Patrolling tasks in multi-robot systems are essential for applications such as surveillance and monitoring, where minimizing the time between visits to any given location is critical. This paper investigates fault-tolerant redistribution strategies for multi-agent patrolling systems in partitioned environments using Unmanned Autonomous Vehicles (UAVs). We propose Heuristic Meeting-based Patrolling (HMP), a novel distributed and fault-tolerant patrolling algorithm. Building on the Heuristic Conscientious Reactive (HCR) strategy and incorporating periodic synchronization meetings, HMP enables decentralized coordination and dynamic fault recovery through minimal communication. UAVs exchange information at shared meeting points, enabling detection of failures and redistribution of responsibilities. We evaluate HMP and its simplified variants in various simulated environments using the Multi-Agent Exploration and Patrolling Simulator (MAEPS). The results demonstrate that HMP offers strong performance under both normal and fault conditions, comparative to state-of-the-art patrolling strategies in terms of idleness metrics. However, we also identify limitations in meeting scheduling under certain fault conditions, which can cause cascading failures. Based on these findings, we discuss potential improvements for future work, including enhanced meeting scheduling and adaptive partitioning strategies.

Exploration of unknown environments is an important task for autonomous robot swarm systems. The faster they can fully explore an area, the faster a coordinated plan can be made, or points of interest found, to support further tasks. Previous algorithms have often focused either on frontier based, or nature-inspired heuristics. We present a human-inspired exploration algorithm, Minotaur, that enables simple and efficient exploration of buildings. We studied how Minotaur and a state-of-the-art algorithm, namely The Next Frontier (TNF), perform. Minotaur follows walls to discover doorways, after which it coordinates with robots in the same room to extend the exploration to rooms accessible through the discovered doorways. Most algorithms assume either perfect communication, or line-of-sight (LOS) communication, which hinders the realism of the simulation results. We then modified an existing simulator to take into account realistic communication technologies that have limited penetration of materials through walls. Comparative experiments between Minotaur, TNF, and a simple greedy algorithm show the superiority of Minotaur when multiple robots are exploring buildings-like maps. However, when considering cave-like maps, Minotaur appears to have bad performance, but the greedy algorithm outperforms TNF, particularly when the algorithms are limited in their communication capabilities.

The evolution of cloud computing, driven by ad-vances in mobile, edge technologies, and AI, has led to the development of the Cognitive Cloud Continuum (COCLCON). However, this paradigm introduces new challenges in managing and optimizing computing resources across a heterogeneous environment. This paper explores best practices for declaring resources within COCLCON, with a focus on efficient resource allocation and transparently declaring available resources by de-vices. In this study, we undertook a non-holistic literature review to identify current technologies used to specify requirements and to determine current gaps in best practices. The main outcome of our work is a proposed schema for Resource Provisioning Declaration, which will allow for increased knowledge related to the available devices and resources within the COCLCON.

Edge-to-cloud computing is an emerging paradigm for distributing computational tasks between edge devices and cloud resources. Different approaches for orchestration, offloading, and many more purposes have been introduced in research. However, it is still not clear what has been implemented in the industry. This work aims to merge this gap by mapping the existing knowledge on edge-to-cloud tools by providing an overview of the current state of research in this area and identifying research gaps and challenges. For this purpose, we conducted a Multivocal Literature Review (MLR) by analyzing 40 tools from 1073 primary studies (220 PS from the white literature and 853 PS from the grey literature). We categorized the tools based on their characteristics and targeted environments. Overall, this systematic mapping study provides a comprehensive overview of edge-to-cloud tools and highlights several opportunities for researchers and practitioners for future research in this area. Editor’s note: Open Science material was validated by the Journal of Systems and Software Open Science Board.

While System of Systems (SoS) architectures for large and complex software projects are gaining momentum, the commonly used modeling and tooling approaches are still general-purpose or oriented towards single systems. Developers could benefit from methods and tools that avoid system-centric details in favor of native SoS modeling support. This paper presents a diagram-centric modeling tool with native SoS modeling support. The tool is implemented as a plugin for the Eclipse Papyrus modeling tool. The tool was showcased as a demo at MODELS'22. The code of the plugin is freely available via Github.

