Finding the frequency locations of the occupied bands is a major challenge in wideband spectrum sensing. The common known method is based on wavelet edge detection. However, the low signal to noise ratio (SNR) may bring many fake edges to the power spectral density (PSD) of the received signal. Furthermore, since the wavelet edge detection works on the assumption that the PSD of the received signal has irregular structures at the edges of the occupied bands, it will fail when the edges are smooth. In response to these problems, a novel method for wideband spectrum sensing based on Multi-Resolution Bayes classifier is proposed in this paper. The proposed method is robustious in low SNR circumstance because Multi-Resolution analysis is used to prevent these fake edges. Based on Bayes classifier, the proposed method can still perform well when the PSD of the received signal is smooth at the edges of the occupied bands. Finally, an approximate threshold selection criterion is developed and the performance of the proposed method based on a Gaussian distribution is discussed. Simulation results are presented to verify the method.

The kinematic equation of a general Stewart-Gough platform is formulated and the error mapping model is derived. The relationships between input and output errors of both a single kinematic link and the whole manipulator are presented and analyzed. The singular values of a Jacobian matrix are used to define three error sensitivity measures, namely the comprehensive error sensitivity, the absolute error sensitivity and the directional error sensitivity. According to these measures, two indicators, the comprehensive error coefficient and the comprehensive error degree, are defined to evaluate the kinematic accuracy for various configurations of this type of mechanism. Based on the structure of a real parallel kinematic machine tool, several kinematic accuracy evaluation experiments are depicted graphically. The study shows that the evaluation measures proposed in this paper are very useful to help designers and operators correctly choose the manipulator configurations for obtaining the high kinematic accuracy.

This paper presents the dynamics of a four degrees of freedom (DOF) hybrid machine tool based on a novel planar 3-DOFs parallel manipulator and a long movement of the worktable. Closed-form solution is developed for the inverse kinematics about the parallel manipulator. The dynamics model of the parallel manipulator is built, which includes the extensible strut, sliders and balances model. The Newton-Euler approach is adopted to derive the inverse dynamic equations of the manipulator. According to the dynamics analysis results, the driving motors that can satisfy the requirements of velocity and accelerate velocity are selected. The analysis results can be of help in the design, trajectory planning, control and application of such devices.