CTM - Other Publications

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    2017 Wireless Days, Porto, Portugal, March 29-31, 2017
    ( 2017) Manuel Ricardo ; Campos,Rui ; Ruela,Jose ; Ricardo Morla ; Teixeira,Filipe ; Luís Manuel Pessoa ; Salgado,Henrique
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    Actas das VII Jornadas sobre Sistemas Reconfiguráveis
    ( 2011) Mário Véstias ; João Canas Ferreira
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    Active Mining of Parallel Video Streams
    ( 2014) Samaneh Khoshrou ; Jaime Cardoso ; Luís Filipe Teixeira
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    Assessment of dispersion map impact on the digital back propagation of long-haul fibre-optic links
    ( 2013) Luís Manuel Pessoa ; Henrique Salgado ; Darwazeh,I
    The back propagation algorithm is one of the best methods known for simultaneous linear and nonlinear impairment mitigation in long-haul fibre-optic links. Better understanding the full potential of such algorithm is key to improve the capacity of future links, whose design is likely to depend on the algorithm performance under different link configurations. In this paper, we carry out a novel and pertinent comparison in terms of the computational complexity requirements of both symmetric and asymmetric back-propagation implementation approaches for different dispersion map configurations, using simple single channel transmission, which results in the proposal of several design rules for the optimized deployment of ultra-long haul optical transport systems. In particular, it is concluded that dispersion unmanaged transmission is preferable in the sense of compatibility with different link design configurations as well as computational complexity requirements and maximum performance that can be achieved.
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    Context-aware low-energy Wi-Fi sensor networks for e-health
    ( 2013) Carvalho,L ; Rui Lopes Campos ; Manuel Ricardo
    Typical sensor networks are formed by low-end, battery operated devices, which rely on low-energy communication technologies, such as Bluetooth, Zigbee and ANT+, due to their energy efficiency. On the other hand, sensor networks increasingly need to be connected to the Internet, which implies adaptations of the TCP/IP stack to fit such wireless technologies. These adaptations bring additional complexity and imply new hardware, thus deployments are cumbersome and sub-optimal. Conversely, Wi-Fi is ubiquitous, can be seamlessly integrated with TCP/IP, and is energy-efficient with the right configurations; yet, its usage is still uncommon in e-health scenarios. For these reasons, we argue that a TCP/IP over Wi-Fi approach should be followed in e-health sensor networks. We propose a novel cross-layer, context-aware network configuration mechanism, which monitors the user and networking contexts and optimizes the configuration of the TCP/IP protocol stack accordingly. Our approach enables seamless integration between e-health wireless sensor networks and the TCP/IP backbone, while improving energy efficiency and reliability. © 2013 IEEE.
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    Design Tradeoffs for Voltage Controlled Crystal Oscillators with Built-in Calibration Mechanisms
    ( 2013) Cardoso,JP ; José Machado da Silva
    Tinting is a critical issue in communication systems, especially for synchronous communications. These show a high dependence on the clock signal purity due to errors that can be introduced into the decision process. This paper addresses the design, on a 130nm CMOS process, of a Radiation Tolerant Voltage Controlled Quartz Crystal Oscillator (VCXO), including techniques to reduce the influence of radiation and noise on its performance. The VCXO is included on a PLL designed to work within High Energy Physics (IIEP) experiments.
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    Diffusion characteristics of ethylene glycol in skeletal muscle (vol 20, 051019, 2015)
    ( 2015) Oliveira,LM ; Maria Inês Carvalho ; Nogueira,EM ; Tuchin,VV
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    The Effect of Data Aggregation on the Performance of a Wireless Sensor Network Employing a Polling Based Data Collecting Technique
    ( 2013) Abdellatif,MM ; José Manuel Oliveira ; Manuel Ricardo
    Wireless Sensor Networks (WSNs) consist of small devices capable of sensing various variables in the environment, process and communicate them through the network. These devices interact together to carry out monitoring tasks. A photo-voltaic (PV) power plant is an example of such network, where each solar panel has a sensor connected to it. The number of interconnected solar panels can become very large in order to cover a large area. Each sensor senses the output of the panel and sends this value to a central node for processing. In this paper we study and compare the performance of a multi-hop wireless sensor network, employing a polling based data collecting technique with data aggregation, against the performance of a one hop network employing two different data collecting techniques. The study considers a wireless network with fixed number of nodes using different values of the offered load, estimating the network throughput for each technique and offered load. The use of a multi-hop setup was chosen in order to reduce transmission power and interference among nodes. Results show that the multi-hop network, using the polling based data collecting technique with data aggregation, performs close to the one hop network using the other two techniques. The study involves both simulation and testbed experimentation.
