利用过采样探测提高线阵扫描相机的空间分辨率

从航天工程的特殊工作环境出发,不单纯在理论上推导如何提高线阵扫描相机的空间分辨率,而是在远距离、低能量的环境下,从系统的角度研究了图像配准程度、信噪比和时间分辨率对空间分辨率的影响关系,进而提出了过采样探测系统的设计约束条件.在不能降低相机时间分辨率和信噪比的条件下,提出了一种利用过采样技术将线阵扫描相机空间分辨率提高20%的新方法.     

基于变采样速率的信号处理

该文讨论了利用过采样、减采样等变采样率处理方法,进行通信信号处理的方法。着重从理论上分析了补零FFT对频率分辨率的影响。并且,区分了实际频率分辨率与可视频率分辨率。讨论了时域采样变化和频域采样变化对频率分辨的不同影响。     

过采样技术在扭矩扳子检定仪中的研究

过采样技术能够有效减小模数转换过程的噪声功率,从而提高模数转换器的分辨率。基于奈奎斯特采样定理,对模数转换器的采样频率和量化误差进行分析。通过理论分析得出,每增加一位分辨率需要增加4倍采样频率,并提出了3个影响过采样技术有效性的因素。通过在扭矩扳子检定仪中的应用过采样技术,使扭矩扳子检定仪的模数转换器提高了4位分辨率。在此基础上,对过采样技术进行了改进,使扭矩扳子检定仪的精度提高到0.3%以上。     

基于过采样技术提高ADC分辨率探析

近年来,许多系统都需要使用模／数转换器ADC进行测量,将模拟信号转换为数字信号。为了简化系统电路和降低生产成本,在充分利用ADC采样速度的条件下,通过过采样技术提高ADC的分辨率。这里基于ADC的基本结构,采用叠加成形函数的方法,介绍了用过采样的方法来达到较高分辨率和信噪比,得出采样技术可以在不使用昂贵的ADC芯片的情况下提高模／数转换的分辨率。     

欠采样与过采样技术研究

数据采集面临两类问题:要有更高的采样率,来满足对高频信号的采样需求;能有更大的采样动态范围,来满足对微弱信号的采样需求。欠采样技术和过采样技术的出现很好地解决这两个问题。文章将解析欠采样和过采样的基本原理,并利用欠采样和过采样解决实际遇到的问题。     

基于FPGA过采样技术及实现

过采样技术应用于通用模块时,低通滤波器的参数随着下抽取率不同而发生改变。本文设计了适合通用模块应用的可变参数低通滤波器,并利用FPGA进行实现。模块测试结果表明:可变参数滤波器设计合理,基于FPGA的过采样模块最高分辨率可达25bit/s。     

不同采样体制对点目标的定量检测性能

围绕单采样和过采样扫描探测体制下的点目标定量检测性能,基于亚像元的采样模型,建立了一定分辨率条件下探测不同高度、尺寸目标的成像链路仿真模型,从目标信号采集能力、背景及杂波水平影响、检测能力和测量特性四个方面对比分析了相同瞬时视场的单采样、过采样以及两倍瞬时视场的过采样三种规格采样体制的目标检测性能。分析结果表明：相同瞬时视场的过采样比单采样更有利于目标信号的采集,检测能力更强,两倍瞬时视场的过采样对目标信号有抑制作用,不利于低信杂比情况下的目标探测;两种规格的过采样对背景信号及杂波均有抑制作用;两种规格的过采样对目标辐射强度都有明显的过采集误差,必须进行修正。     

数字技术中的过采样

过采样已越来越多地用在各种数字系统中,例如ＣＤ机,数字电视,数字通信等。本文的目的在于讨论过采样的特性,特别是有关频谱密度、噪声整形及采样率与量化分辨率的。同时也涉及到过采样的应用及潜力。     

