Modified linear prediction algorithm for narrowband interference suppression in universal mobile telecommunication system

Narrow band interference (NBI) deteriorates the quality of the spectrum, leading to a poorer performance of modern universal mobile telecommunication system (UMTS) spread spectrum systems. The linear prediction algorithm is one of the most significant techniques to overcome NBI and enhance the performance of UMTS systems. In this paper, a modified linear prediction algorithm is proposed for NBI suppression in a conditionally stationary environment. This modification improves the error energy estimation in the auto‐regression model of the linear prediction. The convergence of the proposed algorithm is evaluated, and its robustness is verified using Kullback–Leibler metrics for conditionally stationary NBI signals. Computer simulations are carried out, and the obtained results demonstrate the performance of the proposed algorithm and its compliance with UMTS protocols. Copyright © 2012 John Wiley & Sons, Ltd.     

DSSS系统中线性调频干扰抑制技术研究

扩频通信系统中宽带干扰的抑制技术越来越引起人们的重视。本文以典型的宽带干扰信号线性调频干扰(Linear Frequency—Modulated，LFM)为例，综述了目前直接序列扩频(Direct Sequence Spread Spectrum，DSSS)系统中宽带干扰抑制的研究热点和成果。     

一种新颖的直接序列扩频干扰规避通信系统

针对传统直接序列扩频通信系统(DSSS)因扩频增益受限于可用频带资源和系统复杂度而不足以对抗大功率窄带干扰的问题,论证了截断形式数据矩阵的奇异值分解(SVD)的正交分解性质,并由矩阵能量的角度推导了干扰分量与背景噪声分量的分离算法,结合直扩系统干扰规避基本原理得出一种新的能够规避干扰的扩频序列构造方法,且据此设计出了改进的扩频通信系统方案。仿真结果表明,改进后系统不但具有良好的多址能力和低截获特性,而且可以有效避开强干扰,获得了较传统直扩系统更优的误码性能。     

周期序列DSSS系统抗CW干扰性能分析

在简要论述按传统的基于标准高斯近似(SGA)假设得到的DSSS系统抗单音连续波(CW)干扰性能分析结果的基础上,推导出CW干扰经周期序列DSSS系统相关解扩处理产生的符号判决变量中干扰分量的数学表达式,对周期序列DSSS系统抗CW干扰的实际性能进行了理论分析与仿真。结果表明,周期序列DSSS系统在CW干扰下符号判决变量中的干扰分量呈现固定电平或单频波动,并不近似于标准高斯分布,周期序列DSSS系统抗CW干扰的实际性能与基于SGA假设的分析结果完全不同,其误码性能不仅与干信比、干扰频偏和相位密切相关,还与具体的扩频序列有关。     

DS/FH快跳频系统设计和窄带干扰抑制

跳频通信具有一定的抗窄带干扰的能力,跳速越高抗窄带干扰的能力越强.在DS/FH跳频系统中,解跳之后干扰信号存在于部分的扩频信号,相当于扩频信号内存在时变的干扰信号.文中将Turbo纠错码和分集合并技术联合应用于DS/FH快跳频系统中,利用信号的分集特性,采用奇异值分解的算法检测受干扰的跳频信号,将未受干扰的跳频信号合并,结果表明采用Turbo码的快速跳频方式时可以实现窄带干扰抑制.     

一种高速线阵CCD采集系统的设计

针对线阵CCD（ChargeCoupledDevice）及其外围器件时序复杂的特点,设计了一种高速线阵CCD采集系统。该系统采用MSP430单片机产生PWM信号实现各器件驱动时序,并将采集结果通过串口发送至上位机。介绍了系统组成及各器件时序同步的设计方法。实验结果表明,该线阵CCD采集系统能够很好的满足设计要求,可作为模块化电路集成到其它测量系统中。     

一种新型的扩频通信自适应窄带干扰抑制技术

提出了1种基于IIR带阻滤波器的窄带干扰抑制方式,不但能够对窄带干扰进行精确的频率跟踪,而且能够根据信号电平自适应设置干扰的检测门限,并通过选择最佳的滤波器参数滤除干扰,从而可以将干扰造成的性能损失减小到最低程度,计算机仿真证实了本方法具有良好的窄带干扰抑制效果和较低的实现复杂度。     

