A method for deciphering a maximal-length sequence

A simple method for determining the feedback polynomial coefficients of a maximal-length sequence is derived. The method is to look for the longest run of zeros in the received sequence and use those digits plus the preceeding n digits to compute the feedback polynomial coefficients. This method permits simple hand computation or hard-ware implementation for the computation of the coefficients.     

一种新的图像序列失真模型:动态偏移场模型

针对图像序列失真现象,该文提出一种新的图像序列失真模型:动态偏移场模型。该模型是一个充分参数化的模型,它为目前可观测到的多种失真现象提供了一个统一的描述框架。实验结果表明,动态偏移场模型能够简单有效地描述图像序列失真现象,并为失真校正工作提供了一个由简单到复杂渐进处理的研究平台。     

Prefix synchronised RLL sequences: variable-length graph model

The generation of the prefix synchronised RLL sequence is described by the variable-length graph model. This model leads to a regular structure of adjacency matrix, leading to simple calculations for the channel capacity and the channel sequence power spectral density.<>     

基于离散数字混沌序列的图像加密

由幅值连续的Logistic混沌公式研究了一种幅度值离散数字混沌序列的产生方法,可方便用于硬件实现图像加密。采用函数运算方法由3个不同周期的离散数字混沌序列异或运算获得长周期图像加密序列,将图像加密序列与原始图像异或加密图像。加密和解密仿真对比可见,该方法对初始值具有敏感性。分析表明,所获得的幅度离散数字混沌序列产生方法具有算法简单,信息安全可靠性高,便于硬件实现的特点。     

Generalized polynomial-based receiver for the flat fading channel

This letter presents a simple polynomial predictor-based sequence detector for the Rayleigh nonselective fading channel. Unlike the polynomial predictor-based sequence detector proposed by Borah and Hart, the new receiver is not restricted to constant envelope modulation schemes. Analytical and simulated results are presented. In some instances, the proposed receiver performs within 6 dB of the equivalent maximum-likelihood sequence estimation receiver.     

Binary-Code-Allocation Scheme in DS-CDMA Systems

In this paper, we consider a simple binary-transmitter adaptation in direct-sequence code-division multiple-access systems. We propose a binary-code-allocation scheme for reducing the multiple-access interference (MAI). In this scheme, a user is given an orthogonal binary sequence set. By choosing a better sequence from the sequence set, the user can maximize his/her signal to interference ratio. We examine the scheme analytically by both exact analysis and approximation in equal-power synchronous cases. Theoretically, it is found that the scheme can significantly reduce the MAI. It only involves a few bits of feedback information for the transmitter to adjust the sequences. The scheme can also be modified for multiuser adaptation in asynchronous channels. In a multiuser adaptation, simulations show that the users would have a significantly improved performance against the MAI, and the system throughput can also be increased. It is shown that this binary-code-allocation scheme is a simple, widely applicable, and robust binary-sequence-adaptation scheme     

Delayed versions of maximal-length linear binary sequences

Any delayed version of a linear binary sequence can be obtained from a suitable linear combination of the outputs of the feedback shift register which generates the sequence. A simple method is given for calculating the linear combination required to give a specified delayed version. The method involves polynomial long division, and is not restricted to short sequences.     

Increasing the rate of output for m sequences

By using several linear feedback shift registers running in parallel, producing different phases of the same maximal length sequence or m sequence, it is possible to interleave the outputs to give the original m sequence, thus giving an exceedingly simple technique for the fast generation of m sequences.<>     

Codes satisfying the chain condition

The authors considered weight hierarchies of codes satisfying the chain condition, they called these chain-good. First, they gave a set of simple necessary conditions for a sequence to be chain-good. They proved that given one chain-good sequence, there is an infinite set of chain-good sequences that can be constructed from this one sequence. Finally, they used this result to completely describe the sets of chain-good sequences of dimensions up to 5     

Optimum variable step-size sequence for LMS adaptive filters

An optimum time-varying step-size sequence for adaptive filters employing the least mean squares algorithm is proposed. This step-size sequence is obtained after minimising the mean square error cost function with respect to the step size on an iterative, block-by-block basis. The effect of the various parameters on the optimum step-size sequence is described and a simple approximation of the optimum sequence is proposed. As compared with other optimum approaches, the proposed one gives a considerable reduction in convergence time and is implemented with just one extra multiplication. Computer simulations are performed to confirm the effectiveness of the new approach     

一种混合混沌序列密钥产生设计

利用混沌动力学系统产生流密码,速度快,安全性高,有很好的应用背景和实用价值,是信息安全领域研究的热点之一。利用简单的一维混沌系统,结合密码学知识,设计了一种混合混沌序列密钥的产生方案,该方案技术简单,密钥空间大,伪随机性好,初值敏感性强,迭代次数少,加密效率高。     

A passive star-configured optical local area network using carrier sense multiple access with a novel collision detector

This work describes design and theoretical performance of a passive star-configured multimode optical fiber local area network that employs carrier sense multiple access with collision detection (CSMA/CD). We introduce a novel collision detection method that uses collision sequences constructed from cyclic error-correcting codes and a sequence weight violation rule. Each transmitter has its own unique sequence and all sequences have identical Hamming weight. The collision detection sequence is inserted in each packet header. Our method enables detection of collisions subject to a wider dynamic range variation than competing methods proposed up to now and is extremely simple. The collision detector consists of a counter which estimates the Hamming weight of the received collision detection sequence. It works both for non-return-to-zero and Manchester coding. The collision detector is analyzed for an avalanche photodiode receiver. The general performance analysis is done both with Gaussian approximations and with method of moments. A dynamic range of 17 dB seems possible for a transmitter with an extinction ratio of 100 and a simple receiver with a fixed threshold. An explicit table of 56 collision detection sequences based on the Golay code is presented.     

