Effects of polarization on intersubband transitions of Al_xGa_(1-x)N/GaN multi-quantum wells

The effects of polarization and related structural parameters on the intersubband transitions of A1GaN/GaN multi- quantum wells （MQWs） have been investigated by solving the Schr6dinger and the Poisson equations self-consistently. The results show that the intersubband absorption coefficient increases with increasing polarization while the transition wavelength decreases, which is not identical to the case of the interband transitions. Moreover, it suggests that the well width has a greater effect on the intersubband transitions than the barrier thickness, and the intersubband transition wavelength of the structure when doped in the barrier is shorter than that when doped in the well. It is found that the influences of the structural parameters differ for different electron subbands. The mechanisms responsible for these effects have been investigated in detail.

A Method for Hierarchical Subband HDTV Splitting

In this paper, an investigation is made on compatibility of the video formats TV (625/50/2:1/4:3), EDTV (625/50/1:1/16:9), HDTVint (1250/50/2:1/16:9) and HDTVpro(1250/50/2:1/16:9) in three-dimensional subband coding. A hierarchical method is proposed leading to a more reasonable joint solution for the issues of digital transmission evolution and interlace-to-progressive scanning conversion ill the frame work of bit rate compression. Conventional HDTVint with the diamond shaped spectrum is proposed to be replaced by a kind of 'switching'HDTVin signal which consists of three components and motion detection bits (MDB). The first component and the MDB represent TV. The first plus the second component and the MDB represent EDTV.HDTVpro is splitted into switching HDTVint and extra component. The switching threshold and the length of temporal filter banks are discussed. Rearranging the pixels in subbands is recommended. Based on the proposed method, the transmission system can evolve through four steps: TV, EDTV, HDTVint and HDTVpro Results of bit rate compression are also presented. TV, EDTV, HDTVint and HDTVpro are compressed to approximately 40, 80, 128 and 256 Mbit/s respectively. Interlace scanning has drawbacks such as line flicker and line crawling as the eye follows the line structure in the picture. Progressive version switching TV and HDTVint can be reconstructed using one frame memory without the problems of handling temporal-vertical diamond shaped spectra of conventional TV and HDTVint based on a one-frame memory algorithm in the receiver.

Ultrawide-band radar imagery from multiple incoherent frequency subband measurements

The problem of combined radar imagery from multiple sparse frequency subbands initially incoherent to each other is of practical importance for radar target discrimination.A new coherent processing technique based on probability density analysis of the subband data is proposed,which is applicable for radar imaging from measurements of two or more initially incoherent radar subbands.The coherence parameters for both amplitude and phase are obtained by combining modern spectral analysis with probability density estimation.The major advantage of the proposed technique lies in that it enables much more robust cohering for the sparse subband data of real-world complex targets.

Adaptive Endpoint Detection Based on Subband Speech

An adaptive endpoint detection algorithm based on band energy and adaptive smoothing algorithm is described. This algorithm utilizes the capability of adaptive smoothing algorithm that intensifies the discontinuity between local areas. The band energy features are selected because of their usefulness in detecting high energy regions (in the incoming signal) and making the distinction between speech and noise. Heuristic 'edge-focusing' is used to endpoint detection to save the time in iteration.

A robust subband adaptive filter algorithm for sparse and block-sparse systems identification

This paper presents a new subband adaptive filter(SAF)algorithm for system identification scenario under impulsive interference,named generalized continuous mixed p-norm SAF(GCMPN-SAF)algorithm.The proposed algorithm uses a GCMPN cost function to combat the impul-sive interference.To further accelerate the convergence rate in the sparse and the block-sparse system identification processes,the proportionate versions of the proposed algorithm,the L0-norm GCMPN-SAF(L0-GCMPN-SAF)and the block-sparse GCMPN-SAF(BSGCMPN-SAF)algorithms are also developed.Moreover,the convergence analysis of the proposed algorithm is provided.Simulation results show that the proposed algorithms have a better performance than some other state-of-the-art algorithms in the literature with respect to the convergence rate and the tracking capability.