We propose a framework to compare algorithms for multi agent exploration in an unknown continuous 2d environment. To analyze trade offs we compare algorithms with varying robot hardware requirements. We showcase our approach on Random Ballistic Walk (RBW), frontier-based exploration (The Next Frontier, TNF), Spiraling and Selective Backtracking (SSB), and Local Voronoi Decomposition (LVD). Algorithms that operate in a discrete grid-based space, such as LVD and SSB, are mapped to a continuous space for comparison with other algorithms. To our knowledge, no other extensive comparison of these exploration algorithms operating under the same testing environment has been conducted. The algorithms are tested in a custom 2D physics-driven simulation (Multi Agent Exploration Simulator, MAES), with two types of maps, namely the Cave map (C-Map) and the Building map (B-Map). The performance of each algorithm is evaluated in terms of coverage and exploration of the map. Results show that SSB performed the best in terms of coverage in all tested scenarios. TNF performed the best in terms of exploration, especially on bigger maps. RBW achieved good results in terms of both coverage and exploration in C-Maps, but not in B-Maps. LVD performed similarly to RBW in C-Maps, but better in the B-Maps.

The RoboCup simulator is a playing ground for Agents and Artificial Intelligence research. One of the main challenges provided by RoboCup is generating winning strategies for a set of agents playing soccer, given a partial and noisy view of the game state. Additionally, RoboCup is timing sensitive, and all decisions have to be sent to the server within each tick of 100ms. This paper presents a method for generating strategies by modelling players and scenarios as timed automata in the Uppaal environment. The newest extension of Uppaal, called Uppaal Stratego, allows for synthesising strategies optimising a reward function that is used to guide the decision process. In order to stay within the time frame of 100ms, two approaches were tested, namely forecasting the game state and generating a strategy asynchronously for a later point in time, and generating strategies beforehand and saving them in a lookup table. Four timed automata were developed, and were tested against publicly available methods. We found that strategies could be successfully generated and used within the time constraints of RoboCup using our proposed method. Especially when combined together, our strategies are able to outperform most published methods, but lose against the published world champions.

Defined as the ability for a system to exchange data with another system and consume data from another system, interoperability is a property that most distributed system developers tend to satisfy when designing new systems. In the IoT domain, the WoT W3C standard has been proposed to enable interoperability between devices and platforms.The Arrowhead framework has been implemented to ease IoT automation with the objective to enable IoT interoperability in this domain.This paper discusses how the W3C Web of Things standard can help the IoT automation framework Arrowhead in achieving the interoperability.

We address the problem of energy neutrality in energy harvesting IoT devices by means of a model checking approach, aiming at analyzing the dynamics of the battery charge in energy-neutral IoT devices. Our approach allows to compute the best task schedule and to study the maximum utility when operating on other parameters such as the initial battery charge, the number and structure of the available tasks, the size of the photo-voltaic panel that recharges the device, the day of the year, and the variable weather conditions that affect the energy production. The simulations confirm the state space explosion typical of model checking, but also hint that a small number of alternative tasks can achieve an overall utility very close to a large number of tasks. This conjecture has a strong practical relevance since it can pave the way to the wider adoption of energy neutrality concept in low-power IoT devices.

The SUMO traffic simulator is a mainstream tool that allows to model and analyse traffic and mobility scenarios. Fully realistic scenarios can be appealing for many use cases, but they require an initial large investment of resources for their creation. In fact, the usual workflow comprises the manual creation of a statistics file with detailed information about the city and its properties, up to describing how many people live and work on each road. This step is followed by the application of the tool ACTIVITYGEN to generate activity-based traffic. Current alternatives are based on simple randomly generated traffic, such as by means of the tool randomTrips. We present a compromise between the two approaches, consisting of mathematical techniques to generate schools, city gates, population density with residential and industrial areas, and a city centre. We also introduce an accompanying tool, randomActivityGen, which implements the approach to create ACTIVITYGEN statistics files automatically. Evaluation of generated scenarios shows that population and industry density, schools, and city-gates are placed realistically through testing on five representative Danish cities. The approach is also compared with the output of the tool randomTrips and the LuST scenario.

