划分相位空间的PN码捕获性能分析

频率选择性衰落信道中,接收伪噪声(Pseudo-Noise,PN)码的不确定相位空间中存在多个同相单元。建立检测模型获得了检测过程的检测概率和虚警概率。通过状态转移图结合划分码相位子空间的方法对捕获状态的循环流转进行了描述,获得了捕获性能对信道特性的依赖关系。数值仿真给出了捕获性能随路径数量和接收信噪比等主要参数的变化趋势。     

A parametric method for non-stationary interference suppression in direct sequence spread-spectrum systems

The problem of non-stationary interference suppression in direct sequence spread-spectrum (DS-SS) systems is considered. The phase of interference is approximated by a polynomial within the considered interval. According to the local polynomial Fourier transform (LPFT) principle, the received signal is dechirped by using the obtained phase approximation and the interference is, in turn, suppressed by excising the corrupted low-pass frequency band. For the estimation of polynomial coefficients, we use the product high-order ambiguity function (PHAF), known for its capability to successfully resolve components of a multicomponent polynomial-phase signal (PPS). The proposed method can suppress interferences with both polynomial and non-polynomial phase. In addition, it can suppress both monocomponent and multicomponent interferences. The simulations show that the proposed method outperforms time-frequency (TF) methods, that successfully deal with multicomponent interferences, in terms of the error probability and computational complexity.     

PN序列估计与扩频隐藏信息分析

在非协作信息侦测情况下,提出了一种直接序列扩频(DS-SS)信号PN序列的估计方法,在此基础上实现了扩频隐藏信息的盲提取.该方法以估计序列和扩频信号的累积相关值为目标函数,建立估计序列长度及其构成的两变量优化模型,通过遗传算法求解,可较好地估计出PN序列.通过获取的PN序列与藏密信号的相关性分析,可实现扩频隐藏信息的盲...     

北斗一号用户机抗干扰能力分析

通过建立北斗一号用户机接收信号模型,分析了北斗一号用户机在多种典型干扰样式下的抗干扰性能。由于干扰信号与伪随机码不相关,在北斗一号用户机接收端被扩展,通过信号通频带内的干扰信号功率大大降低,提高了相关器的输出信噪比,达到了抗干扰的目的。     

窄带干扰下基于子空间跟踪的扩频序列估计

针对窄带干扰条件下低信噪比直扩信号扩频序列（Direct Sequence Spread Spectrum,DSSS）的盲估计问题,提出了一种基于子空间跟踪的扩频波形估计算法.该方法避开了直接的特征分解求解,利用滑动窗技术取得码同步,根据求解结果可以估计出信号所夹杂的窄带干扰特征波形,并进一步消除窄带干扰估计出信号的扩频码序列.结果表明,该算法在低信噪比条件下能完成对PN码序列的精确估计,降低了数据的存储量,易于硬件实现.     

Diversity Enhancement of Coded Spread Spectrum Video Watermarking

This paper analyses the effect of signal combination techniques in videowatermark detection. A spatial spread spectrum based watermarking techique isused as embedding method, in combination with common error correction codes(BCH, Reed-Solomon with multilevel signaling, binary convolutional codes withViterbi decoding). Besides an analytical evaluation of the bit error rate, theeffectiveness of the channel coding and diversity techniques is also assessedexperimentally under MPEG-2 video compression.     

Performance analysis of linear MIMO equalizers for multitone DS/SS systems in multipath channels

In [11] the combination of multitone modulation with direct sequence spectrum spreading has been introduced. The performance of a correlation receiver has been evaluated for a multipath channel. In [12] the analysis has been extended to the presence of a multiple access interference. In the present paper we analyze the equalization problem of such a system for a single user scenario. In order to understand the potential of the system we first investigate the steady-state behavior of the MIMO equalizer for an MMSE design. The investigation is carried out for an equalizer following a receiver made of a bank of filters matched to both the symbol shape and the channel, which is a two-path channel. Assuming BPSK symbols an exact expression of the bit error probability before and after equalization is obtained in the form of an integral by means of the characteristic function method. Next adaptive LMS and RLS structures are proposed. The performance of the RLS algorithm is demonstrated.Part of this work has been presented at ICC '95, Seattle, June 1995.This author would like to thank the Belgian NSF for its financial support.This author is a Research assistant of FRIA.     

Correct: A simulated text editor

This paper describes a project to write a simulator for the native mode text editor of one computer, which could be run on a different computer. This was done to give a user of both computers a common editing language. The method of design and construction is presented together with brief details of the syntax and semantics of the editing language.     

Real-time PCR method for detection of the transgenic rice event TT51-1

The insect-resistant transgenic rice event TT51-1 (synonym BT63) has been found illicitly planted and distributed for years although it has never been approved for commercial cultivation in any country up to now. The purpose of this study was to establish a detection method that is specific for this transformation event. The event-specific PCR method produces an amplicon of 120 basepairs (bp) based on the revealed 3′ junction sequence with a limit of detection (LOD) and a limit of quantification (LOQ) being approximately 5 and 10 initial template copies, respectively. Two mixed rice samples with known TT51-1 contents were used to verify the developed real-time PCR system, from which the expected results were observed.     

室外电动大门供配电设计

电动大门触电身亡的事故时有发生,为了防止此类悲剧的发生,防患于未然,就某些室外电动大门存在的电气安全隐患进行了分析,并提出采用局部TT系统或采用隔离变压器供电的措施。对其工作原理及注意事项进行了阐述,对配电设计人员具有借鉴意义。