一种零中频直接序列扩频数字接收技术

直接序列扩频技术在现代无线通信系统中有着广泛的应用,该信号的数字接收是实现对其侦察截获的关键技术之一。本文介绍了直接序列扩频技术原理及其在cdma2000移动通信系统中的应用,提出一种针对cdma2000直接序列扩频信号的零中频数字接收算法,并详细给出了码捕获及跟踪算法、载波同步算法的数学模型推导。实验结果显示,该算法成功地实现了码同步及载波同步,有较好的解调效果。     

面向IR-UWB基于直接序列设计抑制窄带干扰算法

针对窄带系统对超宽带冲激无线电系统(Impulse Radio Ultra-wideband,IR-UWB)的干扰问题,提出基于Rayleighritz理论的直接序列(Direct Sequence,DS)设计方案,记为RRDS。通过设计DS序列,使得IR-UWB频谱在窄带干扰频率点上产生陷波,从而实现抑制干扰的目的,同时,通过RRDS方案,提高IR-UWB系统的误码率。RRDS方案先建立目标矩阵,并求解最小特征值及对应的特征向量。如果特征向量里面的元素有非+1或-1的值,则通过符号函数将特征向量转变为全部由+1,-1组成。若最小特征值是多重,先将所有的特征向量通过符号函数转变为全部由+1或-1组成的向量,并在这些向量里找出使目标矩阵的值最小的特征向量,将此向量作为直接序列DS。仿真结果表明,提出的RRDS方案有效地抑制窄带干扰,并提高了IR-UWB系统的误码率。     

Direct sequence code acquisition in multiplicative and non-Gaussian noises

A new detector for direct sequence spread spectrum code acquisition in multiplicative and non-Gaussian noises is proposed in this article. Modelling the acquisition problem as a hypothesis-testing problem, a detector is derived for multiplicative and non-Gaussian noises, based on the locally optimum detection technique. Numerical results show that the proposed detector can offer substantial performance improvement over the conventional schemes in multiplicative and non-Gaussian noises.     

直扩系统中匹配滤波器捕获方法研究

介绍了直扩系统中利用匹配滤波器方法进行捕获的特点和电路结构,重点研究了在高斯白噪声环境下采用部分周期相关匹配滤波器捕获方法的性能,推导了捕获方法的检测概率和虚警概率。最后利用Simulink对匹配滤波器捕获方法进行了仿真,给出了对应不同匹配长度和不同门限的检测概率和虚警概率曲线。     

New methods for enhancing fine acquisition in dual folding algorithm of long pseudo noise codes

Long code Direct Sequence Spread Spectrum is a good choice for applications where security and antispoofing ability of a spread spectrum connection is concerned. Due to long period of spreading code, acquisition is a challenge for these systems because a trade‐off between detection probability and acquisition time must be made. For confronting this challenge, various algorithms were proposed in the literature but almost all of them focus on expediting the coarse acquisition. In this paper, we consider the efficient dual folding algorithm for coarse acquisition level and propose 3 methods for enhancing the fine acquisition level leading to faster execution of overall acquisition algorithm. The methods are based on estimations from coarse acquisition level that are not used in conventional algorithms for fine acquisition, ie, zero padding. Theoretical expressions of 2 main comparison criteria in acquisition algorithms, ie, detection probability and mean acquisition time, are derived for conventional zero padding and each of the proposed method. Besides, a coarse estimate of resource consumption is provided by the number of floating point operations for each algorithm to make a useful comparison. Considering these 3 parameters, in comparison, the proposed methods surpass zero padding in 1, 2, or all of the 3 aspects. Simulation agrees well with analytical results.     

