Showing papers on "Energy (signal processing) published in 2008"

Transporting information and energy simultaneously

Abstract: The fundamental tradeoff between the rates at which energy and reliable information can be transmitted over a single noisy line is studied. Engineering inspiration for this problem is provided by powerline communication, RFID systems, and covert packet timing systems as well as communication systems that scavenge received energy. A capacity-energy function is defined and a coding theorem is given. The capacity-energy function is a non-increasing concave cap function. Capacity-energy functions for several channels are computed.

Single-cycle nonlinear optics.

Abstract: Nonlinear optics plays a central role in the advancement of optical science and laser-based technologies. We report on the confinement of the nonlinear interaction of light with matter to a single wave cycle and demonstrate its utility for time-resolved and strong-field science. The electric field of 3.3-femtosecond, 0.72-micron laser pulses with a controlled and measured waveform ionizes atoms near the crests of the central wave cycle, with ionization being virtually switched off outside this interval. Isolated sub-100-attosecond pulses of extreme ultraviolet light (photon energy {approx} 80 electron volts), containing {approx} 0.5 nanojoule of energy, emerge from the interaction with a conversion efficiency of {approx} 10{sup -6}. These tools enable the study of the precision control of electron motion with light fields and electron-electron interactions with a resolution approaching the atomic unit of time ({approx} 24 attoseconds).

Statistically optimal analysis of samples from multiple equilibrium states

Abstract: We present a new estimator for computing free energy differences and thermodynamic expectations as well as their uncertainties from samples obtained from multiple equilibrium states via either simulation or experiment. The estimator, which we call the multistate Bennett acceptance ratio estimator (MBAR) because it reduces to the Bennett acceptance ratio estimator (BAR) when only two states are considered, has significant advantages over multiple histogram reweighting methods for combining data from multiple states. It does not require the sampled energy range to be discretized to produce histograms, eliminating bias due to energy binning and significantly reducing the time complexity of computing a solution to the estimating equations in many cases. Additionally, an estimate of the statistical uncertainty is provided for all estimated quantities. In the large sample limit, MBAR is unbiased and has the lowest variance of any known estimator for making use of equilibrium data collected from multiple states. We illustrate this method by producing a highly precise estimate of the potential of mean force for a DNA hairpin system, combining data from multiple optical tweezer measurements under constant force bias.

Eigenvalue based Spectrum Sensing Algorithms for Cognitive Radio

Abstract: Spectrum sensing is a fundamental component is a cognitive radio. In this paper, we propose new sensing methods based on the eigenvalues of the covariance matrix of signals received at the secondary users. In particular, two sensing algorithms are suggested, one is based on the ratio of the maximum eigenvalue to minimum eigenvalue; the other is based on the ratio of the average eigenvalue to minimum eigenvalue. Using some latest random matrix theories (RMT), we quantify the distributions of these ratios and derive the probabilities of false alarm and probabilities of detection for the proposed algorithms. We also find the thresholds of the methods for a given probability of false alarm. The proposed methods overcome the noise uncertainty problem, and can even perform better than the ideal energy detection when the signals to be detected are highly correlated. The methods can be used for various signal detection applications without requiring the knowledge of signal, channel and noise power. Simulations based on randomly generated signals, wireless microphone signals and captured ATSC DTV signals are presented to verify the effectiveness of the proposed methods.

First observation of the Greisen-Zatsepin-Kuzmin suppression.

Abstract: The High Resolution Fly's Eye (HiRes) experiment has observed the Greisen-Zatsepin-Kuzmin suppression (called the GZK cutoff) with a statistical significance of five standard deviations. HiRes' measurement of the flux of ultrahigh energy cosmic rays shows a sharp suppression at an energy of $6\ifmmode\times\else\texttimes\fi{}{10}^{19}\text{ }\text{ }\mathrm{eV}$, consistent with the expected cutoff energy. We observe the ankle of the cosmic-ray energy spectrum as well, at an energy of $4\ifmmode\times\else\texttimes\fi{}{10}^{18}\text{ }\text{ }\mathrm{eV}$. We describe the experiment, data collection, and analysis and estimate the systematic uncertainties. The results are presented and the calculation of the statistical significance of our observation is described.

