The Experts below are selected from a list of 179628 Experts worldwide ranked by ideXlab platform
O Gonzalezmartin - One of the best experts on this subject based on the ideXlab platform.
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x ray variability of 104 active galactic nuclei xmm newton power Spectrum Density profiles
Astronomy and Astrophysics, 2012Co-Authors: O Gonzalezmartin, S VaughanAbstract:archiveprefix: arXiv primaryclass: astro-ph.HE keywords: accretion, accretion disks, Galaxy: nucleus, galaxies: active, X-rays: galaxies eid: A80 adsurl: http://adsabs.harvard.edu/abs/2012A%26A...544A..80G adsnote: Provided by the SAO/NASA Astrophysics Data System
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x ray variability of 104 active galactic nuclei xmm newton power Spectrum Density profiles
arXiv: High Energy Astrophysical Phenomena, 2012Co-Authors: O Gonzalezmartin, S VaughanAbstract:AGN, powered by accretion onto SMBHs, are thought to be scaled up versions of Galactic black hole X-ray binaries (BH-XRBs). In the past few years evidence of such correspondence include similarities in the broadband shape of the X-ray variability power spectra, with characteristic bend times-scales scaling with mass. We have performed a uniform analysis of the power Spectrum densities (PSDs) of 104 nearby (z<0.4) AGN using 209 XMM-Newton/pn observations. The PSDs have been estimated in three energy bands: 0.2-10, 0.2-2, and 2-10 keV. The sample comprises 61 Type-1 AGN, 21 Type-2 AGN, 15 NLSy1, and 7 BLLACS. We have fitted each PSD to two models: (1) a single power-law model and (2) a bending power-law model. Among the entire sample, 72% show significant variability in at least one of the three bands tested. A high percentage of low-luminosity AGN do not show any significant variability. The PSD of the majority of the variable AGN was well described by a simple power-law with a mean index of 2. In 15 sources we found that the bending power law model was preferred with a mean slope of 3 and a mean bend frequency of 2.E-04 Hz. Only KUG1031+398 (REJ1034+396) shows evidence for quasi-periodic oscillations. The `fundamental plane' relating variability timescale, black hole mass, and luminosity is demonstrated using the new X-ray timing results presented here together with a compilation of the previously detected timescales from the literature. Both quantitative (i.e. scaling with BH mass) and qualitative (overall PSD shapes) found in this sample of AGN are in agreement with the expectations for the SMBHs and BH-XRBs being the same phenomenon scaled-up with the size of the BH. The steep PSD slopes above the high frequency bend bear a closer resemblance to those of the `soft/thermal dominated' BH-XRB states than other states.
Lin Maoliu - One of the best experts on this subject based on the ideXlab platform.
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algorithm and simulation of forward link cdma signal spectral regrowth
Vehicular Technology Conference, 2006Co-Authors: Lin Maoliu, Xu QinghuaAbstract:Closed-form expressions for the spectral regrowth of code division multiple access (CDMA) signal passing through a nonlinear amplifier with a digitally modulated carrier are derived using the power series and statistical methods of high-order cumulant. The technique yields an analytical expression for the autocorrelation function of the output signal as a function of the statistics of the input signal transformed by a behavioral model of the amplifier. The third-order nonlinearity is expressed in terms of IP3 to include the memory effects of the circuit in-band and out-of-band reactance. The analysis is based on a time-domain model of the signal and the model is used to derive the power Spectrum Density and other statistical properties of the CDMA signal. Such analytical results are useful in finding optimal operating conditions of the power amplifier.
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analysis and algorithm simulation of forward link cdma signal spectral regrowth
2006Co-Authors: Lin MaoliuAbstract:Closed-form expressions for the spectral regrowth of CDMA signal passing through a nonlinear amplifier with a digitally modulated carrier are derived using the power series and statistical methods of high-order cumulant. The technique yields an analytical expression for the autocorrelation function of the output signal as a function of the statistics of the input signal transformed by a behavioral model of the amplifier. The third-order nonlinearity is expressed in terms of 3 IP to include the memory effects of the circuit in-band and out-of-band reactance. The analysis is based on a time-domain model of the signal and the model is used to derive the power Spectrum Density and other statistical properties of the CDMA signal. Such analytical results are useful in finding optimal operating conditions of the power Amplifier.
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algorithm and simulation of forward link cdma signal spectral regrowth
Acta Electronica Sinica, 2005Co-Authors: Lin MaoliuAbstract:Closed-form expressions for the spectral regrowth of code division multiple access(CDMA) signal passed through a nonlinear amplifier by a digitally modulated carrier are derived using the power series and statistical methods of high order cumulant.The technique yields an analytical expression for the autocorrelation function of the output signal as a function of the statistics of the input signal transformed by a behavioral model of the amplifier.The third-order nonlinearity is expressed in terms of IP3 to include the memory effects of the circuit in-band and out-of-band reactance.The analysis is based on a time-domain model of the signal and the model is used to derive the power Spectrum Density and other statistical properties of the CDMA signal.Such analytical results are useful in finding optimal operating conditions of the power Amplifier.
Xu Qinghua - One of the best experts on this subject based on the ideXlab platform.
