Browsing by Author "Fernandes, Rui"
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- Exploring the use of control packets in LoRa medium access: a scalability analysisPublication . Fernandes, Rui; Oliveira, Rui; Luís, Miguel; Sargento, SusanaLoRa technology has been attesting itself as one of the most prominent and widely adopted low power wide area technologies. Highly compatible with Internet of Things (IoT) applications and urban environments, this technology enables large range communications although with small bandwidths and duty cycle restrictions. In this work, we propose a distinct way of dealing with the Medium Access Control (MAC) in LoRa, through the use of control packets to enhance the technology performance in urban city scenarios, where a large number of nodes is expected. The proposed protocol is asynchronous and takes into account the energy expenditure. We compare this scheme with the standard (LoRaWAN) by considering different network densities and packet sizes, and through different LoRa collision models. Performance results, such as network throughput and fairness index, show that, depending on the ratio between data and control packet lengths, it is possible to greatly improve the bit rate and overall network performance, even if increasing the duty-cycle restriction time due to the addition of overhead.
- Large-scale LoRa networks: a mode adaptive protocolPublication . Luís, Miguel; Sargento, Susana; Fernandes, RuiLow-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.
- Molecular mobility, composition and structure analysis in glycerol plasticised chitosan filmsPublication . Fundo, Joana F.; Fernandes, Rui; Almeida, Pedro L.; Carvalho, Alexandra; Feio, Gabriel; Silva, Cristina L. M.; Quintas, Mafalda A. C.This study was developed with the purpose to investigate the effect of polysaccharide/plasticiser concentration on the microstructure and molecular dynamics of polymeric film systems, using transmission electron microscope imaging (TEM) and nuclear magnetic resonance (NMR) techniques. Experiments were carried out in chitosan/glycerol films prepared with solutions of different composition. The films obtained after drying and equilibration were characterised in terms of composition, thickness and water activity. Results show that glycerol quantities used in film forming solutions were responsible for films composition; while polymer/total plasticiser ratio in the solution determined the thickness (and thus structure) of the films. These results were confirmed by TEM. NMR allowed understanding the films molecular rearrangement. Two different behaviours for the two components analysed, water and glycerol were observed: the first is predominantly moving free in the matrix, while glycerol is mainly bounded to the chitosan chain. (C) 2013 Elsevier Ltd. All rights reserved.