扩频调制的伪码跟踪技术分析

在直接序列扩频传输系统中,接收端通常利用匹配滤波器实现扩频信号的初始同步,利用伪码跟踪环实现本地码字对其相位的精确跟踪。伪码跟踪的准确性直接影响解扩的性能。伪码跟踪中采用归一化的鉴相算法,通过合理的环路参数、相干累加长度和非相干累加次数设计,可以提高伪码跟踪的准确性。针对直接序列扩频信号,通过理论和仿真分析得到了码跟踪环中的相干累加长度和非相干累加次数这2个关键参数与载波频差、扩频比以及误码率之间的关系,可以为扩频码定时跟踪的设计提供依据。     

非相干扩频接收机伪码跟踪环设计及FPGA实现

伪码跟踪环的设计是实现非相干扩频接收机的关键环节。为了实现非相干扩频接收机的伪码跟踪,设计了能量归一化的延迟锁定跟踪环,给出了环路的实现结构及环路参数的计算方法。分析了非相干扩频的特点,指出环路设计的关键点,在此基础上阐述了码环鉴别器、环路滤波器、超前滞后码发生器的设计及实现方法,并给出一套具体的实现参数。Modelsim仿真结果及FPGA实测数据表明所设计的环路能对伪码进行精确跟踪。     

扩频码跟踪及同步失锁的研究与实现

针对扩频通信系统中的PN码同步问题,在分析扩频码跟踪方法的基础上,讨论了同步失锁问题,给出非相干延迟锁定环的计算公式和降低同步失锁误判的方法,并对其进行Matlab仿真及FPGA硬件调试.结果表明:该同步系统能够很好地跟踪接收端PN码的相位变化,失锁电路能够有效工作,并准确判断出同步失锁状况.     

扩频通信中PN码序列的捕获

扩频信号的捕获与跟踪是扩频接收机进行定位解扩的基础,文中基于FPGA进行了扩频信号捕获与跟踪的设计实现。分析了该方案的匹配滤波器、载波跟踪环、码跟踪环的设计与实现方法。并通过BPSK调制,使用非相干扩频通信的PN码并行捕获算法实现信号的捕获。     

QPSK扩频调制信号载波跟踪环路设计

扩频接收基带通常需要载波跟踪环来完成本地载波与接收信号载波的同步,科斯塔斯环是常用的非相干载波相位跟踪环,具有较好的鉴相特性。本文基于常规的单路单载波解调的科斯塔斯环原理,对科斯塔斯环做了改进,提出了对双通道平衡QPSK扩频基带所用载波跟踪环科斯塔斯环的改进方法,并推导出环路误差鉴相信号,用Matlab进行了仿真实验,结果证明利用本环路可实现载波稳定跟踪。     

DS-UWB中扩频同步技术的研究及其FPGA实现

为了简化扩频系统中同步接收机的电路结构,针对DS-UWB无载波的特性,设计了一种无需载波跟踪环,工作在码片速率的扩频解扩及其同步电路,采用Verilog HDL描述电路,然后对该电路进行了功能和时序仿真,最后在Altera的CycloneⅡ系列芯片上验证了该电路,并用逻辑分析仪观测波形.结果表明,电路工作正确可靠,占用逻辑单元数仅694个,最高工作频率为113 MHz,同步精度可以达到1/4个码片.     

基于FRFT的CSS系统同步设计与实现

基于分数阶傅里叶变换的Chirp扩频是一种新型非相干的线性调频通信系统,其特点在于同步模块简化易实现跳频功能,形成具有更强抗干扰能力的二维扩频抗干扰。通过分析系统的同步需求,设计了一种基于前导序列检测和包络检测的一体化同步方案。该方案在较低信噪比条件下正常工作,收敛时间比BPSK基带信号缩短一半。通过在DSP器件上的系统实现验证了方案的正确性和可行性,该方案对其他非相干系统的同步具有借鉴意义。     

GPS接收机中的码分多址信号处理研究

介绍了基于码分多址信号处理的GPS(全球定位系统)接收机的算法和电路设计。GPS接收机电路的信号处理任务主要是对数字化后的基带扩频信号进行载波跟踪、解调、解扩、码跟踪,从而得到符号数据。着重讨论了GPS接收机中信号处理部分的COSTAS、码跟踪、帧同步生成电路三大模块的功能任务、原理、算法及其相应的电路设计。通过这些研究工作,可以进一步设计出当前应用日益普遍的GPS接收机电路,该电路具有功能全面、通用性好、可靠性高等特点。     