The emergence of new Information and Communication Technologies, such as the Internet of Things and big data and data analytics provides opportunities as well as challenges for the domain of interest, and this paper discusses their importance in condition monitoring and maintenance. In addition, the Open system architecture for condition-based maintenance (OSA-CBM), and the Predictive Health Monitoring methods are gone through. Thereafter, the paper uses bearing fault data from a simulation model with the aim to produce vibration signals where different parameters of the model can be controlled. In connection to the former mentioned a prototype was developed and tested for purposes of simulated rolling element bearing fault systems signals with appropriate fault diagnostic and analytics. The prototype was developed taking into consideration recommended standards (e.g., the OSA-CBM). In addition, the authors discuss the possibilities to incorporate the developed prototype into the Arrowhead framework, which would bring possibilities to: analyze various equipment geographically dispersed, especially in this case its rolling element bearing; support servitization of Predictive Health Monitoring methods and large-scale interoperability; and, to facilitate the appearance of novel actors in the area and thus competition.

Traditionally, the development workflow of Arrow-head applications is based on the usage of source code skeletons. This makes it difficult to update applications when the skeletons are changed, for example to fix security vulnerabilities or add new functionality. In fact, to update an application the developer has to either recreate the application on the new skeleton version or recreate the skeleton changes on the previous version of the application. Instead, we propose a client library, which allows the developers to create Arrowhead applications by referring to a library. Not only does this allow the Arrowhead Consortium to update the library without requiring changes to applications, it also eases the creation of new Arrowhead applications, reduces code duplication and increases readability. This paper describes the design and the structure of this client library, provides insights on how to employ the library in applications, and surveys a few sample applications that use the library.

Nowadays, collecting complex information regarding a machine status is the enabler for advanced maintenance activities, and one of the main players in this process is the sensor. This paper describes modern maintenance strategies that lead to Proactive Maintenance (PM), which is the most advanced one. The paper discusses the sensors that can be used to support maintenance, as pertaining to different categories, spanning from common off-the-shelf sensors, to specialized sensors monitoring very specific characteristics, and to virtual sensors. The paper proceeds then to detail three different real world examples of project pilots that make use of the described sensors, and draws a comparison between them. In particular, each scenario has got unique characteristics and prefers different families of sensors, but on the other hand provides similar characteristics on other aspects. In fact, the paper concludes with a discussion regarding how each scenario can benefit from PM and from advanced sensing.

Cyber-Physical Systems (CPS) are creating new market opportunities and business models for all kind of European Industries. CPS-based platforms are increasing in their size and target application areas in a steady manner. However, even if progress is made every day supported by continuous technological advancements, CPS application and deployment is still challenging. Many solutions have been made available or is currently under development in several research projects/ initiatives. Typically, these solutions show no interoperability between each other and are tailored to a specific application context. Thus, there is an urgent need for a clear definition of what a CPS-populated system actually is. This will provide a common ground for designing and building interoperable CPS-populated systems. Interoperability represents one of the most challenging problems for such systems essentially due to their intrinsic characteristics: heterogeneity, distribution and networked. These must be addressed to allow the cooperation and collaboration between all the actors of the system. In this landscape, the MANTIS project is aimed to provide a reference model for interoperable and interconnected CPS-populated systems for maintenance-related ecosystems, which is the focus of this paper.

This paper presents an architecture that supports Quality of Service (QoS) in an Arrowhead-compliant System of Systems (SoS). The Arrowhead Framework supports local cloud functionalities for automation applications, provided by means of a Service Oriented Architecture (SOA), by offering a number of services that ease application development. On such applications the QoS guarantees are required for service fruition, and are themselves requested as services from the framework. To fulfil this objective we start by describing the Arrowhead architecture and the components needed to dynamically in run-time negotiate a system configuration that guarantees the QoS requirements between application services.

This paper presents how the ICT infrastructure developed in the European ENCOURAGE project, centered around a message oriented middleware, enabled energy savings in buildings and households. The components of the middleware, as well as the supervisory control strategy, are overviewed, to support the presentation of the results and how they could be achieved. The main results are presented on three of the pilots of the project, a first one consisting of a single household, a second one of a residential neighborhood, and a third one in a university campus.

The Arrowhead Framework is a European effort that aims to apply Service Oriented Architecture to the embedded systems' world. The Event Handler system is a component that supports the handling of events, and in that sense it enriches service-oriented applications with the capabilities of interacting via the publish/subscribe paradigm. In fact, the Event Handler system is in charge of the notification of events that occur in a given Arrowhead compliant installation, manages producers and consumers of events, allows filtering of messages, and manages historical data regarding events. This latter capability is performed either on local files, on a database, or through another component of the Arrowhead Framework - the Historian system. The net result of the integration of the Event Handler in an Arrowhead Framework simplifies and empowers the communication of its components, as it is demonstrated in the paper with two examples: the management of application faults, and the support to quality of service of orchestrated services.

