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Interference alignment is a key technique for communication scenarios with multiple interfering links. In several such scenarios, interference alignment was used to characterize the degrees of freedom of the channel. However, thes...
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Interference alignment is a key technique for communication scenarios with multiple interfering links. In several such scenarios, interference alignment was used to characterize the degrees of freedom of the channel. However, these degree-of-freedom capacity approximations are often too weak to make accurate predictions about the behavior of channel capacity at finite signal-to-noise ratios (${ssr SNR}{rm s}$). The aim of this paper is to significantly strengthen these results by showing that interference alignment can be used to characterize capacity to within a constant gap. We focus on real, time-invariant, frequency-flat X-channels. The only known solutions achieving the degrees of freedom of this channel are either based on real interference alignment or on layer-selection schemes. Neither of these solutions seems sufficient for a constant-gap capacity approximation. In this paper, we propose a new communication scheme and show that it achieves the capacity of the Gaussian X-channel to within a constant gap. To aid in this process, we develop a novel deterministic channel model. This deterministic model depends on the ${textstyle{{1}over{2}}}log ({ssr SNR})$ most-significant bits of the channel coefficients rather than only the single most-significant bit used in conventional deterministic models. The proposed deterministic model admits a wider range of achievable schemes that can be translated to the Gaussian channel. For this deterministic model, we find an approximately optimal communication scheme. We then translate this scheme for the deterministic channel to the original Gaussian X-channel and show that it achieves capacity to within a constant gap. This is the first constant-gap result for a general, fully-connected network requiring interference alignment.
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Currently, wavelength division multiplexing technology is widely used for exploiting the huge bandwidth of optical networks. It allows simultaneous transmission of traffic on many nonoverlapping channels (wavelengths). These chann...
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Currently, wavelength division multiplexing technology is widely used for exploiting the huge bandwidth of optical networks. It allows simultaneous transmission of traffic on many nonoverlapping channels (wavelengths). These channels support traffic demands in the gigabits per second (Gb/s) range; however, since the majority of devices or applications only require a bandwidth of megabits per second (Mb/s), this is a waste of bandwidth. This problem is efficiently solved by multiplexing a number of low-speed traffic demands (Mb/s) onto a high-speed wavelength channel (Gb/s). This is known as the traffic grooming problem. Since traffic grooming is an NP-hard problem, in this paper, we propose two novel multiobjective evolutionary algorithms for solving it. The selected algorithms are multiobjective variants of the standard differential evolution (DEPT) and variable neighborhood search. With the aim of ensuring the performance of our proposals, we have made comparisons with the well-known fast Nondominated Sort Genetic Algorithm (NSGA-II), Strength Pareto Evolutionary Algorithm 2, and other approaches published in the literature. After performing diverse comparisons, we can conclude that our novel approaches obtain promising results, highlighting in particular the performance of the DEPT algorithm.
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Although globally deployed for flicker assessment, the flickermeter presented by International Electrotechnical Commission (IEC) Standard 61000-4-15 has been proved to suffer from some deficiencies regarding voltage rectangular mo...
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Although globally deployed for flicker assessment, the flickermeter presented by International Electrotechnical Commission (IEC) Standard 61000-4-15 has been proved to suffer from some deficiencies regarding voltage rectangular modulation and interharmonics. The latter results in flickermeter inability to accurately measure flicker for non-incandescent lamps, which are ubiquitous nowadays. The flickermeter inaccuracies tend to arise from its demodulator. So far, few solutions have been provided. Furthermore, the existing solutions deal with only the interharmonic case. This paper introduces a method to address IEC flickermeter deficiencies by developing a digital signal processing block that demodulates the voltage in a real-time manner for voltages that include interharmonics or are affected by rectangular modulation. The suggested demodulator implements discrete Fourier transform inside a sliding window. For rectangular modulation, this approach is used to demodulate the voltage. Meanwhile, for the interharmonics problem, this approach provides the interharmonic frequency. Using the measured frequency, least error squares technique is then employed inside another sliding window to find the interharmonics amplitude. On this basis, a modified flickermeter is devised. Performance of the modified flickermeter is evaluated and its effectiveness is verified using the results obtained from an experimental set-up. The contribution of this paper is not limited to IEC flickermeter modification; the proposed method can be employed for any application requiring interharmonic measurement.
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In modern multiuser communication systems, users are allowed to enter or leave the system at any given time. Thus, the number of active users is an unknown and time-varying parameter, and the performance of the system depends on h...
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In modern multiuser communication systems, users are allowed to enter or leave the system at any given time. Thus, the number of active users is an unknown and time-varying parameter, and the performance of the system depends on how accurately this parameter is estimated over time. The so-called problem of user identification, which consists of determining the number and identities of users transmitting in a communication system, is usually solved prior to, and hence independently of, that posed by the detection of the transmitted data. Since both problems are tightly connected, a joint solution is desirable. In this paper, we focus on direct-sequence (DS) code-division multiple-access (CDMA) systems and derive, within a Bayesian framework, different receivers that cope with an unknown and time-varying number of users while performing joint channel estimation and data detection. The main feature of these receivers, compared with other recently proposed schemes for user activity detection, is that they are natural extensions of existing maximum a posteriori (MAP) equalizers for multiple-input–multiple-output communication channels. We assess the validity of the proposed receivers, including their reliability in detecting the number and identities of active users, by way of computer simulations.
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This paper presents a new method able to estimate the health condition of components in a wind turbine based on the on-line information collected about their observable lives. The proposed method uses the information coming in rea...
