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- Modeling LoRa Communications in Estuaries for IoT Environmental Monitoring SystemsPublication . Gutiérrez Gaitán, Miguel; D'Orey, Pedro; Cecílio, José; Rodrigues, Marta; Santos, Pedro Miguel; Pinto, Luis; Oliveira, Anabela; Casimiro, António; Almeida, LuisLow-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.
- Empirical Evaluation of the Performance of Electric Vehicles for Taxi OperationPublication . Neves, João; Loureiro, Ana; D'Orey, Pedro; Miguéis, Vera; Costa, Álvaro; Ferreira, MichelElectric mobility with all of its advantages has gained momentum during the last decade with increasing utilization by many sectors of the society. However, professional fleets’ operators (e.g. taxis) are still conservative in switching to this new mobility paradigm. In this paper, we empirically evaluate whether electric vehicles together with normal charging speeds could replace current internal combustion engine vehicles for taxi mobility and study the implications for the taxi business. To perform this study we resort to a detailed and large mobility dataset of a taxi fleet collected in a mid-sized European city. The results provide a first indication that such transition towards electric mobility is feasible for the vast majority of the vehicles of the fleet and that simple AC chargers at taxi stands could suffice to provide the necessary range autonomy.
- Assessing Communication Strategies in C-ITS using n-Person Prisoner 19s Dilemma PerspectivePublication . Costa, António; Kokkinogenis, Zafeiris; D'Orey, Pedro; Rossetti, Rosaldo J. F.In Cooperative Intelligent Transport Systems, road users and traffic managers share information for coordinating their actions to improve traffic efficiency allowing the driver to adapt to the traffic situation. Its effectiveness, however, depends on the user’s decision-making process, which is the main source of uncertainty in any mobility system and depends on the ability of the infrastructure to communicate timely and reliably. To cope with such a complex scenario, this paper proposes a game theory perspective based on the n-Person Prisoner’s Dilemma as a metaphor to represent the uncertainty of cooperation underlined by communication infrastructures in traveller information systems. Results highlighted a close relationship between the emergence of cooperation and network performance, as well as the impact of the communication failure on the loss of cooperation sustainment, which was not recovered after the system was re-established.
- Joint Scheduling, Routing and Gateway Designation in Real-Time TSCH NetworksPublication . Gutiérrez Gaitán, Miguel; Almeida, Luis; Watteyne, Thomas; D'Orey, Pedro; Santos, Pedro Miguel; Dujovne, DiegoThis research proposes a co-design framework for scheduling, routing and gateway designation to improve the real-time performance of low-power wireless mesh networks. We target time-synchronized channel hopping (TSCH) networks with centralized network management and a single gateway. The end goal is to exploit existing trade-offs between the three dimensions to enhance traffic schedulability at systems' design time. The framework we propose considers a global Earliest-Deadline-First (EDF) scheduler that operates in conjunction with the minimal-overlap (MO) shortest-path routing, after a centrality-driven gateway designation is concluded. Simulation results over varying settings suggest our approach can lead to optimal or near-optimal real-time network performance, with 3~times more schedulable flows than a naive real-time configuration.
- Minimal-Overlap Centrality-Driven Gateway Designation for Real-Time TSCH NetworksPublication . Gutiérrez Gaitán, Miguel; D'Orey, Pedro; Santos, Pedro M.; Almeida, LuisThis research proposes a novel minimal-overlap centrality-driven gateway designation method for real-time wireless sensor networks (WSNs). The goal is to enhance network schedulability by design, particularly, by exploiting the relationship between path node-overlaps and gateway designation. To this aim, we define a new metric termed minimal-overlap network centrality which characterizes the overall overlapping degree between all the active flows in the network when a given node is selected as gateway. The metric is then used to designate as gateway the node which produces the least overall number of path overlaps. For the purposes of evaluation, we assume a time-synchronized channel-hopping (TSCH) WSN under centralized earliest-deadline-first (EDF) scheduling and shortest-path routing. The assessment of the WSN traffic schedulability suggests our approach is dominant over classical network centrality metrics, namely, eigenvector, closeness, betweenness, and degree. Notably, it achieves up to 50% better schedulability than a degree centrality benchmark.
- Demonstrating RA-TDMAs+ for robust communication in WiFi mesh networksPublication . Almeida, Diogo; Gutiérrez Gaitán, Miguel; D'Orey, Pedro; Santos, Pedro M.; Pinto, Luís; Almeida, LuisThis work will demonstrate a new flavor of the RA-TDMA set of protocols, namely RA-TDMAs+, which uses IEEE-802.11 (WiFi) COTS hardware in ad-hoc mode to set up a dynamic mesh network of mobile nodes with highbandwidth. The protocol uses topology tracking to configure the TDMA frame and robust relative synchronization to define the TDMA slots without resorting to a global clock and in the presence of interfering traffic. The demo will set up a small-scale testbed using COTS hardware, thus evidencing the feasibility of the approach, and it will show 1clive plots 1d of the temporal (synchronization) and topological views of the network.
