TAR channel access mechanism for VANET safety-critical situations

International audienceVehicular Ad-hoc Network (VANET) is among the most relevant forms of mobile ad-hoc networks. VANET helps improving traffic safety and efficiency. By exchanging information between each others, vehicles can warn drivers or even prepare for dangerous situation. These warnings can be about critical situations like vehicles merging in a highway. Detecting and warning about such situations require a reliable communication between vehicles increasing thus the need for an efficient medium access control (MAC) protocol. In this paper, we propose to apply Transmit And Reserve (TAR), an ad-hoc medium access protocol, to vehicular communications. We integrated TAR into NS-3 simulator and evaluated its performance compared to IEEE 802.11 DCF in a vehicular network context. The evaluation results show that TAR is an efficient medium access protocol for VANET critical situations as it increases the throughput reduces the medium access delays and provides close to optimal short term fairness

Increasing Reliability of a TSCH Network for the Industry 4.0

International audienceTime Slotted Channel Hopping (TSCH) networks are emerging as a promising technology for the Internet of Things and the Industry 4.0 where ease of deployment, reliability, short latency, flexibility and adaptivity are required. Our goal is to improve reliability of data gathering in such wireless sensor networks. We present three redundancy patterns to build a reliable path from a source to a destination. The first one is the well-known two node-Disjoint paths. The second one is based on a Triangular pattern, and the third one on a Braided pattern. A comparative evaluation is carried out to analyze the reliability achieved, the number of failures tolerated, the number of message copies generated and the energy consumed by each node to ensure that at least one copy of the message is delivered to the destination. These results are validated by simulations

OA-DVFA: A Distributed Virtual Forces-based Algorithm to Monitor an Area with Unknown Obstacles

International audienceDeployment of sensor nodes to fully cover an area has caught the interest of many researchers. However, some simplifying assumptions are adopted such as knowledge of obstacles, centralized algorithm... To cope with these drawbacks, we propose OA-DVFA (Obstacles Avoidance Distributed Virtual Forces Algorithm) a self-deployment algorithm to ensure full area coverage and network connectivity. This fully distributed algorithm is based on virtual forces to move sensor nodes. In this paper, we show how to avoid the problem of node oscillations and to detect the end of the deployment in a distributed way. We evaluate the impact of the number, shape and position of obstacles on the coverage rate, the distance traveled by all nodes and the number of active nodes. Simulation results show the very good behavior of OA-DVFA

Beacon Advertising in an IEEE 802.15.4e TSCH Network for Space Launch Vehicles

International audienceIn space launch vehicles, a NASA study shows that the mass per channel of 0.45 kg for a wiring approach can be reduced to 0.09 kg for a wireless approach. 8 A question arises: which wireless technology is able to meet the requirements of space launch vehicles in terms of latency, throughput and robustness. The IEEE 802.15.4e amendment has been designed to meet such requirements. More specifically, the Time Slotted Channel Hopping (TSCH) mode has been designed for industrial automation, process control and equipment monitoring. It supports multichannel and multihop communications and uses a slotted medium access on several channels. In this paper, we focus on the time needed by a joining node to detect beacons advertising the TSCH network. An Enhanced beacon is a TSCH frame that contains information on synchronization, channel hopping and timeslot used in the advertised network. However, the advertising policy is left unspecified by the IEEE 802.15.4e standard and is under the responsibility of a layer upper than the MAC one. Since beacons are broadcast, they are lost in case of collisions: the vital information they carry is lost. The main problem is how to avoid collisions between two devices that are not neighbors. In this paper, we propose a Deterministic Beacon Advertising Algorithm, called DBA. The goal of DBA is to ensure that beacons are transmitted on all frequencies used by the TSCH network, regularly and without collision. With DBA, the exact value for the maximum time for a joining node to detect a beacon can be computed easily. We use the NS3 Simulator to evaluate this time as well as the the number of message losses, considering different network topologies (star or multihop). We compare the performance of DBA with this of two algorithms existing in the state of the art

