针对多频线谱激励下的结构振动主动控制中的频率失配问题,以并联结构滤波⁃x最小均方(filtered⁃x least mean square,简称FxLMS)算法为基础,提出一种混合自适应振动主动控制方法。前馈通道通过多个带通滤波器将多频线谱激励振动的参考信...针对多频线谱激励下的结构振动主动控制中的频率失配问题,以并联结构滤波⁃x最小均方(filtered⁃x least mean square,简称FxLMS)算法为基础,提出一种混合自适应振动主动控制方法。前馈通道通过多个带通滤波器将多频线谱激励振动的参考信号解耦成为多个单频线谱信号,多个独立自适应滤波器调节权值抑制单一频带上的振动,提升收敛速度;反馈通道提升了算法对于扰动信号频谱发生时变及宽频噪声扰动的鲁棒性。给出该混合自适应振动主动控制算法的稳定性及收敛性分析过程,得到算法稳定与收敛的正实条件。基于Adams与Simulink联合仿真,以及搭建结构微振动主动控制实验系统,验证了混合自适应振动主动控制算法的有效性。实验结果表明,混合自适应振动主动控制算法能够有效抑制多个目标频谱的结构微振动,并在扰动频率失配以及宽频噪声中表现出较好的鲁棒性。展开更多
Spectrum sharing for efficient reuse of licensed spectrum is an important concept for cognitive radio technologies.In a spectrum-sharing system(SSS),deploying the antennas in a distributed manner can offer a new spati...Spectrum sharing for efficient reuse of licensed spectrum is an important concept for cognitive radio technologies.In a spectrum-sharing system(SSS),deploying the antennas in a distributed manner can offer a new spatial dimension for the efficient reuse of licensed frequency bands.To improve the whole performance of multiple secondary users(SUs),this paper addresses the problem of coordinated multi-SU spectrum sharing in a distributed antenna-based SSS.By adopting the Hungarian method,the primal decomposition method and pricing policy,we propose a coordinated multi-user transmission scheme,so as to maximize the sum-rate of SUs.Simulation results show that the proposed method can significantly enhance the system performance,and the computational complexity is low.展开更多
In this paper,a blind multiband spectrum sensing(BMSS)method requiring no knowledge of noise power,primary signal and wireless channel is proposed based on the K-means clustering(KMC).In this approach,the KMC algorith...In this paper,a blind multiband spectrum sensing(BMSS)method requiring no knowledge of noise power,primary signal and wireless channel is proposed based on the K-means clustering(KMC).In this approach,the KMC algorithm is used to identify the occupied subband set(OSS)and the idle subband set(ISS),and then the location and number information of the occupied channels are obtained according to the elements in the OSS.Compared with the classical BMSS methods based on the information theoretic criteria(ITC),the new method shows more excellent performance especially in the low signal-to-noise ratio(SNR)and the small sampling number scenarios,and more robust detection performance in noise uncertainty or unequal noise variance applications.Meanwhile,the new method performs more stablely than the ITC-based methods when the occupied subband number increases or the primary signals suffer multi-path fading.Simulation result verifies the effectiveness of the proposed method.展开更多
The vibration signals of multi-fault rolling bearings under nonstationary conditions are characterized by intricate modulation features,making it difficult to identify the fault characteristic frequency.To remove the ...The vibration signals of multi-fault rolling bearings under nonstationary conditions are characterized by intricate modulation features,making it difficult to identify the fault characteristic frequency.To remove the time-varying behavior caused by speed fluctuation,the phase function of target component is necessary.However,the frequency components induced by different faults interfere with each other.More importantly,the complex sideband clusters around the characteristic frequency further hinder the spectrum interpretation.As such,we propose a demodulation spectrum analysis method for multi-fault bearing detection via chirplet path pursuit.First,the envelope signal is obtained by applying Hilbert transform to the raw signal.Second,the characteristic frequency is extracted via chirplet path pursuit,and the other underlying components are calculated by the characteristic coefficient.Then,the energy factors of all components are determined according to the time-varying behavior of instantaneous frequency.Next,the final demodulated signal is obtained by iteratively applying generalized demodulation with tunable E-factor and then the band pass filter is designed to separate the demodulated component.Finally,the fault pattern can be identified by matching the prominent peaks in the demodulation spectrum with the theoretical characteristic frequencies.The method is validated by simulated and experimental signals.展开更多