Fractional charge perspective on the band gap in density-functional theory

Abstract: The calculation of the band gap by density-functional theory (DFT) is examined by considering the behavior of the energy as a function of number of electrons. It is explained that the incorrect band-gap prediction with most approximate functionals originates mainly from errors in describing systems with fractional charges. Formulas for the energy derivatives with respect to number of electrons are derived, which clarify the role of optimized effective potentials in prediction of the band gap. Calculations with a recent functional that has much improved behavior for fractional charges give a good prediction of the energy gap and also ${\ensuremath{\epsilon}}_{\mathrm{HOMO}}\ensuremath{\simeq}\ensuremath{-}I$ for finite systems. Our results indicate that it is possible, within DFT, to have a functional whose eigenvalues or derivatives accurately predict the band gap.

Cohesive energy curves for noble gas solids calculated by adiabatic connection fluctuation-dissipation theory

Abstract: We present first-principles calculations for the fcc noble gas solids Ne, Ar, and Kr applying the adiabatic connection fluctuation-dissipation theorem (ACFDT) to evaluate the correlation energy. The ACFDT allows us to describe long-range correlation effects including London dispersion or van der Waals interaction on top of conventional density functional theory calculations. Even within the random phase approximation, the typical $1∕{V}^{2}$ volume dependence for the cohesive energy of the noble gas solids is reproduced, and equilibrium cohesive energies and lattice constants are improved compared to density functional theory calculations. Furthermore, we present atomization energies for ${\mathrm{H}}_{2}$, ${\mathrm{N}}_{2}$, and ${\mathrm{O}}_{2}$ within the same post-density-functional-theory framework, finding an excellent agreement with previously published data.

Synchrotron Self-Compton Analysis of TeV X-ray Selected BL Lacertae Objects

Abstract: We introduce a methodology for analysis of multiwavelength data from X-ray selected BL Lac (XBL) objects detected in the TeV regime. By assuming that the radio--through--X-ray flux from XBLs is nonthermal synchrotron radiation emitted by isotropically-distributed electrons in the randomly oriented magnetic field of a relativistic blazar jet, we obtain the electron spectrum. This spectrum is then used to deduce the synchrotron self-Compton (SSC) spectrum as a function of the Doppler factor, magnetic field, and variability timescale. The variability timescale is used to infer the comoving blob radius from light travel-time arguments, leaving only two parameters. With this approach, we accurately simulate the synchrotron and SSC spectrum of flaring XBLs in the Thomson through Klein-Nishina regimes. Photoabsorption by interactions with internal jet radiation and the intergalactic background light (IBL) is included. Doppler factors, magnetic fields, and absolute jet powers are obtained by fitting the {\em HESS} and {\em Swift} data of the recent giant TeV flare observed from \object{PKS 2155--304}. For the contemporaneous {\em Swift} and {\em HESS} data from 28 and 30 July 2006, respectively, Doppler factors $\gtrsim 60$ and absolute jet powers $\gtrsim 10^{46}$ ergs s$^{-1}$ are required for a synchrotron/SSC model to give a good fit to the data, for a low intensity of the IBL and a ratio of 10 times more energy in hadrons than nonthermal electrons. Fits are also made to a TeV flare observed in 2001 from Mkn 421 which require Doppler factors $\gtrsim 30$ and jet powers $\gtrsim 10^{45}$ erg s$^{-1}$.

Maximum Eigenvalue Detection: Theory and Application

Abstract: Channel sensing, i.e., detecting the presence of primary users, is a fundamental problem in cognitive radio. Energy detection is optimal for detecting independent and identically distributed (iid) signals, but not optimal for detecting correlated signals. In this paper, a method is proposed based on the sample covariance matrix calculated from a limited number of received signal samples. The maximum eigenvalue of the sample covariance matrix is used as the test statistic. Since the covariance matrix catches the correlations among the signal samples, the proposed method is better than the energy detection for correlated signals. For iid signals, the method approaches to the energy detection. The random matrix theory is used to analyze the method and set the threshold. Similar to energy detection, the methods do not need any information of the source signal and the channel as a priori. Also, no synchronization is needed. Simulations based on wireless microphone signals and iid signals are presented to verify the method.

Optimizing energy transmission in a leadless tissue stimulation system

Abstract: Method and systems for optimizing acoustic energy transmission in implantable devices are disclosed. Transducer elements transmit acoustic locator signals towards a receiver assembly, and the receiver responds with a location signal. The location signal can reveal information related to the location of the receiver and the efficiency of the transmitted acoustic beam received by the receiver. This information enables the transmitter to target the receiver and optimize the acoustic energy transfer between the transmitter and the receiver. The energy can be used for therapeutic purposes, for example, stimulating tissue or for diagnostic purposes.

