The quaternion Fourier transform plays a vital role in the representation of two-dimensional signals. This paper characterizes spectrum of quaternion-valued signals on the quaternion Fourier transform domain by the pa...The quaternion Fourier transform plays a vital role in the representation of two-dimensional signals. This paper characterizes spectrum of quaternion-valued signals on the quaternion Fourier transform domain by the partial derivative.展开更多
The discrete Fourier transform（DFT） is used for fractional Brownian motion（FBM） surface synthesis in tribology（i.e., contact, sliding, and sealing, etc）. However, the relationship between fractal parameters（fra...The discrete Fourier transform（DFT） is used for fractional Brownian motion（FBM） surface synthesis in tribology（i.e., contact, sliding, and sealing, etc）. However, the relationship between fractal parameters（fractal dimension and scale factor） and traditional parameters, the influence of fractal parameters on surface appearance, have not been deeply discussed yet. These lead to some kind of difficulty to ensure the synthesized surfaces with ideal fractal characteristic, required traditional parameters and geometric appearance. A quantitative relationship between fractal parameters and the root mean square deviation of surface （Sq） is derived based on the energy conservation property between the space and frequency domain of DFT. Under the stability assumption, the power spectrum of a FBM surface is composed of concentric circles strictly, a series of FBM surfaces with prescribed Sq could be synthesized with given fractal dimension, scale factor, and sampling numbers, but the ten-point height（Sz）, the skewness（Ssk） and the kurtosis（Sku） are still in random, where the probability distributions of Sz and Ssk are approximately normal distribution. Furthermore, by iterative searching, a surface with desired Abbott-Firestone curve could be obtained among those surfaces. An intuitive explanation for the influence of fractal dimension and scale factor on surface appearance is obtained by discussing the effects on the ratio of energy between high and low frequency components. Based on the relationship between Sq and surface energy, a filtering method of surface with controllable Sq is proposed. The proposed research ensures the synthesized surfaces possess ideal FBM properties with prescribed Sq, offers a method for selecting desired Abbott-Firestone curve of synthesized fractal surfaces, and makes it possible to control the Sq of surfaces after filtering.展开更多
A novel spectral representation based on fractional Fourier transform （FrFT） is proposed and applied to birdcall analysis. The FrFT-based spectrogram of a signal is derived and compared with its FT-based counterpart...A novel spectral representation based on fractional Fourier transform （FrFT） is proposed and applied to birdcall analysis. The FrFT-based spectrogram of a signal is derived and compared with its FT-based counterpart, and the spectrum gathering method is used to show the energy distribution related to the pitch frequency. The fixed transform order and adaptive orders for FrFT are tested. The fixed order can be obtained empirically or calculated according to the known chirp rate. The adaptive optimal orders are determined by using ambiguity function. Experimental results with birdcalls show that the FrFT-based spectrogram with an optimal transform order has higher resolution than its STFT-based counterpart, and the better performance can be achieved if adaptive orders are used.展开更多
A new method for the rejection of linear frequency modulation (LFM) interference in direct sequence spread spectrum (DSSS) system based on the fractional Fourier transform is proposed, and the configuration of the rec...A new method for the rejection of linear frequency modulation (LFM) interference in direct sequence spread spectrum (DSSS) system based on the fractional Fourier transform is proposed, and the configuration of the receiver with an interference exciser is also presented. Based on the property that the fractional Fourier transform of a signal is equivalent to rotating the signal in the time-frequency plane, the received signal is transform into a certain fractional Fourier domain, this transform will result in the least spectrum overlap between the signal and interference. Then, a narrowband filter is exploited to extract most of the interference energy. The performance analyses show that remarkable improvements in signal-to-noise ratio (SNR) and bit-error-ratio (BER) are obtained.展开更多
针对射频指纹识别中单一特征无法全面表示信号的完整性,且类间特征差异较小从而限制识别准确率等问题,提出了一种基于时频和双谱特征融合的DA-ResNeXt50(ResNeXt50 with dense connection and ACBlock)射频指纹识别方法。首先,对采集到...针对射频指纹识别中单一特征无法全面表示信号的完整性,且类间特征差异较小从而限制识别准确率等问题,提出了一种基于时频和双谱特征融合的DA-ResNeXt50(ResNeXt50 with dense connection and ACBlock)射频指纹识别方法。首先,对采集到的不同设备的信号分别进行短时傅里叶变换(short-time Fourier transform,STFT)和双谱变换,将得到的图像二值化处理并拼接,综合利用两种变换分别在时频域和高阶统计特性上的优势,更全面地提取和表征不同设备的射频指纹特征;然后,提出了DA-ResNeXt50网络模型,借鉴密集连接思想,使四层残差单元每一层都与前面所有层直接相连,促进了特征的复用和传递,能更好地捕捉类间细微差异;最后,使用非对称卷积模块(asymmetric convolution block,ACBlock)替换模型最后一层残差单元的3×3卷积,可以有效地增加网络的感受野,增强卷积核的骨架部分,从而提高射频指纹识别性能。实验结果表明,相较于使用单一特征提取方法,提出的特征融合方法的性能有较大的提升,改进后的模型与多种经典模型相比,具有较高的识别精度。展开更多
文摘The quaternion Fourier transform plays a vital role in the representation of two-dimensional signals. This paper characterizes spectrum of quaternion-valued signals on the quaternion Fourier transform domain by the partial derivative.
