基于信息编码的神经能量计算

通过神经元活动期间神经能量的计算, 发现关于神经元 的活动需要消耗能量的观点并不完整. 计算表明神经元在动作电位发放期间先吸收 能量然后再消耗能量. 依据这个重要发现, 能够解释当脑内神经元被激活时脑血流 量大幅增加而耗氧量却增加很少这一难以解释的神经生理学现象. 同时还能够解释外部刺激信息和知觉的产生会有同步效应这一认知神经科学界也难 以解释的现象.     

Fractal coding of subbands with an oriented partition

We propose a new image compression scheme based on fractal coding of the coefficients of a wavelet transform, in order to take into account the self-similarity observed in each subband. The original image is first decomposed into subbands containing information in different spatial directions and at different scales, using an orthogonal wavelet-generated filter bank. Subbands are encoded using local iterated function systems (LIFS), with range and domain blocks presenting horizontal or vertical directionalities. Their sizes are defined according to the correlation lengths and resolution of each subband. The edge degradation and the blocking effects encountered at low bit-rates using conventional LIFS algorithm are reduced with this approach. The computation complexity is also greatly decreased by a 12:1 factor in comparison to fractal coding of the full resolution image. The proposed method is applied to standard test images. The comparison with other fractal coding approaches and with JPEG shows an important increase in terms of PPSNR/bit-rate. Especially for images presenting a privileged directionality, the use of adaptive partitions results in about 3 dB improvement in PPSNR. We also discuss the distorsion versus rate improvement obtained on high-frequency subbands when fractal coding instead of pyramidal vector quantization is used. Our approach achieves a real gain in PPSNR for low bit-rates between 0.3 and 1.2 bpp.     

Performance analysis of spectrally encoded hybrid WDM-OCDMA network employing optical orthogonal modulation format against eavesdropper

In this paper, the spectrally encoded hybrid WDM-OCDMA network employing 60 Gbps non-return to zero/differential quadrature phase shift keying (NRZ/DQPSK) orthogonally modulated data signal operating over 100 km SMF+DCF has been proposed. In proposed hybrid WDM-OCDMA network, the orthogonal modulation formats are used to enhance per channel capacity and the spectral amplitude optical coding for enhancing the confidentiality of data from unauthorized user or eavesdropper. The impact of input power, transmission distance and energy per bit to noise power spectral density ratio (E_b/N₀) on the performance of WDM-OCDMA network in terms of output optical power, timing diagram, BER, Q-factor and probability of error free code detection has been investigated. It can also be determined that orthogonal modulation formats are promising option to increase per channel capacity as compared to conventional modulation format and these are less vulnerable to chromatic dispersion (CD) and polarization mode dispersion (PMD). Meanwhile, the performance of proposed hybrid network is compared with existing OCDMA network which show the feasibility of proposed WDM-OCDMA network in future generation optical networking.     

基于SSFBG的±π/2和0/π相移编码的安全性比较

分别采用0/π和±π/2相移的方式对光脉冲信号进行了编码,并比较了基于超结构光纤光栅的0/π和±π/2两种相移编码方式的安全性,通过研究分析两编码器所生成的编码波形来评估各自的安全性。结果表明,0/π相移编码器生成的编码波形中存在明显的凹陷,光学码信息易被窃取,安全性低;而±π/2相移编码器生成的编码波形能隐秘地将光学码信息隐藏于编码波形中,大幅改善了编码安全性,提高了通信安全。     

指纹图像的定量化区域矢量编码与识别

为了识别一幅图像 ,通常需要对它进行编码 ,提取特征信息。大体上可以归纳为两类方法 :统计方法和语言(或结构 )学方法。两类方法各有优缺点。第一类方法很少利用图像本身的结构关系 ,而第二类方法则没有考虑图像在环境中所受的噪声干扰。因此把二者结合起来 ,各取其长 ,是可取的途径。在统计方法的基础上 ,考虑了指纹的结构特点 ,按纹理方向进行分组 ,对它们实行定量化编码 ,并由此建立了方向矢量样本形式 ,给出了试验结果。这种方法的样本数据量小 ,构造过程简单 ,匹配和识别的信噪比高 ,不易产生错误匹配和判别。     