采用过采样提高C8051F020片内ADC分辨率的研究

模数转换的分辨率与器件的数字位数有关,位数越多分辨率越高,分辨率越高器件的成本也越高。C8051F020的片内ADC是12位的,为了既降低系统成本又获得较高的分辨率,介绍了过采样和求均值方法的实现原理。该方法有效提高转换的分辨率和信噪比,但增加CPU处理时间并降低了数据吞吐率。     

利用过采样技术提高ADC测量分辨率

针对目前单片机内嵌ADC分辨率较低,而外接高分辨率ADC成本又较高的情况,提出了用“过采样”技术使在有用的测量频带内的信噪比得到改善,从而提高ADC测量的分辨率。并利用Matlab对其结论进行仿真,且在TMS320LF2407 DSP上予以实现,结果表明信噪比和测量分辨率明显提高。     

时-空过采样系统对点目标成像仿真与验证

为了验证时-空过采样系统对点目标探测的优越性,设计了红外点目标成像仿真及实验系统,研究并验证了时-空过采样获得的点目标图像形状、能量分布特点。首先,对比分析了时-空过采样系统与常规采样系统对点目标扫描成像原理;然后,对时-空过采样系统成像过程建立模型,通过仿真研究该系统对点目标的成像特点;最后,设计红外点目标成像实验并对实验数据进行分析。仿真及实验结果证明了时-空过采样克服了单采样对点目标成像能量分散的问题,图像信噪比至少提高2倍以上,且验证了经时-空过采样后,点目标像素之间具有特定的相关规律。利用时-空过采样的点目标成像特点,可为点目标的快速检出提供有利条件。     

A bandpass mismatch noise-shaping technique for /spl Sigma/-/spl Delta/ Modulators

A simple bandpass mismatch noise-shaping technique for /spl Sigma/-/spl Delta/ modulators is presented. This technique uses the data-directed scrambler structure and achieves /spl sim/20 dB improvement in signal-to-noise ratio (SNR) for an oversampling ratio (OSR) of 32. Compared to the technique of bandpass mismatch noise shaping of Lin and Schreier, here, the SNR is improved by /spl sim/ 7dB resulting in a 1-bit improvement in resolution. The selection logic is half the size of the logic in Lin and Schreier and is fully compatible with the low-pass selection logic of Kwan et al.. This compatibility allows implementation of bandpass/low-pass modulator as a single product.     

A CMOS stereo 16-bit D/A converter for digital audio

A complete monolithic stereo 16-bit D/A converter primarily intended for use in compact-disc players and digital audio tape recorders is described. The D/A converter achieves 16-bit resolution by using a code-conversion technique based upon oversampling and noise shaping. The band-limiting filters required for waveform smoothing and out-of-band noise reduction are included. Owing to the oversampling principle most applications will require only a few components for an analog postfilter. The converter has a linear characteristic and linear phase response. The chip is processed in a 2-/spl mu/m CMOS process and the die size is 44 mm/SUP 2/. Only a single 5-V supply is needed.     

光子累计方法在成像激光雷达中的应用研究

介绍了一套自行研制的采用光子计数探测的1064nm激光雷达系统。理论分析了光子计数探测技术和信噪比的改善．实验研究了改善信噪比的脉冲累计方法。给出了光子累计脉冲与信噪比之间的平方根关系,以及不同距离下的探测结果。另外,讨论了光子累计在两种成像方式下,相同参数的数值模拟和比较。结果表明：采用大发射光束和光子累积方法进行探测的信噪比,比单光束、大光强和逐行扫描方式的探测在理论上要好些。即探测概率高。     

基于过采样的混合滤波器组性能优化

模拟误差是制约混合滤波器组信号重构精度的主要原因,如何降低由模拟误差导致的分解滤波器组系数误差成为了首要问题。引入过采样技术,研究在不同过采样率下8通道混合滤波器组的性能,寻找到过采样率最优值约等于7%。在不同模拟误差下对基于过采样的混合滤波器组的性能进行仿真,结果表明,原型结构和双阶型结构的混叠值相近,但后者对模拟误差的敏感度比前者大。信号重构阶段,在最小二乘法的基础上采用频带加权法进行误差校准。在1%模拟误差内,采用7%过采样率的原型混合滤波器组相比无过采样,平均混叠值下降了约50 dB,最大混叠值下降了约94 dB。仿真验证了引入过采样的有效性。     