Joint Baud and Frame Synchronization in Direct Detection Optical Communications

The maximum-likelihood frame synchronizer was recently derived for direct-detection optical communications assuming baud synchronization. In this paper we present an extension to those results when pulse-position modulation is used and jointly derive baud and frame synchronization from slot synchronization. The optimum rule is seen to consist of a simple correlation term and a nonlinear correction term. Simulation results for the optimum rule compared to analytical and simulation results for the simple correlation rule show that equivalent performance for the simple correlation rule requires a substantial increase in signal power. To design good synchronization patterns, we use a divergence measure derived from the optimum rule. A simple algorithm is derived to test whether a given sequence is good or not.     

DSSS信号的扩频序列估计

提出了一个在非协作通信中对直接扩频序列(Direct Spread Spectrum Sequence,DSSS)信号的扩频序列进行估计的简单而有效的算法。在算法中我们提出了两个测度函数,一个用于搜索扩频序列在接收信号中的起始位置,另一个用于序列中的逐码片(chip)估计。理论分析和计算机仿真表明了此算法的有效性。     

Source enumeration in a correlated signal environment

The authors present a simple method for determining the number of signals impinging on a uniform linear array that is applicable even in the extreme case of fully correlated signals. This technique uses what they term modified rank sequences, which is a modification of the construction implicit in the matrix decomposition method of Di (1981). They prove that if a particular rank sequence stabilizes (the last two terms of the sequence are equal) to a value strictly less then the common row size of the defining block matrices, then this value equals the number of signals, provided that the number of signals has not exceeded a Bresler-Macovski (1986) type bound. Using the above characterization of stability, they formulate an algorithm that either determines the number of signals or indicates that the resolution capability of the algorithm has been exceeded. They also provide theorems that show that under certain conditions, a rank sequence can stabilize to a value strictly less than the number of signals. This result allows them to find simple counterexamples to all of the existing rank sequence methods     

Comma-free synchronization of binary counters (Corresp.)

The structure of the "parity check" sequence formed on a binary counter has been well studied and is known as a Thue-Morse sequence [1]-[4]. It is shown that this sequence can be used in a simple synchronization scheme that can be engineered with a minimum of hard-ware.     

Making MLSD decisions by thresholding the matched filter output

This paper presents an iterative detector that, by thresholding the output of the matched filter, gives maximum-likelihood sequence detector (MLSD) decisions on binary, antipodally modulated symbols that have been corrupted by intersymbol interference and additive Gaussian noise. The detector will make decisions on some, but often not all, of the symbols in a transmitted sequence, and those decisions will be the same decisions as the MLSD would have made. The number of symbols that are detected is stochastic, varying from sequence to sequence. The basis of the detector is a bound on a crossterm of the quadratic form in the log-likelihood function for the transmitted sequence. The detector is simple in structure, consisting of a matched filter and two variable threshold values for each symbol     

基于时钟和地址的跳频序列的产生和性能分析

在一般跳频系统中，跳频序列是由递归算法产生的，如PN序列以及混沌序列、模糊序列等。本文介绍的基于时钟和地址的跳频序列提供了一种新的产生方法。这种序列是由长比特设备地址和不断变化的长比特时钟信息经过一系列运算而产生的，即基于时钟和地址和跳频序列，该序列具有理想的均匀频谱特性和很长的周期；序列线性跨距很长，不容易被智能干扰机干扰；序列的汉明相关特性也很好；这个特点在多址接入通信中非常有用。该序列另一个重要特征是硬件实现简单容易，事实上，这种序列巳成功应用于蓝牙跳频系统中。本文主要介绍这种跳频序列的设计产生过程，并对序列的各种性能进行分析。     

基于MutiSIM的蔡氏混沌序列仿真研究

混沌序列是非线性方程描述的确定系统所产生的介于周期振荡与噪声之间的一种复杂振荡序列.蔡氏电路是一个经典,且简单的三阶自治系统,能够产生丰富的混沌现象。在对蔡氏电路进行数学建模的基础上,采用MultiSIM仿真软件对其进行仿真,并分析其产生的混沌信号的功率谱,从而找出一个最佳的电路参数,得到一个最好的,可用的混沌序列。     

基于一种特定混沌映射的跳频序列

使用一种简单的分段线性映射构造混沌跳频序列。用于跳频通信中取代传统的伪随机序列（PN序列），分析了此混沌序列的周期性。平衡性，汉明相关特性和线性间隔，最后给出了混沌序列的神经网络实现。仿真和实验结果表明，此序列具有较好的统计特性。应用于跳频多址通信中，可获得较好的抗干扰。抗截获能力。