计算全息干涉实现防伪和信息的加密存储

提出一种位相编码计算全息干涉防伪术。这种方法用迂回位相法对光波进行位相编码,然后用这个编码的光波和另一由计算全息产生的参考光波干涉,从干涉图样中可以读出所记录的信息,没有参考计算全息图则无法读出记录的信息。这种计算防伪全息图的特点是设计灵活、使用方便、可由白光再现。具有很强的防伪力度。     

经典分形集测度上估的计算机搜索Ⅰ──对典型例子Sierpinski垫片编码技术的剖析

分形集的Hausdorff测度是一个非线性科学的理论课题,至今结果甚少,即使对于一些生成很有规则的经典分形集亦是如此间．SISrpinski垫片就是这样一个经典分形集,但因其预分形的图形尚未被研究者解析地认识,所以对其Hausdorff测度的研究进展很慢．文献问猜测1十年之后,这个猜测才被文献问以估值否定．接着,文献同又得到更好的估值出由于采取了对Sierpinski垫片发生规则的编码技术,从而方便地得到H”（S）的一个上方估值函数o（x）．上面提到的一系列猜测值或上方估值,依次由0（1／2）,o（l／4）,以司对给出,而则给出TH”（S）…     

Metric‐based node synchronization of the Viterbi decoder in satellite applications

Convolutional codes are used in digital communication systems to correct errors that occur during transmission. Their use is now commonplace, particularly in power‐limited satellite and deep space communication systems. Before the decoder can correctly decode the received continuous bit sequence, however, it must establish where codewords begin and end in this sequence. The process of determining codeword boundaries is called node synchronization. In this paper we develop a node synchronization algorithm based on metric difference values with the objectives of simple implementation and reliable performance. Focusing on satellite applications, we consider the constraint length 7, rate ½ convolutional code standardized by the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA); the approach we develop can be extended to other convolutional coding systems. Through simulation, we investigate the statistics of the received sequence, and highlight correlation in the sequence of the decoder metric values. In the light of these observations, we propose a synchronization algorithm, and develop a first‐order analysis of this simple up/down counter framing technique. We recommend framing parameters based on both the analytical results and the expected response of the framing algorithm to correlated metric values. Development of a simple node synchronization algorithm that accommodates correlated metric values has not been reported previously in the literature. Simulation results confirm that reliable node synchronization is possible with this very simple approach. Copyright © 2000 John Wiley & Sons, Ltd.     

Image/video communications: joint source/channel coding

Transmission of image/video messages over communication networks is becoming a standard way of communication due to very efficient compression algorithms that reduce required channel capacity to an acceptable level. However, all compression standard techniques are strongly sensitivitive to channel disturbances and their application is suitable only for practically noiseless channels. In standard noisy channels, the effect of errors on a compressed data bit stream can be divided into two categories: systematic errors defined by the structure of data blocks, and random errors caused by amplitude changes of transmitted components. A systematic error can be detected at the receiver through control of the data stream structure and corrected by error concealment methods or by automatic repeat request (ARQ) procedures. Random errors, noise and burst‐like errors, as well as impulse noise, should be controlled through channel coding. It is reasonable that an integrated source and channel coding methods should be preferred and should give better coding performance. In this paper, a new framework for an image/video coding approach has been presented in which the source and channel coding is integrated in a unique procedure. Image compression is performed in a standard way of the JPEG algorithm based on discrete cosine transform (DCT) and error control coding is based on the real/complex‐number (N,M) BCH code using discrete Fourier transform (DFT) specified with zeros in the time domain, i.e. with roots in the frequency domain. Efficiency of the proposed method is tested on two examples, an one‐dimensional real‐valued time sequence coded by real‐number (20,16) BCH code using DFT, and an example of an image coded by complex (10,8) BCH code using DFT with the correction ability of up to 8 impulses per transmitted 8×8 block. In addition, two decoding methods based on Berlekamp–Massey algorithm (BMA) and the minimum‐norm algorithm (MNA) have also compared. Copyright © 1999 John Wiley & Sons, Ltd.     

数字图象在广播电视综合信息网中的应用

首先介绍数字图象通信的意义、优点及压缩编码技术的进展，然后介绍某一广播电视综合信息网中数字图象通信的应用。