Hardware-Constrained Hybrid Coding of Video Imagery

The design, implementation, and performance of a video bandwidth compression system is described. In this system, compression is obtained by several methods including the use of DCT/DCPM hybrid coding, frame rate reduction, and resolution reduction. The overall compression ratio is up to 1000:1. The hardware-constrained design of the DCT and the DPCM is described and a new method is derived to solve the optimum integer bit-assignment problem associated with the block quantization process in the DPCM. Computer simulation results are presented which predict that the performance of the system using the derived optimal bit assignment method is superior to those obtained by other bit assignment methods. The real-time hybrid coding system design is optimized for a set of ?modified? average statistics to compress a wide variety of input video images. This approach eliminates the problem of nonzero dc mean value which could otherwise cause serious degradations in the system performance. The compression system is fully implemented and the quality of the reconstructed video as predicted by computer simulation has been demonstrated by the actual hardware performance. The PSNR of the reconstructed imagery is in excess of 36 dB at 2 bits per pixel.     

Comparison of Electrooptic Modulation Methods

A comparison is made among normal AM, wide-band analog FM, and PCM as applied to transmission of real-time TV pictures via an electrooptic space communication system. The comparison is based on the requirement to receive a subjectively noise-free TV picture. Based on the results of this comparison, it is concluded that analog-FM subcarrier modulation is the best practical choice for transmission of real-time TV pictures in space via a laser beam. In addition to providing performance equivalent to that of coherent PCM, this type of modulation can be implemented with comparatively simple equipment.     

一种基于HVS的图像质量评价方法

通过充分分析人类视觉系统(HVS) 的亮度、纹理、边缘等特性, 给出相应的视觉特性计算模型,在此基础上提出一种结合HVS特性的加权峰值信噪比计算方法.实验结果表明该模型计算出的HVS值能充分反映人类视觉系统的屏蔽特性;图像质量评价方法的评价结果与主观评价结果相一致,效果优于传统图像质量评价方法.     

PCM系统中数字相敏检波器的设计与仿真

在PCM（埋地管道电流测绘）系统中，实际的信号采集需要解决在非常恶劣的环境中对ELF（甚低频）信号的精确测量的问题。传统的方法一般都采用APSD（模拟相敏检波器）来实现，然而在实际的电路中用模拟相敏检波器效果并不是很理想，结果存在严重的误差。针对目前模拟相敏检波器存在的问题，设计一种DPSD（数字相敏检波器）实现消除PCM系统中ELF信号中工频干扰的目的。该检波器能有效的克服模拟相敏检波器的缺点，更精确的进行微弱信号的检测，最后使用MATLAB仿真软件对模拟和数字相敏检波器进行了仿真比较。     

Adaptive detection schemes in compound-Gaussian clutter

Radar detection of coherent pulse trains embedded in compound-Gaussian disturbance with partially known statistics is discussed. We first give a thorough derivation of two recently proposed adaptive detection structures. Next, we derive a different detection scheme exploiting the assumption that the clutter is wide-sense stationary. Resorting to the theory of circulant matrices, in fact, we demonstrate that the estimation of the structure of the clutter covariance matrix can be reduced to the estimation of its eigenvalues, which in turn can be (efficiently) done via fast Fourier transform codes. After a thorough performance assessment, mostly carried on via computer simulations, the results show that the newly proposed detector achieves better performance than the two previously introduced adaptive detectors. Moreover, a sensitivity analysis shows that, even though this detector does not strictly guarantee the constant false alarm rate property with respect to the clutter covariance matrix, it is robust, in the sense that its performance is only slightly affected by variations in the clutter temporal correlation     

On the Optimum Design of PCM Signals with System Constraints

This paper considers the design of PCM signals with system constraints using Pontryagin's maximum principle. The transmitter signal as well as the correlation signal are determined while maximizing the output signal-to-noise ratio. Both the single and three-pole transmitter filters are considered. An upper bound has been obtained on the performance of PCM signals with constraints.     

