无线通信系统中的低码率空时网格码

空时网格编码能在频带利用率、分集增益、调制方式与编码网络图复杂度之间达到最佳的折衷。本文给出了几种低码率空时网格码的好码。理论分析和系统仿真表明,在相同的频带利用率下,该空时网格码可具有比空时块码级联卷积码具有更好的误码率性能,更适合于对频带利用率要求不高的功率受限无线通信系统。     

Stark level analysis for Er-doped ZBLAN glass

From the absorption and emission spectra recorded in a conventional way at 13 K, the Stark levels in manifolds from ⁴I_15/2 to ²H_9/2 for Er³⁺-doped ZBLAN (ZrF₄–BaF₂–LaF₃–AlF₃–NaF) glass have been investigated by means of the effective crystal field model previously proposed to describe the average of local symmetries occupied by rare earth ions in oxide glasses [1]. This model, based on the principle of descending symmetry, used the symmetry group chain scheme. Crystal field strength, homogeneous and inhomogeneous widths of levels have been determined, and the former models and results about optical properties for rare earth ions in heavy metal fluoride glasses are discussed. In fluoride glasses, the rare earth ions appear more evenly distributed than in oxide glasses, and the crystal field strength is weaker than in oxide glasses.     

Optical PPM CDMA Communication System with Optical Hard Limiter

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一种新颖的Turbo码MAP译码器

根据Turbo码trellis结束的情况及Turbo码的特征本文提出了一种新的Turbo码MAP译码器。这是基于MAP译码器中两个组成译码器性能的不一致所作改进,从分析和仿真结果我们可以看到该方法的优势。     

一种多跳无线网扩频码分配算法

在多跳分组无线网中使用码分多址(CDMA)技术可以明显地降低隐终端问题对网络造成的影响.码分配是多跳无线网中使用CDMA的基本问题.码分配的目的在于提高扩频码的空间重用、降低分组冲突以及反映网络的动态变化.本文提出了一种多跳无线网扩频码分配算法,证明了其正确性并与其它算法比较了复杂度.与以往的算法追求降低码的数目不同,本算法是假设扩频码的数目有一定的冗余,寻求算法的方便、快捷和低通信开销.     

基于字体颜色的文本数字水印算法

根据人眼对蓝色最不敏感的特性,提出了通过修改文本字符的蓝色成分使其嵌入水印信息的一种文本数字水印算法。理论分析及实验结果表明,该算法具有水印容量大、鲁棒性较强的特点,可以弥补当前文本数字水印算法存在的鲁棒性较差、水印容量小的缺点。它在电子文档的版权保护等领域有广泛的应用前景。     

利用酉几何进一步构造带仲裁的认证码

该文利用有限域上的酉几何构作了三类新的带仲裁的认证码,计算了码的参数;当编码规则按等概率分布选取时,计算出各种攻击成功的概率。研究结果表明可用酉几何进一步构作多类带仲裁的认证码。     

Low rate convolutional and turbo codes based on non‐linear cyclic codes

Low rate convolutional and turbo codes that output non‐linear cyclic (NLC) codewords of length n = 2^m, m being a positive integer, are described. These codes have a very low coding rate, which makes them especially suitable for spread spectrum systems where they can be used for simultaneously achieving error correction and bandwidth expansion. Due to the cyclic properties and codeword length of the component codes, branch metrics can be efficiently computed using the fast Fourier transform (FFT), enabling simple implementation of the encoder and decoder. Among the possible NLC base codes, special attention is given to the Tomlinson, Cercas, Hughes (TCH) codes family due to their good autocorrelation properties. It is shown by simulation that the turbo codes schemes studied usually perform better than traditional turbo codes (in this paper the universal mobile telecommunications system (UMTS), rate 1/3 turbo code was used as a reference). This improvement is accomplished at the cost of bandwidth expansion. One of the advantages of the presented solutions over other low rate codes is their ability to improve the synchronization process at the receiver due to the good autocorrelation properties of the available NLC codes (especially TCH codes). A comparison of performance between the UMTS uplink connection and an equivalent system using the proposed codes for a multiuser scenario in a multipath fading channel is presented showing the possibility of capacity increase when using these codes. Copyright © 2006 John Wiley & Sons, Ltd.     

LDPC码的快速编码研究

根据LDPC码在删除信道下的译码算法重新阐述了基于稀疏校验矩阵码的快速编码方法,同时指出了Tornado码和RA码能够达到线性编码的原因．文中通过对快速编码的实现进行分析,提出了两种能够达到线性复杂度编码的码构造方法,仿真结果表明,采用这些方法构造的LDPC码在AWGN信道下的纠错性能不差于随机构造的LDPC码．     

一种非相干检测下的低复杂度正交编码调制解调方案

提出了一种适用于低码率应用环境的低复杂度非相干正交调制解调方案．信息比特首先经过一个Zigzag码线性编码器,然后将满足奇偶校验关系的编码比特映射为一个PPM符号发送出去．再根据PPM的软输出解调和正交Hadamard码译码之间的等价关系,就可以在接收端将解调和译码看作一个整体处理,这样不但避免了解调和译码之间的迭代运算,而且可以应用快速Hadamard变换(FHT)和基于FHT的后验概率译码(APP-FHT)来降低译码复杂度．还应用联合设计的线性交织器进一步改善本方案中存在的错误平层问题．仿真结果表明,本方案在降低复杂度的同时具有和其他方案可比的性能．