Axion Cosmology and the Energy Scale of Inflation

Abstract: We survey observational constraints on the parameter space of inflation and axions and map out two allowed windows: the classic window and the inflationary anthropic window. The cosmology of the latter is particularly interesting; inflationary axion cosmology predicts the existence of isocurvature fluctuations in the cosmic microwave background, with an amplitude that grows with both the energy scale of inflation and the fraction of dark matter in axions. Statistical arguments favor a substantial value for the latter, and so current bounds on isocurvature fluctuations imply tight constraints on inflation. For example, an axion Peccei-Quinn scale of ${10}^{16}\text{ }\text{ }\mathrm{GeV}$ excludes any inflation model with energy scale $g3.8\ifmmode\times\else\texttimes\fi{}{10}^{14}\text{ }\text{ }\mathrm{GeV}$ ($rg2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$) at 95% confidence, and so implies negligible gravitational waves from inflation, but suggests appreciable isocurvature fluctuations.

MPPT techniques for PV Systems: Energetic and cost comparison

Abstract: In the future solar energy will be very important energy source. More than 45% of necessary energy in the world will be generated by photovoltaic array. Therefore it is necessary to concentrate our forces in order to reduce the application costs and to increment their performances. In order to reach this last aspect, it is important to note that the output characteristic of a photovoltaic array is nonlinear and changes with solar irradiation and the cellpsilas temperature. Therefore a maximum power point tracking (MPPT) technique is needed to draw peak power from the solar array in order to maximize the produced energy. This paper presents a comparative study of ten widely-adopted MPPT algorithms; their performance is evaluated using the simulation tool Simulinkreg. In particular, this study compares the behaviors of each technique in presence of solar irradiation variations.

In-band spectrum sensing in cognitive radio networks: energy detection or feature detection?

Abstract: In a cognitive radio network (CRN), in-band spectrum sensing is essential for the protection of legacy spectrum users, with which the presence of primary users (PUs) can be detected promptly, allowing secondary users (SUs) to vacate the channels immediately. For in-band sensing, it is important to meet the detectability requirements, such as the maximum allowed latency of detection (e.g., 2 seconds in IEEE 802.22) and the probability of mis-detection and false-alarm. In this paper, we propose an effcient periodic in-band sensing algorithm that optimizes sensing-frequency and sensing-time by minimizing sensing overhead while meeting the detectability requirements. The proposed scheme determines the better of energy or feature detection that incurs less sensing overhead at each SNR level, and derives the threshold aRSSthreshold on the average received signal strength (RSS) of a primary signal below which feature detection is preferred. We showed that energy detection under lognormal shadowing could still perform well at the average SNR

Determination of Battery Storage Capacity in Energy Buffer for Wind Farm

Abstract: Design of a battery energy storage system (BESS) in a buffer scheme is examined for the purpose of attenuating the effects of unsteady input power from wind farms. The design problem is formulated as maximization of an objective function that measures the economic benefit obtainable from the dispatched power from the wind farm against the cost of the BESS. Solution to the problem results in the determination of the capacity of the BESS to ensure constant dispatched power to the connected grid, while the voltage level across the dc-link of the buffer is kept within preset limits. A computational procedure to determine the BESS capacity and the evaluation of the dc voltage is shown. Illustrative examples using the proposed design method are included.

Blindly Combined Energy Detection for Spectrum Sensing in Cognitive Radio

Abstract: In this letter, a method is proposed to optimally combine the received signal samples in space and time based on the principle of maximizing the signal-to-noise ratio (SNR). After the combining, energy detection (ED) is used. However, optimal combining needs information of the source signal and channel, which is usually unknown. To overcome this difficulty, a method is proposed to blindly combine the signal samples. Similar to energy detection, blindly combined energy detection (BCED) does not need any information of the source signal and the channel a priori. BCED can be much better than ED for highly correlated signals, and most importantly, it does not need noise power estimation and overcomes ED's susceptibility to noise uncertainty. Also, perfect synchronization is not required. Simulations based on wireless microphone signals and randomly generated signals are presented to verify the methods.