To overcome the problem of channel fading and noise uncertainty,cooperative spectrum sensing(CSS)is developed to enhance the sensing performance in cognitive radio networks(CRNs).Considering that the non-ideal reporti...To overcome the problem of channel fading and noise uncertainty,cooperative spectrum sensing(CSS)is developed to enhance the sensing performance in cognitive radio networks(CRNs).Considering that the non-ideal reporting channels of CSS can cause an adverse impact on the detection performance,the throughput maximization problem for multi-channel CSS cognitive radio under reporting channel errors is investigated.While providing all the primary users with sufficient protection,the average throughput of secondary users(SUs)is maximized by jointly optimizing the sensing duration,detection threshold and SU assignment.To address the non-convex optimization problem,the optimal energy detection threshold is derived first.Then,a sub-optimal greedy algorithm is proposed to obtain the optimal sensing duration and the optimal SU assignment.Analysis and simulation results show that the proposed algorithm can output the same performance as the exhaustive search algorithm at a much lower level of complexity.It is also shown that the impact of imperfect reporting channels should be considered especially in low signal-to-noise ratio environments and the reporting channel errors significantly reduce the performance of CSS.展开更多
Nonlinear distortion introduced by an amplifier when subjected to a multisine excitation decreases the measurement accuracy in many metrological and measurement areas. In this paper, we performed qualitative and quant...Nonlinear distortion introduced by an amplifier when subjected to a multisine excitation decreases the measurement accuracy in many metrological and measurement areas. In this paper, we performed qualitative and quantitative analyses of the nonlinear distortion with the multisine excitations constrained by a constant power spectral density. We present the numerical results with respect to different tone spacings,nonlinear orders, harmonic phases and tone distributions. Moreover, three as-pects of contributions are made to further reveal the distortion mechanism. First, we find that the type Ⅱ components for Schr- oeder-phase multisines distribute uniformly but not all in anti-phase to the type I components for the second order nonlinearity. Second,we simulate the variance of the type I and Ⅱ components and their summation to explain the principle of reducing the type Ⅱ distortion by averaging the results obtained using multiple realizations of random-phase multisines. Third, we observe a special distortion distribution mechanism for the Schroeder-phase multisine excitation The results contribute to a better estima-tion and understanding of the nonlinear distortion.展开更多
This paper addresses the problem of joint optimization of subchannel selection and spectrum sensing time for multiband cognitive radio networks under the sensing capability constrains. In particular, we construct a mu...This paper addresses the problem of joint optimization of subchannel selection and spectrum sensing time for multiband cognitive radio networks under the sensing capability constrains. In particular, we construct a multiband spectrum sensing framework, and derive the probabilities of detection and false alarm taking the different subchannel gain into account. Furthermore, we formulate the multi- band sensing as a two-parameter optimization prob- lem under the sensing capability constrains and guaranteeing the QoS of the secondary user. Moreover, we develop a semi-analytical optimization scheme to achieve the optimal solution.展开更多