基于自适应滤波的PCM／FSK软件解调方法

提出了一种新的PCM／FSK数字信号解调方法。通过采用最小均方误差自适应滤波算法，跟踪信号的单一频率，分析输出信号的包络，实现PCM／FSK信号的解调。详细介绍了此种解调方法的基本原理及实现过程，分析了影响解调性能的因素。计算机仿真结果表明，此方法比差分解调性能优越，抗干扰能力强，便于软件编程及DSP器件实现，具有一定的应用价值。     

Analysis and design optimization of monopulse receivers forsecondary surveillance radar

The sensitivity to calibration and component errors of the receiver configurations used for monopulse processing of secondary surveillance radar (SSR) replies is analyzed. The effects of video gain error in amplitude processors and large Gaussian perturbations in phase processors are discussed. Phase processors are shown to be robust to variations in antenna difference pattern null depth. A half-angle phase processor that yields the benefits of phase processing without the sensitivity to system errors associated with conventional implementations is described     

Performance of a Two-Sample Mann-Whitney Nonparametric Detector in a Radar Application

The detection of signals in an unknown, typically non-Gaussian noise environment, while attempting to maintain a constant false-alarm rate, is a common problem in radar and sonar. The raw receiver data is commonly processed initially by a bank of frequency filters. The further processing of the outputs from the filter bank by a two-sample Mann-Whitney detector is considered. When the noise statistics in all filters are identical, the Mann-Whitney detector is distribution free, i. e., the false-alarm probability may be prescribed in advance regardless of the precise form of the noise statistics. The primary purpose of this paper is to demonstrate the potential advantage of nonparametric detectors over conventional detectors. The signal detection performance of the Mann-Whitney detector is compared to that of an ordinary linear envelope detector plus integrator in the presence of Gaussian and several hypothetical forms of non-Gaussian noise. This comparison is made for both uniform and nonuniform distributions of noise power across the filter bank. Besides providing a much more constant false-alarm rate than the conventional detector, the Mann-Whitney detector's signal detection performance is found also to be much less sensitive to the form of the noise statistics. In one case, its detection sensitivity is found to be 11 dB better than that of the conventional detector. Even when the noise power density is made moderately nonuniform across the filter bank, the detection performance of the Mann-Whitney detector is found not to be significantly affected.     

航拍视频拼图中基于梯度域的多帧图像融合方法

图像融合是视频拼图中获得高质量合成图像的重要步骤。利用梯度信息引导插值融合重合区域较小的两幅图像已经取得较好的效果,然而对于视频拼图而言,相邻两帧图像之间重合区域大,且多帧图像之间交叠重合,给这种方法的实际应用带来限制。为解决这一问题,设计梯度域内同时融合多帧图像的策略,利用图像的自然边界将拼图平面进行区域划分,在各区域内分别定义引导矢量场和边界条件,实现各划分区域的一次性融合。为克服拼图平面的过划分问题,提出相应的帧选择方法和区域合并算法。将该策略用于视频拼图实验,获得了视觉效果良好的合成图像,并提高了融合效率。     

Multi-objective approach in GNSS code discriminator design

In spread spectrum ranging system receivers such as the Global Navigation Satellite System (GNSS) receivers, a discriminator is used in the code tracking loop to provide an error signal for the tracking of incoming signals. Typically, the discriminator manipulates several correlator outputs to form the correction signal. A multi-objective approach is adopted here to design the coefficients associated with a multi-correlator-based discriminator to lead to a better performance tradeoff in large tracking range, acceptable multipath-induced bias, high sensitivity, free of ambiguity, and small variance. It is shown that the multiple-objective problem can be tackled via a quadratic/linear programming method, rendering the optimal coefficient vector for the implementation of the discriminator. In addition, as the discriminator design is often subject to conflicting requirements, it is shown that the proposed design approach is capable of establishing bounds on achievable performance. Examples with respect to BPSK (binary phase-shift keying) NRZ (nonreturn-to-zero), and BOC (binary-offset carrier) signals are given to illustrate the design approach.     

Effects of Perturbations on the Performance of Optimum/Adaptive Arrays

An investigation of the effects of system and medium perturbations, and the deviations of signal field statistics from usual assumptions, on the performance of adaptive arrays is presented. The emphasis is placed on the determination of the sensitivity of the adaptive processors to perturbations, rather than its overall performance in a representative background. The numerical results are limited to CW signals, and a frequency domain element space adaptive beam-former is modeled for the majority of the results. Representative comparative results including frequency domain beam space, time domain element space, and matched array processors are also given.     

