Leila Azouz Saidane

TDMA-Based MAC Protocols for Vehicular Ad Hoc Networks: A Survey, Qualitative Analysis, and Open Research Issues

Vehicular ad hoc networks (VANETs) have attracted a lot of attention in the research community in recent years due to their promising applications. VANETs help improve traffic safety and efficiency. Each vehicle can exchange information to inform other vehicles about the current status of the traffic flow or a dangerous situation such as an accident. Road safety and traffic management applications require a reliable communication scheme with minimal transmission collisions, which thus increase the need for an efficient medium access control (MAC) protocol. However, the design of the MAC in a vehicular network is a challenging task due to the high speed of the nodes, the frequent changes in topology, the lack of an infrastructure, and various QoS requirements. Recently, several time-division multiple-access (TDMA)-based MAC protocols have been proposed for VANETs in an attempt to ensure that all the vehicles have enough time to send safety messages without collisions and to reduce the end-to-end delay and the packet loss ratio. In this paper, we identify the reasons for using the collision-free MAC paradigm in VANETs. We then present a novel topology-based classification, and we provide an overview of TDMA-based MAC protocols that have been proposed for VANETs. We focus on the characteristics of these protocols, as well as on their benefits and limitations. Finally, we give a qualitative comparison, and we discuss some open issues that need to be tackled in future studies in order to improve the performance of TDMA-based MAC protocols for vehicle-to-vehicle communications.

Mobility Enhanced RPL for Wireless Sensor Networks

In this paper, we investigate the problem of supporting mobility over RPL (IPv6 Routing Protocol for Low power and Lossy Networks) when applied to route traffic in Wireless Sensor Networks (WSNs). RPL is a routing protocol adapted for information routing with low power, low storage and processing sensor devices, in static topologies commonly found in WSNs, but which is not directly designed for mobile scenarios. Specifically, RPL actively decreases control traffic, at the price of lower reactivity to topology changes. In this paper, we propose to introduce some new mechanisms to the native RPL that reconcile decrease in control traffic and reactivity. They are based on an identification of mobile nodes, and furthermore they enhance RPL behavior in case of node mobility. Our approach will be, henceforth, called ME-RPL (Mobility Enhanced RPL).

A survey on fault tolerance in small and large scale wireless sensor networks

Fault tolerance is one of the most important wireless sensor networks requirements. It ensures that the network continues to function correctly even when some components fail. In fact, fault tolerance is a need in this type of networks due to sensor node characteristics, radio communications and hostile environments in which these networks are deployed. In this survey, we give an overview of WSN mechanisms that provide or improve the fault tolerance property of wireless sensor networks. However, the different solutions presented in this survey are not only intended to mechanisms dedicated to fault tolerance, but they also include all the mechanisms allowing the prevention of fault occurrence such as energy aware routing and data aggregation and compression. Besides the classification of fault tolerance mechanisms according to the tasks they target (data management, flow management), we also propose a new classification based on the network size, since the performance of the majority mechanisms depends on the size in terms of geographical area and number of nodes. Thus, a well performing protocol conceived for small networks may be inadequate for large networks and vice versa.

Sensors Deployment Enhancement by a Mobile Robot in Wireless Sensor Networks

An inherent concern for a wireless sensor network(WSN)is the coverage problem. Sensors are usually deployed in the wild to create a network of sensors intended to monitor or control a target area: Sensor networks are assumed unattended in various environments such as disaster areas, hazard fields, or battle fields. However, random node deployment often makes initial sensing holes inside the deployed area inevitable even in an extremely high density network. Furthermore, enhancing coverage is important for sensor networks to provide continuous sensing services. The most challenging aspects of the studies conducted on this topic have been supporting autonomous system with self maintenance capability where sensors and robots work together. This paper proposes to use a mobile robot to assist the initial sensors deployment and to improve sensing coverage and connectivity of monitored area. Given a set of points of interest on the surface, we study how to guide the robot to effectively eliminate coverage holes and collect redundant sensors. We propose a set of heuristics for this problem and we will verify the performance through simulation. The superior coverage and connectivity efficiency of the proposed approach is demonstrated by conducting a comparative analysis and simulation with a greedy approach.

A multi-objective genetic algorithm-based Adaptive Weighted Clustering Protocol in VANET

Vehicular Ad hoc NETworks (VANETs) are a major component recently used in the development of Intelligent Transportation Systems (ITSs). VANETs have a highly dynamic and portioned network topology due to the constant and rapid movement of vehicles. Currently, clustering algorithms are widely used as the control schemes to make VANET topology less dynamic for Medium Access Control (MAC), routing and security protocols. An efficient clustering algorithm must take into account all the necessary information related to node mobility. In this paper, we propose an Adaptive Weighted Clustering Protocol (AWCP), specially designed for vehicular networks, which takes the highway ID, direction of vehicles, position, speed and the number of neighboring vehicles into account in order to enhance the stability of the network topology. However, the multiple control parameters of our AWCP, make parameter tuning a nontrivial problem. In order to optimize the protocol, we define a multi-objective problem whose inputs are the AWCPs parameters and whose objectives are: providing stable cluster structures, maximizing data delivery rate, and reducing the clustering overhead. We address this multi-objective problem with the Non-dominated Sorted Genetic Algorithm version 2 (NSGA-II). We evaluate and compare its performance with other multi-objective optimization techniques: Multi-objective Particle Swarm Optimization (MOPSO) and Multi-objective Differential Evolution (MODE). The experiments reveal that NSGA-II improves the results of MOPSO and MODE in terms of spacing, spread, ratio of non-dominated solutions, and inverse generational distance, which are the performance metrics used for comparison.