Fault-Tolerant and Constrained Relay Node Placement in Wireless Sensor Networks

International audienceDeployment of sensor nodes to fully cover an area has caught the interest of many researchers. However, some simplifying assumptions are adopted such as knowledge of obstacles, centralized algorithm... To cope with these drawbacks, we propose OA-DVFA (Obstacles Avoidance Distributed Virtual Forces Algorithm) a self-deployment algorithm to ensure full area coverage and network connectivity. This fully distributed algorithm is based on virtual forces to move sensor nodes. In this paper, we show how to avoid the problem of node oscillations and to detect the end of the deployment in a distributed way. We evaluate the impact of the number, shape and position of obstacles on the coverage rate, the distance traveled by all nodes and the number of active nodes. Simulation results show the very good behavior of OA-DVFA

Collision Avoidance on Shared Slots in a Wireless Slotted Network: Models and Simulations

International audienceIn this paper we propose an analysis of a slotted based protocol designed for devices of the Internet of Thing (IoT). In contrast to other TDMA-based protocols this scheme uses a random technique to access shared slots which presents similarities with CSMA protocols. In practice the transmissions are scheduled in a given back-off window of slots whose duration allows the transmission of a packet and its acknowledgment. Therefore this protocol can be analyzed according to the methodology introduced by Bianchi for the IEEE 802.11 protocol even if the protocol studied differs in many aspects. The model we use is also particular because we succeed in obtaining a Markov model even if the scheme used to send a packet (in a node) may depend on the transmission of the previous packet. We distinguish two protocols; in the first one, at the initial stage or after a successful transmission, the packets are transmitted without any back-off, whereas in the second protocol each transmission is always preceded by the count down of a random back-off. Extensive simulations validate the models of both protocols and a comparative performance evaluation is carried out

Collision avoidance in shared slots in wireless devices of the Internet of Things: models and simulations

International audienceIn this paper we propose an analysis of a slot-based protocol designed for devices of the Internet of Things (IoT). In contrast to other TDMA-based protocols, this scheme uses a random technique to access shared slots, similarly to CSMA protocols. In practice, the transmissions are scheduled in a given back-off window of slots whose duration allows the transmission of a packet and its acknowledgment. Therefore this protocol can be analyzed according to the methodology introduced by Bianchi for the IEEE 802.11 protocol even if the protocol studied differs in many aspects. The model we use is also particular because we succeed in obtaining a Markov model even though the scheme used to send a packet (in a node) may depend on the transmission of the previous packet. We distinguish two protocols; in the first one, at the initial stage or after a successful transmission, the packets are transmitted without any back-off, whereas in the second protocol each transmission is always preceded by the count down of a random back-off. Extensive simulations validate the both protocols models. In addition, the performances of these protocols are compared with those of slotted Aloha and a protocol using a constant backoff window. Index Terms Wireless networks, Model, Collision Avoidance, Shared slots, Medium Access, Markov Model, Slotted Aloha

Scheduling transmissions with latency constraints in an IEEE 802.15.4e TSCH network

International audienceTime Slotted Channel Hopping (TSCH), specified in the IEEE 802.15.4e amendment, has been designed for industrial automation, process control and equipment monitoring. It uses a slotted medium access on several channels in parallel and supports multihop communications. In this paper, we study how applications with data delivery constraints can be supported by a TSCH network. We first propose a framework based on a multislotframe that allows the coexistence of Data Slotframes and Control Slotframes. We then determine a lower bound on the minimum number of slots required to perform data gathering, taking into account the number of channels, the number of interfaces of the sink, the number of packets generated by each sensor node as well as the number of children of the sink. These feasibility conditions are established for two cases: with spatial reuse and without. We propose a debt-based scheduler that for simple topologies, provides a schedule minimizing the slotframe size. Finally, we consider a network configuration representative of an industrial application and evaluate the performance of the TSCH network in terms of data delivery delay and queue size for each sensor node, using the NS-3 simulator. Simulation results confirm the theory

Building an IEEE 802.15.4e TSCH network

International audience—Most wireless sensor networks that are currently deployed use a technology based on the IEEE 802.15.4 standard. However, this standard does not meet all requirements of industrial applications in terms of latency, throughput and robustness. That is why the IEEE 802.15.4e amendment has been designed, including the Time Slotted Channel Hopping (TSCH) mode. In this paper, we focus on how to build a TSCH network and evaluate the time needed to form the network, using the NS3 simulator. A new beacon advertising algorithm is proposed for TSCH networks. A comparative performance evaluation with solutions already published is done

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