In this paper, a residual echo cancellation method is proposed that uses an estimation of the minimum mean-square error (MMSE) based on a statistical model of a speech signal and an echo signal. After the suppression of the echo signal based on the adaptive filter, residual echo is further reduced by the proposed MMSE estimator and the results are compared with the conventional Wiener filter based method.

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One of the metrics used to ensure an efficient management of network services is the packet delay. However, packet delay is highly variable due to queuing mechanism in many network devices, including the host systems. In this paper, the protocol stack packet delay on Linux system is presented. Also, a new RTT probe model based on packet train is proposed in order to achieve a stable RTT measurement without making any modification, optimization and tuning to the current Linux kernel. Experiment results show that using packet train the minimum peak RTT could be determined from the “tail” packets and that its variation is within few microseconds.

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Electron backscatter diffraction (EBSD) technique has been applied to the strain distribution measurements for GaN based heterostructures for the first time. From the results for the simple AlGaN/GaN structures on GaN substrates, it was confirmed that this method has high spatial resolution of about 80nm and gives quantitatively reasonable strain values. The EBSD technique was then applied to the heterostructures grown on Si substrates to study the role of an AlN/GaN multilayer prior to the growth of a thick GaN layer. It was clarified that there exists a compressive strain in the GaN layer, especially near the interface to the AlN/GaN multilayer. This compressive strain will be relevant to the suppression of the crack generation in the thick GaN layer.

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