Synthetic aperture radar image compression using tree-structured edge-directed orthogonal wavelet packet transform

Currently, wavelet-based coding algorithms are popular for synthetic aperture radar (SAR) image compression, which is very important for reducing the cost of data storage and transmission in relatively slow channels. However, standard wavelet transform is limited by spatial isotropy of its basis functions that is not completely adapted to represent image entities like edges or textures, which means wavelet-based coding algorithms are suboptimal to image compression. In this paper, a novel tree-structured edge-directed orthogonal wavelet packet transform is proposed for SAR image compression. Inspired by the intrinsic geometric structure of images, the new transform improves the performance of standard wavelet by filtering along the regular direction first and then along the orthogonal direction with directional lifting structure. The cost function of best basis selection is designed by textural and directional information for tree-structured edge-directed orthogonal wavelet packet transform. The new transform including speckle reduction can be used to construct SAR image coder with the embedded block coding with optimal truncation for transform coefficients, and arithmetic coding for additional information. The experimental results show that the proposed approach outperforms JPEG2000 and Fast wavelet packet (FWP), both visually and item of PSNR values.     

基于正交脉冲波形的高速超宽带通信系统

提出了基于小波函数的两个正交脉冲,其功率谱密度满足美国通信委员会(FCC)对UWB系统的频谱限制。在此基础上提出了使用脉冲波形的极性调制和正交脉冲波形的形状调制相结合的一种高速超宽带通信系统,可以同时传送多个比特信息提高传信率。     

QAM-OFDM雷达通信共享信号长时间相参积累算法

QAM-OFDM(Quadrature Amplitude Modulation-Orthogonal Frequency Division Multiplexing)雷达通信共享信号因携带随机通信信息,其脉压旁瓣的随机性较大,类似噪声的影响。针对该问题,采用基于Keystone变换的长时间相参积累算法抑制其旁瓣。在共享信号模型的基础上,分析了其脉压旁瓣受随机通信信息的影响以及采用长时间相参积累抑制其旁瓣的可行性,然后采用Keystone变换校正其长时间相参积累产生的距离单元走动,并进行多普勒模糊补偿处理。理论分析和仿真结果表明,该方法使得回波能量积累集中,能有效实现共享信号脉压旁瓣的抑制。     

恒包络OFDM雷达通信一体化研究

提出一种新的OFDM雷达通信一体化系统模型,通过DFT预编码和交织式子载波映射解决了OFDM信号峰均功率比较高的问题,实现了OFDM信号的包络恒定。同时,给出一体化系统信号处理方案,在通信接收端,通过传统的OFDM信号解调得到通信数据。在雷达接收端,通过二维联合搜索和时域相位测量进行目标速度的估计;结合相关处理和频域相位测量,实现雷达的高精度测距。仿真结果表明,在保证通信传输功能的前提下,一体化系统能够实现厘米级别的测距精度和米每秒级别的测速精度。     

正交频分复用系统及其关键技术研究

在无线移动通信中,要求提供高速率和高质量的通信服务,而正交频分复用（OFDM）技术因具有频带利用率高和抗多径能力强等优点,近年来正受到广泛的重视,成为第四代移动通信系统的核心技术之一。在对该技术的基本思想介绍的基础上,分别对其优缺点进行了分析,且详细地阐述了OFDM系统中的关键技术及存在的问题。     

基于OFDM技术的有线传输系统仿真

文章对高速载波调制解调技术原理及其实现技术进行了研究,并根据MIL-STD-1553A/B实际传输的硬件系统,建立信道模型及噪声模型。该系统由基带信号处理和线缆驱动两部分组成,通过对传输系统中各处理模块的分析,并利用Matlab Simulink仿真平台进行系统级仿真,仿真结果表明OFDM调制解调技术获得10-5较低的误码率,可应用于已有的1553总线这样的高速有线传输系统。     

正交试验在软件测试用例设计中的应用

由于软件规模越来越大,软件测试要达到一定的测试覆盖率,生成的测试用例数目相当惊人。为了合理分配有限的测试资源,提出了一种基于正交试验的软件测试用例生成方法。简要介绍正交试验的基本概念,结合正交法的特点阐述其在设计软件测试用例方面的适用性及使用过程,最后给出实例。结果表明,生成测试用例数量较少,且测试效果能够得到保证。     

OFDM光纤通信中非线性补偿技术研究

为了降低非线性对正交频分复用（OFDM）光纤通信系统性能的影响,采用了一种适用于OFDM光纤通信系统的电非线性后置补偿方法。此方法基于OFDM光纤通信系统中的光纤模型,采用非线性薛定谔方程（NLSE）进行非线性后置补偿,用对称分步傅里叶算法对方程进行解析,并通过数值仿真证明了该方法能够很好地解决OFDM光纤通信系统的非线性问题,提高系统性能。     

跳频通信电台组网的建模与仿真

随着跳频通信在无线通信中日益广泛的应用,跳频电台的组网也就成为一个重要的课题。跳频碰撞作为跳频电台组网的关键技术,但这方面可见的研究文献却很少。本文首先介绍了跳频电台组网理论容限的数学模型,然后以53个有效频点为例,设计出了非重复碰撞的跳频图案。最后,对异步组网时跳频图案的性能和碰撞问题进行了仿真。     

基于RGB-LED的高速双向可见光传输系统(英文)

In this paper,we propose and experimentally demonstrate a bi-directional indoor communication system based on visible light RGB-LED.Spectrally efficient modulation formats(QAM-OFDM),advanced digital signal processing,pre- and postequalization are adopted to compensate the severe frequency response of indoor channel.In this system,we utilize red-green-blue Light emitting diodes(LEDs),of which each color can be used to carry different signals.For downlink,the low frequencies of each color are used while for uplink,the high frequencies are used.The overall data rate of downlink and uplink are 1.15-Gb/s and 300-Mb/s.The bit error ratios(BERs) for all channels after0.7 m indoor delivery are below pre-forwarderror-correction(pre-FEC) threshold of3.8×l0~(-3) To the best of our knowledge,this is the highest data rate in bi-directional visible light communication system.