Monte Carlo simulation of in-plane spin-polarized transport in GaAs/GaAlAs quantum well in the three-subband approximation

We develop a Monte Carlo （MC） tool incorporated with the three-subband approximation model to investigate the in-plane spln-polarized transport in GaAs/GaAlAs quantum well. Using the tool, the effects of the electron occupation of higher subbands and the intersuhband scattering on the spin dephasing have been studied. Compared with the corresponding results of the simple one-snbband approximation model, the spin dephasing length is reduced four times under 0.125 kV/cm of driving electric field at 300K by the MC tool incorporated with the three-subband approximation model, indicating that the three-subbarld approximation model predicts significantly shorter spin dephasing length with temperature increasing. Our simulation results suggest that the effects of the electron occupation of higher subbands and the intersubband scattering on the spln-dependent transport of GaAs 2-dhuensional electron gas need to be considered when the driving electric field exceeds the moderate value and the lattice temperature is above 100K. The simulation by using the MC tool incorporated with the three-subband approximation model also indicates that, under a eertain driving electric field and lattice temperature, larger channel widths cause spins to be depolarized faster. Ranges of the three components of the spins are different for three different injected spin polarizations due to the anisotropy of spin-orbit interaction.

Temperature-dependent subband mobility characteristics in n-doped silicon junctionless nanowire transistor

We have investigated the temperature-dependent effective mobility characteristics in impurity band and conduction subbands of n-doped silicon junctionless nanowire transistors. It is found that the electron effective mobility of the first subband in 2-fold valleys is higher than that of the second subband in 4-fold valleys. There exists a maximum value for the effective subband mobilities at low temperatures, which is attributed to the increase of thermally activated electrons from the ionized donors in the impurity band. The experimental results indicate that the effective subband mobility is temperature-dependent on the electron interactions by thermal activation, impurity scattering, and intersubband scattering.

一种结合Subband-NDFT和改进Goertzel滤波器的DTMF解调算法(英文)

基于Goertzel逻辑判断算法[1],提出了一种将Goertzel逻辑判断和Subband-NDFT相结合的新的解调DTMF信号的算法.Subband-NDFT通过放弃高频分量达到快速计算DFT的目的.软件仿真表明新的算法具有比Goertzel逻辑判断算法更快的解调速度,并且满足ITU在SNR上对DTMF信号的规定.

A high fidelity VQ coding algorithm with region adaptive subbanding

Image subbands can be obtained by using filterbank. Traditional compression method uses direct entropy coding for each subband. After studying the energy distribution in image subbands, we proposed a vector quantization (VQ) coding algorithm to image subband. In the algorithm, vector quantizers were adaptively designed for high-frequency bands in an image. In particular, the edges of the image were examined and fewer bits were assigned to high-energy regions. The experimental result showed that the algorithm had higher SNR and higher compression ratio than possible by traditional subband coding, JPEG and JPEG 2000.

Electronic Wave Functions and Subband Energies in Superlattice with a Complex Basis

Electronic wave functions and energies in superlattice with a complex basis have been obtained that are more general than those of Pan et al.[Phys.Rev.B 44(1991)5668].This paper gives not only subbands but also wave functions for all values of the wave number for superlattice with a complex basis.

Subband adaptive filter with variable reusing order of coefficient vectors

To increase the convergence rate of the improved normalized subband adaptive filter,a simple but effective method is presented to change the reusing order of coefficient vectors of the adaptive filter. At the beginning of adaptation the algorithmjust uses its current coefficient vector to update the adaptive filter to maintain fast convergence rate,while in steady state it employs several most recent coefficient vectors to update the adaptive filter to reduce misalignment. Simulation results showthat the proposed algorithmcan obtain both fast convergence rate and small steady-state misalignment.

