To improve frame synchronization precision, a scheme named training symbol correlation （TSC） is presented for orthogonal frequency division multiplexing （ OFDM ） system. Based on the solution from Schmidl and Cox,...To improve frame synchronization precision, a scheme named training symbol correlation （TSC） is presented for orthogonal frequency division multiplexing （ OFDM ） system. Based on the solution from Schmidl and Cox, a timing metric related to TSC scheme is put forward and examined. The specific method to select a threshold value provides more precise detection results, which can be shown by performance comparison between the two schemes through Monte Carlo simulation. Taking IEEE 802.1 la WLAN standard as an example, the proposed approach is superior to the most popular Schmidl scheme in terms of BER.展开更多
The workpiece frames relative to each robot base frame should be known in advance for the proper operation of twin-robot nondestructive testing system. However, when two robots are separated from the workpieces, the t...The workpiece frames relative to each robot base frame should be known in advance for the proper operation of twin-robot nondestructive testing system. However, when two robots are separated from the workpieces, the twin robots cannot reach the same point to complete the process of workpiece frame positioning. Thus, a new method is proposed to solve the problem of coincidence between workpiece frames. Transformation between two robot base frames is initiated by measuring the coordinate values of three non-collinear calibration points. The relationship between the workpiece frame and that of the slave robot base frame is then determined according to the known transformation of two robot base frames, as well as the relationship between the workpiece frame and that of the master robot base frame. Only one robot is required to actually measure the coordinate values of the calibration points on the workpiece. This requirement is beneficial when one of the robots cannot reach and measure the calibration points. The coordinate values of the calibration points are derived by driving the robot hand to the points and recording the values of top center point（TCP） coordinates. The translation and rotation matrices relate either the two robot base frames or the workpiece and master robot. The coordinated are solved using the measured values of the calibration points according to the Cartesian transformation principle. An optimal method is developed based on exponential mapping of Lie algebra to ensure that the rotation matrix is orthogonal. Experimental results show that this method involves fewer steps, offers significant advantages in terms of operation and time-saving. A method used to synchronize workpiece frames in twin-robot system automatically is presented.展开更多
Frame and frequency synchronization are essential for orthogonal frequency division multiplexing （OFDM） systems. The frame offset owing to incorrect start point position of the fast Fourier transform （FFT） window,...Frame and frequency synchronization are essential for orthogonal frequency division multiplexing （OFDM） systems. The frame offset owing to incorrect start point position of the fast Fourier transform （FFT） window, and the carrier frequency offset （CFO） due to Doppler frequency shift or the frequency mismatch between the transmitter and receiver oscil ators, can bring severe inter-symbol interference （ISI） and inter-carrier interference （ICI） for the OFDM system. Relying on the relatively good correlation charac-teristic of the pseudo-noise （PN） sequence, a joint frame offset and normalized CFO estimation algorithm based on PN preamble in time domain is developed to realize the frame and frequency synchronization in the OFDM system. By comparison, the perfor-mances of the traditional algorithm and the improved algorithm are simulated under different conditions. The results indicate that the PN preamble based algorithm both in frame offset estimation and CFO estimation is more accurate, resource-saving and robust even under poor channel condition, such as low signal-to-noise ratio （SNR） and large normalized CFO.展开更多
In order to realize high precision industrial operations,based on the POE formula,an effective approach to calibrate the robot's actual base frame(ABF) is proposed. Due to the existence of manufacturing errors,the...In order to realize high precision industrial operations,based on the POE formula,an effective approach to calibrate the robot's actual base frame(ABF) is proposed. Due to the existence of manufacturing errors,the ABF deviates slightly from nominal base frame( NBF). Using external precision measurement,the ABF can be established only through the three dimension(3D) position of the robot's end-effector.To ensure the orthonormal constraints of rotation matrix as well as the precise solutions,Procrustes Analysis is introduced,where an optimal orthogonal matrix is solved out by the Lagrange Multiplier method and Singular Value Decomposition(SVD). Furthermore,calibration experiment on a serial 6-DOF robot is performed,where a FARO laser tracker is utilized to measure the 3D position. Finally, calibration result indicates that the positioning accuracy has been significantly improved after calibration. The calibration method is also applicable to other similar problems,such as multi-robot coordination and robot hand-eye system calibration.展开更多
Using operator-theoretic-methods, we give some characterizations for a dual generalized frame of a generalized frame in a separable Hilbert space H. We also prove a result concerning two strongly disjiont generalized ...Using operator-theoretic-methods, we give some characterizations for a dual generalized frame of a generalized frame in a separable Hilbert space H. We also prove a result concerning two strongly disjiont generalized frames.展开更多
Motivated by the applications to generalized Howell designs and multiply constant-weight codes, we establish an asymptotic existence theorem for(k, λ)-frames of type g^n with a pair of orthogonal frame resolutions vi...Motivated by the applications to generalized Howell designs and multiply constant-weight codes, we establish an asymptotic existence theorem for(k, λ)-frames of type g^n with a pair of orthogonal frame resolutions via decompositions of edge-colored complete digraphs into prescribed edge-colored subgraphs.展开更多
文摘To improve frame synchronization precision, a scheme named training symbol correlation （TSC） is presented for orthogonal frequency division multiplexing （ OFDM ） system. Based on the solution from Schmidl and Cox, a timing metric related to TSC scheme is put forward and examined. The specific method to select a threshold value provides more precise detection results, which can be shown by performance comparison between the two schemes through Monte Carlo simulation. Taking IEEE 802.1 la WLAN standard as an example, the proposed approach is superior to the most popular Schmidl scheme in terms of BER.
