Instituto de Telecomunicações

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Publications

Large-scale LoRa networks: a mode adaptive protocol

Publication . Luís, Miguel; Sargento, Susana; Fernandes, Rui

Low-power wide-area networks (LPWANs) are probably the most promising radio access technologies for Internet-of-Things (IoT) applications. Amongst these, one of the most auspicious solutions is LoRa, a versatile technology highly compatible with urban environments, enabling long-range communications. Most of the LoRa-based medium access protocols operate under the ALOHA rationale, whose performance is known to be fairly poor. This work targets the medium access in single-channel large-scale LoRa networks, proposing a new protocol, denoted as the LoRa mode adaptive protocol (LoRa-MAP), which manages to maintain the best possible connection between end nodes and the gateway, by adapting the LoRa's physical layer parameters and making use of control packets for its coordination without violating the duty-cycle constraints of both end nodes and gateway. An analysis on different medium access schemes is conducted, aiming to perceive how different parameters and network layouts influence the coordination process. An energy expenditure analysis is conducted comparing LoRa-MAP to simpler solutions to study the impact of additional transmission/listening periods. The simulation results have shown that the proposed solution increases the LoRa network scalability, deeming it a great candidate for IoT environments.

2021-09-01Journal article

Restricted access

The contribution of submarine optical fiber telecom cables to the monitoring of earthquakes and tsunamis in the NE Atlantic

Publication . Matias, Luis; Carrilho, Fernando; Sá, Vasco; Omira, Rachid; Niehus, Manfred; Corela, Carlos; Barros, José; Omar, Yasser

Recent developments in optical fiber cable technology allows the use of existing and future submarine telecommunication cables to provide seismic and sea-level information. In this work we study the impact of three different technologies, 1) SMART, Science Monitoring and Reliable Telecommunications; 2) DAS, Distributed Acoustic Sensing, and; 3) LI, Laser Interferometry, for effective earthquake and tsunami monitoring capabilities on the NE Atlantic. The SW Iberia is the source area of the largest destructive earthquake that struck Europe since the year 1000, the November 1, 1755 event. This earthquake generated also a destructive tsunami affecting the whole basin. This tectonically active area is crossed by the CAM (Continent-Azores-Madeira) submarine cable on a ring configuration. Due to the end of cable lifetime the current cables need to be replaced by 2024 and the technical requirements must be defined in mid-2021. The Azores archipelago is the focus of frequent seismic crizes and occasionally destructive earthquakes. A common feature of these seismic events is that they take place offshore, an area that is difficult to monitor from land-based instruments. In this work we evaluate the contribution of SMART cables to the earthquake monitoring and tsunami early warning system in SW Iberia and show how DAS and LI can improve earthquake monitoring on two active domains of the Azores. For tsunami early warning, we show how the offshore sea-level measurements provide clean offshore tsunami records when compared to coastal observations by tide gauges, which greatly improves the efficiency of the system. For earthquake monitoring, the data processing operational routine is examined using Monte-Carlo simulations. These take into consideration the errors in phase picking and the uncertainty on the 1D velocity model used for earthquake location. Quality of earthquake location is examined using the difference between the true location and the centroid of the computed epicenters and by the overall ellipse of uncertainty obtained from 100 runs. The added value provided by instrumented submarine telecommunication cables to mitigate earthquake and tsunami risk demonstrated in this work will help authorities and the society in general to take the political decisions required for its full implementation worldwide.

2021-07-20Journal article

Open access

3D antenna characterization for WPT applications

Publication . Jordão, Marina; Pires, Diogo; Belo, Daniel; Pinho, Pedro; Carvalho, Nuno Borges

The main goal of this paper is to present a three-dimensional (3D) antenna array to improve the performance of wireless power transmission (WPT) systems, as well as its characterization with over-the-air (OTA) multi-sine techniques. The 3D antenna consists of 15 antenna elements attached to an alternative 3D structure, allowing energy to be transmitted to all azimuth directions at different elevation angles without moving. The OTA multi-sine characterization technique was first utilized to identify issues in antenna arrays. However, in this work, the technique is used to identify which elements of the 3D antenna should operate to transmit the energy in a specific direction. Besides, the 3D antenna design description and its characterization are performed to authenticate its operation. Since 3D antennas are an advantage in WPT applications, the antenna is evaluated in a real WPT scenario to power an RF-DC converter, and experimental results are presented.

2021-06-29Journal article

Open access

Assessing the impact of the loss function and encoder architecture for fire aerial images segmentation using deeplabv3+

Publication . Harkat, Houda; Nascimento, Jose; Bernardino, Alexandre; Ahmed, Hasmath Farhana Thariq

Wildfire early detection and prevention had become a priority. Detection using Internet of Things (IoT) sensors, however, is expensive in practical situations. The majority of present wildfire detection research focuses on segmentation and detection. The developed machine learning models deploy appropriate image processing techniques to enhance the detection outputs. As a result, the time necessary for data processing is drastically reduced, as the time required rises exponentially with the size of the captured pictures. In a real-time fire emergency, it is critical to notice the fire pixels and warn the firemen as soon as possible to handle the problem more quickly. The present study addresses the challenge mentioned above by implementing an on-site detection system that detects fire pixels in real-time in the given scenario. The proposed approach is accomplished using Deeplabv3+, a deep learning architecture that is an enhanced version of an existing model. However, present work fine-tuned the Deeplabv3 model through various experimental trials that have resulted in improved performance. Two public aerial datasets, the Corsican dataset and FLAME, and one private dataset, Firefront Gestosa, were used for experimental trials in this work with different backbones. To conclude, the selected model trained with ResNet-50 and Dice loss attains a global accuracy of 98.70%, a mean accuracy of 89.54%, a mean IoU 86.38%, a weighted IoU of 97.51%, and a mean BF score of 93.86%.

2022-04-22Journal article

Open access

Sparsity-promoting approach to polarization analysis of seismic signals in the time-frequency domain

Publication . Mohammadigheymasi, Hamzeh; Crocker, Paul; Fathi, Maryam; Almeida, Eduardo; Silveira, Graça; Gholami, Ali; Schimmel, Martin

Time - frequency (TF)-domain polarization analysis (PA) methods are widely used as a processing tool to decompose multicomponent seismic signals. However, as a drawback, they are unable to obtain sufficient resolution to discriminate between overlapping seismic phases, as they generally rely on a low-resolution time-frequency representation (TFR) method. In this article, we present a new approach to the TF-domain PA methods. More precisely, we provide an in-detailed discussion on rearranging the eigenvalue decomposition polarization analysis (EDPA) formalism in the frequency domain to obtain the frequency-dependent polarization properties from the Fourier coefficients owing to the Fourier space orthogonality. Then, by extending the formulation to the TF domain and incorporating sparsity promoting TFR (SP-TFR), we improve the resolution when estimating the TF-domain polarization parameters. Finally, an adaptive SP-TFF is applied to extract and filter different phases of the seismic wave. By processing earthquake wave-forms, we show that, by combining amplitude, directivity, and rectilinearity attributes on the sparse TF-domain polarization map of the signal, we are able to extract (or filter) different phases of seismic waves. The SP-TFF method is evaluated on synthetic and real data associated with the source mechanism of the M-w = 8.2 earthquake that occurred in the south-southwest of Tres Picos, Mexico. A discussion on the results is given, verifying the efficiency of the method in separating not only the Rayleigh waves from the Love waves hut also in discriminating them from the body and coda waves. The codes and datasets are available at https://github.com/SigProSeismology/SP-TFF, contributing to the geoscience community.

2022-01-07Journal article

Restricted access