OFDM-CDMA is an attractive technique for broadband wireless communication. However, the high peakto-average power ratio (PAPR) of the downlink signals, generated from multiple spread codes, remains a serious problem...OFDM-CDMA is an attractive technique for broadband wireless communication. However, the high peakto-average power ratio (PAPR) of the downlink signals, generated from multiple spread codes, remains a serious problem. In this paper, a low-complexity multiple signal representation (MSR) scheme is proposed to control the PAPR problem in downlink OFDM-CDMA systems. The proposed scheme generates multiple candidate signals by a novel user grouping scheme, which is without distortion and can provide more PAPR reduction than the conventional MSR schemes, such as partial transmit sequence (PTS) and selective mapping (SLM). Furthermore, a low-complexity processing structure is developed using a novel joint spreading and inverse fast Fourier transform (S-IFFT) to simplify the generation of multiple candidate signals. Complexity analysis and numerical results show that the OFDM-CDMA systems employing the proposed scheme have better tradeoff between PAPR reduction and computational complexity, compared with the conventional MSR schemes.展开更多
Pulse signal recovery is to extract useful amplitude and time information from the pulse signal contaminated by noise. It is a great challenge to precisely recover the pulse signal in loud background noise. The conven...Pulse signal recovery is to extract useful amplitude and time information from the pulse signal contaminated by noise. It is a great challenge to precisely recover the pulse signal in loud background noise. The conventional approaches,which are mostly based on the distribution of the pulse energy spectrum,do not well determine the locations and shapes of the pulses. In this paper,we propose a time domain method to reconstruct pulse signals. In the proposed approach,a sparse representation model is established to deal with the issue of the pulse signal recovery under noise conditions. The corresponding problem based on the sparse optimization model is solved by a matching pursuit algorithm. Simulations and experiments validate the effectiveness of the proposed approach on pulse signal recovery.展开更多
A method for estimating current harmonics of an induction motor is introduced which is used for sensorless monitoring of a mechanical system driven by the motor. The method is based on an adaptive signal representatio...A method for estimating current harmonics of an induction motor is introduced which is used for sensorless monitoring of a mechanical system driven by the motor. The method is based on an adaptive signal representation and is proposed to extract weak harmonics from a noisy current signal, especially in the presence of additive interference caused by transient modulation waves. As an application, a rotor unbalance experiment of rotating machinery driven by an induction motor is carried out, The result shows that the eccentricity harmonic magnitude of a current signal obtained by the method represents the rotor unbalance conditions sensitively. Vibration analysis is used to validate the proposed method.展开更多
The problem of two-dimensional direction finding is approached by using a multi-layer Lshaped array. The proposed method is based on two sequential sparse representations,fulfilling respectively the estimation of elev...The problem of two-dimensional direction finding is approached by using a multi-layer Lshaped array. The proposed method is based on two sequential sparse representations,fulfilling respectively the estimation of elevation angles,and azimuth angles. For the estimation of elevation angles,the weighted sub-array smoothing technique for perfect data decorrelation is used to produce a covariance vector suitable for exact sparse representation,related only to the elevation angles. The estimates of elevation angles are then obtained by sparse restoration associated with this elevation angle dependent covariance vector. The estimates of elevation angles are further incorporated with weighted sub-array smoothing to yield a second covariance vector for precise sparse representation related to both elevation angles,and azimuth angles. The estimates of azimuth angles,automatically paired with the estimates of elevation angles,are finally obtained by sparse restoration associated with this latter elevation-azimuth angle related covariance vector. Simulation results are included to illustrate the performance of the proposed method.展开更多
The subspaces of FMmlet transform are investigated. It is shown that some of the existing transforms like the Fourier transform, short-time Fourier transform, Gabor transform, wavelet transform, chirplet transform, th...The subspaces of FMmlet transform are investigated. It is shown that some of the existing transforms like the Fourier transform, short-time Fourier transform, Gabor transform, wavelet transform, chirplet transform, the mean of signal, and the FM-1let transform, and the butterfly subspace are all special cases of FMmlet transform. Therefore the FMmlet transform is more flexible for delineating both the linear and nonlinear time-varying structures of a signal.展开更多
基金Supported in part by DoCoMo Beijing Labs Co., Ltd., International Sci. & Tech. Cooperation Project of the Ministry of Sci. & Tech. of China(Grant No. 2008DFA11700)the National Natural Science Foundation of China (Grant Nos. 60902026, 60602008)
文摘OFDM-CDMA is an attractive technique for broadband wireless communication. However, the high peakto-average power ratio (PAPR) of the downlink signals, generated from multiple spread codes, remains a serious problem. In this paper, a low-complexity multiple signal representation (MSR) scheme is proposed to control the PAPR problem in downlink OFDM-CDMA systems. The proposed scheme generates multiple candidate signals by a novel user grouping scheme, which is without distortion and can provide more PAPR reduction than the conventional MSR schemes, such as partial transmit sequence (PTS) and selective mapping (SLM). Furthermore, a low-complexity processing structure is developed using a novel joint spreading and inverse fast Fourier transform (S-IFFT) to simplify the generation of multiple candidate signals. Complexity analysis and numerical results show that the OFDM-CDMA systems employing the proposed scheme have better tradeoff between PAPR reduction and computational complexity, compared with the conventional MSR schemes.