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algorithm and simulation of forward link cdma signal spectral regrowth
Vehicular Technology Conference, 2006Co-Authors: Lin Maoliu, Xu QinghuaAbstract:Closed-form expressions for the spectral regrowth of code division multiple access (CDMA) signal passing through a nonlinear amplifier with a digitally modulated carrier are derived using the power series and statistical methods of high-order cumulant. The technique yields an analytical expression for the autocorrelation function of the output signal as a function of the statistics of the input signal transformed by a behavioral model of the amplifier. The third-order nonlinearity is expressed in terms of IP3 to include the memory effects of the circuit in-band and out-of-band reactance. The analysis is based on a time-domain model of the signal and the model is used to derive the power Spectrum Density and other statistical properties of the CDMA signal. Such analytical results are useful in finding optimal operating conditions of the power amplifier.
S Vaughan - One of the best experts on this subject based on the ideXlab platform.
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x ray variability of 104 active galactic nuclei xmm newton power Spectrum Density profiles
Astronomy and Astrophysics, 2012Co-Authors: O Gonzalezmartin, S VaughanAbstract:archiveprefix: arXiv primaryclass: astro-ph.HE keywords: accretion, accretion disks, Galaxy: nucleus, galaxies: active, X-rays: galaxies eid: A80 adsurl: http://adsabs.harvard.edu/abs/2012A%26A...544A..80G adsnote: Provided by the SAO/NASA Astrophysics Data System
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x ray variability of 104 active galactic nuclei xmm newton power Spectrum Density profiles
arXiv: High Energy Astrophysical Phenomena, 2012Co-Authors: O Gonzalezmartin, S VaughanAbstract:AGN, powered by accretion onto SMBHs, are thought to be scaled up versions of Galactic black hole X-ray binaries (BH-XRBs). In the past few years evidence of such correspondence include similarities in the broadband shape of the X-ray variability power spectra, with characteristic bend times-scales scaling with mass. We have performed a uniform analysis of the power Spectrum densities (PSDs) of 104 nearby (z<0.4) AGN using 209 XMM-Newton/pn observations. The PSDs have been estimated in three energy bands: 0.2-10, 0.2-2, and 2-10 keV. The sample comprises 61 Type-1 AGN, 21 Type-2 AGN, 15 NLSy1, and 7 BLLACS. We have fitted each PSD to two models: (1) a single power-law model and (2) a bending power-law model. Among the entire sample, 72% show significant variability in at least one of the three bands tested. A high percentage of low-luminosity AGN do not show any significant variability. The PSD of the majority of the variable AGN was well described by a simple power-law with a mean index of 2. In 15 sources we found that the bending power law model was preferred with a mean slope of 3 and a mean bend frequency of 2.E-04 Hz. Only KUG1031+398 (REJ1034+396) shows evidence for quasi-periodic oscillations. The `fundamental plane' relating variability timescale, black hole mass, and luminosity is demonstrated using the new X-ray timing results presented here together with a compilation of the previously detected timescales from the literature. Both quantitative (i.e. scaling with BH mass) and qualitative (overall PSD shapes) found in this sample of AGN are in agreement with the expectations for the SMBHs and BH-XRBs being the same phenomenon scaled-up with the size of the BH. The steep PSD slopes above the high frequency bend bear a closer resemblance to those of the `soft/thermal dominated' BH-XRB states than other states.
Hiroyuki Kawai - One of the best experts on this subject based on the ideXlab platform.
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complexity reduced mld based on qr decomposition in ofdm mimo multiplexing with frequency domain spreading and code multiplexing
EURASIP Journal on Advances in Signal Processing, 2011Co-Authors: Kouji Nagatomi, Hiroyuki Kawai, Kenichi HiguchiAbstract:This paper presents a new maximum likelihood detection- (MLD-) based signal detection method for orthogonal frequency division multiplexing (OFDM) multiple-input multiple-output (MIMO) multiplexing with frequency domain spreading and code multiplexing. The proposed MLD reduces the computational complexity by utilizing signal orthogonalization based on QR decomposition of the product of the channel and spreading code matrices in the frequency domain. Simulation results show that when the spreading factor and number of code multiplexed symbols are 16, the proposed MLD reduces the average received signal energy per bit-to-noise Spectrum Density ratio (Eb/N0) for the average packet error rate (PER) of 10-2 by approximately 12 dB compared to the conventional minimum mean-squared error- (MMSE-) based filtering for 4-by-4 MIMO multiplexing (16QAM with the rate-3/4 Turbo code is assumed).
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complexity reduced mld based on qr decomposition in ofdm mimo multiplexing with frequency domain spreading and code multiplexing
Wireless Communications and Networking Conference, 2009Co-Authors: Kouji Nagatomi, Kenichi Higuchi, Hiroyuki KawaiAbstract:This paper presents a new maximum likelihood detection (MLD)-based signal detection method for orthogonal frequency division multiplexing (OFDM) multiple input multiple output (MIMO) multiplexing with frequency domain spreading and code multiplexing. The proposed MLD reduces the computational complexity by utilizing signal orthogonalization based on QR decomposition of the product of the channel and spreading code matrices. Simulation results show that when the spreading factor and number of code multiplexing are 16, the proposed MLD reduces the average received signal energy per bit-to-noise Spectrum Density ratio (Eb/N0) for the average packet error rate (PER) of 10-2 by approximately 12 dB compared to the conventional minimum mean squared error (MMSE)-based filtering for 4-by-4 MIMO multiplexing (16QAM with rate-3/4 Turbo code is assumed).
