Search

Low-power wide-area networks are extending beyond the conventional terrestrial domain. Coastal zones, rivers, wetlands, among others, are nowadays common deployment settings for Internet-of-Things nodes where communication technologies such as LoRa are becoming popular. In this article, we investigate large-scale fading dynamics of LoRa line-of-sight links deployed over an estuary with characteristic intertidal zones, considering both shore-to-shore and shore-to-vessel communications. We propose a novel methodology for path loss prediction which captures i) spatial, ii) temporal and iii) physical features of the RF signal interaction with the environmental dynamics, integrating those features into the two-ray propagation model. To this purpose, we resort to precise hydrodynamic modeling of the estuary, including the specific terrain profile (bathymetry) at the reflection point. These aspects are key to accounting for a reflecting surface of varying altitude and permittivity as a function of the tide. Experimental measurements using LoRa devices operating in the 868~MHz band show major trends on the received signal power in agreement with the methodology's predictions.

Human populations and natural ecosystems are bound to be exposed to ionizing radiation from the deposition of artificial radionuclides resulting from nuclear accidents, nuclear devices or radiological dispersive devices (“dirty bombs”). On the other hand, Naturally Occurring Radioactive Material industries such as phosphate production or uranium mining, contribute to the on site storage of residuals with enhanced concentrations of natural radionuclides. Therefore, in the context of the European agreements concerning nuclear energy, namely the European Atomic Energy Community Treaty, monitoring is an essential feature of the environmental radiological surveillance. In this work, we obtain 3D maps from outdoor scenarios, and complete such maps with measured radiation levels and with its radionuclide signature. In such scenarios, we face challenges such as unknown and rough terrain, limited number of sampled locations and the need for different sensors and therefore different tasks. We propose a radiological solution for scouting, monitoring and inspecting an area of interest, using a fleet of drones and a controlling ground station. First, we scout an area with a Light Detection and Ranging sensor onboard a drone to accurately 3D-map the area. Then, we monitor that area with a Geiger–Müller Counter at a low-vertical distance from the ground to produce a radiological (heat)map that is overlaid on the 3D map of the scenario. Next, we identify the hotspots of radiation, and inspect them in detail using a drone by landing on them, to reveal its radionuclide signature using a Cadmium–Zinc–Telluride detector. We present the algorithms used to implement such tasks both at the ground station and on the drones. The three mission phases were validated using actual experiments in three different outdoor scenarios. We conclude that drones can not only perform the mission efficiently, but in general they are faster and as reliable as personnel on the ground.

Bicycles are becoming increasingly more equipped with embedded connected devices, by design or through after market products, to support applications such as fitness monitoring and tracking. Bluetooth (BT) and BT Low Energy (BLE) technology is often embedded in such devices to support connectivity to a personal mobile device or a dock, when parked. BT/BLE transmit periodic beacons for node discovery that can be explored for $\mathrm{V}2\mathrm{X}$ applications, such as safety and fleet management. We present a distributed system that explores periodic BT beacons sent by a module embedded in a bicycle to opportunistically locate nodes of interest (NOI). We address the particular application of stolen bicycle detection. In a scenario in which a bicycle is stolen and has its communication system tampered with but BLE remains functional, a service provider (e.g., fleet operator, authorities) is informed of this new NOI and shares an updated NOI list with the NOI detection-enabled bicycles. In turn, the bicycles flag contacts with stolen bicycles to the provider backoffice, at the earliest convenience (depending on available communications interfaces: immediately if cellular is available, or opportunistically when passing by a dock). We describe the operation and software architecture of the system, and an actual implementation in COTS equipment. Experimental measurements of the communication range and a demonstration of the system for oroof-of-concept are also reported.