基金Supported by International S&T Cooperation Program of China(Grant No.2012DFA70260)High-end CNC Machine and Basic Manufacturing Equipment of Chinese Key National Science and Technology(Grant No.2011ZX04014-081)
文摘The workpiece frames relative to each robot base frame should be known in advance for the proper operation of twin-robot nondestructive testing system. However, when two robots are separated from the workpieces, the twin robots cannot reach the same point to complete the process of workpiece frame positioning. Thus, a new method is proposed to solve the problem of coincidence between workpiece frames. Transformation between two robot base frames is initiated by measuring the coordinate values of three non-collinear calibration points. The relationship between the workpiece frame and that of the slave robot base frame is then determined according to the known transformation of two robot base frames, as well as the relationship between the workpiece frame and that of the master robot base frame. Only one robot is required to actually measure the coordinate values of the calibration points on the workpiece. This requirement is beneficial when one of the robots cannot reach and measure the calibration points. The coordinate values of the calibration points are derived by driving the robot hand to the points and recording the values of top center point（TCP） coordinates. The translation and rotation matrices relate either the two robot base frames or the workpiece and master robot. The coordinated are solved using the measured values of the calibration points according to the Cartesian transformation principle. An optimal method is developed based on exponential mapping of Lie algebra to ensure that the rotation matrix is orthogonal. Experimental results show that this method involves fewer steps, offers significant advantages in terms of operation and time-saving. A method used to synchronize workpiece frames in twin-robot system automatically is presented.
基金supported by the National Natural Science Foundation of China(6130110561102069)+2 种基金the China Postdoctoral Science Foundation Funded Project(2013M531351)the Nanjing University of Aeronautics and Astronautics Founding(NN2012022)the Open Fund of Graduate Innovated Base(Laboratory)for the Nanjing University of Aeronautics and Astronautics(KFJJ120219)
文摘Frame and frequency synchronization are essential for orthogonal frequency division multiplexing （OFDM） systems. The frame offset owing to incorrect start point position of the fast Fourier transform （FFT） window, and the carrier frequency offset （CFO） due to Doppler frequency shift or the frequency mismatch between the transmitter and receiver oscil ators, can bring severe inter-symbol interference （ISI） and inter-carrier interference （ICI） for the OFDM system. Relying on the relatively good correlation charac-teristic of the pseudo-noise （PN） sequence, a joint frame offset and normalized CFO estimation algorithm based on PN preamble in time domain is developed to realize the frame and frequency synchronization in the OFDM system. By comparison, the perfor-mances of the traditional algorithm and the improved algorithm are simulated under different conditions. The results indicate that the PN preamble based algorithm both in frame offset estimation and CFO estimation is more accurate, resource-saving and robust even under poor channel condition, such as low signal-to-noise ratio （SNR） and large normalized CFO.
基金Sponsored by the Applied Major Research Program of Science and Technology Commission Foundation of Beijing(Grant No.141100003514003)
文摘In order to realize high precision industrial operations,based on the POE formula,an effective approach to calibrate the robot's actual base frame(ABF) is proposed. Due to the existence of manufacturing errors,the ABF deviates slightly from nominal base frame( NBF). Using external precision measurement,the ABF can be established only through the three dimension(3D) position of the robot's end-effector.To ensure the orthonormal constraints of rotation matrix as well as the precise solutions,Procrustes Analysis is introduced,where an optimal orthogonal matrix is solved out by the Lagrange Multiplier method and Singular Value Decomposition(SVD). Furthermore,calibration experiment on a serial 6-DOF robot is performed,where a FARO laser tracker is utilized to measure the 3D position. Finally, calibration result indicates that the positioning accuracy has been significantly improved after calibration. The calibration method is also applicable to other similar problems,such as multi-robot coordination and robot hand-eye system calibration.
基金the National Natural Science Foundation of China (19771056)
文摘Using operator-theoretic-methods, we give some characterizations for a dual generalized frame of a generalized frame in a separable Hilbert space H. We also prove a result concerning two strongly disjiont generalized frames.
基金supported by National Natural Science Foundation of China(Grant Nos.11431003 and 11471032)Fundamental Research Funds for the Central Universities(Grant Nos.2016JBM071 and 2016JBZ012)
文摘Motivated by the applications to generalized Howell designs and multiply constant-weight codes, we establish an asymptotic existence theorem for(k, λ)-frames of type g^n with a pair of orthogonal frame resolutions via decompositions of edge-colored complete digraphs into prescribed edge-colored subgraphs.