Generation of Stable, Low-Divergence Electron Beams by Laser-Wakefield Acceleration in a Steady-State-Flow Gas Cell

Abstract: Laser-driven, quasimonoenergetic electron beams of up to $\ensuremath{\sim}200\text{ }\text{ }\mathrm{MeV}$ in energy have been observed from steady-state-flow gas cells. These beams emitted within a low-divergence cone of $2.1\ifmmode\pm\else\textpm\fi{}0.5\text{ }\text{ }\mathrm{mrad}$ FWHM display unprecedented shot-to-shot stability in energy (2.5% rms), pointing (1.4 mrad rms), and charge (16% rms) owing to a highly reproducible gas-density profile within the interaction volume. Laser-wakefield acceleration in gas cells of this type provides a simple and reliable source of relativistic electrons suitable for applications such as the production of extreme-ultraviolet undulator radiation.

Rayleigh-wave dispersive energy imaging using a high-resolution linear radon transform

Abstract: Multichannel Analysis of Surface Waves (MASW) analysis is an efficient tool to obtain the vertical shear-wave profile. One of the key steps in the MASW method is to generate an image of dispersive energy in the frequency-velocity domain, so dispersion curves can be determined by picking peaks of dispersion energy. In this paper, we propose to image Rayleigh-wave dispersive energy by high-resolution linear Radon transform (LRT). The shot gather is first transformed along the time direction to the frequency domain and then the Rayleigh-wave dispersive energy can be imaged by high-resolution LRT using a weighted preconditioned conjugate gradient algorithm. Synthetic data with a set of linear events are presented to show the process of generating dispersive energy. Results of synthetic and real-world examples demonstrate that, compared with the slant stacking algorithm, high-resolution LRT can improve the resolution of images of dispersion energy by more than 50%.

Structural, thermodynamic, and electronic properties of plutonium oxides from first principles

Abstract: We report ab initio calculations of the structural, electronic, optical, and thermodynamic properties of plutonium oxides (${\text{PuO}}_{2}$ and $\ensuremath{\beta}{\text{-Pu}}_{2}{\text{O}}_{3}$). In order to describe the basic features of the electronic structure, a method suited to take into account strong local correlations has to be used. We apply the local density approximation/generalized gradient approximation ($\text{LDA}/\text{GGA})+U$ approximations to these compounds and compare them with the calculations of Sun et al. [J. Chem. Phys. 128, 084705 (2008)]. Whereas a good agreement is obtained for ${\text{PuO}}_{2}$, our LDA and $\text{LDA}+U$ results differ strongly from this study in the case of ${\text{Pu}}_{2}{\text{O}}_{3}$. In particular, the effect of the Hubbard parameter $U$ on the volume is qualitatively and quantitatively different. Moreover, thermodynamic quantities differ. We thus focus our study on ${\text{Pu}}_{2}{\text{O}}_{3}$ and emphasize the importance of a careful and systematic search of the ground state in $\text{LDA}+U$: In particular, different hints for the occupation matrices corresponding to the electronic configurations allowed by symmetry have to be tried. This procedure is absolutely necessary to find the absolute minimum of the energy. Reliable and accurate quantitative results are given for ${\text{Pu}}_{2}{\text{O}}_{3}$. We thus recover a more physical behavior coherent with calculations on other systems, such as cerium oxides.

Comparison of envelope extraction algorithms for cardiac sound signal segmentation

Abstract: This paper describes a comparative study of the envelope extraction algorithms for the cardiac sound signal segmentation. In order to extract the envelope curves based on the time elapses of the first and the second heart sounds of cardiac sound signals, three representative algorithms such as the normalized average Shannon energy, the envelope information of Hilbert transform, and the cardiac sound characteristic waveform (CSCW) are introduced. Performance comparison of the envelope extraction algorithms, and the advantages and disadvantages of the methods are examined by some parameters.

Optimal thermoelectric figure of merit of a molecular junction

Abstract: We show that a molecular junction can give large values of the thermoelectric figure of merit $ZT$, and so it could be used as a solid-state energy-conversion device that operates close to the Carnot efficiency. The mechanism is similar to the Mahan-Sofo model for bulk thermoelectrics\char22{}the Lorenz number goes to zero violating the Wiedemann-Franz law while the thermopower remains nonzero. The molecular state through which charge is transported must be weakly coupled to the leads, and the energy level of the state must be of order ${k}_{B}T$ away from the Fermi energy of the leads. In practice, the figure of merit is limited by the phonon thermal conductance; we show that the largest possible $ZT\ensuremath{\sim}{({\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{G}}_{\text{th}}^{\text{ph}})}^{\ensuremath{-}1/2}$, where ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{G}}_{\text{th}}^{\text{ph}}$ is the phonon thermal conductance divided by the thermal conductance quantum.