Modern observation systems can be composed by heterogeneous entities (e.g., buoys, USVs, UAVs, on-shore sensors, etc.) that rely on dependable communications for coordination and data collection, often provided by over-water radio-frequency (RF) links. In tide-affected water bodies, RF links at a fixed height from the shore can experience the so-called tidal fading, a cyclic time-varying tide-induced interference. To mitigate it, the classical space-diversity reception technique (i.e., the use of two or more receiver antennas positioned at different heights) is often applied, commonly combined with the consideration of having one of the antennas at the largest possible height. Yet, this approach does not always ensure the best performance. In this work, we focus on static over-water links of short-to-medium-range distances that use antennas installed at a few meters above surface. We leverage the geometrical basis of the two-ray propagation model to investigate the optimal single-antenna height design that minimizes overall average path losses over a given tidal range. We then extend this analysis to incorporate a second receiver antenna and identify its optimal antenna height. Analytical results show that our method considerably outperforms the more classical approach, thus enabling superior (average) link capacities.

In the design of shore-to-shore and shore-to-vessel wireless links, the impact of the ray reflected on the surface is often neglected. It adds that, in some coastal areas, the geometry of the reflection changes over time due to tides. When choosing an antenna height for an inshore node, often the largest possible height is used, but this approach can lead to signal degradation. The two-ray model is the most fundamental path loss model to account for the contribution of the reflected ray. We carried out experimental measurements at the shores of a freshwater body to verify that the two-ray model can predict the major trends of the path loss experienced by a 2.4 GHz over-water wireless link. We focus on short-to-medium distance links, with antennas installed a few meters above surface. We observed considerable consistency between measurements and model estimates, leading us to conclude that the two-ray model may bring benefits when applied to the network design of over-water links affected by tidal variations, which is our end-goal.

Radiological monitoring is fundamental for compliance with radiological protection policies in the aftermath of radiological events, such as nuclear accidents, terrorism, and out-of-commission uranium mines. An effective strategy for radiation monitoring is to use radiation detectors coupled with Unmanned Aerial Vehicles (UAVs), enabling for quicker surveillance of large areas without involving the need of human presence in the target area. The main aim of this study was to formulate the parameters for a UAV flight strategy in preparation for future field measurements using Geiger&ndash, Muller Counters (GMC) and Cadmium Zinc Telluride (CZT) spectrometers. As a proof of concept, the prepared flight strategy will be used to survey out-of-commission uranium mines in northern Portugal. Procedures to assure the calibration of the CZT and verification of the GMCs were conducted, as well as a sensitivity analysis of the sensors considering different acquisition times, distance to source, and detector response time. This article reports specific parameters, such as UAV distance to ground, time of exposition, speed, and the methodology to perform the identification and calculate the activity of possible radioactive sources. An effective flight strategy is also presented, aiming to use radiation detectors coupled with UAVs to undertake extensive monitoring of areas with enhanced levels of environmental radiation, which is of prime importance due to the lasting hazardous effects of enhanced environmental radiation in the nearby ecosystem and population.

DSIE-Doctoral Symposium in Informatics Engineering, now in its 15th Edition, is an opportunity for the PhD students of ProDEI (Doctoral Program in Informatics Engineering of FEUP) to show up and prove they are ready for starting their respective thesis work. The complete DSIE’20 meeting lasts one day and a half and includes one invited talk by an academic researcher, Professor Alipio Jorge, from the Faculty of Sciences, University of Porto. Professors responsible for ProDEI program’s current edition are proud to participate in DSIE’20 meeting and would like to acknowledge all the students who have been deeply involved in the success of this event. Hopefully, this involvement contributes to their better understanding of the themes addressed during the MSR course, the best scientific research methods and the good practices for writing scientific papers and conveying novel ideas.

Sensor technologies will play a key role in the success of Remote Maintenance (RM) systems for future fusion reactors. In this paper, three key types of sensor technologies of particular interest in the robotics field at the moment are evaluated, namely: Colour-Depth cameras, LIDAR (Light Detection And Ranging), and Millimetre-Wave (mmWave) RADAR. The evaluation of the sensors is performed based on the following criteria: the types of data they provide, the accuracy at different distances, and the potential environmental resistance of the sensor (namely gamma radiation). The authors review the progress in making these three types of sensor capable of operating in Fusion facilities and discuss possible mitigations. Experiments are performed to demonstrate the pros and cons of each type of sensor by collecting data from radar, colour-depth camera and LIDAR, simultaneously. The paper concludes with a performance comparison between sensors, as well as discussing the possibility of combining them, fostering redundancy in case of failure of any individual sensor device.

