Spectrum Sensing Performance in Cognitive Radio Networks with Multiple Primary Users

Radio Spectrum sensing has been a topic of strong research in the last years due to its importance to Cognitive Radio (CR) systems. However, in Cognitive Radio Networks (CRNs) with multiple Primary Users (PUs), the Secondary Users (SUs) can often detect PUs that are located outside the sensing range, due to the level of the aggregated interference caused by that PUs. This effect, known as Spatial False Alarm (SFA), degrades the performance of CRNs, because it decreases the SUs’ medium access probability. This work characterizes the SFA effect in a CRN, identifying possible actions to attenuate it. Adopting Energy-based sensing (EBS) in each SU, this work starts to characterize the interference caused by multiple PUs located outside a desired sensing region. The interference formulation is then used to write the probabilities of detection and false alarm, and closed form expressions are presented and validated through simulation. The first remark to be made is that the SFA can be neglected, depending on the path loss factor and the number of samples collected by the energy detector to decide the spectrum’s occupancy state. However, it is shown that by increasing the number of samples needed to increase the sensing accuracy, the SUs may degrade their throughput, namely if SUs are equipped with a single radio that is sequentially used for sensing and transmission. Assuming this scenario, this paper ends by providing a bound for the maximum throughput achieved in a CRN with multiple active PUs and for a given level of PUs’ detection inside the SUs’ sensing region. The results presented in the paper show the impact of path loss and EBS parameterization on SUs’ throughput and are particularly useful to guide the design and parametrization of multi-hop CRNs, including future ad hoc cognitive radio networks considering multiple PUs

Successful Packet Reception Analysis in Multi-Packet Reception Wireless Systems

In this letter, we analyze the individual probability of receiving a packet when $n$ nodes transmit simultaneously to a single receiver and a multi-packet reception (MPR) scheme is adopted at the physical layer. The main contribution of this letter is the characterization of the average number of packets successfully received. The generic methodology proposed to compute the probability of successful reception of a packet is obtained taking into account the stochastic nature of the path loss due to the spatial distribution of the nodes, as well as shadowing and fast fading effects. The accuracy of the theoretical approach is finally assessed through simulations, showing that for a generic MPR system, there is an optimal number of transmitters that maximize the average number of received packets

Performance analysis of interference-aware multi-packet reception networks

This work is supported by the European Regional Development Fund (FEDER), through the Competitiveness and Internationalization Operational Programme (COMPETE 2020) of the Portugal 2020 and Programa Operacional Regional LISBOA (LISBOA 2020), and by national funds through Fundação para a Ciência e Tecnologia (FCT), under the projects CoSHARE (LISBOA-01-0145-FEDER-0307095-PTDC/EEITEL/30709/2017), InfoCent-IoT (POCI-01-0145-FEDER-030433), and project UID/EEA/50008/2019.Decentralized wireless networks are gaining increasing popularity as they do not need a fixed infrastructure. Simultaneously, multiple research initiatives have led to different findings at the PHY layer of the wireless communication systems, which include Multi-Packet Reception (MPR) techniques that enable a receiver to decode multiple packets that are transmitted simultaneously. However, the distributed nature of decentralized wireless networks demands different network control policies that should take into account the MPR capabilities to increase the network performance. This work studies the performance of a wireless network composed of multiple transmitters that are willing to transmit to a single receiver. This receiver has MPR capability and adopts an Energy-based Sensing (EBS) technique to enable uplink users’ transmissions without interfering with the ongoing transmissions from other transmitters. The first remark to be made is that the MPR technique performance depends on the channel propagation conditions and on the amount of time the receiver needs to detect the spectrum’s occupancy state. However, it is shown that by increasing the number of samples needed to increase the sensing accuracy, the receiver may degrade its throughput, namely if the receiver is equipped with a single radio, that is sequentially used for sensing and transmitting (split-phase operation). The results presented in the paper show the impact of the channel propagation condition and EBS parameterization on wireless network throughput and the cases where the receiver MPR capture performance is greatly improved by the use of a spectrum sensing technique.publishersversionpublishe

Improving path duration in high mobility vehicular ad hoc networks

In this paper, we consider a high-speed highway mobility scenario, where the available knowledge about the network’s topology is used to improve the routing path duration. The improvement is mainly due to the use of a topology control algorithm, which increases the path duration by decreasing the probability of path breaks. For network regions having an enough density of vehicles, the packets are preferentially routed over the oldest links created by the vehicles moving in the same direction. For smaller values of vehicles’ density, the routing preferentially uses the most recent links created in both moving directions. This choice is shown to increase the routing path duration. The topology control scheme here proposed can be easily integrated in the existing routing protocols: we describe how to integrate it in the Optimized Link-State Routing Protocol (OLSR).1 We compare the performance of our approach with other routing protocols for different values of vehicles’ density. The comparison includes end-to-end path delay, path availability and path length (in number of hops). Finally, we evaluate the path duration achieved with our approach, concluding that it exhibits a significant improvement over the most relevant topology and position-based routing protocols