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    End-to-End Delay Estimation using RPL Metrics in WSN
    ( 2013) Pedro Filipe Pinto ; António Pinto ; Manuel Ricardo
    Critical monitoring applications can use wireless sensor networks to transport delay sensitive data. This data may demand bounded delays in order to be considered useful by the receiver. In these cases, an accurate and real-time estimation of the end-to-end delay could be used to anticipate the data usefulness prior to sending it. A novel real-time and end-to-end delay estimation mechanism is proposed in this paper, which considers processing times and two new RPL metrics. Results show that our proposal is more accurate than the ETT-based solution for delay estimation, and it does not significantly degrade the network performance.
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    Experimental evaluation of a differential GPS-over-fiber system for aircraft attitude determination
    ( 2013) Oliveira,JMB ; Luís Manuel Pessoa ; Henrique Salgado ; Proudley,G ; Charlton,D ; White,H
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    Experimental evaluation of a R-EAM and noise impact analysis for UWB and Wi-Fi transmission in RoF networks
    ( 2013) Luís Manuel Pessoa ; Oliveira,JMB ; Coelho,DV ; Castro,JCS ; Henrique Salgado
    The performance of a reflective electro-absorption modulator transceiver is assessed in terms of both slope efficiency (SE) and responsivity in a radio-over-fiber network. Different biasing schemes are analyzed, specifically zero bias (passive solution), bias for maximum SE, and bias for maximum responsivity. Finally, two case studies on multiband orthogonal frequency division multiplexing ultra-wide band and Wi-Fi are presented, for which the optimum setup parameters are determined.
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    Experimental Evaluation of Optimum Modulation Formats for Pico-Cellular Access Networks Based on Resonant Tunneling Diodes
    ( 2013) Luís Manuel Pessoa ; Monteiro,MC ; Mário Rui Pereira ; Henrique Salgado ; Romeira,B ; Figueiredo,JML
    Pico-cell based access networks are increasingly seen as a promising solution for the growing mobility and bandwidth user demands. A recently developed resonant tunneling diode oscillator integrated with a photodetector and a laser diode (RTD-PD-LD), is being considered as a viable low cost pico-cell solution for radio-over-fiber based distributed antenna systems. In this paper we experimentally evaluate both the uplink and downlink error vector magnitude performance of the RTD-PD-LD for different phase and frequency modulation formats. We conclude that frequency modulated formats achieve better performance in both uplink and downlink configurations, yet, Gaussian Minimum Shift Keying format also appears to be a practical alternative.
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    FPGAs Based Hardware Applied to Block-Based Motion Estimation for Real-time Video Processing
    ( 2000) Luís Corte Real ; José Carlos Alves ; Jaime Cardoso
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    Guest Editorial: Immersive Media Experiences
    ( 2016) Paula Viana ; Chambel,T ; Bove,VM ; Strover,S ; Thomas,G
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    Immersive media experiences (immersiveme 2013 workshop at ACM multimedia)
    ( 2013) Chambel,T ; Bove,VM ; Strover,S ; Paula Viana ; Thomas,G
    Immersive media has the potential for strong impact on users' emotions and their sense of presence and engagement. The main objective of this workshop is to bring together researchers, students, media producers, service providers and industry players in the area of emergent immersive media. The workshop will provide a platform for a deep discussion on ongoing work, recent achievements and experiences. It is expected not only to consolidate experiences but also to identify aspects where strong collaboration among all the interested players is needed and to point towards future working directions. Copyright © 2013 ACM.
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    Implementation of a new method to digital audio equalization
    ( 1999) Gabriel Falcão Fernandes ; Luís Gustavo Martins ; Miguel Falcão ; Aníbal Ferreira