For communications, in certain scenarios, the spatial proximity between nodes obviates the need for a cellular connection, and MANETs can provide better solutions. An example is audio communication in bicycle platoons: cyclists ride in a cluster, but may be spread over hundreds of meters and their spatial arrangement can vary, leading to volatile links. In this work, we showcase a novel implementation of VoIP that was tailored for a MANET composed of embedded devices installed in bicycles, operating over multicast. We describe the architecture of our system, which builds on off-the-shelf hardware and software, and list the parameter values that result in reasonable audio quality. Preliminary results show that high packet delivery ratios (above 70%) can be attained with our system in platoon-riding conditions, despite no link (or network) retransmissions.

Vehicular communication is rapidly becoming a standard reality, and precise models are necessary for accurate performance estimates. Alongside cars and trucks, smaller vehicles such as scooters and bicycles are also set to participate in V2X networking, but have received considerably less attention. In this work, we present an extensive characterization of the gain pattern of a bicycle and antenna system for the IEEE 802.11g standard. We measure the radiation patterns of the antenna of a commodity 2.4 GHz WiFi module mounted on six distinct positions on the body of six archetypal bicycles in an anechoic chamber. The RSSI sample set per angle and antenna position is characterized statistically and input into an empirical model of the gain pattern of the bicycle-antenna system. We define a bicycle-to-X propagation model that pairs the proposed bicycle-antenna gain and a log-distance shadowing path loss model, and conduct outdoor measurement campaign for evaluation. We observe that the gain model measured in chamber matches the measured RSSI at small distances, whereas at larger distances it provides less accuracy.

When using multiple networked autonomous mobile robots to sense a given area online, it is of high importance to assure the network connectivity even when the robots move in the scope of their application target. In previous work we have used a topological graph property known as bi-connectivity to turn the multi-robot network robust to dropout faults while the robots were sensing a certain area or tracking a target. In this paper we continue that work by including wireless signal strength information as a measure of link quality, adapting the robots' positions to make sure each robot is connected to any other robot by at least two separate routes over time. The proposed algorithm is decentralized and based on consensus theory. We use a solution of the Traveling Salesman Problem to turn the initial arbitrary topology graph into a virtually bi-connected one. We validate our method with simulations that consider asymmetric and intermittent attenuation in the propagation model. The obtained results show that without our method the network can be disrupted while our method compensates unexpected attenuation. This work is particularly suited to networks of UAVs that sense a target area, online.

Bicycle-to-bicycle (Bi2Bi) communication can be implemented by well-established technologies in the 2.4GHz ISM band: IEEE 802.11, Bluetooth or IEEE 802.15.4. These technologies have distinct performance due to different physical and data link layers. In this paper, we characterize the mentioned 2.4 GHz-operating technologies over opportunistic links established between bicycles using commodity hardware. We find that, in Bi2Bi links, Blue-tooth, IEEE 802.11 at 24 Mbit/s, and IEEE 802.11 with automatic rate adaptation can communicate only in the immediate surroundings (under 15m of range), to maxima of 1.5 Mbit/s, 17 Mbit/s and 25 Mbit/s, respectively. IEEE 802.15.4 and IEEE 802.11 at 1 Mbit/s sustain connectivity up to 30 and 40 meters and peak transfer rates of 50 kbit/s and 800 kbit/s respectively. In addition, we observed that, in all measurement scenarios, link performance depended strongly on whether bicycles were approaching or moving away, rather than on whether one was at the front or back of the other.