Fault tolerant multi-channel allocation scheme for wireless sensor networks

One of the most common needs in wireless sensor networks (WSNs) is the continuity of network function even in the presence of some node failures. This is called fault tolerance. In general, fault tolerant solutions can be preventive or reactive: the preventive techniques aim to prevent the failure by minimizing and balancing the energy consumption in each node, while the reactive techniques intervene after a failure was detected. In this paper, we propose a new preventive/reactive fault tolerant scheme dedicated to manage the energy consumption and reconnect the WSN in case of articulation node failure. The specificity of this scheme is the use of multichannel communications, allowing simultaneous data transmission, which decreases the interferences between nodes and then decreases data retransmissions. The second task of this scheme targets the reorganization of the network after a network portioning episode. Such episode means that the WSN is partitioned in many segments after an articulation node failure. More precisely, we present here two heuristics for channel allocation/reallocation and WSN reorganization after a network failure. The performances of the proposed scheme is evaluated and proved through simulation.

Three dimensional mobile wireless sensor networks redeployment based on virtual forces

In many applications such as precision agriculture (fruit tree plantation, olive groves) or environmental monitoring, wireless sensors are, very often, randomly scattered in the 3D area of interest. Such applications require full three-dimensional coverage. Undoubtedly, an initial random deployment does not achieve neither full coverage of the 3D area of interest, nor network connectivity. Thus, a redeployment algorithm has to be introduced in order to ensure these two goals. Our contribution is the design of 3D-DVFA, a distributed deployment algorithm based on virtual forces in three dimensional wireless sensor networks where sensor nodes are assumed to be mobile and autonomous. We simulate its behavior with NS3. The extensive simulations results demonstrate the effectiveness of the 3D algorithm proposed that provides full 3D area coverage and network connectivity.

Optimized Handoff with Mobility Prediction Scheme Using HMM for femtocell networks

In this paper, we propose a new approach for optimizing the handoff decision in femtocell networks using Hidden Markov Model. To do so, we formulate the handoff problem as an optimization problem whose objective is to find the best Femtocell Access Point (FAP) assignment strategy that minimizes the number of unnecessary handoffs while maintaining a good quality of wireless communications. We have used Hidden Markov Model prediction tools to predict the target FAP by observing the geographic positions of the mobile. To evaluate the effectiveness of our proposal, we conducted extensive simulations. Results show that our proposed approach minimizes the number of handoffs by up to 7 times and enhances the dwell time in the FAP by up to 42% in comparison with others handoff decision making strategies commonly used in related cellular modeling works.

Ant Colony Optimization based hierarchical data dissemination in WSN

Wireless Sensor Networks (WSN) consist of nodes with limited power deployed in the area of interest. Nodes cooperate to collect, transmit and forward data to a base station. In WSN, clustering and scheduling techniques ensure collecting data in an energy efficient manner. In this paper, we present a Power Aware Scheduling and Clustering algorithm based on Ant Colony Optimization (PASC-ACO). In the proposed approach, energy is saved by scheduling some nodes in the active state to generate data and keep network connectivity, while putting others in the sleep state. Then, ACO algorithm is used for routing data packets in the network in order to minimize the energy wasted in transferring the redundant data sent by sensors in a densely deployed network. ACO scheme can play a significant role in the enhancement of network lifetime by selecting the optimum path to reach the base station. The PASC-ACO algorithm was studied by simulation for various network scenarios. The results confirm that our proposed scheme outperforms other existing techniques such as LEACH, M-GEAR and our pervious work PASC. PASC-ACO achieves better performances in terms of lifetime by balancing the energy load among all the nodes.

Routing-based multi-channel allocation with fault recovery for Wireless Sensor Networks

One of the common challenges in Wireless Sensor Networks (WSNs) is the degradation of the performance due to several factors. In one hand, the interference between concurrent transmissions can affect the efficiency of the network and considerably degrades its performance. The exploitation of the multiple channels available in sensor technology and the development of protocols for WSNs can be a solution to mitigate this interference. In this case, the way the channels are assigned has a significant impact on the performance of multi-channel communication. In the other hand, the faults occurred in WSNs are another factor that degrades the WSN performance. In this paper, we propose a distributed energy-efficient solution for multi-channel allocation based on the routing. This solution implements a fault recovery mechanism to reconnect the network after an articulation node failure. A main task of the proposed approach is to minimize the number of interferences when allocating the limited number of available channels. As a second task, the approach minimizes the energy consumption by defining a sleeping/activity strategy. The fault recovery mechanism aims to restore the network connectivity and reallocate channels without affecting the whole WSN. The performance of the proposed solution is evaluated by simulation.