The evolution of the electrical grid into a smart grid, allowing user production, storage, and exchange of energy; remote control of appliances; and, in general, optimizations over how the energy is managed and consumed, is an evolution into a complex information and communication technology (ICT) system. With the goal of promoting an integrated and interoperable smart grid, a number of organizations all over the world started uncoordinated standardization activities, which caused the emergence of a large number of incompatible architectures and standards. There are now new standardization activities that have the goal of organizing existing standards and produce best practices to choose the right approach(es) to be employed in specific smart grid designs. This paper follows the lead of the National Institute of Standards and Technology (NIST) and the European Telecommunications Standards Institute/European Committee for Standardization/European Committee for Electrotechnical Standardization (ETSI/CEN/CENELEC) approaches in trying to provide taxonomy of existing solutions; our contribution reviews and relates current ICT state of the art with the objective of forecasting future trends based on the orientation of current efforts and on relationships between them. The resulting taxonomy provides guidelines for further studies of the architectures, and highlights how the standards in the last mile of the smart grid are converging to common solutions to improve ICT infrastructure interoperability.

With the reduction in size and cost of sensor nodes, dense sensor networks are becoming more popular in a wide-range of applications. Many such applications with dense deployments are geared towards finding various patterns or features such as peaks, boundaries and shapes in the spread of sensed physical quantities over an area. However, collecting all the data from individual sensor nodes can be impractical both in terms of timing requirements and the overall resource consumption. Hence, it is imperative to devise distributed information processing techniques that can help in identifying such features with a high accuracy and within certain time constraints. In this paper, we exploit the prioritized channel-access mechanism of dominance-based Medium Access Control (MAC) protocols to efficiently obtain exterma of the sensed quantities. We show how by the use of simple transforms that sensor nodes employ on local data it is also possible to efficiently extract certain features such as local extrema and boundaries of events. Using these transformations, we show through extensive evaluations that our proposed technique is fast and efficient at retrieving only sensor data point with the most constructive information, independent of the number of sensor nodes in the network.

Industrial processes use energy to transform raw materials and intermediate goods into final products. Many efforts have been done on the minimization of energy costs in industrial plants. Apart from working on “how” an industrial process is implemented, it is possible to reduce the energy costs by focusing on “when” it is performed. Although, some manufacturing plants (e.g. refining or petrochemical plants) can be inflexible with respect to time due to interdependencies in processes that must be respected for performance and safety reasons, there are other industrial segments, such as alumina plants or discrete manufacturing, with more degrees of flexibility. These manufacturing plants can consider a more flexible scheduling of the most energy-intensive processes in response to dynamic prices and overall condition of the electricity market. In this scenario, requests for energy can be encoded by means of a formal structure called flex-offers, then aggregated (joining several flex-offers into a bigger one) and sent to the market, scheduled, disaggregated and transformed into consumption plans, and eventually, into production schedules for given industrial plant. In this paper, we describe the flex-offer concept and how it can be applied to industrial and home automation scenarios. The architecture proposed in this paper aims to be adaptable to multiples scenarios (industrial, home and building automation, etc.), thus providing the foundations for different concept implementations using multiple technologies or supporting various kinds of devices.

In this paper we analyze some of the existing solutions for Message-Oriented Middleware (MOM), which can be used on industrial environments, and that are, at the same time, capable of handling large quantities of data and of providing adequate Quality-of-Service (QoS) levels for its supported applications. We also make a proposal for the generic structure of a middleware layer supported on a MOM.

Energy is becoming a vital resource in wireless networks and with the introduction of high data rate wireless technologies the future Wireless Personal Area Networks (WPANs) will be able to support demanding applications e.g. interactive games, video sharing etc. and as a result the energy saving mechanisms will become more demanding and challenging. The mobile devices with hybrid character, containing ad hoc and infrastructure access, will need mechanisms that keep them connected in an energy efficient way. For the node to be connected to either a cluster or a solitary node knowledge of the neighbor devices are required to choose a suitable node for cooperative communication; this discovery of information is under the scope of this paper. We present a context based beaconing mechanism both for node discovery and cooperative cluster formation. We have exploited the available beacon Information Elements (IEs) of UWB to embed our own information elements of interest e.g. Energy level, status of node, willingness, etc. to facilitate node discovery and cooperation. A Context Extraction Function (CxEF) has been created to insert and extract information in the beacon. We have also presented a detailed representation of bit mapping for energy and cooperation in beacons. The simulation results show that our mechanism saves a considerable amount of energy compared to other techniques which perform blind node discovery without using context information.

