a real threat in breaking communications and packet loss accordingly. This paper proposes a fast handover procedure based on a smart association decision to handle mobility and to ensure continuous communication in IEEE 802.15.4 WSNs. In our proposed procedure, the mobile node can anticipate the coordinator change upon detecting the degradation of the link quality indicator. Then, it performs a fast re-association based on our smart criterion and it resumes the forwarding of stored packets. Simulations show that our fast handover procedure ensures better network performances than a similar approach. © 2015, Institute for Computer Sciences, Social Informatics and Telecommunications Engineering, All rights Reserved.


Ouni S.,CRISTAL Laboratory | Gherairi S.,CRISTAL Laboratory | Kamoun F.,CRISTAL Laboratory
International Journal of Sensor Networks | Year: 2011

The sensor networks raise fundamental problems for the scientific community. These problems are due to the wireless communications, the density of nodes distribution, the resources constraints (energy, processor and memory), the low nodes reliability and the strongly distributed nature of the supported application. The specific particularities of the sensor networks make it difficult the guarantee of the real-time quality of service which remains currently an important challenge. This paper presents novel protocol solutions for sensor networks in hard real-time environments. We try to get the optimisation of both constraints at the same time: real-time communication delay guarantee and the energy consumption. Our routing and medium access strategy allows the load balancing, the interferences reduction and the real-time guarantee, for being based on a dynamic generation of real-time communication trees. The simulation results show that our routing and medium access protocols help the traffic load balancing to increase the system lifetime and the guarantee of real-time traffics. © 2011 Inderscience Enterprises Ltd.


Azzaz S.,CRISTAL Laboratory | Saidane L.A.,CRISTAL Laboratory
PE-WASUN'12 - Proceedings of the 9th ACM Symposium on Performance Evaluation of Wireless Ad Hoc, Sensor, and Ubiquitous Networks | Year: 2012

In this paper, we have proposed two distributed preven- tive maintenance strategies dedicated for large-scale wireless sensor networks (WSNs) using a reduced number of mo- bile robots : (i) Fixed Distributed Preventive Maintenance Strategy denoted by F-DPMS, (ii) Adaptive Distributed Pre- ventive Maintenance Strategy denoted by A-DPMS. F-DPMS and A-DPMS are based on a simple analytical model to estimate the expected failures. To share the sensors repair load among the available robots, F-DPMS subdivides theWSN sensing area in equal surface subareas. Each main- tainer robot is assigned to a single one area to deal with its anticipated failures. In contrary, A-DPMS uses an adaptive area partitioning technique depending on the distribution of failures over the network map, in order to balance the repair load sharing. Simulation has shown that both F-DPMS and A-DPMS provide a null network dysfunction time with a sufficient number of robots. Obtained results show also that A-DPMS requests a minimal number of robots lower than F- DPMS. But, it produces a heavier signaling cost. To remedy this problem, we have proposed a new version of A-DPMS denoted by A-DPMS*. The novel maintenance strategy re- duces not only the introduced signaling messages, but also the traveled distance achieved by the maintainer robots to replace the expected failures. Copyright 2012 ACM.


Ayoub Z.T.,CRISTAL laboratory | Ouni S.,CRISTAL laboratory
Lecture Notes of the Institute for Computer Sciences, Social-Informatics and Telecommunications Engineering, LNICST | Year: 2014

Many Wireless Sensor Network applications such as healthcare and wildlife monitoring require the support of nodes mobility. However, the mobility has large impact on the network behavior namely the dynamic network topology and the synchronization loss of mobile nodes. Given that, this paper proposes two new re-association procedures for reliable handover to deal with nodes mobility in IEEE 802.15.4 WSNs. In the first approach, the handover process is triggered by parent nodes based on their residual energy. In the second approach, the handover process is triggered by mobile nodes upon location change. Both approaches allow to minimize data packet loss during the handover process while optimizing energy consumption. We used simulation in order to highlight the efficiency of our proposals namely in terms of network throughput and reliability. © Institute for Computer Sciences, Social Informatics and Telecommunications Engineering 2014.


Azzaz S.,CRISTAL Laboratory | Saidane L.A.,CRISTAL Laboratory
HP-MOSys'12 - Proceedings of the ACM Workshop on High Performance Mobile Opportunistic Systems | Year: 2012

Generally, the Quality of Service (QoS) in a wireless sensor network (WSN) is measured by the sensing area coverage degree and the connectivity between the deployed sensors. To conserve and protect these QoS parameters, we have used a limited number of mobile maintainer robots to handle the eventual network failed sensors. In this paper, we have introduced two Centralized Preventive Maintenance Strategies (CPMS) dedicated for theWSNs. Indeed, with an analytical energy model representing the energy consumption of each network's node, a central manager robot estimates the expected sensors failures to be repaired by the available robots before the total depletion of their energies. To schedule the available maintainer robots, we have introduced two Centralized Preventive Maintenance Strategies (CPMS) for WSNs with two scheduling approaches used to obtain the convenient maintainer robot scheduling for a fixed number of anticipated failures (fixed window): (i) CPMS with the Nearest available robot heuristic Backtrack- ing robot scheduling algorithm (CPMS-NB) and (ii) CPMS with a Genetic robot scheduling Algorithm (CPMS-GA). Simulation results show that the CPMS-GA scheduling algorithm is more complex than that of CMSA-NB, but it gives a better network dysfunction time with a minimal robot traveling distance. Copyright © 2012 by the Association for Computing Machinery, Inc. (ACM).

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