基金Supported by the National Natural Science Foundation of China(61501385)Science and Technology Planning Project of Sichuan Province,China(2016JY0242,2016GZ0210)Foundation of Southwest University of Science and Technology(15kftk02,15kffk01)
文摘Pulse signal recovery is to extract useful amplitude and time information from the pulse signal contaminated by noise. It is a great challenge to precisely recover the pulse signal in loud background noise. The conventional approaches,which are mostly based on the distribution of the pulse energy spectrum,do not well determine the locations and shapes of the pulses. In this paper,we propose a time domain method to reconstruct pulse signals. In the proposed approach,a sparse representation model is established to deal with the issue of the pulse signal recovery under noise conditions. The corresponding problem based on the sparse optimization model is solved by a matching pursuit algorithm. Simulations and experiments validate the effectiveness of the proposed approach on pulse signal recovery.
基金This paper is sponsored by National Natural Science Foundation of China under Grant No.50475087
文摘A method for estimating current harmonics of an induction motor is introduced which is used for sensorless monitoring of a mechanical system driven by the motor. The method is based on an adaptive signal representation and is proposed to extract weak harmonics from a noisy current signal, especially in the presence of additive interference caused by transient modulation waves. As an application, a rotor unbalance experiment of rotating machinery driven by an induction motor is carried out, The result shows that the eccentricity harmonic magnitude of a current signal obtained by the method represents the rotor unbalance conditions sensitively. Vibration analysis is used to validate the proposed method.
基金Supported by the National Natural Science Foundation of China(61331019,61490691)
文摘The problem of two-dimensional direction finding is approached by using a multi-layer Lshaped array. The proposed method is based on two sequential sparse representations,fulfilling respectively the estimation of elevation angles,and azimuth angles. For the estimation of elevation angles,the weighted sub-array smoothing technique for perfect data decorrelation is used to produce a covariance vector suitable for exact sparse representation,related only to the elevation angles. The estimates of elevation angles are then obtained by sparse restoration associated with this elevation angle dependent covariance vector. The estimates of elevation angles are further incorporated with weighted sub-array smoothing to yield a second covariance vector for precise sparse representation related to both elevation angles,and azimuth angles. The estimates of azimuth angles,automatically paired with the estimates of elevation angles,are finally obtained by sparse restoration associated with this latter elevation-azimuth angle related covariance vector. Simulation results are included to illustrate the performance of the proposed method.
基金This work was supported in part by the National Natural Science Foundation of China ( Grant No.60172026) the Basic Research Foundation of Tsinghua University (Grant No. JC2001028) and by the Scientific Innovation Foundation of Ph. D. Candidates of Tsingh
文摘The subspaces of FMmlet transform are investigated. It is shown that some of the existing transforms like the Fourier transform, short-time Fourier transform, Gabor transform, wavelet transform, chirplet transform, the mean of signal, and the FM-1let transform, and the butterfly subspace are all special cases of FMmlet transform. Therefore the FMmlet transform is more flexible for delineating both the linear and nonlinear time-varying structures of a signal.