Sistema de apoio à decisão para o transporte não urgente de doentes em veículo partilhado

O transporte não urgente de doentes em Portugal foi alvo de reformulação legislativa de modo a reduzir os custos que acarretava. Neste artigo apresentam-se métodos heurísticos para a formação de agrupamentos de doentes a serem transportados na mesma viatura. São apresentados resultados computacionais que validam os algoritmos desenvolvidos. Os algoritmos podem ser facilmente integrados num sistema de apoio à decisão.Fundação para a Ciência e a Tecnologia (FCT)COMPETE Programa Operacional Fatores de Competitividade (POFC) Ref FCOMP-01-0124-FEDER-02060

Agent-based micro simulation to assess the performance of roundabouts considering different variables and performance indicators

Traffic congestion problems in intersections are usually solved by building infrastructures such as roundabouts. Several variables influence its performance, e.g. geometry, size and driving behaviour. Thus, it becomes necessary to compare these variables. This paper proposes a simulation model, developed to compare the performance of roundabouts, employing the object and agent modelling paradigms of Simio, to model the individual behaviour of vehicles. The results indicate the optimum size of roundabouts is around 40 meters of diameter and that the driving style has a greater influence on the performance of the roundabout than its unbalancing. In addition, it was found that roundabouts considering unbalancing and human behaviour decreased: The flow of vehicles in 8%, the waiting time per vehicle in 3 minutes, the queue size in 90%, the number of stops per vehicle in 88% and vehicles spent three times more fuel, than the roundabouts that did not consider these variables.(undefined)info:eu-repo/semantics/publishedVersio

Caracterização de uma conta de vidro proveniente do povoado fortificado calcolítico da Moita da Ladra (Vila Franca de Xira)

The full excavation of the fortified Chalcolithic settlement of Moita da Ladra by one of us (J.L.C.) has shown the existence of a single archaeological layer corresponding to the occupation of the site during the second half of the 3rd millennium BC. Among the archaeological remains collected during the field campaigns there is a bead, with a spheroid shape, longitudinally fractured, presenting a black matrix with numerous whitish spots. The fracture presents a vitreous greasy surface, and exposes a suspension cylindrical bore. Various techniques were used to identify the material that was used in the manufacture of the artifact, including CHN elemental analysis, EDXRF, μ-PIXE and XRD, conducted by the other authors. It was found that the material is not organic (carbon is absent), presenting significant amounts of the elements Si, K, Ca, Ti, Fe, Sr, Zr, and Sb. The X-ray diffraction spectra indicates that the material has an essentially vitreous nature, being the whitish particles dispersed in the vitreous mass identified as quartz. μ-PIXE results show a chemical composition that is consistent with an artificial glass, which implies a much more recent chronology for the bead than that of the Chalcolithic archaeological layer where it was recovered. Thus, although the bead was recorded from a Chalcolithic context, its provenance must be ascribed to the Late Bronze Age occupation recorded nearby and resulting from the early Phoenician trade.info:eu-repo/semantics/publishedVersio

The Maré Museum: an integrated project of community development

Cadernos de SociomuseologiaThe Maré Museum, founded on 8 May 2006, arose from the desire of the inhabitants of the community to have a place of memory, a place that is immersed in the past and looks to the future, a place that reflects on this community, on their conditions and identities and on their territorial and cultural diversity. The intention of the Maré Museum is to break with the tradition that the experiences to be recollected and the places of memory to be remembered are those elected by the official version, the "winner" version of the story that restricts the representations of history and memory of large portions of the population. The Maré Museum, as a pioneer initiative in the city scene, proposed to expand the museological concept, so that it is not restricted to intellectual social groups and cultural spaces that are not accessible to the general population. The museum has established recognition that the slum is a place of memory and so has initiated a museographic reading of the Mare community. .

Discrete simulation software ranking -A top list of the worldwide most popular and used tools

This paper documents a work on all-purpose discrete event simulation tools evaluation. Selected tools must be suitable for process design (e.g. manufacturing or services industries). Rather than making specific judgments of the tools, authors tried to measure the intensity of usage or presence in different sources, which they called "popularity". It was performed in several different ways, including occurrences in the WWW and scientific publications with tool name and vendor name. This work is an upgrade to the same study issued 5 years ago (2011), which in its turn was also an upgrade of 10 years ago (in 2006). It is obvious that more popularity does not assure more quality, or being better to the purpose of a simulation tool; however, a positive correlation may exist between them. The result of this work is a short list, of 19 commercial simulation tools, with probably the nowadays' most relevant ones.This work has been co-supported by SI I&DT project in joint-promotion nº 36265/2013 (HMIEXCEL) and by FCT Fundação para a Ciência e Tecnologia - project: PEst-OE/EEI/UI0319/2014. REFERENCESinfo:eu-repo/semantics/publishedVersio