It is necessary to re-think the current access selection polices to the simultaneously available wireless networks, whose number is growing, and the appropriate management mechanisms, to enhance the experience for the final user, for example in terms of QoS and energy efficiency. The IEEE 802.21 standard introduces link layer intelligence as well as related network information to upper layers in order to optimize handovers between networks of different technologies (WiMAX, Wi-Fi, 3GPP, etc.). As the integration of multiple wireless interfaces in mobile terminals becomes ordinary it is important to efficiently manage those interfaces. Not only to conveniently provide the requested services to the user, but also to do that in an energy efficient way in order to allow higher mobility by extending the battery life of its mobile terminal. In this paper the IEEE 802.21 standard is used while considering handovers between WiMAX and Wi-Fi, through an implementation in ns-2 introducing a simple, but effective, location-assisted energy saving technique.

The growing presence of concurrent heterogeneous wireless access networks, together with the increasing service demands from the end-users, require re-thinking of current access selection polices and appropriate management mechanisms, namely concerning quality of service, energy efficiency, etc. The recent IEEE 802.21 standard introduces link layer intelligence as well as related network information to upper layers in order to optimise handovers between networks of different technologies, such as WiMAX, Wi-Fi and 3GPP. With the massification of mobile terminals with multiple wireless interfaces it is important to efficiently manage those interfaces not only to appropriately provide the requested services to the user, but also to do that in an energy efficient way in order to allow higher mobility to the user by extending the battery life of its terminal. The study the IEEE 802.21 standard is briefly introduced, presented in the signalling in a handover between WiMAX and Wi-Fi, and exploited through an implementation in ns-2 introducing a simple, but effective, energy-saving approach.

Multi-standard mobile devices are allowing users to experience higher data rates and ubiquitous connectivity. These advances are achieved on the expense of higher energy consumption due to the multiple active wireless interfaces. In this paper, we use one advantage of the multiple interfaces, namely short range communications. Mobile terminals (MTs) form short range cooperative network to take advantage of the good channel quality of short range links to save energy of MTs. In this cooperative network, the energy of all MTs is treated as a pool of resources, which is available for all MTs in the network. Toward this end, we propose a combinatorial optimization game to identify the problem. We derive the core solution for the relay selection game in cooperative networks. A mathematical framework to compute the achieved energy saving is derived. Simulation results using the solution of the game show that energy saving can be achieved using short range cooperation in wireless networks. The results also show the effectiveness of the proposed node selection game.

In-network storage of data in Wireless Sensor Networks (WSNs) is considered a promising alternative to external storage since it contributes to reduce the communication overhead inside the network. Recent approaches to data storage rely on Geographic Hash Tables (GHT) for efficient data storage and retrieval. These approaches, however, assume that sensors are uniformly distributed in the sensor field, which is seldom true in real applications. Also they do not allow tuning the redundancy level in the storage according to the importance of the data to be stored. To deal with these issues, we propose an approach based on two mechanisms. The first is aimed at estimating the real network distribution. The second exploits data dispersal method based on the estimated network distribution. Experiments through simulation show that our approach approximates quite closely the real distribution of sensors and that our dispersal protocol sensibly reduces data losses due to unbalanced data load.

Data Centric Storage is a recent paradigm that results more efficient than other storage techniques (such as local or external storage) in Wireless Sensor Networks (WSN). In this work we consider the use of this storage paradigm in WSN based on the ZigBee standard. In particular we propose a novel protocol (Z-DaSt) that exploits the routing and addressing features of ZigBee (that are based on routing trees) to distribute data to the sensors. The protocol also features Quality of Service in the storage of data by enabling the user to specify the amount of redundancy to be used in the storage of each datum. This work evaluates Z-DaSt by analysis and simulation, and compares its performance to DCS-GHT. The simulation results show that Z-DaSt is a viable alternative to DCS-GHT for practical cases, in particular for low to moderate network densities.