基金supported by National Natural Science Foundation of China(Grant Nos.51175085,51205062)Fujian Provincial Natural Science Foundation of China(Grant Nos.2011J01299,2012J01206)Development Foundation for Science and Technology of Fuzhou University,China(Grant No.2011-XY-10)
文摘The discrete Fourier transform（DFT） is used for fractional Brownian motion（FBM） surface synthesis in tribology（i.e., contact, sliding, and sealing, etc）. However, the relationship between fractal parameters（fractal dimension and scale factor） and traditional parameters, the influence of fractal parameters on surface appearance, have not been deeply discussed yet. These lead to some kind of difficulty to ensure the synthesized surfaces with ideal fractal characteristic, required traditional parameters and geometric appearance. A quantitative relationship between fractal parameters and the root mean square deviation of surface （Sq） is derived based on the energy conservation property between the space and frequency domain of DFT. Under the stability assumption, the power spectrum of a FBM surface is composed of concentric circles strictly, a series of FBM surfaces with prescribed Sq could be synthesized with given fractal dimension, scale factor, and sampling numbers, but the ten-point height（Sz）, the skewness（Ssk） and the kurtosis（Sku） are still in random, where the probability distributions of Sz and Ssk are approximately normal distribution. Furthermore, by iterative searching, a surface with desired Abbott-Firestone curve could be obtained among those surfaces. An intuitive explanation for the influence of fractal dimension and scale factor on surface appearance is obtained by discussing the effects on the ratio of energy between high and low frequency components. Based on the relationship between Sq and surface energy, a filtering method of surface with controllable Sq is proposed. The proposed research ensures the synthesized surfaces possess ideal FBM properties with prescribed Sq, offers a method for selecting desired Abbott-Firestone curve of synthesized fractal surfaces, and makes it possible to control the Sq of surfaces after filtering.
基金Sponsored by the National Natural Science Foundation of China(60605015)
文摘A novel spectral representation based on fractional Fourier transform （FrFT） is proposed and applied to birdcall analysis. The FrFT-based spectrogram of a signal is derived and compared with its FT-based counterpart, and the spectrum gathering method is used to show the energy distribution related to the pitch frequency. The fixed transform order and adaptive orders for FrFT are tested. The fixed order can be obtained empirically or calculated according to the known chirp rate. The adaptive optimal orders are determined by using ambiguity function. Experimental results with birdcalls show that the FrFT-based spectrogram with an optimal transform order has higher resolution than its STFT-based counterpart, and the better performance can be achieved if adaptive orders are used.
文摘A new method for the rejection of linear frequency modulation (LFM) interference in direct sequence spread spectrum (DSSS) system based on the fractional Fourier transform is proposed, and the configuration of the receiver with an interference exciser is also presented. Based on the property that the fractional Fourier transform of a signal is equivalent to rotating the signal in the time-frequency plane, the received signal is transform into a certain fractional Fourier domain, this transform will result in the least spectrum overlap between the signal and interference. Then, a narrowband filter is exploited to extract most of the interference energy. The performance analyses show that remarkable improvements in signal-to-noise ratio (SNR) and bit-error-ratio (BER) are obtained.
文摘针对射频指纹识别中单一特征无法全面表示信号的完整性,且类间特征差异较小从而限制识别准确率等问题,提出了一种基于时频和双谱特征融合的DA-ResNeXt50(ResNeXt50 with dense connection and ACBlock)射频指纹识别方法。首先,对采集到的不同设备的信号分别进行短时傅里叶变换(short-time Fourier transform,STFT)和双谱变换,将得到的图像二值化处理并拼接,综合利用两种变换分别在时频域和高阶统计特性上的优势,更全面地提取和表征不同设备的射频指纹特征;然后,提出了DA-ResNeXt50网络模型,借鉴密集连接思想,使四层残差单元每一层都与前面所有层直接相连,促进了特征的复用和传递,能更好地捕捉类间细微差异;最后,使用非对称卷积模块(asymmetric convolution block,ACBlock)替换模型最后一层残差单元的3×3卷积,可以有效地增加网络的感受野,增强卷积核的骨架部分,从而提高射频指纹识别性能。实验结果表明,相较于使用单一特征提取方法,提出的特征融合方法的性能有较大的提升,改进后的模型与多种经典模型相比,具有较高的识别精度。
