Papers by Keyword: Differential Signal

Abstract: In this paper, we present an optimum weighted approach for wideband spectrum sensing. Distributed compressive sensing technology is exploited to obtain dramatic rate reductions while differential procedure is deduced to extremely enhance the detection sensitivity. The measurements are collected from each SU at a fusion center, where a C-out-of-J method is proposed to dramatically heighten the detection performance. SCSMP recovery algorithm is utilized to reconstruct the signals, which are then weighted by the estimated SNRs. Corroborating simulation results show that the raised algorithm can effectively reduce sampling rates at each SU, substantially raise the detection performance and saliently improve system robustness against noise.

Abstract: Automatic modulation classification plays a significant role in intelligent communication. A new method based on feature extraction is proposed for the recognition of M-ary Phase Shift Keying (MPSK) signals. As features, fourth and eighth order cumulants of the input samples and phase differential sequences were applied. It is shown that the cumulant-based features have robust anti-noise ability. Simulation results demonstrate that the correct classification probability (Pcc) with the proposed algorithm is higher than the existing approaches at low signal-to-noise ratio (SNR).

Abstract: In this paper, absolute and differential eddy current signals from various shapes and sizes of defects in the steam generator tube are numerically predicted and their slope characteristics are investigated. The signal variations due to frequency increase are also observed. Then, the analysis of mixed defect signals affected by a ferromagnetic support plate is attempted. Axisymmetric finite element modeling is used for signal prediction and the slope angle of signal is used importantly in analyzing the signal. Results show that differential signals are useful for locating the position of a defect inside the support plate hole, while absolute signals are easy to presume and interpret even though the effect of support plate is mixed in the signal. Understanding of respective signal characteristics and relationship between them will be helpful for more reliable defect characterization.

Abstract: Steam generator tubes are expanded inside tubesheet holes and the crevice gap between tubesheet and the tube should be minimized. To examine tube expansion area, eddy current testing is usually used. In this paper, absolute and differential signals are computed by a numerical method for several different locations of transition region and signal variations due to tubesheet, tube expansion and operating frequencies are observed. Results show that low frequency is good for identifying the location of tubesheet, and high frequency is good for the measurement of expanded tube diameter and the recognition of transition region. In general, absolute signal is good for measuring tube diameter and the differential signal has advantages of locating tubesheet and both ends of the transition region.

Abstract: In this paper, eddy current signals from various anomalous defects in the steam generator tube are numerically predicted and their signal slope characteristics are investigated. The signal variations due to increased frequencies are also observed. Based on the accumulated knowledge, the analysis of compound signal is attempted which includes the effect of support plate. Both differential and absolute bobbin probe signals are analyzed. For the signal prediction, axisymmetric finite element modeling is used and this leads us to the utilization of slope angle analysis of the signal. Results show that differential signals are useful for locating the position of defect under the support plate, while absolute signals are easy to presume and interpret even though the effect of support plate is mixed. Combined use of these two types of signals will help us accomplish a more reliable inspection.