Power spectrum estimation from values of noisy autocorrelations

The problem of estimating the power spectrum from noisy autocorrelation values is considered in this paper, and it is proposed that in order to reduce errors, oversampling of the available time domain data should be employed. The oversampling problem is discussed from the frame theory point of view, and it is shown that the frame reconstruction represents an improvement upon the standard correlogram, windowing, and autoregressive modelling approaches.     

基于数字锁相相关计算结构的优化算法

为了兼顾数字锁相检测的速度和精度,提高信号检测系统的综合性能,该文提出了一种基于数字锁相相关计算结构的高速算法并结合过采样对算法性能优化。该方法在过采样的基础上将采样频率还原为4倍于原信号的频率,快速数字锁相算法对下抽样后q个周期的4q个采样点进行加减法运算即可实现,与传统数字锁相算法相比几乎消除了所有的乘法运算,大幅度地提高了数字锁相算法实现的速度。同时引入修正因子改善了由于降采样所带来的误差。实验结果表明,该方法既有过采样和锁相检测的高精度,能够检测到较低信噪比的信号,又具备较高的速度,使得该算法对微弱信号的实时检测在普通微处理器上的实现成为可能。     

Oversampled pipeline A/D converters with mismatch shaping

The authors present a pipeline A/D converter with improved linearity (SNDR). The SNDR improvement is achieved through a combination of oversampling and mismatch shaping, which modulates the distortion energy out-of-band. At an oversampling ratio of four and 64, and a component mismatch of 0.1%, 9 and 35 dB improvements in SNDR are achieved, respectively, in comparison to a converter with no mismatch shaping     

Layered maximum likelihood detection for MIMO systems in frequency selective fading channels

By transmitting different substreams in different antennas simultaneously, a multiple element antenna array system provides increased capacity that grows linearly with the number of transmit antennas. Layered space-time processing that performs ing, detection and cancellation for each substream can be used for reception, with a linear growth in receiver complexity. This paper considers this multi-input multi-output system over a slow time-varying frequency selective Rayleigh fading channel environment. With the equivalent channel tap delay line model, each delayed tap in every transmit-receive antenna pair can be considered as an imaginary antenna transmitting a delayed version of the substreams. Based on this idea, we propose a layered maximum likelihood detection (L-MLD) scheme which performs layered processing and maximum likelihood detection for each substream and its delayed elements. To further improve the performance, a group maximum likelihood detection (G-MLD) scheme is also proposed by grouping the substreams and performing layered processing in groups and maximum likelihood detection within the group. However, both schemes increase the required number of receiving antennas, which increases hardware cost and size. To reduce this requirement, we propose the use of oversampling technique to increase the dimension of the received signal. Simulation results show that the L-MLD scheme achieves frequency diversity and outperforms existing schemes such as the V-BLAST system with OFDM and multi-input multi-output decision feedback equalizers (MIMO-DFE). Moreover, the G-MLD scheme performs better than L-MLD with an increased detection complexity. In addition, it was showed that further increasing the oversampling rate beyond the minimum requirement does not improve the performance.     

The Diversity Gain and ICI Suppression for OFDM Systems Over Doubly Selective Channels

How to compensate the detrimental impact of intercarrier interference (ICI) on BER performance is the key issue of signal detection for orthogonal frequency division multiplexing (OFDM) systems in doubly selective channels. In this paper, we propose an optimal linear ICI suppression algorithm with successive detection based on oversampling at the receiver, by which the OFDM systems can benefit from doubly selective channels for achieving both the multipath diversity and Doppler diversity. To reduce the additional computational complexity caused by oversampling, a low complexity implementation method for this algorithm is also presented. Simulations results show that the proposed algorithm can enhance the BER performance with the increase of the Doppler spread and the oversampled factor.