At-Surface Reflectance and Albedo from Satellite for Operational Calculation of Land Surface Energy Balance

Abstract: This paper presents a rapid, operational method for estimating at-surface albedo applicable to Landsat and MODIS satellite sensors for typical cloud-free, low-haze conditions and sensor view angles less than 20°. At-surface albedo estimates are required input to various surface energy balance models that are applied operationally. The albedo calculation method was developed using the SMARTS2 radiative transfer model and has been applied in recent versions of the University of Idaho METRIC model as a component of the surface energy balance for determining evapotranspiration. The albedo procedure uses atmospheric correction functions developed to require only general humidity data and a digital elevation model. The atmospheric correction functions have a reduced structure to enhance their operational applicability in routine instantaneous surface energy balances and to estimate evapotranspiration. The method does not require high levels of knowledge in atmospheric physics and radiation transfer processes, c...

Phase-field crystal study of grain-boundary premelting

Abstract: We study the phenomenon of grain-boundary premelting for temperatures below the melting point in the phase-field crystal model of a pure material with hexagonal ordering in two dimensions. We investigate the structures of symmetric tilt boundaries as a function of misorientation $\ensuremath{\theta}$ for two different inclinations and compute in the grand canonical ensemble the ``disjoining potential'' $V(w)$ that describes the fundamental interaction between crystal-melt interfaces as a function of the premelted layer width $w$, which is defined here in terms of the excess mass of the grain boundary via a Gibbs construction. The results reveal qualitatively different behaviors for high-angle grain boundaries that are uniformly wetted, with $w$ diverging logarithmically as the melting point is approached from below, and low-angle boundaries that are punctuated by liquid pools surrounding dislocations, separated by solid bridges. The latter persist over a superheated range of temperature. This qualitative difference between high- and low-angle boundaries is reflected in the $w$ dependence of the disjoining potential that is purely repulsive [${V}^{\ensuremath{'}}(w)l0$ for all $w$] for misorientations larger than a critical angle ${\ensuremath{\theta}}_{c}$, but switches from repulsive at small $w$ to attractive at large $w$ for $\ensuremath{\theta}l{\ensuremath{\theta}}_{c}$. In the latter case, $V(w)$ has a minimum that corresponds to a premelted boundary of finite width at the melting point. Furthermore, we find that the standard wetting condition ${\ensuremath{\gamma}}_{\text{gb}}({\ensuremath{\theta}}_{c})=2{\ensuremath{\gamma}}_{\text{sl}}$ gives a much too low estimate of ${\ensuremath{\theta}}_{c}$ when a low-temperature value of the grain-boundary energy ${\ensuremath{\gamma}}_{\text{gb}}$ is used. In contrast, a reasonable lower-bound estimate can be obtained if ${\ensuremath{\gamma}}_{\text{gb}}$ is extrapolated to the melting point, taking into account both the elastic softening of the material at high homologous temperature and local melting around dislocations.

Giant dipole resonance as a quantitative constraint on the symmetry energy

Abstract: The possible constraints on the poorly determined symmetry part of the effective nuclear Hamiltonians or effective energy functionals, i.e., the so-called symmetry energy $S(\ensuremath{\rho})$, are very much under debate. In the present work, we show that the value of the symmetry energy associated with Skyrme functionals, at densities \ensuremath{\rho} around 0.1 fm${}^{\ensuremath{-}3}$, is strongly correlated with the value of the centroid of the Giant Dipole Resonance (GDR) in spherical nuclei. Consequently, the experimental value of the GDR in, e.g., $^{208}\mathrm{Pb}$ can be used as a constraint on the symmetry energy, leading to $23.3 \mathrm{MeV}lS(\ensuremath{\rho}=0.1 {\mathrm{fm}}^{\ensuremath{-}3})l24.9$ MeV.

GLRT-Based Spectrum Sensing for Cognitive Radio

Abstract: In this paper, we propose several spectrum sensing methods designed using the generalized likelihood ratio test (GLRT) paradigm, for application in a cognitive radio network. The proposed techniques utilize the eigenvalues of the sample covariance matrix of the received signal vector, taking advantage of the fact that in practice, the primary signal in a cognitive radio environment will either occupy a subspace of dimension strictly smaller than the dimension of the observation space, or have a spectrum that is non-white. We show that by making various assumptions on the availability of side information such as noise variance and signal space dimension, several feasible algorithms result which all outperform the standard energy detector.