The frequency distribution of different ingredients in-ray spectra,e.g.,photo-peak,fluctuations of counts and Compton region,is separately analyzed.After wavelet transform of-ray spectra,the wavelet coefficients of a ...The frequency distribution of different ingredients in-ray spectra,e.g.,photo-peak,fluctuations of counts and Compton region,is separately analyzed.After wavelet transform of-ray spectra,the wavelet coefficients of a photo-peak increase with transforming scales and these coefficients show direct proportion with intensity of peak at determinate scale.A novel algorithm based on wavelet transform is proposed and studied.The results indicate that most of the photo-peaks in multi-spectra can be determined accurately,the-rays energy and intensity of the peak can also be determined.This method has the prospect of being applied in on-line multi-spectra analysis in such fields as radioprotection and nuclear safety monitoring.展开更多
文摘针对多频线谱激励下的结构振动主动控制中的频率失配问题,以并联结构滤波⁃x最小均方(filtered⁃x least mean square,简称FxLMS)算法为基础,提出一种混合自适应振动主动控制方法。前馈通道通过多个带通滤波器将多频线谱激励振动的参考信号解耦成为多个单频线谱信号,多个独立自适应滤波器调节权值抑制单一频带上的振动,提升收敛速度;反馈通道提升了算法对于扰动信号频谱发生时变及宽频噪声扰动的鲁棒性。给出该混合自适应振动主动控制算法的稳定性及收敛性分析过程,得到算法稳定与收敛的正实条件。基于Adams与Simulink联合仿真,以及搭建结构微振动主动控制实验系统,验证了混合自适应振动主动控制算法的有效性。实验结果表明,混合自适应振动主动控制算法能够有效抑制多个目标频谱的结构微振动,并在扰动频率失配以及宽频噪声中表现出较好的鲁棒性。
基金supported in part by the National Science Foundation of China for Young Scholars under grant No.61201186The National Basic Research Program undergrant No.2012AA01A502+5 种基金National Natural Science Foundation of China under grant No.61201192National S&T Major Project under grant No.2014ZX03003003-002Tsinghua-HUAWEI Joint R&D on Soft Defined Protocol StackTsinghua-HUAWEI Joint Research on 5G Air Interface TechnicalTsinghua-Qualcom joint research programIndependent innovation on Future Virtualization Platform under grant No.015Z02-3
文摘Spectrum sharing for efficient reuse of licensed spectrum is an important concept for cognitive radio technologies.In a spectrum-sharing system(SSS),deploying the antennas in a distributed manner can offer a new spatial dimension for the efficient reuse of licensed frequency bands.To improve the whole performance of multiple secondary users(SUs),this paper addresses the problem of coordinated multi-SU spectrum sharing in a distributed antenna-based SSS.By adopting the Hungarian method,the primal decomposition method and pricing policy,we propose a coordinated multi-user transmission scheme,so as to maximize the sum-rate of SUs.Simulation results show that the proposed method can significantly enhance the system performance,and the computational complexity is low.
基金Projects(61362018,61861019)supported by the National Natural Science Foundation of ChinaProject(1402041B)supported by the Jiangsu Province Postdoctoral Scientific Research Project,China+1 种基金Project(16A174)supported by the Scientific Research Fund of Hunan Provincial Education Department,ChinaProject([2016]283)supported by the Research Study and Innovative Experiment Project of College Students,China
文摘In this paper,a blind multiband spectrum sensing(BMSS)method requiring no knowledge of noise power,primary signal and wireless channel is proposed based on the K-means clustering(KMC).In this approach,the KMC algorithm is used to identify the occupied subband set(OSS)and the idle subband set(ISS),and then the location and number information of the occupied channels are obtained according to the elements in the OSS.Compared with the classical BMSS methods based on the information theoretic criteria(ITC),the new method shows more excellent performance especially in the low signal-to-noise ratio(SNR)and the small sampling number scenarios,and more robust detection performance in noise uncertainty or unequal noise variance applications.Meanwhile,the new method performs more stablely than the ITC-based methods when the occupied subband number increases or the primary signals suffer multi-path fading.Simulation result verifies the effectiveness of the proposed method.
