Monomode fibre polarisation scrambler

A technique for the pseudodepolarisation of a long-coherence-length source is described, which is based on a simple polarisation modulation scheme. Using a length of high-birefringence fibre wound on to a piezoelectric transducer, a simple all-fibre polarisation scrambler can be constructed.     

Characterisation of differential group delay of fibre devices with high resolution and enhanced immunity to environmental perturbation

By integrating a fibre polarisation scrambler with the modified phase shift modulation technique, differential group delay characterisation is demonstrated with high wavelength and delay resolution, and enhanced measurement immunity to environmental perturbation.     

Parallel scrambler for high-speed applications

In order to improve the speed limitation of serial scrambler, we propose a new parallel scrambler architecture and circuit to overcome the limitation of serial scrambler. A very systematic parallel scrambler design methodology is first proposed. The critical path delay is only one D-register and one xor gate of two inputs. Thus, it is superior to other proposed circuits in high-speed applications. A new DET D-register with embedded xor operation is used as a basic circuit block of the parallel scrambler. Measurement results show the proposed parallel scrambler can operate in 40 Gbps with 16 outputs in TSMC 0.18-/spl mu/m CMOS process.     

Reduction of polarization-dependent gain due to signal-to-signal Raman interaction in fiber Raman amplifier

An excellent polarization-dependent gain (PDG) suppression technique using a polarization scrambler is proposed in this letter. Investigations on PDG due to signal-to-signal Raman interaction among 40 wavelength-division-multiplexer signal channels were carried out experimentally to evaluate the system performance after incorporating a polarization scrambler in the system. It was confirmed by experiment that the use of polarization scrambler is an effective way to reduce PDG caused by signal-to-signal Raman interaction.     

Novel mode scrambler for reducing mode dependence in multimode optical waveguides

A novel mode scrambler for multimode optical waveguides is proposed to stabilise branching characteristics against the mode excitation conditio. A 2 × 2 optical star coupler is fabricated using this mode scrambler, and a stable branching ratio is realised with an excess insertion loss of 2.7 dB.     

Quality Analog Scramblers Using Frequency-Response Masking Filter Banks

A very low complexity frequency-domain analog speech scrambler having high-quality speech reconstruction is proposed. The scrambler uses frequency-response masking filter banks which have low computational complexity and narrow transition widths. The proposed system does not require bandwidth expansion, and is robust for transmission channels with distortion characteristics. Preliminary investigations showed that speech scrambled using this method is nearly unintelligible to the casual eavesdropper.     

Measurement of baseband frequency response of multimode fibre by using a new type of mode scrambler

For measuring the frequency response of an optical fibre, a mode scrambler utilising a sinusoidal bend and a new set-up based on the attenuation-comparison method have been proposed. Measurements for multimode step-index fibres have revealed that the long-fibre response can be closely predicted from the short-fibre response, using an appropriate choice for the scrambler parameter.     

降低OFDM系统中峰均比的PTS处理优化

正交频分复用系统存在较高的峰均比,介绍了峰均比产生的原理和降低峰均比值的部分传输序列算法,分析了算法性能和目前存在的问题,提出了一种预置固定扰码的PTS算法,该方法通过将固定扰码序列的边带信息预置在优化处理之前,使边带信息作为待优化数据源的一部分优化,这种方法消除了传统PTS中边带信息产生的峰均比值对系统的二次影响。通过仿真分析证明了将边带信息前置的PTS方法在算法复杂度较低的情况下,能有效减少边带信息带来的附加峰均比值的影响。     

Scrambler blind recognition method based on soft information

Two scrambler blind recognition methods based on soft information were proposed for received signal in non-cooperative ways.The first method established a cost function of the scrambler coefficients by using the soft information,and adopted the optimization theory of real number field for positive solution.So it didn’t need to traverse the closed set of test polynomial any more.The second method built conformity degree concept with the soft information,and used the size of conformity of each test scrambler polynomial as the discriminant criteria.So it made more full use of the received information compared to the hard sentence recognition algorithm.Simulation results show that the first method can shorten the recognition time of a synchronous scrambler polynomial from 5 min 18 s to 8 s compared with the traversal method put forward by Cluzeau,and the second method has 2 dB SNR gain when to achieve the relatively high accuracy compared with the hard sentence recognition algorithm.     