Unmanned Aerial Vehicles (UAVs) are becoming an important tool for facilities monitoring, target tracking, surveillance, etc. In many of these contexts, a UAV needs to reach an area of interest (AOI) while streaming data to a ground station (GS) where one or more drones are controlled by an operator. In remote areas, intermediate UAVs can act as relays and form a line network to extend range. Interactive control requires a live video stream where both throughput and delay are important, which limits the number of relays and thus maximum range. However, throughput also depends on the quality of the links. It is known that in open space scenarios, where links can be considered similar, maximum throughput is achieved with equal spacing of the relays. This is not the case near large obstacles or high interference areas, in which links can be rather asymmetric. In this paper, we address this scenario and show that maximum throughput is achieved with uneven relay spacing but balanced packet delivery ratios. We propose a new distributed protocol fit to high throughput streams on line networks that tracks and balances the quality of neighboring links by moving the relay nodes accordingly. Real world experiments with multiple AR.Drone 2.0 UAVs show that variable link length in a scenario with asymmetric links generates gains in packet delivery up to \(40\%\) and throughput up to \(300\%\).

Unmanned Aerial Vehicles (UAVs) are rapidly becoming an important tool for applications like surveillance, target tracking and facility monitoring. In many of these contexts, one or more UAVs need to reach an area of interest (AOI) while streaming live video to a ground station (GS) where one or more operators inspect the AOI and carry out fine control of UAVs position. In remote areas, intermediate UAVs can act as relays and form a line network to extend range. Interactive control requires a live video stream where both throughput and delay are important. In this paper, we show that routing packets over CSMA/CA (native medium access protocol of WiFi, the most common wireless technology among UAVs) behaves poorly in this context due to link asymmetries. We propose a novel distributed, adaptive and self-synchronized TDMA protocol (DVSP) that both enhances delay and packet delivery while operating on commodity hardware and leveraging a standard UDP/IP protocol stack. We prove that DVSP converges to a global solution that minimizes delay using local information, only, thus in a fully distributed manner. Real world experiments with multiple UAVs show gains in delay up to 75%, and packet delivery up to 50%, without sacrificing goodput.

Recent advances in Unmanned Aerial Vehicles (UAVs) have enabled a myriad of new applications many of which provide aerial vision-based sensing. In intrusion detection or target tracking applications, it is important to reach a given area of interest in the shortest time, and create an online data streaming connection to a monitoring station for immediate delivery of content to the operator. However, if the area of interest (AOI) is not contained in the field of view of a single UAV, it is necessary to move the sensor-UAV to sweep the region in order to provide the most fresh information as possible. In order to improve the collection time of the AOI, we can cooperatively use multiple UAVs creating an array of moving cameras, that always remain connected without breaks in communication. In this work, we validate our approach with a simulation that captures physical models and the application layer of each UAV, as well as the wireless network. We propose an optimal solution to sweep the AOI as well as a decentralised formation control algorithm that maintains UAVs equally separated along the optimal path that covers the whole AOI, even with external disturbances such as wind gusts. We show a seven-fold increase in the refresh rate of the AOI coverage when comparing to a solution without the optimal sweeping and decentralised formation control.

Recent advances in Unmanned Aerial Vehicles (UAVs) have enabled a myriad of new applications in many different domains from personal entertainment to process and infrastructure online monitoring in large industrial sites, among other. Our work focuses on how one can use several small UAVs collaboratively to provide extended reach to an online video monitoring system. We demonstrate how a TDMA overlay using 802.11 radios on low-cost commercial-off-the-shelf (COTS) UAVs can be used to enable high channel utilization in multi-hop networks, by avoiding mutual interference. This paper presents an extensive network characterisation and modelling of the quality of the UAV-to-UAV link, in terms of packet delivery ratio as a function of distance, packet size and orientation. We show that this platform is non-omnidirectional in the flight plane and that UAV-to-UAV communication ceases around 75m. Then, we solve the mathematical problem of finding the optimal link length and number of hops that maximize the end-to-end throughput, as we extend the network. We validate our mathematical model with extensive experimental campaigns transmitting payloads up to 200m (over 802.11g @ 54MBps).