Modeling the power consumption of a Wifibot and studying the role of communication cost in operation time

Mobile robots are becoming part of our every day living at home, work or entertainment. Due to their limited power capabilities, the development of new energy consumption models can lead to energy conservation and energy efficient designs. In this paper, we carry out a number of experiments and we focus on the motors power consumption of a specific robot called Wifibot. Based on the experimentation results, we build models for different speed and acceleration levels. We compare the motors power consumption to other robot running modes. We, also, create a simple robot network scenario and we investigate whether forwarding data through a closer node could lead to longer operation times. We assess the effect energy capacity, traveling distance and data rate on the operation time

Design Considerations for Time-Slotted LoRa(WAN)

One of the most common issues in wireless networks is the problem of increasing the network capacity by alleviating or eliminating collisions with the minimum possible cost. The combination of time division protocols together with efficient slot allocation mechanisms is an effective way to achieve scalability and provide high reliability. In this paper, I describe the parameters that must be taken into account when designing LoRa(WAN)-based time-slotted protocols. I show that the LoRaWAN case differs from any other synchronous wireless solution mainly due to the characteristics of the LoRa physical layer and the regional radio duty cycle restrictions. I also propose a frame structure which has been adopted during the implementation of a time-slotted LoRa approach

Routage multi-flots économe en énergie dans les réseaux de capteurs et actionneurs

International audienceL'introduction d'actionneurs capables de se déplacer sur ordre dans les réseaux de capteurs a permis l'émergence d'un nouveau genre de protocoles de routage. Ceux-ci tirent parti de cette nouvelle possibilité de relocaliser les éléments du réseau pour adapter dynamiquement sa topologie au trafic. Ils vont ainsi faire se déplacer physiquement les nœuds au fur et à mesure du routage afin d'optimiser le coût des transmissions radio. Toutefois, dans les réseaux de capteurs, il y a souvent plusieurs nœuds géographiquement proches pour reporter un même événement à la station de base. Les messages routés empruntent alors différents chemins qui sont physiquement proches, et certains nœuds appartiennent à plusieurs d'entre eux. Ces derniers vont alors sans cesse devoir se relocaliser sur les différents chemins et donc mourir prématurément. En réponse à ce problème, nous proposons PAMAL, le premier protocole de routage qui optimise la topologie réseau et sait tirer avantage des intersections des chemins de routage de manière complètement locale. PAMAL va ainsi provoquer la fusion des chemins de routage qui se croisent, et ce de plus en plus près des sources au cours et du temps. Les résultats de simulations montrent que ce comportement associé à un mécanisme d'agrégation permet d'améliorer la durée de vie du réseau de 37 %

A network architecture for high volume data collection in agricultural applications

An important requirement for Internet of Things applications is the ability to provide fast and energy efficient data collection from wireless sensors. When sensor nodes are located far from the data collection point, currently available long range protocols present challenges associated with a very low data rate and often unreliable connections resulting in excessive energy consumption related to data transmission. To address this problem, we propose a simple and energy-efficient data collection architecture for smart agricultural purposes which require wireless sensing. The architecture involves data collection from nodes located in remote fields or on animals leveraging off the use of drones as a data collection mechanism. In particular, drones can fly over the desired areas (points) and collect high volumes of data that would be otherwise difficult to transfer directly to the sink in a reasonable amount of time and using reasonable amounts of energy. We describe the different components and stages that constitute the proposed architecture emphasizing the networking component. We propose the use of different communication technologies, such as LoRa and WiFi, depending on the data collection requirements. We present an in-lab development of this architecture as a proof-of-concept as well as preliminary results for the architecture. The results reveal that the proposed solution is potentially capable of achieving data collection at high volume, however, the performance does not consider the highest spreading factors of LoRa

Autonomous collision-free scheduling for LoRa-based industrial Internet of Things

LoRa-based transmissions suffer from extensive collisions even for low node numbers due to unregulated access to the medium. In order to tackle this problem, we propose a collision-free time-slotted scheduling approach where each node autonomously decides when to transmit a packet based on its unique identifier which is converted to a slot number using a modulo operation. We report through simulations and real experiments that this approach can provide very high reliability when the nodes are synchronized. Moreover, it does not require any additional communication overhead apart from a broadcast packet emitted by the gateway. Our comparison with the native LoRa, as well as to a slotted-LoRa version, shows significant performance gains in terms of packet delivery ratio, especially in the case of low node populations

Node Discovery and Replacement Using Mobile Robot

International audienceA critical problem of wireless sensor networks is the network lifetime, due to the device's limited battery lifetime. The nodes are randomly deployed in the field and the system has no previous knowledge of their position. To tackle this problem we use a mobile robot, that discovers the nodes around it and replaces the active nodes, whose energy is drained, by fully charged inactive nodes. In this paper we propose two localized algorithms, that can run on the robot and that decide, which nodes to replace. We simulate our algorithms and our findings show that all nodes that fail are replaced in a short period of time

Utiliser des drones pour recharger efficacement des capteurs

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Connectivity restoration and amelioration in wireless ad-hoc networks: A practical solution

International audienceConnectivity restoration after a node failure is one of the major issues in wireless ad-hoc networks. In particular, failures can lead to a network partitioning and a huge loss of information. Therefore, a fast mechanism is needed to heal the network between the partitions. In this paper, we consider the scenario where an intermediate node failures and a mobile system is moving autonomously to restore connectivity and provide the best service. We propose a fast connectivity restoration algorithm that is based only on local information. We implement our solution on a real robotic platform and we present some experimental results using a simple case scenario

Spread and shrink: Point of interest discovery and coverage with mobile wireless sensors

International audienceIn this paper we tackle the problem of deploying mobile wireless sensors while maintaining connectivity with a sink throughout the deployment process. These mobile sensors should discover some points of interest (PoI) in an autonomous way and continuously report information from the observed events to the sink. Unlike previous works, we design an algorithm that uses only local information and local interactions with surrounding sensors. Moreover, unlike other approaches, our algorithm implements both the discovery and the coverage phase. In the discovery phase, the mobile sensors spread to discover new events all over the field and in the second phase, they shrink to concentrate only on the discovered events, named points of interest. We prove that connectivity is preserved during both phases and the spreading phase is terminated in a reasonable amount of time. Real experiments are conducted for small-scale scenarios that are used as a “proof of concept”, while extensive simulations are performed for more complex scenarios to evaluate the algorithm performance. A comparison with an existing work which uses virtual forces has been made as well. The results show the capability of our algorithm to scale fast in both discovery, coverage and shrinking phases