基于构造代价函数求解的自同步扰码盲识别方法

由于卷积码序列的0,1 bit的概率几乎均衡,对于卷积码自同步加扰的扰码盲识别,现有的基于输入序列0, 1 bit概率不均衡性的识别方法均已失效,为此该文提出一种新的自同步扰码盲识别方法。首先将卷积码自同步加扰序列进行分块处理,通过加扰数据块与卷积码校验向量相乘产生新的序列;然后以最大化新生成序列间线性约束关系成立概率为准则,利用解调输出的软判决序列建立自同步扰码反馈多项式系数的代价函数;最后根据自同步扰码反馈多项式的项数特点,在求解代价函数时改进了动态搜索烟花算法,增加了对烟花个体元素值的约束操作,由求解出的参量值识别出自同步扰码反馈多项式。仿真实验验证了所提方法的有效性,该方法无需遍历搜索反馈多项式,且具有较好的鲁棒性,所需数据量小,随着数据量的增大和扰码阶数的降低,其识别正确率逐渐提高。     

A Speech Scrambler Using the Fast Fourier Transform Technique

This paper describes an analog speech scrambler using the FFT technique (FFT scrambler). The FFT scrambler provides highly secured scrambled signal by permuting a large number of FFT coefficients. Important items to be considered in the designing of the FFT scrambler are discussed, such as FFT frame length, permutation of FFT coefficients, and frame synchronization, in addition to the configuration of the experimental FFT scrambler. Possible causes for the degradation of the descrambled signal, such as transmission channel group delay and intersymbol interference, are also discussed, together with experimental results.     

Reducible rank codes and their applications to cryptography

We present a new family of so-called reducible rank codes which are a generalization of rank product codes . This family includes maximal rank distance (MRD) codes for lengths n>N in the field F/sub N/. We give methods for encoding and decoding reducible rank codes. A public key cryptosystem based on these codes and on the idea of a column scrambler is proposed. The column scrambler "mixes" columns of a generator (parity-check) matrix of a code. It makes the system more resistant to structural attacks such as Gibson's attacks. Possible attacks on the system are thoroughly studied. The system is found to be secure against known attacks for public keys of about 16 kbits and greater.     

编码加扰序列的帧同步盲识别

在同步情况下,基于对偶码可有效重建线性扰码的反馈关系,但非合作通信方同样需要完成盲同步.在无噪声条件下,针对编码加扰序列的盲同步问题,结合反馈多项式检测提出了帧同步盲识别算法.利用初始帧同步中探测的反馈多项式倍式集,可同时完成扰码反馈多项式和扰码序列的估计.实现初始同步后,可借助解扰数据帧结构属性完成精确同步;然后,将算法推广到了含噪信道情况;最后,基于Walsh-Hadamard变换给出了检测统计量的规范计算方案,以降低计算复杂度.     

Annealed optical fibre mode scrambler

A mode scrambler based on an annealed step-index fibre is shown to have reproducible performance and source-launch-alignment insensitivity. Devitrification produces scattering centres in the fibre that distribute light uniformly over both angle and radius. An all-fibre mode scrambler with a 10 cm length and an insertion loss <3.5 dB is demonstrated     

Reconfigurable microstrip antenna with polarisation diversity

A single probe-fed reconfigurable microstrip patch antenna with symmetric cross slots is proposed. By controlling four pin diodes on the patch slots, the proposed antenna has right hand circular polarisation, left hand circular polarisation or linear polarisation.     

Polarisation conservation in single-mode fibres

There exist proper orthogonal elliptical polarisation states, which are maintained over long fibre length without converting. When one of the proper polarisation states is excited, orthogonal polarisation less than ?40 dB is confirmed after 5 km single-mode fibre transmission. It is also proposed that twisted single-mode fibres show a high degree of polarisation for any incident polarisation state. The polarisation characteristics are hardly affected by external perturbations.     

PCM Jitter Suppression by Scrambling

Jitter suppression in a chain of baseband PCM repeaters is studied. It is shown that a scrambler is very effective for systematic jitter suppression and that beyond 5 stages little additional suppression results. The probability of mark in the scrambler output converges to 0.5, independently of that in the input PCM signal. Experimental results confirm the analysis and show the ability of the scrambler to reduce the systematic jitter. The timing information disappearance of PCM repeatered lines when the scrambler is applied is also discussed.     

Adaptive dummy spectrum insertion method used in asynchronous speech scrambling

An adaptive dummy spectrum insertion method which is applied to the asynchronous analogue-digital-analogue (ADA) speech scrambler is presented. Related analysis and computer simulation results are given. Both analysis and simulation results indicate that the method greatly improves the security of the scrambler, and maintains good speech quality.<>     

扰码器初始参数盲重建算法

非合作通信条件下,针对扰码器初始参数估计问题,第三方需在通信参数不完全所知的情况下,对抗干扰、重建反馈多项式和估计初始状态,以重建扰码器。首先,根据对偶码特性和多信息流抗干扰技术,构造具有低误码率特性并包含扰码器特征参数的新序列;其次,采用低重量倍式搜索算法和基于对偶码的快速相关攻击算法,分别对新构造序列的反馈多项式和初始状态进行估计;最后,根据新序列与扰码的关系,重建扰码器初始参数。仿真结果表明,算法可在信噪比为0 dB条件下有效对抗噪声干扰并重建扰码器。      

SDH骨干网并行加扰/解扰技术研究

研究了SDH扰码序列的性质,在此基础上提出了两种实用化的并行加扰/解扰方案:基于矩阵推导的并行加扰/解扰和一种新的基于查找表结构的并行加扰/解扰,并总结了这两种方案所各自具有的优势,为解决任意位宽和阶数的并行扰码/解扰器的实现问题提供了新的思路.