The problem of defining a support for multidimensional range queries on P2P overlays is currently an active field of research. Several approaches based on the extension of the basic functionalities offered by Distributed Hash Tables have been recently proposed. The main drawback of these approaches is that the locality required for the resolution of a range query cannot be guaranteed by uniform hashing. On the other way, locality preserving hashing functions do not guarantee a good level of load balancing. This paper presents Hivory, a P2P overlay based on a Voronoi tessellation defined by the objects published by peers. Each object is mapped to a site of the Voronoi tessellation and the corresponding Delaunay Triangulation defines the P2P overlay. A hierarchy of Voronoi diagrams is defined by exploiting clusters of objects paired with the same site of the Voronoi diagram. A new Voronoi diagram including the peers of the cluster is created so that the query resolution may be refined by a top down visit of the Voronoi hierarchy. The paper presents the proposed solution, analysis its complexity, and provides a set of experimental results.

In-network storage of data in wireless sensor networks contributes to reduce the communications inside the network and to favor data aggregation. In this paper, we consider the use of erasure codes in combination to in-network storage. We provide an abstract model of in-network storage to show how erasure codes can be used, and we discuss how this can be achieved in two cases of study. We also define a model aimed at evaluating the probability of correct data encoding and decoding, and we exploit this model and simulations to show how the parameters of the erasure code and the network should be configured in order to achieve correct data coding and decoding with high probability even in presence of sensors faults.

Information assurance in critical infrastructure is an issue that has been addressed generally focusing on real-time or quasi real-time monitoring of the critical infrastructure; so that action could be undertaken when anomalies arise, to avoid more severe consequences to the infrastructure. In this paper, we relax the hypothesis of intervening when anomalies are detected: we focus on sensed data survivability. Specifically, we study this problem in a specific critical infrastructure: pipelines. The problem we introduce is how to place sensors in such a way that the sensed data related to the monitoring of the pipeline will survive even in presence of a partial destruction of the infrastructure. The contributions of this paper are twofold. First, we introduce the problem of sensed data survivability in critical infrastructure. In this framework, the goal is to have the sensed data to survive to the infrastructure failure, so that the phenomena that lead to the failure could be better understood and possibly tackled in similar deployment. Second, we provide a model that allows to produce an optimal network topology with respect to the level of information assurance desired, while satisfying deployment constraints, such as available bandwidth and available energy of the sensors. We believe that the work addressed in this paper could foster further research in the field of information assurance in critical infrastructure.

This paper presents VoRaQue, a software layer supporting range queries on Voronoi P2P overlays. VoRaQue maps data in a 2-dimensional space. The P2P overlay is defined by links connecting nodes that are close in the 2-dimensional space and by a set of long-range links which guarantee a poly-logarithmic routing. When a query is submitted, VoRaQue finds out a node belonging to the region defined by the query. A multicast spanning tree covering that region is then built by applying compass routing, a distributed protocol to embed a spanning tree into a Delaunay Triangulation. The paper presents the basic VoRaQue protocol, then introduces a set of optimizations and finally presents some experimental results.

SMEPP Light is a middleware for Wireless Sensor Networks (WSNs) based on mote-class sensors. It is derived from the specification developed under the framework of the SMEPP project, to deal with the hardware and software constraints ofWSNs. SMEPP Light features group management, grouplevel security

Storage of sensed data in wireless sensor networks is essential when the sink node is unavailable due to failure and/or disconnections, but it can also provide efficient access to sensed data to multiple sink nodes. Recent approaches to data storage rely on Geographic Hash Tables for efficient data storage and retrieval. These approaches however do not support different QoS levels for different classes of data as the programmer has no control on the level of redundancy of data (and thus on data dependability). Moreover, they result in a great unbalance in the storage usage in each sensor, even when sensors are uniformly distributed. This may cause serious data losses, waste energy and shorten the overall lifetime of the sensornet. In this paper, we propose a novel protocol, Q-NiGHT, which (1) provides a direct control on the level of QoS in the data dependability, and (2) uses a strategy similar to the rejection method to build a hash function which scatters data approximately with the same distribution as sensors. The benefits of Q-NiGHT are assessed through a detailed simulation experiment, also discussed in the paper. Results show its good performance on different sensors distributions on terms of both protocol costs and load balance between sensors. 1