TDMA scheduling strategies for vehicular ad hoc networks: from a distributed to a centralized approach

International audienceVehicular Ad hoc NETworks, known as VANETs, are deployed to reduce the risk of road accidents as well as to improve passenger comfort and safety by allowing vehicles to exchange different kinds of data. Medium Access Control protocols, namely those that are based on TDMA technique play a primary role in providing bounded transmission delay while minimizing data packet loss. However, due to mobility constraints and frequent changes in topology, slot scheduling is a more challenging task in VANETs than in other networks. Many MAC protocols based on TDMA for vehicular networks have been proposed to date. Among them, CTMAC is a centralized scheduling mechanism, while DTMAC, VeMAC and AD-HOCMAC are three distributed TDMA based MAC protocols. In this paper, we evaluate and analyze the performance these four protocols. The scenarios used in the simulation experiments take into account density variation factor that influences protocol performance. We use the MOVE and SUMO tools to generate realistic mobility scenarios. Performance metrics such as access collision, merging collision rate, packet loss and overhead are evaluated using NS-2.34

Performance evaluation of a TDMA-based multi-hop communication scheme for reliable delivery of warning messages in vehicular networks

International audienceVehicular Ad hoc NETworks, known as VANETs, are deployed to reduce the risk of road accidents as well as to improve passenger comfort by allowing vehicles to exchange different kinds of data, both between the vehicles themselves and potentially between the vehicles and the infrastructure. One of the major issues in VANETs is the need to improve safety information delivery over long distances. Hence, VANETs require efficient and stable routing protocols that can allow the safety information to be disseminated in a timely manner. We recently proposed TRPM, a TDMA-aware routing protocol for multi-hop communication based on a cross layer approach between the Medium Access Control (MAC) and the routing layers, in which the intermediate vehicles are selected according to their geographic position and the position of their time-slot in the TDMA scheduling frame. The main purpose of this paper is to analyze the efficiency of the TRPM protocol. To do so an analytical model is presented in which expressions are derived to calculate two performance metrics: the delivery delay and packet loss rate. In order to validate the mathematical model and the protocol, a comparison between simulation and analytical results is presented using the network simulator ns-2 and the realistic road traffic simulator MOVE/SUMO

A Centralized TDMA based Scheduling Algorithm for Real-Time Communications in Vehicular Ad Hoc Networks

International audience—As wireless technologies inside smart cars are increasing , Vehicular Ad hoc NETworks (VANETs) are becoming a promising way to enhance driver and passenger safety by enabling each vehicle to provide a warning in real time when a critical event is predicted. These applications require reliable broadcast schemes with minimum access delay and transmission collisions, which thus increase the need for an efficient Medium Access Control (MAC) protocol. However, the design of an efficient MAC protocol in VANET networks is a challenging task due to the high speed of the nodes, the frequent changes in network topology and various QoS requirements. Motivated by this observation, in this paper we present a Centralized TDMA based MAC protocol named CTMAC for real-time communications in VANETs. In our solution, Road Side Units (RSUs) are used as central coordinators to schedule and maintain time slot assignment for the vehicles in their coverage areas. In this work, we will show how interference between vehicles in the overlapping regions can be avoided without using any complex spectrum mechanisms such as CDMA or OFDMA. The simulation results reveal that CTMAC significantly outperforms the VeMAC and ADHOC MAC protocols. in terms of transmission collisions and the overhead required to create and maintain the TDMA schedules

A Novel Angle-based Clustering Algorithm for Vehicular Ad Hoc Networks

International audienceA vehicular ad hoc network (VANET) is a mobile network in which vehicles acting as moving nodes communicate with each other through an ad hoc wireless network. VANETs have become the core component of Intelligent Transportation Systems (ITS) which aim to improve the road safety and efficiency. Only if the communication scheme used in a VANET is stable can these aims be achieved. Frequent changes in network topology and breaks in communication raise challenging issues in the design of communication protocols for such networks. Currently, clustering algorithms are being used as the control schemes to reduce changes in VANET topologies. However, the design of a clustering algorithm becomes a difficult task in VANETs when there are many road segments and intersections. In this work, we propose an Angle based Clustering Algorithm (ACA), which exploits the angular position and the direction of the vehicles to select the most stable vehicles that can act as cluster heads for a long period of time. The simulation results reveal that ACA significantly outperforms other clustering protocols in terms of cluster stability