Δ self-consistent field method to obtain potential energy surfaces of excited molecules on surfaces

Abstract: We present a modification of the $\ensuremath{\Delta}$ self-consistent field ($\ensuremath{\Delta}\text{SCF}$) method of calculating energies of excited states in order to make it applicable to resonance calculations of molecules adsorbed on metal surfaces, where the molecular orbitals are highly hybridized. The $\ensuremath{\Delta}\text{SCF}$ approximation is a density-functional method closely resembling standard density-functional theory (DFT), the only difference being that in $\ensuremath{\Delta}\text{SCF}$ one or more electrons are placed in higher lying Kohn-Sham orbitals instead of placing all electrons in the lowest possible orbitals as one does when calculating the ground-state energy within standard DFT. We extend the $\ensuremath{\Delta}\text{SCF}$ method by allowing excited electrons to occupy orbitals which are linear combinations of Kohn-Sham orbitals. With this extra freedom it is possible to place charge locally on adsorbed molecules in the calculations, such that resonance energies can be estimated, which is not possible in traditional $\ensuremath{\Delta}\text{SCF}$ because of very delocalized Kohn-Sham orbitals. The method is applied to ${\text{N}}_{2}$, CO, and NO adsorbed on different metallic surfaces and compared to ordinary $\ensuremath{\Delta}\text{SCF}$ without our modification, spatially constrained DFT, and inverse-photoemission spectroscopy measurements. This comparison shows that the modified $\ensuremath{\Delta}\text{SCF}$ method gives results in close agreement with experiment, significantly closer than the comparable methods. For ${\text{N}}_{2}$ adsorbed on ruthenium (0001) we map out a two-dimensional part of the potential energy surfaces in the ground state and the $2\ensuremath{\pi}$ resonance. From this we conclude that an electron hitting the resonance can induce molecular motion, optimally with 1.5 eV transferred to atomic movement. Finally we present some performance test of the $\ensuremath{\Delta}\text{SCF}$ approach on gas-phase ${\text{N}}_{2}$ and CO in order to compare the results to higher accuracy methods. Here we find that excitation energies are approximated with accuracy close to that of time-dependent density-functional theory. Especially we see very good agreement in the minimum shift of the potential energy surfaces in the excited state compared to the ground state.

Resummation and NLO matching of event shapes with effective field theory

Abstract: The resummed differential thrust rate in ${e}^{+}{e}^{\ensuremath{-}}$ annihilation is calculated using soft-collinear effective theory (SCET). The resulting distribution in the two-jet region ($T\ensuremath{\sim}1)$ is found to agree with the corresponding expression derived by the standard approach. A matching procedure to account for finite corrections at $Tl1$ is then described. There are two important advantages of the SCET approach. First, SCET manifests a dynamical seesaw scale $q={p}^{2}/Q$ in addition to the center-of-mass energy $Q$ and the jet mass scale $p\ensuremath{\sim}Q\sqrt{(1\ensuremath{-}T)}$. Thus, the resummation of logs of $p/q$ can be cleanly distinguished from the resummation of logs of $Q/p$. Second, finite parts of loop amplitudes appear in specific places in the perturbative distribution: in the matching to the hard function, at the scale $Q$, in matching to the jet function, at the scale $p$, and in matching to the soft function, at the scale $q$. This allows for a consistent merger of fixed order corrections and resummation. In particular, the total NLO ${e}^{+}{e}^{\ensuremath{-}}$ cross section is reproduced from these finite parts without having to perform additional infrared regulation.

Energy Detection Using Estimated Noise Variance for Spectrum Sensing in Cognitive Radio Networks

Abstract: In this paper, we analyze the performance of spectrum sensing based on energy detection. We do not assume the exact noise variance is known a priori. Instead, an estimated noise variance is used to calculate the threshold used in the spectrum sensing based on energy detection. We propose a new analytical model to evaluate the statistical performance of the energy detection. We claim some characteristics of this model, and analyze how these characteristics affect the performance of spectrum sensing. The analytical results are verified through numerical examples and simulations. Through these examples, we demonstrate the effectiveness of our analytical model: we show how it can be used to set the appropriate threshold such that more spectrum sharing can be facilitated, especially when combined with cooperative spectrum sensing method.