扩频通信系统干扰及其仿真技术

扩展频谱技术有多种基本实现方式,本文主要介绍的是直接序列扩频技术,特别针对二进制的PSK调制解调技术,直接序列扩频系统的抗干扰能力分析与直接序列扩频系统的同步方法,并进行了相关仿真分析。     

不同频率位置的窄带干扰对DSSS通信性能的影响分析

衡量窄带干扰抑制算法性能高低的一个主要标准是评估干扰处于最恶劣频率位置时的干扰输出平均功率的大小。在扩频序列周期很长且严格平衡的理想条件下,最恶劣干扰的频率位置为DSSS信号载波频率。基于典型的m序列DSSS系统,分析了处在不同频率位置的窄带干扰对DSSS系统的影响,所得结果与理想条件有所不同,这对于扩频系统的设计与应用具有指导意义。     

基于分段相关－视频积累方法的多驻留伪码捕获系统优化设计

针对载波多普勒下的伪码捕获问题,分析了基于分段相关-视频积累方法的多驻留伪码捕获系统的最优性能。推导了正交双通道检测器的检测概率和虚警概率表达式,给出了多驻留系统的捕获时间均值表达式;通过采用遗传算法对系统进行优化设计,增大了系统的多普勒容限,降低了捕获时间;分析了驻留级数、多普勒和载噪比等对捕获系统性能的影响。研究成果可用于指导扩频系统接收机伪码捕获模块的设计。     

DS-CDMA中扩频信号的循环平稳特性分析

介绍了循环平稳信号的基本概念，对DS—CDMA系统中直接序列扩频信号的循环平稳特性进行了详细的理论分析，通过计算机仿真实验验证了分析结果；仿真同时说明了利用信号的循环平稳特性可以进行有效地信号提取和干扰抑制，具有极大的应用前景。     

基于Simulink的直接序列扩频通信系统仿真设计

以Matlab提供的可视化仿真工具Simulink搭建直接序列扩频通系统仿真模型,利用Simulink对直接序列扩频通系统的发射机模块和接收机模块进行仿真设计,通过传输过程中各个波形和频谱变换图,研究直扩系统误码率、信噪比和扩频增益的关系。在给定的仿真条件下,运行测试仿真模型,结果表明,该系统信噪比较高,性能较好,且在误码率保持不变的情况下,增加直扩通信系统的扩频增益可以增加输出端的信噪比。     

一种改进的PN码捕获技术研究

在直接序列扩频系统中应用频域捕获方法,可以显著缩短捕获时间,本文提出了在伪码寄存器全1状态后添0的办法,完美的解决伪码与FFT运算长度不匹配的问题。本文采用双重频率步进的扫频方法,有效地减少在低信噪比条件下的捕获时间。     

A direct sequence spread spectrum code acquisition circuit for wireless sensor networks

Narrow band (NB), spread spectrum (SS), and ultra wide band (UWB) are three physical layer bandwidth types used in wireless sensor networks (WSN). SS and UWB technologies have many advantages over NB, which make them preferable for WSN. Synchronisation of different nodes in a WSN is an important task that is necessary to improve cooperation and lifetime of nodes. Code acquisition is the main step of a node’s time synchronisation. In this article, a pseudo noise code generator and a code acquisition circuit are proposed, designed and tested using direct sequence SS technique. To investigate the properties of the designed circuits, simulations are carried out via Xilinx Foundation Series software in the real mode. The results demonstrate excellent performance of the proposed algorithms and circuits in all realistic conditions. The code acquisition circuit proposed an adaptive testing window for single dwell serial search method. The code acquisition circuit is a clock phase free approach, thus the clock coherency step is cancelled. Moreover, clock phase difference between transmitter and receiver nodes does not mostly affect the acquisition and thus synchronisation time.     

扩频体制低轨卫星通信信号捕获与跟踪系统设计

针对扩频体制下低轨卫星信号的捕获及跟踪等系统设计实现问题,根据卫星信号模型进行了捕获及跟踪算法设计,重点对基于快速傅里叶变换的快速捕获算法、锁频环、锁相环和码跟踪环路进行了设计,并进行了工程系统实现。试验验证表明,该系统可以实现码分多址体制低轨卫星信号捕获、跟踪处理,工作性能参数满足系统需求。