Comments on Transmission System Using Pseudonoise Modulation of Linear Chirps

The combination of phase shift keying (PSK) with different chirp waveforms is investigated in respect to its signal form and spectrum shape. A reasonable compromise for low probability of exploitation and jam sensitivity is found for a system where the chirp bandwidth is in the vicinity of the bitrate of the pseudonoise code.     

远程多路视频信号无线传输采集系统设计

设计了一种远程多路视频信号传输采集系统,通过模拟信号远程无线传输的方式将摄像头获得的视频信息传输到监控计算机,由计算机上的图像采集卡进行采集,由监控软件进行多路信号的显示,该系统在多机器人系统中取得了良好的应用效果。     

基于DSP平台的机载高清视频编码器设计与实现

针对无人机(UVA)航拍对高清视频的需求,设计并实现了基于数字信号处理器(DSP)平台的MPEG-4高清视频编码器,具有体积小、功耗低和可靠性高的特点.根据DSP片内资源设计了存储器分配方案,优化了编码过程中的数据流传输,降低了数据访问对编码速度的影响.针对视频编码算法中复杂度较高的部分,采用了基于预测的运动估计,减少...     

超重力下相变材料熔化过程的数值模拟

通过数值模拟的方法,研究了地球重力和超重力条件下相变材料(PCM)的熔化过程,分析了超重力对PCM熔化过程的影响。采用的超重力大小为5倍和10倍地球重力,方向与热流进入方向相反。模拟结果表明,由于PCM导热系数偏小,熔化初期加热面发生过热,须通过耦合其他强化换热措施予以减弱甚至消除。超重力对于PCM熔化过程的影响十分显著。随着超重力的增加,熔化界面的波动幅度增大,熔化速度加快,加热面温度下降,这是因为熔化过程中液相的自然对流作用显著增强。此外,超重力对PCM熔化过程的增强幅度会随超重力的增加而减小,表明超重力的强化换热作用有一定限度,当超过一定值时,该强化作用的效果相对减弱。     

基于IP网络的多点视频会议系统的设计与实现

结合实际,深入论述了一种基于IP网络的多点视频会议系统的设计与实现,该系统能基于TCP／IP宽带广域网传输视频、语音、静态图像和文字等多种多媒体信息,能应用于异地故障诊断、网上电子会议、远程技术支持培训等多种领域。     

北斗B1 QPSK调制信号的高灵敏度捕获算法

卫星信号在复杂环境中功率存在衰减,导致其低于接收机正常捕获范围,给信号捕获带来较大困难。在分析北斗B1频点信号体制及研究码并行捕获算法基础上,提出了针对北斗B1 QPSK调制信号的双通道并行搜索捕获算法,设计了优化的相干、非相干码并行捕获算法,解决了信噪比较低环境中北斗卫星信号捕获困难的问题。利用卫星信号模拟器产生的仿真信号对双通道并行捕获算法和相干、非相干累加捕获算法进行验证与分析,结果表明,前者性能明显优于单通道捕获,后者较普通捕获算法具有更理想的捕获灵敏度。     

基于运动形态学的掠地飞行器视频检测方法

 结合数学形态学、视频图像运动分析以及数学统计分析方法，提出了一种用于空中预警控制系统(AWACS)的小型掠地飞行器运动形态学视频检测方法。该方法首先应用形态学tophat滤波提取出视频图像中的可疑目标(SO)，并求取SO的运动参数，利用真实目标和类目标干扰的不同运动特性，应用数学统计的方法对各运动参数进行分析以剔除部分类目标干扰，从而获得潜在目标(PT)的灰度分布和运动参数。在应用形态学tophat滤波器进行可疑目标提取中，一种新的金字塔型结构元的引入有效减少了虚警数量。外场试验表明，该检测方法能够有效抑制航拍掠地飞行器视频图像中的地物干扰，降低虚警目标的数量。     

基于FPGA的高清CCD视频信号预处理电路的设计

在高清CCD图像传感器KAI-2093和视频信号处理芯片AD9847工作原理的基础上,设计了高清CCD成像系统视频信号处理电路。选用FPGA器件作为硬件设计载体,使用VHDL语言对AD9847的初始化配置和驱动时序发生器进行了硬件描述。采用ISE10．1软件对所做的设计进行了功能仿真。仿真结果表明,所研制的高清CCD视频信号处理电路不仅可以满足高清CCD成像系统视频处理的要求,而且性能可靠,使用灵活。