基于深度神经网络的多聚焦红外图像非线性增强

当红外图像中含有多个聚焦目标主体时,会导致红外图像质量下降,部分区域出现模糊,因此,提出基于深度神经网络的多聚焦红外图像非线性增强方法。在引导滤波的作用下,从红外图像中获取细节层图像和背景层图像,在细节层图像中建立局部清晰度评价函数,得到清晰的细节层和背景层并融合二者。利用构建的深度神经网络结构,建立非线性增益函数,通过设定阈值和调整子带系数,实现对多聚焦红外图像的非线性增强。测试结果表明,所提方法在增强图像过程中,并没有改变原始图像的亮度和纹理波动;增强后的图像信息熵比原图像提高了57%左右,图像抗噪性能值更高,平均为7.4 dB,图像更清晰,SSIM值更趋近于1,平均为0.98,增强后的图片与原图片图像相似度更高,更接近于真实图像。

An extended binary subband canonical correlation analysis detection algorithm oriented to the radial contraction-expansion motion steady- state visual evoked paradigm

The radial contraction-expansion motion paradigm is a novel steady-state visual evoked experimental paradigm,and the electroencephalography(EEG)evoked potential is different from the traditional luminance modulation paradigm.The signal energy is concentrated chiefly in the fundamental frequency,while the higher harmonic power is lower.Therefore,the conventional steady-state visual evoked potential recognition algorithms optimizing multiple harmonic response components,such as the extended canonical correlation analysis(eCCA)and task-related component analysis(TRCA)algorithm,have poor recognition performance under the radial contraction-expansion motion paradigm.This paper proposes an extended binary subband canonical correlation analysis(eBSCCA)algorithm for the radial contraction-expansion motion paradigm.For the radial contraction-expansion motion paradigm,binary subband filtering was used to optimize the weighting coefficients of different frequency response signals,thereby improving the recognition performance of EEG signals.The results of offline experiments involving 13 subjects showed that the eBSCCA algorithm exhibits a better performance than the eCCA and TRCA algorithms under the stimulation of the radial contraction-expansion motion paradigm.In the online experiment,the average recognition accuracy of 13 subjects was 88.68%±6.33%,and the average information transmission rate(ITR)was 158.77±43.67 bits/min,which proved that the algorithm had good recognition effect signals evoked by the radial contraction-expansion motion paradigm.

无源声呐水下多目标融合跟踪方法

针对海洋环境噪声导致弱目标在不同子频带检测结果差异较大,致使以全频带探测结果为输入的跟踪算法出现性能退化的问题,提出一种子带融合跟踪方法。该方法利用改进的高斯混合概率假设密度滤波器对各频率子带输出的方位估计结果进行跟踪,并采用广义协方差交集准则对子带跟踪结果进行融合,以获得综合各子带信息的跟踪结果。仿真结果表明,所提方法可以提高弱目标在各子带信噪比不均衡情况下的跟踪能力,且运算时间与对比方法较为接近。海试数据处理结果进一步验证了所提方法的有效性。

应用于宽频带通信干扰对消的重构滤波器设计

围绕宽频带通信干扰对消的需求,提出了新的子带划分与重构框架,并对子带划分滤波器组与重构滤波器进行设计,简化了完全重构条件,使得重构滤波器具备过渡带幅度互补特性。仿真与实验结果表明,设计的重构滤波器可以有效降低重构后通信信号的误码率,并且解决了子带信号拼接过程中的频谱起伏现象。所提出的子带划分与重构框架及重构滤波器设计展现了良好的通信信号重构效果,可为宽频带干扰对消的子带划分与重构工程实践提供新的理论方法与技术路线。