Optimized trajectories of multi-robot deploying wireless sensor nodes

International audienceA main reason to the growth of wireless sensor networks deployed worldwide is their easy and fast deployment. In this paper we consider deployments assisted by mobile robots where static sensor nodes are deployed by mobile robots in a given area. Each robot must make a tour to place its sensor nodes. All sensor nodes must be placed at their precomputed positions. The Multi-Robot Deploying wireless Sensor nodes problem, called the MRDS problem, consists in minimizing the longest tour duration (i.e. the total deployment duration), the number of robots used and the standard deviation between duration of robots tours. After a formal definition of the MRDS problem, we show how to use a multi-objective version of genetic algorithms, more precisely the NSGA-II algorithm, to solve this multi-objective optimization problem. The solutions belonging to the best Pareto front are given to the designer in charge of selecting the best trade-off taking into account various criteria. We then show how to extend this method to take obstacles into account, which is more representative of real situations

TDMA-aware Routing Protocol for Multi-hop Communications in Vehicular Ad Hoc Networks

International audienceVehicular Ad-Hoc Networks (VANETs) have become an emerging technology due to the variety of their applicationsin Intelligent Transportation Systems (ITS). By creating a vehicular network, each vehicle can exchange information toinform drivers in other vehicles about the current status of the traffic flow or a dangerous situation. Multi-hop communicationsis an effective method that can be used for information exchange over distances greater than the transmission range of thetransmitting vehicle. However, it is a great challenge to ensure a stable multi-hop communication link with a low delivery delaydue to the high mobility of the vehicles involved. The goal of this paper is to design a TDMA aware Routing Protocolfor Multi-hop wireless vehicular ad hoc networks (TRPM) in order to provide the ability to transmit/receive packets over longdistances. The proposed routing scheme is based on a medium access control protocol, in which the intermediate vehicles areselected based on the TDMA scheduling. The simulation results reveal that our routing protocol significantly outperforms otherprotocols in terms of average end-to-end delay, average number of relay vehicles and the average delivery ratio

Optimized Trajectory of a Robot Deploying Wireless Sensor Nodes

International audienceMobile robots can be used to deploy static wireless sensor nodes to achieve the coverage and connectivity require-ments of the applications considered. Many solutions have been provided in the literature to compute the set of locations where the sensor nodes should be placed. In this paper, we show how this set of locations can be used by a mobile robot to optimize its tour to deploy the sensor nodes to their right locations. In order to reduce both the energy consumed by the robot, its exposure time to a hostile environment, as well as the time at which the wireless network becomes operational, the optimal tour of the robot is this minimizing the delay. This delay must take into account not only the time needed by the robot to travel the tour distance but also the time spent in the rotations performed by the robot each time it changes its direction. This problem is called the Robot Deploying Sensor nodes problem, in short RDS. We first show how this problem differs from the well-known traveling salesman problem. We then propose an integer linear program formulation of the RDS problem. We propose various algorithms relevant to iterative improvement by exchanging tour edges, genetic approach and hybridization. The solutions provided by these algorithms are compared and their closeness to the optimal is evaluated in various configurations. I. CONTEXT AND MOTIVATIONS More and more applications are supported by wireless sen-sor networks. They cover areas as diverse as structural health monitoring, smart metering, industrial process monitoring, precision farming, smart cities, control of traffic lights, smart home, etc. The main reason for this tremendous development lies in the ease of deployment of wireless sensor networks. However, to meet the application requirements in terms of coverage and connectivity while minimizing the number of wireless sensors deployed, some rules must be followed. In short, full coverage of an area means that any event occurring in this area will be detected by at least one sensor node. Connectivity means that the information related to any event detected by a sensor node can be delivered to a special wireless node, called the sink, in charge of processing the data gathered from the sensor nodes. Many papers in the literature deal with these two big issues that are coverage and connectivity, leading to various problems mainly depending on the item to cover (area, points of interest, barrier) and on the type of coverage requested (full/partial, permanent/intermittent). The interested reader can refer to [1] for a survey of these problems and their solutions. Concerning the deployment achieved to meet these appli-cation requirements, they differ in their goal, their constraints and their implementation (e.g., centralized versus distributed). Most deployments aim at minimizing the number of sensor nodes deployed for cost reasons to achieve the application requirements. Another goal that is frequently encountered in crisis situation (e.g., after a disaster) where a wireless sensor network must be fastly deployed in order to on the one hand help rescuers to save victimes and on the other hand assist in damage assessment. In such cases, the goal is to minimize the time needed to deploy an operational wireless network. This goal is also targeted in hostile environment, where the exposure duration must be reduced. For cost reasons, static sensor nodes are more frequent than mobile ones. That is why in this paper, we focus on the computation of the minimum-delay tour of a mobile robot that has to deploy static wireless sensor nodes at positions that have been previously computed to meet the application requirements in terms of coverage and connectivity