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This paper presents a new method able to estimate the health condition of components in a wind turbine based on the on-line information collected about their observable lives. The proposed method uses the information coming in real-time to characterize risk indicators for failure modes of the main components of a wind turbine operating under different normal conditions. The estimation of these risk indicators is based on normal behaviour models previously fitted with real data about the typical life of a component carrying out its functions within its own environment. The maintenance plan applied to the components of a wind turbine can be dynamically rescheduled according to the observed values of the risk indicators in a component using the resources that are really needed. Two approaches are presented to determine thresholds for alerting about risky health conditions: a maximum limit that the risk indicator should not overpass according to its life condition, and technical and economical feasibility. These approaches are the main foundations for a new maintenance model able to integrate in a natural way different information coming from the operation and maintenance of a component, and so capable of maximising the lifespan of the asset. Some real examples of the application of these new concepts in components of a wind turbine will be described.
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“Haptic rendering” or “haptic display” can be broadly defined as conveying information about virtual objects or data to a user through the sense of touch. Among all applications of haptic rendering, force-feedback display of c...
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“Haptic rendering” or “haptic display” can be broadly defined as conveying information about virtual objects or data to a user through the sense of touch. Among all applications of haptic rendering, force-feedback display of contact interactions with rigid and deformable virtual models through the sense of touch has matured considerably over the last decade. In this paper, we present a general framework for force-feedback display of rigid and virtual environments, and we outline its major building blocks. We focus on computational aspects, and we classify algorithms and representations successfully used in the three major subproblems of force-feedback display: collision detection, dynamics simulation, and constrained optimization. In addition, force-feedback display is an integral part of a multimodal experience, often involving both visual and auditory display; therefore, we also discuss the choice of algorithms and representations for force feedback as a part of multimodal display.
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The charging flexibility of electric vehicles (EV) when aggregated by a market agent creates an opportunity for selling manual reserve in the electricity market. This paper describes a new optimization algorithm for optimizing man...
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The charging flexibility of electric vehicles (EV) when aggregated by a market agent creates an opportunity for selling manual reserve in the electricity market. This paper describes a new optimization algorithm for optimizing manual reserve bids. Furthermore, two operational management algorithms covering alternative gate closures (i.e., day-ahead and hour-ahead) are also described. These operational algorithms coordinate EV charging for mitigating forecast errors. A case-study with data from the Iberian electricity market and synthetic EV time series is used for evaluating the algorithms.
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This paper presents a novel cross-coupled current conveyor based CMOS transimpedance amplifier (TIA) design to obtain an input capacitive load insensitive and very low noise structure. The proposed structure is presented with an i...
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This paper presents a novel cross-coupled current conveyor based CMOS transimpedance amplifier (TIA) design to obtain an input capacitive load insensitive and very low noise structure. The proposed structure is presented with an implementation in GlobalFoundries' 0.18-$mu{rm m}$ 1.8-V industry compatible CMOS technology. The whole TIA circuit consumes only 31.5 mW of dc power. Measured results show a ${-}{rm 3}~{rm dB}$ bandwidth of about 4 GHz with a 0.25 pF photodiode capacitance. The single-ended transimpedance gain for positive output port is 46 ${rm dB }Omega$. The measured single-ended input-referred noise current spectral density is kept below 18 ${rm pA}/sqrt{rm Hz}$ within the TIA frequency band. The optical sensitivity for a bit-error-rate of $10^{{-}12}$ is ${-}{rm 15}~{rm dBm}$ with 4.25 Gb/s $2^{31}{-}1$ proactive Reed–Solomon bypass data pattern. This cross-coupled structure also facilitates building an input-insensitive differential TIA. The simulation result shows a stable frequency response over a wide range of input capacitance from 0.05 to 0.5 pF.
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As the output current levels of power converters increase, interleaved topologies become widely used. A well-known topology is the interleaved buck converter (IBC), which presents as main characteristic an inherent low ripple outp...
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As the output current levels of power converters increase, interleaved topologies become widely used. A well-known topology is the interleaved buck converter (IBC), which presents as main characteristic an inherent low ripple output current source behavior in addition to high efficiency and small volume. At the same time, it is necessary to drive high-intensity discharge (HID) lamps with nearly constant current/power and low-frequency square-wave shape due to HID lamp voltage source characteristics and their acoustic resonance issue. This way, an IBC can be advantageous for supplying such lamps, particularly in high power levels where efficiency and volume become more critical parameters. The goal of this paper is a proposal of an electronic ballast based on a two-cell IBC for high-power HID lamps, with current control loop, voltage sensing, and constant power. A dc model based on averaged state-space technique is obtained for the ballast, as well as an ac model based on small-signal disturbances. A complete concept with a digitally implemented closed loop has been developed and a prototype has been built, successfully achieving performance targets. This paper describes the most relevant aspects of the complete design and presents results both experimental and from simulation in MATLAB/Simulink software.
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One of the main objectives of research into intrabody communication (IBC) is the characterization of the human body as a transmission medium for electrical signals. However, such characterization is strongly influenced by the cond...
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One of the main objectives of research into intrabody communication (IBC) is the characterization of the human body as a transmission medium for electrical signals. However, such characterization is strongly influenced by the conditions under which the experiments are performed. In addition, the outcomes reported in the literature vary according to the measurement method used, frequently making comparisons among them unfeasible. Further studies are still required in order to establish a methodology for IBC characterization and design. In this paper, both galvanic and capacitive coupling setups have been implemented and a comprehensive set of measurements has been carried out by analyzing fundamental IBC parameters such as optimum frequency range, maximum channel length, and type of electrodes, among others. Consequently, practical conclusions regarding the experimental conditions that optimize IBC performance for each coupling technique have been obtained.
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