A cluster-based analysis of propagation characteristics in MIMO relay channels based on wideband measurement

In this paper, the characteristics of clusters induced by a variety of propagation mechanisms in the link from the relay station （RS） to the mobile station （MS） are presented. Based on the results of high resolution channel parameter estimation, an automatic framework integrated with the manual intervention is utilized to perform the cluster identification and tracking. The power proportion and angular spread of clusters are investigated in both the line-of-sight （LOS） and non-line-of-sight （NLOS） scenarios. The measurement results indicate that the channel characteristics of clusters are different from the link from the base station to the MS due to the lower height of the RS antennas.

Spatial characteristics and capacity investigation of indoor hotspot channel based on wideband MIMO measurement at 4.9 GHz

In this article, results obtained from wideband multiple-input multiple-output channel measurements at 4.9 GHz are presented. Measurements were performed in an indoor hotspot scenario with both line-of-sight and non-line-of-sight propagation conditions. Vertical polarized uniform linear arrays （ULAs） with different antenna spacing and orientation were utilized for investigating the impact of antenna configurations on the system performance. Based on measured channel impulse responses, the spatial correlation of ULA is analyzed and compared with the theoretical values calculated from the power azimuth spectrum. Following that, the eigenvalue statistics and capacity with respect to antenna spacing and orientation are given and compared. The diversity-multiplexing tradeoff （DMT） of measured channels at operational signal-to-noise ratio （SNR） is also presented. The reason why the DMT of measured channels is much lower than that ofi.i.d. Rayleigh channels is specified.

An assessment on the wideband and narrowband methods for ultrasonic blood flow measurements

A comparison study on the ultrasonic blood flow estimation methods is carried out in this paper. The methods are divided into two classes-narrowband and wideband techniques.The pulsed Doppler systems and the autocorrelation methods are essentially the narrowband estAnators. They give the results with low velocity resolution and probably the aliased spectrum.The wider the frequency band of the signals, the worse the results. Time domain crosscorrelation technique, wideband makimum likelihood estimation and 2D Fourier transform method are three wideband techniques. The high velocity resolution and the ability of anti-aliasing are shown by these wideband estimation strategies.

Partial Discharge Measurement and Analysis in High Voltage IGBT Modules Under DC Voltage

Insulation performance of high voltage IGBT modules is one of the key attributes in power system applications.However,the existing standards of IGBT devices and research on the evaluation of insulation performance of high voltage IGBT modules are insufficient;for example,partial discharge resistance under DC voltage blocking condition is not considered.In this paper,a new test was proposed to allow the measurement of partial discharges in all the components of IGBT modules under DC voltage.The topology of the measuring circuit is arranged in the polarity discrimination way to exclude the interference,and the voltage and discharge current waveforms during the partial discharge process are measured by the wideband time domain measurement technique.According to the proposed test,the discharge phenomenon of the IGBT modules below the rating voltage were detected.A comprehensive waveform analysis on the voltage and discharge current was performed,and the influence of the applied voltage on the waveform parameters was obtained.The waveform parameters are influenced by the applied voltage and insulation structure,which enables the discrimination of the causes of the observed partial discharge in the IGBT module under DC voltage by the waveform analysis technique.Based on the waveform analysis technique,the types and causes of the observed partial discharges were discussed and inferred,and the correctness of the inference was further verified by observation.The proposed test and waveform analysis technique provide the possibility to evaluate and distinguish partial discharges in the high voltage IGBT module under DC voltage,which may be helpful to insulation performance evaluation and insulation defect diagnosis in high voltage IGBT module.