Using Road IDs to Enhance Clustering in Vehicular Ad hoc Networks

International audience—Vehicular ad hoc networks (VANETs) where vehicles act as mobile nodes is an instance of Mobile Ad hoc NETworks (MANETs), which are essentially developed for intelligent transportation systems. A challenging problem when designing communication protocols in VANETs is coping with high vehicle mobility, which causes frequent changes in the network topology and leads to frequent breaks in communication. The clustering technique is being developed to reduce the impact of mobility between neighboring vehicles. In this paper, we propose an Adaptive Weighted Cluster Protocol for VANETs, which is a road map dependent and uses road IDs and movement direction in order to make the clusters structure as stable as possible. The experimental results reveal that AWCP outperforms four other most commonly used clustering protocols in terms of control packet overhead, the packet delivery ratio, and the average cluster lifetime, which are the most usual metrics used for comparing performance

A Fully Distributed TDMA based MAC Protocol for Vehicular Ad Hoc Networks

—The Vehicular Ad-Hoc NETwork (VANET) consists of a set of vehicles moving on roads which can communicate with each other through ad hoc wireless devices. VANET has attracted a lot of attention in the research community in recent years with the main focus on its safety applications. One of the challenges for vehicular network is the design of an efficient Medium Access Control (MAC) protocol due to the hidden node problem, the high speed of the nodes, the frequent changes in topology, the lack of an infrastructure, and various QoS requirements. Motivated by this observation, we design a fully distributed and location-based TDMA scheduling scheme for VANETs networks, named DTMAC. The main goal of this work is to propose a MAC protocol that can provide fairness in accessing the transmission medium, as well as reduce access collision and merging collision under various conditions of vehicular density without having to use expensive spectrum and complex mechanisms such as CDMA or OFDMA. An analytical model of the average access collision probability and throughput are derived which can be used to evaluate the performance of DTMAC protocol as well as to validate the simulation results under different traffic conditions

A Multi-Objectif Genetic Algorithm-Based Adaptive Weighted Clustering Protocol in VANET

International audience—Vehicular Ad hoc NETwork (VANET) is the main component that is used recently for the development of Intelligent Transportation Systems (ITSs). VANET has a highly dynamic and portioned network topology due to the constant and rapid movement of vehicles. Recently, the clustering algorithms are widely used as the control schemes to make VANET topology less dynamic for MAC, routing and security protocols. An efficient clustering algorithm must take into consideration 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 neighbors vehicles into account in order to enhance the network topology stability. However, the multiple control parameters of our AWCP, make parameter tuning a non-trivial problem. In order to optimize AWCP protocol, we define a multi-objective problem whose inputs are the AWCPs parameters and whose objectives are: providing stable cluster structure as possible, maximizing data delivery rate, and reducing the clustering overhead. We then face this multi-objective problem with the the Multi-Objective Genetic Algorithm (MOGA). 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 analysis reveal that NSGA-II improves the results of MOPSO and MODE in terms of the spacing, spread, and ratio of non-dominated solutions and generational distance metrics used for comparison