扩频通信信号多分辨重叠正交变换抗干扰仿真

为了提高扩频通信安全性能,提出一种基于滤波器的扩频通信信号抗干扰方法。分析扩频通信信号多分辨重叠的变化特点,针对变化特点利用综合滤波器倒转通信信号的冲激响应时间,并通过滤波器分解扩频通信信号。分析扩频通信信号有源干扰机理,实现噪声干扰辨别,获取多分辨变换域矢量条件。在此基础上,基于滤波器的输入状态和输出状态得出扩频通信信号的估计误差,对接收信号的矢量进行多分辨重叠正交变换,并修正信号的子带能量估计结果。最后引入前向纠错编码方法提高扩频通信信号在弱信号环境中的抗干扰性能,确保通信信号可靠传输。通过实验验证在不同参数条件下所提方法的抗干扰效果,通过对比结果证明上述方法能有效地实现扩频通信信号抗干扰。

An Adaptive Acoustic Echo Cancellation Algorithm Based on Subband Decomposition and Conjugate Gradient Method

An adaptive conjugate gradient algorithm based on subbands decomposition structure is proposed for acoustic echo cancellation in this paper. Through frequency decomposition technique and conjugate gradient algorithm, adaptive filters operate in each decimated sub-band, This new algorithm can ensure convergence with high speed and reduce computational complexity. Simulation results indicate that the proposed algorithm demonstrates good performance for acoustic echo cancellation.

Adaptive Subband Bit and Power Loading Algorithm and its Application to OFDM Based IEEE 802 .16e

For OFDM systems with hundreds or thousands subcarriers with the adaptive bit and power loading according to each subcarrier , the signaling overhead will be awfully large. However, the adaptive bit and power loading according to “subband” is an effective solution to this problem, with which the signaling overhead is expected to be dramatically decreased at the cost of some performance loss. In this paper, based on Ref . [5] but with some modification to the subband bit and power loading algorithm, we apply the algorithm to the IEEE 802.16e OFDM system. The results show that the modified subband bit and power loading algorithm can achieve better BER performance and the signaling overhead is reduced by 75% at the cost of performance loss less than 1 dB if the number of subcarriers per subband is 4 when the BER is around 10^-3.

Application of subband adaptive filtering techniques to ultrasonic detection in multilayers

The ultrasonic testing for the defects of complete disbond in multi-layered structure with lower acoustic impedance beneath a high acoustic impedance overburden is one of the difficult problems in ultrasonic nondestructive testing field. A model of a multi-layered steel-rubber composite plate is depicted. Because the acoustic impedance of the steel differs far from that of the couplant water and the rubber, the energy of the signal reflected from the debonded rubber layers is very weak. More over, the flaw echoes are masked by the strong echoes reverberated in the steel plate. It's nearly impossible to identify the debonding echoes directly. The subband adaptive filtering method is discussed in the paper, where the subband decomposition is performed by mutual wavelet packets decomposition on the criterion of maximizing the cross-correlation between the signals. The simulations on both synthetic and real signals are presented. The echoes from the delaminated flaw at the depth of 5 mm in the rubber from the calculated signal, and echoes from the flaw at the depth of 3 mm from the real signal are extracted successfully.

基于子带处理与相关系数的风电机组功率异常波动检测

风电机组功率的周期性异常波动容易引起电网的低频振荡,威胁电网安全;而风电机组功率信号是一种非线性、非平稳信号,其异常波动频率存在不确定性,为异常波动特征的提取与检测带来困难。为此,文章提出一种基于子带处理与相关系数的风电机组功率异常波动检测方法。其首先将原始功率信号通过高通滤波器去除趋势项,然后采用子带处理滤波器组进行信号分解,得到一系列子带信号;将去除趋势项后的功率信号与各子带信号分别计算互相关系数,并根据互相关系数实现周期性异常波动所在子带的定位及子带筛选;基于筛选所得子带信号进行信号重构得到高信噪比重构信号;采用峰值检波与自相关分析相结合的检测方法,识别重构信号中特定幅值周期性异常波动发生时段,从而达到风电机组功率信号周期性异常波动检测的目的。现场数据测试结果表明,对于0.06 Hz、0.32 Hz等不同频率的功率周期性异常波动,该方法能够准确识别其所在子带及特征。