基金Project(2018YJS137)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(51275030)supported by the National Natural Science Foundation of China
文摘The vibration signals of multi-fault rolling bearings under nonstationary conditions are characterized by intricate modulation features,making it difficult to identify the fault characteristic frequency.To remove the time-varying behavior caused by speed fluctuation,the phase function of target component is necessary.However,the frequency components induced by different faults interfere with each other.More importantly,the complex sideband clusters around the characteristic frequency further hinder the spectrum interpretation.As such,we propose a demodulation spectrum analysis method for multi-fault bearing detection via chirplet path pursuit.First,the envelope signal is obtained by applying Hilbert transform to the raw signal.Second,the characteristic frequency is extracted via chirplet path pursuit,and the other underlying components are calculated by the characteristic coefficient.Then,the energy factors of all components are determined according to the time-varying behavior of instantaneous frequency.Next,the final demodulated signal is obtained by iteratively applying generalized demodulation with tunable E-factor and then the band pass filter is designed to separate the demodulated component.Finally,the fault pattern can be identified by matching the prominent peaks in the demodulation spectrum with the theoretical characteristic frequencies.The method is validated by simulated and experimental signals.
基金The National Natural Science Foundation of China(No.61771126)the Key Research and Development Plan of Jiangsu Province(No.BE2018108)。
文摘To overcome the problem of channel fading and noise uncertainty,cooperative spectrum sensing(CSS)is developed to enhance the sensing performance in cognitive radio networks(CRNs).Considering that the non-ideal reporting channels of CSS can cause an adverse impact on the detection performance,the throughput maximization problem for multi-channel CSS cognitive radio under reporting channel errors is investigated.While providing all the primary users with sufficient protection,the average throughput of secondary users(SUs)is maximized by jointly optimizing the sensing duration,detection threshold and SU assignment.To address the non-convex optimization problem,the optimal energy detection threshold is derived first.Then,a sub-optimal greedy algorithm is proposed to obtain the optimal sensing duration and the optimal SU assignment.Analysis and simulation results show that the proposed algorithm can output the same performance as the exhaustive search algorithm at a much lower level of complexity.It is also shown that the impact of imperfect reporting channels should be considered especially in low signal-to-noise ratio environments and the reporting channel errors significantly reduce the performance of CSS.
基金National Natural Science Foundation of China(No.61372041,No.61001034)
文摘Nonlinear distortion introduced by an amplifier when subjected to a multisine excitation decreases the measurement accuracy in many metrological and measurement areas. In this paper, we performed qualitative and quantitative analyses of the nonlinear distortion with the multisine excitations constrained by a constant power spectral density. We present the numerical results with respect to different tone spacings,nonlinear orders, harmonic phases and tone distributions. Moreover, three as-pects of contributions are made to further reveal the distortion mechanism. First, we find that the type Ⅱ components for Schr- oeder-phase multisines distribute uniformly but not all in anti-phase to the type I components for the second order nonlinearity. Second,we simulate the variance of the type I and Ⅱ components and their summation to explain the principle of reducing the type Ⅱ distortion by averaging the results obtained using multiple realizations of random-phase multisines. Third, we observe a special distortion distribution mechanism for the Schroeder-phase multisine excitation The results contribute to a better estima-tion and understanding of the nonlinear distortion.
文摘This paper addresses the problem of joint optimization of subchannel selection and spectrum sensing time for multiband cognitive radio networks under the sensing capability constrains. In particular, we construct a multiband spectrum sensing framework, and derive the probabilities of detection and false alarm taking the different subchannel gain into account. Furthermore, we formulate the multi- band sensing as a two-parameter optimization prob- lem under the sensing capability constrains and guaranteeing the QoS of the secondary user. Moreover, we develop a semi-analytical optimization scheme to achieve the optimal solution.
基金supported by the Fundamental Research Funds for the Central Universities (Grant No.13QN50)the National Natural Science Foundation of China (Grant No.11275271)
文摘The frequency distribution of different ingredients in-ray spectra,e.g.,photo-peak,fluctuations of counts and Compton region,is separately analyzed.After wavelet transform of-ray spectra,the wavelet coefficients of a photo-peak increase with transforming scales and these coefficients show direct proportion with intensity of peak at determinate scale.A novel algorithm based on wavelet transform is proposed and studied.The results indicate that most of the photo-peaks in multi-spectra can be determined accurately,the-rays energy and intensity of the peak can also be determined.This method has the prospect of being applied in on-line multi-spectra analysis in such fields as radioprotection and nuclear safety monitoring.