基于迭代函数系统的彩色植物模拟

阐述了迭代函数系统(iterated function system,IFS)的基本理论,讨论了几种基于IFS的彩色树木的模拟技术,并研究了迭代过程中随机因素和吸引子对色彩植物模拟的影响.     

An automatization of Barnsley''s algorithm for the inverse problem of iterated function systems

We present an automatization of Barnsley's manual algorithm for the solution of the inverse problem of iterated function systems (IFSs). The problem is to retrieve the number of mappings and the parameters of an IFS from a digital binary image approximating the attractor induced by the IFS. M.F. Barnsley et al. described a way to solve manually the inverse problem by identifying the fragments of which the collage is composed, and then computing the parameters of the mappings (Barnsley et al., Proc. Nat. Acad. Sci. USA, vol.83, p.1975-7, 1986; Barnsley, "Fractals Everywhere", Academic, 1988; Barnsley and Hurd, L., "Fractal Image Compression", A.K. Peters, 1992). The automatic algorithm searches through a finite set of points in the parameter space determining a set of affine mappings. The algorithm uses the collage theorem and the Hausdorff metric. The inverse problem of IFSs is related to the image coding of binary images. If the number of mappings and the parameters of an IFS, with not too many mappings, could be obtained from a binary image, then this would give an efficient representation of the image. It is shown that the inverse problem solved by the automatic algorithm has a solution and some experiments show that the automatic algorithm is able to retrieve an IFS, including the number of mappings, from a digital binary image approximating the attractor induced by the IFS.     

Parameter analysis of fractal image compression and its applications in image sharpening and smoothing

In recent years, numerous fractal image compression (FIC) schemes and their applications in image processing have been proposed. However, traditional FIC ignores the importance of affine parameters in the iterated function system (IFS) and affine parameters are kept invariant for a certain image in almost all of these schemes. By analyzing fractal compression technology in this paper, we show that the affine parameters in IFS can vary with different image quality measurements. A positive correlation exists between the image contrast of fractal decoded image and affine scalar multiplier. This strong correlation demonstrates that an image can be sharpened or smoothed using fractal compression technology.     

分形天线的IFS实现与特性分析

分形最基本的特征就是自相似特性与分数维，可以很好的用于设计天线。文章讲述了用IFS(迭代函数系统)实现分形天线的过程。并对一些典型的分形天线及分形天线阵列的特性进行了分析。     

Using neural network based nonlinear IFS to model time sequences

A novel neural network based iterated function system (IFS) model is presented in this paper while the precondition to ensure the model is also explored. Applying it to some practical data, the given signal can be approximated exactly by the attractor generated by this model, which provides another way to resolve fractal inverse problem.     

基于分形自仿射特性的混沌预测方法研究

研究了一类特殊非线性系统———混沌系统的局部预测问题。分析了分形的自仿射特性 ,将迭代函数系统(IFS)引入到混沌时间的预测中 ,从而将混沌预测问题转化为在相空间迭代寻找一个最佳的仿射算子和仿射子集 ,由此修正了最邻点的选取准则。从理论上证明了方法的可行性。结合局部超平面近似法 ,给出了迭代预测算法。数字仿真表明了该方法不仅提高了一步预测的精度 ,还具有多步较好的预测能力。     

Analysis of Modified Square Sierpinski Gasket fractal microstrip antenna for Wireless communications

In this paper, the slot loaded microstrip antenna has been developed with Sierpinski gasket technique. The proposed Modified Square Sierpinski Gasket (MSSG) fractal antenna involves a square patch utilizing Sierpinski gasket (triangular) structure. Four triangular slots are loaded at each iteration. The structure is then simulated using commercially available Ansoft HFSS simulator. The multi-band operation has been achieved by the proposed antenna at 15.915 GHz, 20.045 GHz, 23.077 GHz, 27.77 GHz frequencies with −20 dB, −25 dB, −22 dB, −28 dB return loss respectively which works well for Ku (12–18 GHz) and K (18–27 GHz) band. The consistent result is obtained after simulation and the validity of fabricated design is checked by the measured result. The designed antenna is an attractive candidate for applications like wireless multi-band communication systems.     

Wavelet transform and scale space filtering of fractal images

In this correspondence, we consider wavelet transform and scale space filtering as special cases of general scale shift mapping (SSM). Then, the SSM is used as a tool for characterizing the geometrical complexity of uniform fractals. This tool can reveal the construction rule of fractals and estimate fractal dimension. Finally, we use the results obtained from scale shift mapping to estimate iterated function system (IFS) codes of a class of fractal images. Some examples have been illustrated to demonstrate its good performance.     

改进型Sierpinski分形微带天线仿真

将HFSS高频仿真软件对不同张角下的二阶Sierpinski分形天线进行仿真,得到不同情况下的回波损耗参数和方向图。Sierpinski分形天线具有多频段的特性,由其自相似分形结构决定。在一定角度下的二阶Sierpinski分形天线具有双频特性,可以广泛应用于卫星通信和移动通信。     

Using iterated function systems to model discrete sequences

Two iterated function system (IFS) models are explored for the representation of single-valued discrete-time sequences: the self-affine fractal model and the piecewise self-affine fractal model. Algorithms are presented, one of which is suitable for a multiprocessor implementation, for identification of the parameters of each model. Applications of these models to a variety of data types are given where signal-to-noise ratios are presented, quantization effects of the model parameters are investigated, and compression ratios are computed     

基于分形的混合图象压缩方法

分形图象压缩方法是近年来迅速兴起的一种高倍率图象压缩方法，它依据分形原理，利用迭代函数系统（IFS）来抽取自然图象中的自相似性，达到压缩图象的目的；解码时利用拼帖定理来快速恢复图象。然而它最大的缺点是速度太慢。为此，本文将分形图象压缩同传统的块截取变换方法（BlockTruncatingCoding）结合，在压缩速度、压缩倍数和压缩失真方面有个折衷，达到较好的性能。     

