Unfolding the frequency spectrum for undersampled wideband data

In this letter, we discuss the problem of unfolding the frequency spectrum for undersampled wideband data. The problem is of relevance to state-of-the-art radio frequency measurement systems, which capture repetitive waveform based on a sampling rate that violates the Nyquist constraint. The problem is presented in a compact form by the inclusion of a complex operator called the CN operator. The ease-of-use problem formulation eliminates the ambiguity caused by folded frequency spectra, in particular those with lines standing on multiples of the Nyquist frequency that are captured with erroneous amplitude and phase values.     

一种多幅欠采样图像的凸集投影超分辨率重建方法

介绍了一种由多幅欠采样低分辨率图像重建一幅高分辨率图像的凸集投影超分辨率重建技术。首先介绍了超分辨率空间域迭代重建方法中一个至关重要的因素--成像过程模型;其次通过介绍凸集投影的理论依据,给出了插值-模拟采样迭代超分辨率重建方法的模型和重建步骤;最后通过实验数据对算法进行了验证。     

一种欠采样应用的高精度低功耗采样/保持电路

设计了一种可用于欠采样情况的高精度、低功耗采样/保持电路。在40 MHz时钟频率下,采样90 MHz输入信号时可达11位以上精度。采用电容翻转结构的采样/保持电路,以消除电容失配的影响;使用栅压自举开关,以提高线性度,实现欠采样输入;并设计了一种高增益、大带宽、低功耗的增益自举套筒式共源共栅(telescopic cascode)运算放大器。电路采用SMIC 0.35μmCMOS工艺实现,电源电压为3.3 V,功耗仅为7.6 mW。     

Potential use of the undersampling technique in the acquisition of nuclear magnetic resonance signals

This communication reviews the use of undersampling techniques to acquire NMR signals. Undersampling transforms bandpass free induction decay (FID) signals, centered at high frequencies, into lowpass signals or bandpass signals centered at much lower frequencies. Consequently, the analog electronic stages that perform the demodulation can be eliminated, gaining in stability and reducing the phase distortion while maintaining an equivalent or better signal to noise ratio when an adequate sampling rate is chosen. The technique has been tested on a BRUKER BIOSPEC BMT 47 40, and the results show that undersampling could be used to process NMR and MRI signals, extending the range of applications of the ‘digital radio’ techniques to NMR and MRI apparatus.     

用多重交织抽样方法消除频谱混叠

光电成象系统的抽样过程引起图象频谱分布在频谱空间的无限重复,如果抽样过程不满足系统的Ｎｙｑｕｉｓｔ条件,相邻的频谱项就会产生混叠,本文提出用多重交织抽样的方法来消除频谱混叠现象,用光学传递函数方法论述了这种方法的原理,并进行了误差分析。     

时空欠采样线性调频信号参数及其二维到达角联合估计

针对宽频段(2-18GHz)内非平稳来波信号的参数估计和测向问题,提出一种时空欠采样线性调频信号参数与二维到达角联合估计方法。该方法首先用时域解线调方法估计调频斜率,然后在分数阶傅里叶变换(FRFT)域进行滤波,实现信号提取。利用参考阵元及其延时通道进行无模糊初始频率估计,通过构建FRFT波束空间阵列模型实现无模糊测向。数值仿真表明,该方法能够实现宽频段内多个线性调频信号的参数和二维到达角精确估计,在低信噪比下仍有较好的估计性能。     

All-digital 2-channel parallel undersampling and reconstruction of band-limited signals

In this paper, we show that a band-limited signal can be reconstructed from two undersampled sequences of the signal, and further propose a 2-channel multirate undersampling and reconstruction method for band-limited signals. With such an approach, the sampling rate can be reduced to about one half of the Nyquist sampling rate. This method also has the advantage that no analog filters are needed to decompose the signal into two components with narrower bandwidths. Furthermore, the parallel processing of the two sampled sequences will lead to improved system performances. Finally, we consider the synchronization between the two sampled sequences, and show that the two A/D converters can be readily synchronized.     

基于安全样本筛选的不平衡数据抽样方法

针对欠抽样可能导致有用信息的丢失,以及合成小类的过抽样技术(SMOTE)可能使大类和小类间类重叠更严重的问题,文中提出基于安全样本筛选的欠抽样和SMOTE结合的抽样方法(Screening_SMOTE).利用安全筛选规则,识别并丢弃大类中部分对确定决策边界无价值的实例和噪音实例,采用SMOTE对筛选后数据集进行过抽样.基于安全样本筛选的欠抽样既避免原始数据中有价值信息的丢失,又丢弃大类中的噪音实例,缓减过抽样数据集类重叠的问题.实验表明在处理不平衡数据集,特别是维数较高的不平衡数据集时Screening_SMOTE的有效性.     

数系中具有噪声保护的解模糊问题

本文介绍了DFT与对称/非对称数系(SNS/ANS)之间的关系,并讨论了噪声对数系中解模糊的影响。把ANS中对噪声不敏感的解模糊原理推广到SNS系统中,给出了具有噪声保护的SNS无模糊带宽公式,在此基础上提出了欠采样条件下对噪声不敏感的SNS实时频率解模糊算法。