- MobiWise: Eco-routing decision support leveraging the Internet of thingsPublication . Aguiar, Ana; Fernandes, Paulo; Guerreiro, Andreia; Tomás, Ricardo; Agnelo, João; Santos, José Luís; Araújo, Filipe; Coelho, Margarida C.; Fonseca, Carlos M.; D'Orey, Pedro; Luís, Manuel; Sargento, SusanaEco-routing distributes traffic in cities to improve mobility sustainability. The implementation of eco-routing in real-life requires a diverse set of information, including different kinds of sensors. These sensors are often already integrated in city infrastructure, some are technologically outdated, and are often operated by multiple entities. In this work, we provide a use case-oriented system design for an eco-routing service leveraging Internet-of-Things (IoT) technologies. The methodology involves six phases: 1) defining an eco-routing use case for a vehicle fleet; 2) formulating a routing problem as a multi-objective optimisation to divert traffic at a relevant hub facility; 3) identifying data sources and processing required information; 4) proposing a microservice-based architecture leveraging IoT technologies adequate to a multi-stakeholder scenario; 5) applying a microscopic traffic simulator as a digital twin to deal with data sparsity; and 6) visually illustrating eco-routing trade-offs to support decision making. We built a proof-of-concept for a mid-sized European city. Using real data and a calibrated digital twin, we would achieve hourly total emissions reductions up to 2.1%, when applied in a car fleet composed of 5% of eco-routing vehicles. This traffic diversion would allow annual carbon dioxide and nitrogen oxides savings of 400 tons and 1.2 tons, respectively.
- Minimal-Overlap Centrality for Multi-Gateway Designation in Real-Time TSCH NetworksPublication . Gutiérrez Gaitán, Miguel; Almeida, Luis; D'Orey, Pedro; Santos, Pedro M.; Watteyne, ThomasThis article presents a novel centrality-driven gateway designation framework for the improved real-time performance of low-power wireless sensor networks (WSNs) at system design time. We target time-synchronized channel hopping (TSCH) WSNs with centralized network management and multiple gateways with the objective of enhancing traffic schedulability by design. To this aim, we propose a novel network centrality metric termed minimal-overlap centrality that characterizes the overall number of path overlaps between all the active flows in the network when a given node is selected as gateway. The metric is used as a gateway designation criterion to elect as a gateway the node leading to the minimal number of overlaps. The method is then extended to multiple gateways with the aid of the unsupervised learning method of spectral clustering. Concretely, after a given number of clusters are identified, we use the new metric at each cluster to designate as cluster gateway the node with the least overall number of overlaps. Extensive simulations with random topologies under centralized earliest-deadline-first (EDF) scheduling and shortest-path routing suggest our approach is dominant over traditional centrality metrics from social network analysis, namely, eigenvector, closeness, betweenness, and degree. Notably, our approach reduces by up to 40% the worst-case end-to-end deadline misses achieved by classical centrality-driven gateway designation methods.
- The trade-offs between Fog Processing and Communications in latency-sensitive Vehicular Fog ComputingPublication . Júnior, Francisco Mendonça; Kokkinogenis, Zafeiris; Dias, Kelvin; D'Orey, Pedro; Rossetti, Rosaldo J. F.In a vehicular fog computing paradigm, connected autonomous vehicles are envisioned as processing nodes (i.e. fog nodes) so that end-devices may offload processing tasks to them. As such, both local and distributed processing on fog nodes will depend heavily on wireless network conditions and the current traffic demand. In this work, we investigate the trade-offs on the operation of fog nodes under different vehicle densities and network conditions and formalize a Time Constrained One-Shot Open First Price Auction for resource allocation in vehicular fog computing. Through a large-scale simulation study, we assess important aspects of the performance of fog nodes in Vehicular Fog Computing. We show that current wireless network standards may dictate the limits of processing despite the availability of processing power of fog nodes. Our results indicate the existence of tradeoffs on the operation of fog nodes regarding message overhead and processing redundancy to achieve high task completion ratio. Finally, we evaluate the social welfare distribution of the task allocation achieved using the auction where higher message rates lead to higher costs.
- Correlating the Effect of Covid-19 Lockdown with Mobility Impacts: A Time Series Study Using Noise Sensors DataPublication . D'Orey, Pedro; Pascale, Antonio; Coelho, Margarida C.; Mancini, Simona; Guarnaccia, ClaudioThe Covid-19 crisis forced governments around the world to rapidly enact several restrictions to face the associated health emergency. The Portuguese government was no exception and, following the example of other countries, established various limitations to flat the contagions curve. This led to inevitable repercussions on mobility and environmental indicators including noise. This research aims to assess the impact of the lockdown due to Covid-19 disease on the noise levels recorded in the city of Porto, Portugal. Data from four noise sensors located in strategic spots of the city were used to calibrate and validate Time Series Models, allowing to impute the missing values in the datasets and rebuild them. The trend and the cyclic information were extracted from the reconstructed datasets using decomposition techniques. Finally, a Spearman correlation analysis between noise levels values and traffic volumes (extracted from five inductive loop detectors, located nearby the noise sensors) was performed. Results show that the noise levels series present a daily seasonal pattern and the trends values decreased from 6.7 to 7.5 dBA during the first lockdown period (March-May 2020). Moreover, the noise levels tend to gradually rise after the removal of restrictions. Finally, there is a monotonic relationship between noise levels and traffic volumes values, as confirmed by the positive moderate-to-high correlation coefficients found, and the sharp drop of the former during March-May 2020 can be attributed to the strong reduction of road traffic flows in the city.