IPS - ESTS – DEE - Comunicações em congressos
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- Adaptive Allocation of Virtual Radio Resources overHeterogeneous Wireless NetworksPublication . Caeiro, Luísa; Cardoso, Filipe; Correia, LuísVirtual Networks and cloud services are hot topics nowadays, being considered, together with the information centric approach, key elements for the Future Internet. In this paper, an adaptive radio resource allocation mechanism for virtual resources sharing a common heterogeneous wireless infrastructure is presented and evaluated. The Virtual Network Radio Resource Allocation (VRRA) strategy being proposed takes advantage of the set of shared resources available within a cluster of wireless resources from different Radio Access Technologies (RATs), optimising their utilisation in order to maintain the contracted capacity. Simulation results show that the introduction of VRRA allows supporting the minimum bandwidth requirement in a wireless cluster, composed of several physical base stations from different RATs. For the Virtual Network providing high data rates and guaranteed services as presented in this paper, the Virtual Network Operator Satisfaction Level can be improved by 40% with the introduction of VRRA mechanisms.
- Addressing Multiple Virtual Resources in the Same Geographical AreaPublication . Caeiro, Luísa; Cardoso, Filipe; Correia, LuísThis paper addresses the virtualisation of wireless access in order to provide the required capacity (data rate) to a Virtual Base Station (VBS). The approach is based on a Virtual Radio Resource Allocation algorithm, OnDemandVRRA, which manages the allocation of the physical radio resources to VBSs’ end-users, in order to follow the contract and maintaining isolation among VBSs, according to the type of guarantees of the VBSs, the amount of contracted capacity, and VBSs’ utilisation. Taking the variability of the wireless medium into account, the algorithm continuously influences the RRM mechanisms, namely admission control and MAC scheduling, to be aware of the VBSs’ state relative to the service level agreement, in order to compensate for this variability. The algorithm has been tested to evaluate its behaviour, concerning the amount of VBSs created over a given geographical area served by a set of base stations. It can be concluded that changing the quantity of created VBSs as well as the contracted data rate in the cluster, GRT VBSs get their minimum contracted data rate. It is also verified that the best Radio resource Unit (RU) efficiency is achieved when the strategy for the overall capacity provision is to limit the capacity contracted by GRT VNets, overbooking the capacity contracted by BE VNets. In this case, the RU efficiency increases 30% comparing to the situation where the overbooking is done by GRT VBSs.
- Alinhamento Pedagógico Construtivo na Aprendizagem Dinâmica sobre Máquinas ElétricasPublication . Rafael, Silviano
- An Adaptive PID Speed Controller for an 8/6 Switched Reluctance MachinePublication . Rafael, Silviano; Santos, P. J.; Pires, A. J.This paper presents a classical controller with parameters adaptation capability, in an automatic way. This controller is based on a PID where a parameters adaptation algorithm is used and applied to the switched reluctance motor (SRM) speed control. This PID design do not require any kind of adjustment or calibration from the operator. The parameters adaptation algorithm implemented is based on one fuzzy system with a Takagi-Sugeno inference mechanism with some simplifications. These simplifications had the goal to select the parameters adaptation algorithm contributing for a fast controller response. The developed adaptive PID algorithm was modelled and simulated.
- Beamforming Strategies for Energy Efficient Transmission in LTEPublication . Cardoso, Filipe; Correia, Luís; Petersson, Sven; Boldi, MauroThe actual internet traffic growth is challenging the sustainability of mobile networks, therefore, the energy efficiency of the mobile communication infrastructure becomes a topic of particular relevance. Decreasing CO2 emissions and energy demands while expanding the mobile infrastructure to satisfy traffic demands is essential. In this paper the energy efficient use of beamforming techniques and active antennas, in which an advanced antenna is utilized to direct the transmitted signal in a narrow direction, is evaluated. Slow beamforming based on reconfigurable antennas, exploits medium/long term variations of traffic in order to save energy. Fast beamforming, on the contrary, is immediately following the traffic distribution and can even allow saving more energy. From simulations it is observed that, when compared to existing state-of-art bases base stations, in a dense urban environment reconfigurable beamforming allows a maximum gain of about 8%. Adaptive beamforming, allows an additional consumed power reduction of up to 40%. Hence, the overall power consumption reduction that can be achieved by combining these techniques can be as high as 50%.
- Bidirectional Boost/Buck Quadratic Converter for Distributed Generation Systems with Electrochemical Storage SystemsPublication . Foito, Daniel José Medronho; Cordeiro, A.The increasing number of distributed generation systems using renewable and non-conventional energy sources show the trend of future generation systems. Most of these systems require power electronic converters as an interface between the DC voltage buses and electrochemical storage systems. Such storage systems, like batteries or supercapacitors, usually need bidirectional DC-DC converters to allow their charge or discharge according with necessary operation conditions. In this paper, a non-isolated bidirectional Buck-Boost converter with high voltage gain for electrochemical storage devices used in distributed generation systems is presented. To achieve high voltage gain ratios, the proposed topology presents quadratic characteristics in both step-down (Buck) and step-up (Boost) operation modes. In addition to the wide conversion range, it presents continuous input and output current, reduced charging/discharging ripple and simple control circuitry. All these features allow the energy exchange smoothly and continuously resulting in a longer durability of storage devices. The principle of the operation of the proposed converter in both operation modes, as well as their theoretical analysis will be discussed. The performance of this bidirectional power converter is confirmed through simulation and experimental results.
- Bidirectional DC-DC Converter with High Voltage Gain for the Charge/Discharge Control of Storage SystemsPublication . Pires, Vítor Fernão; Foito, Daniel José Medronho; Martins, J. F.This paper presents a study of a bidirectional dc-dc converter with high voltage gain to regulate the charge and discharge of electrochemical storage systems. The converter is characterized by quadratic voltage gain characteristics in both directions. In this context it can be used to regulate a dc interface between the storage system and a dc/ac converter connected to the electrical grid. It will be analysed the converter in ideal and non-ideal conditions. A control system to regulate the output voltages and currents are also proposed. Simulation results are presented in order to validate the control system associated to the converter for the charge/discharge of the storage system.
- Charging electric vehicles from photovoltaic generation with intermediate energy storagePublication . Silva, Carlos; Sousa, Duarte M.; Roque, António
- Comparing the Power Losses of Power Supplies for Fast-Field Cycling Nuclear Magnetic Resonance EquipmentPublication . Lima, Marco; Pereira, Bruno; Sousa, Duarte M.; Roque, António; Margato, ElmanoThe main feature of the Fast-Field Cycling (FFC) Nuclear Magnetic Resonance (NMR) power supplies is to drive a controlled current fulfilling the requirements of this technique. This feature allows fast switching the current of the FFC magnet and performing accurate and repetitive current cycles. When designing this equipment the power losses is not a fundamental parameter of the optimization process but are estimated in order to validate the topology of the final solution giving that the efficiency of the power solution influences the power consumption, and therefore the operational costs, which should be minimized. Under this context, from the power efficiency viewpoint, the power losses of two possible solutions are compared and discussed in this paper. Typical FFC current cycles are used as reference in order to balance the pros and cons of both solutions.
- Comparing two Power Supplies for Fast-Field Cycling Nuclear Magnetic Resonance Relaxometers: Power Losses and PerformancePublication . Lima, Marco; Pereira, Bruno; Sousa, Duarte M.; Roque, António; Margato, Elmano