A design approach for a dual-polarized, dual-band-reject frequency selective surface using a new Fractal element

In this paper we propose a novel frequency selective surface (FSS) as a band-reject filter for microwave frequencies. Here we suggest an innovative Fractal geometry named as FSS with Sierpinski fractal tripole elements (SFTE-FSS). The structure is analyzed with Ansoft Designer software package using the Method of Moment (MoM) technique. Then we compare the performance of the structure with that of Sierpinski dipole FSS. After all we perform a parametric study on SFTE-FSS. Using the information obtained by parametric study, we optimize the structure. The results show an interesting dual-polarized, dual-band behavior of the filter response. Finally, we bring experimental results and compare them with simulation results to verify the design process.     

Modeling of fractal antennas

Results on the numerical analysis of the Sierpinski and Koch fractal antennas are presented. It is shown that self-similarity of fractal structures affects electromagnetic properties of antenna structures created on the basis of these fractals. It is demonstrated that the Sierpinski and Koch fractal antennas are multiband structures; therefore, these antennas can be used for the development of radar and telecommunications systems. A technique is proposed for generation of an irregular determinate fractal structure that can be used for the development of a frequency-independent fractal antenna.     

A simple Bayesian multistage interference canceller for multiuserdetection in TDD-CDMA receivers

A simple multiuser detector (MUD) is proposed for channels affected by severe multipath and is then suitable for time-division duplexing code-division multiple-access (TDD-CDMA) receivers. For each user, after coherent combining and despreading, a suitable “Bayesian” memoryless nonlinearity gives symbol-by-symbol the expected values of the transmitted data. These are employed for soft removal of intersymbol and multiple-access interference (MAI) from the received sequences. The procedure is iterated in a multistage structure until final decisions are taken. From the comparison with other solutions, the proposed receiver exhibits better performance (close to the ideal canceller) and equal or minor complexity     

一种新型加载Sierpinski垫片天线的设计

提出一种新型分形结构加载的Sierpinski垫片天线。该天线采用新型加载技术并充分利用了此新型结构的空间自填充能力。结果表明,此新型分形结构加载的Sierpinski垫片天线比Koch分形加载更能缩减天线的尺寸,并且能降低谐振频率,具有宽频带特性,可以实现Sierpinski分形天线的小型化、多频段特性。     

Compact CPW-fed Sierpinski fractal monopole antenna

A novel compact and uniplanar CPW-fed Sierpinski fractal monopole antenna is presented. A fractal radiating element represents the fourth iteration of the Sierpinski gasket with scale factor /spl delta/=1.5. The antenna is printed on a single layer dielectric substrate and fed by 50 /spl Omega/ CPW transmission line. The multiband operation of the planar fractal structure is confirmed experimentally.     

改进型Sierpinski三角形分形多频天线研究

分形天线可以实现多频工作和尺寸减缩,在军用与民用方面都有着很大的发展潜力.研究了一种新结构形式的改进型Sierpinski分形天线,与普通结构相比,其可以通过调节各个三角形的高度比例来调整频比,且结构简单,加工制作更容易.仿真结果验证了改进型Sierpinski多三角形天线的多频特性.     

Weight distribution and performance of the iterated product of single-parity-check codes

We consider the iterated product of binary single-parity-check (spc) codes. We show that their weight distribution asymptotically approaches that of random coding if the smallest code length in the product approaches infinity. According to a specific criterion, the best choice of the product parameters consists of taking all spc codes of equal length. Estimates of the weight distribution obtained by simulation show that even moderately long codes have a weight distribution close to that obtained in the average by random coding. We also discuss decoding of these codes by iterated replication decoding and report results of its simulation.     

IFS图像空间结构特征及自动目标检测

一个迭代函数系—IFS(Iterated Function System ) 由一组压缩映射组成, 它描述了研究对象“整体”和“局部”之间的变换构成关系.对于图像来讲,IFS描述了图像“整体”和“局部”之间的空间变换关系,因此,IFS可以视为图像的空间结构模型,而与IFS有关的参数可以视为反映图像空间结构的特征.IFS的提出起源于分形图像压缩的研究,因此IFS与分形之间存在着密切的和内在的联系.IFS的理论中有两个重要的结论: 一是如果IFS中的压缩映射均为仿射变换,则IFS的吸引子将是一个分形集合;二是实际中所遇到的图像都可以用IFS的吸引子逼近.根据这两个结论,如果限定IFS中的压缩变换均为仿射变换,又图像本身具有分形结构,即图像“整体”和“细节”之间存在仿射变换关系,则用IFS的吸引子逼近图像所产生的误差很小(理论误差值= 0);如果图像本身不具有分形结构,则逼近误差很大.所以,根据IFS逼近误差的大小,即可判定被研究的图像是否具有分形结构特征.大量的理论研究和实验数据分析表明,自然背景的图像符合分形模型,而人造目标的图像不符合分形模型.因此,可以根据IFS逼近误差的大小实现对自然背景中人造目标的检测.提取图像IFS的算法有多种.本文采用Bath FractalTransform (BFT)算法,它是一个原理简单、实现方便、运算速度快的     

Sierpinski分形天线特性分析

Sierpinski分形天线的结构具有自相似性,从而天线具有良好的多频带特性。文中主要研究了Sierpinski分形天线频带位置随天线张角和比例因子变化的一般规律,并简要的分析了Sierpinski分形天线阵,绘出了其远场方向图,讨论了其低副瓣特性。