基于采样率变换与FFT的GPS系统C/A码捕获改进算法

针对全球定位系统民用粗码信号快速捕获算法速度慢、不易于硬件实现的不足,提出了基于采样率变换和FFT的GPS信号C/A码捕获算法。利用采样平均的方法把采样率为5Msps的输入信号降低为1.024Msps,然后利用FFT进行粗捕,得到粗略的伪码相位,最后对粗略的伪码相位周围的原始数据进行循环相关处理得到精确的伪码相位估计值,降低了对后续跟踪环的动态要求。仿真结果表明该算法运算量小可以快速实现C/A码的粗捕,得到高精度的捕获结果,同时该算法可以利用现有1024点的FFT处理核(IP),便于在硬件上实现。     

传感器网络推拉混合模式代码传输方法

代码传输是实现无线传感器网络应用重构的关键技术.首先研究传感器网络环境自适应应用重构(EAAR)模型的两种代码传输模式-拉模式和推模式,并结合两种模式的特点提出一种适用于分簇传感器网络的能量有效代码传输模式-基于簇的混合代码传输(Cluster-based Hybrid Code Transmission, CHCT).在该模式下,簇头节点采用拉方式从基站获取代码,簇内节点采用推方式进行代码传输.仿真实验验证了方法的有效性并讨论了影响CHCT性能的主要参数.     

Raptor码在下行协作无线蜂窝系统中的研究

不同于传统的采用固定码率编码的协作中继系统,在发送端不知道信道状态信息(channel state in formation,CSI)时,提出协作蜂窝系统下行链路中使用无限码率Raptor码及分布式空时分组码(distributed space-time block code,DSTBC)的新方案,并研究该方案有效性、可靠性和健壮性的问题。理论分析和仿真结果证明,当发送端不知道CSI时,结合应用Raptor码和DSTBC,即使在低信噪比(signal-to-noise ratio,SNR)环境中仍能降低总传输时间及能量消耗,给无线蜂窝系统带来显著的性能增益。     

广义交叉乘积累加码

为设计具有线性编、译码复杂度及逼近香农限性能的信道编码结构,在并行级联的单奇偶校验码之间引入交叉结构以构成外码,以累加器为内码,提出了一种新的串行级联编码--广义交叉乘积累加码。以外信息转移图为工具对广义交叉乘积累加码进行设计,并给出一个广义交叉乘积累加码的设计示例。分析及仿真结果表明,该示例具有线性编、译码复杂度,其收敛门限距香农限仅有约0.32 dB的距离。     

Design of an anti-jamming GPS receiver based on orthogonal projection method

Code delay and Doppler shifted frequency could not be captured by using the conventional GPS receiver in strong interference environments because the received GPS signals which traveled a long distance are very weak. An anti-jamming GPS receiver is proposed. The interferences in the received signals are cancelled by using subspace projecting technique, and the resulting interference-free signals are processed by a weight vector which maximizes the signal-to-noise ratio. Simulation is conducted, and the resu...     

ON THE CONSTRUCTION OF ALGEBRAIC-GEOMETRIC CODES

1,Illtroduction'SincetheearlypapersbyG0ppa[1-31,algebralc-ge0metriccodeshavebeeninthespotlight0fcodingthe0reticresearchf0rab0uttwodecades.NumerousexcitingresultshavebeenachievedusingGoppa'sconstructi0noflinearcodesfromalgebralccurvesoverfinitefields,bothbyalgebraicge0metorsandcodingtheorists.Becauseofthedifficultyofthesubject,severalexplanatorypaPersandtextbookshaveappeared,seeforinstance[4-8].Inthispaperwepresentaquitedtherentpointofviewconcerningalgebraic-geometriccodes.Itiswellknownthataq…     

基于软件历史仓库和抽象语法树的相似缺陷识别方法

软件开发过程中,软件开发人员常常通过搜索软件历史仓库(historical software repository, HSR),再经复制/粘贴以实现软件复用。HSR中会保存被复用的代码的缺陷及修复信息,辅助处理相似缺陷。基于此,提出一种基于HSR挖掘的相似缺陷识别方法。首先,基于变更日志的分析,从HSR中提取出已知缺陷的模块,建立bug模块库。然后,采用基于抽象语法树(abstract syntax tree, AST)的相似代码检测方法,识别待测试软件与bug模块库中相似的代码,并借助HSR中保存的相应缺陷及修复信息,完成待测试软件中可能包含潜在缺陷的模块的识别。同时,为提高相似代码的识别精度,优化基于AST的代码特征度量。在18个C程序、164对克隆代码上进行实验,结果表明所提方法能够识别出全部相似代码且性能优于已有工具。在人工构建的bug模块库上验证了代码相似性对相似缺陷识别的作用。最后,在8个真实的大型C项目上进行验证,平均缺陷召回率达到94%,表明挖掘HSR可以有效地为跨项目传播的相似代码提供缺陷理解支持。     

Design and implementation of 1 GHz high speed data acquisition system

With the development of current electronic technology, numerous high-speed data acquisition systems provide a variety of potential benefits. This article describes a high-speed data acquisition system which consists of ECL logic and TTL logic devices, samples and stores data with a 1 GHz clock. This system is accomplished easily and works stably. A performance test of this system has been undertaken and the results show that the effective number of bits (ENOB) is more than 6.5 bits.     

Capacity analysis of high-rank line-of-sight MIMO channels

Matrix perturbation theory is utilized to investigate high-rank line of sight multiple input multiple output channels in a microwave relay system. The upper and lower bounds of channel capacity are derived based on space time block codes technique and singular values decomposition. A useful constraint for designing LOS MIMO channels is developed by the use of the condition number of the MIMO channel matrix. The theoretical analysis of channel capacity is confirmed by the simulation. The results show that the proposed method is able to give a physical explanation of the high-rank LOS MIMO channel matrix characteristics.     

末段脉冲修正迫弹攻击区建模与仿真

为了确定采用激光半主动制导的末段脉冲修正迫弹的攻击区域,建立了导引头目标捕获域模型,分析了迫弹受到的脉冲控制力及控制力矩,推导出六自由度有控弹道方程组,给出了脉冲最大修正区域模型,并提出了攻击区建模和仿真的方法.利用上述模型对给定启控条件下的攻击区进行了仿真计算,得到了不同导引头参数及不同脉冲冲量作用下的攻击区域图.结果表明,提供的模型及仿真方法适用于该类弹箭攻击区的求解,对于导引头、脉冲发动机的设计也有一定的参考价值.