一种扩频接收机的设计分析

基于直接序列(DSSS)扩频通信原理,阐述了直接序列扩频接收机的组成和工作原理,对解扩解调部分进行了详细设计,给出了关键模块的原理和实现方法;尤其对扩频信号的自动增益控制、伪码捕获、伪码跟踪、载波跟踪以及定时同步等电路进行了细致论述,并说明了注意事项;最后,给出了硬件实现方式和测试数据。设计采用低成本的现场可编程门阵列(FPGA)和数字信号处理器(DSP)实现,具有灵活性强、速度快等特点,而且通过工程应用证明了设计是正确可行的。     

扩频信号的捕获与跟踪

针对直接序列扩频信号,介绍了其发射和接收部分基本组成,给出了系统接收部分的具体设计框图。重点讨论了对扩频信号的捕获与跟踪的方法,其中包括扩频码的捕获与跟踪以及载波的捕获与跟踪。对各模块的性能进行了分析,提出了在高速信号处理板(以FPGA和DSP为基础)中对扩频信号的捕获与跟踪的实现方案。经工程验证,能够实现伪码同步和载波同步,解调出所需信号。     

多径衰落信道下的扩频码设计与联合检测

在多径衰落信道CDMA系统中，扩频码设计与联合检测为提高系统容量的两个重要手段。在扩频码设计中，通过构造零相关窗码可以消除MAI和ISI，从而提高系统容量。当扩频码相关特性不理想时，通过联合检测也可以消除干扰，提高系统容量。但二者都有一定局限性，对于零相关窗码来说，它的码字资源十分有限，对于联合检测来说，当用户数很大，它的复杂度不能容忍。该文将扩频码设计与联合检测结合起来，提出了一种具有组间零相关窗特性的新型扩频码。在扩频码设计时考虑联合检测，可以增加码字资源，在联合检测中考虑扩频设计，又可以降低联合检测的复杂度。     

The effects of polarization mode dispersion on 2D wavelength-hopping time spreading code routed networks

In this study, we investigate the effects of multiple access interference (MAI) and polarization mode dispersion (PMD) in 2D wavelength-hopping time spreading optical code paths. The main results show the MAI effects and PMD constraint at the outage probability. The contribution of these sources of interference is analysed to choose the better design of code parameters in order to increase the performance of networks based on optical code paths. These results could be applied to determine the parameters design in code/wavelength routed networks.     

An evolutionary approach to designing complex spreading codes for DS-CDMA

This paper proposes a novel evolutionary approach to spreading code design in direct sequence code division multiple access (DS-CDMA). Specifically, a multiobjective evolutionary algorithm (EA) is used to generate complex spreading sequences that are optimized with respect to the average mean-square cross- and/or autocorrelation (CC and/or AC) properties. A theoretical model is developed in order to demonstrate the optimality of the generated codes. The proposed algorithm enables spreading code design with no constraints on the code length. Furthermore, it is possible to generate K/spl ges/N codes of length N with very little cost in correlation properties. This results in significant capacity enhancement in DS-CDMA systems.     

Analysis of an adaptive decorrelating detector for synchronous CDMAchannels

Multiuser detection allows for the efficient use of bandwidth in code-division multiple-access (CDMA) channels through mitigation of near-far effects and multiple-access noise limitations. The decorrelating detector, developed by Lupas and Verdu (1989), is a linear multiuser detector that is asymptotically optimal in terms of near-far resistance when certain communication parameters are completely known to the detector. In this paper, a simple adaptive decorrelating detector is developed by placing constraints on the set of spreading codes to be used by the active users. This adaptive detector has two modules: it first decorrelates the existing users, and then it determines the spreading code of a new user entering the network with or without the use of a training sequence. Maximum likelihood detection is proposed for determining the new user's spreading code. The performance of this algorithm is studied by investigating the probability of making an error in determining the new user's spreading code as a function of the number of samples used to make the determination, the number of users transmitting, and the signal to noise ratio of the new user with respect to the ambient Gaussian noise     

Optimization of High Performance Generation Method Based RoF System by Employing Optic Amplifier Link

Spread spectrum linked to optimization techniques play a very important role in today’s world. Optimization gives the best one among all the solutions and the spread spectrum is used to minimize distortion, hence optimized spreading code is very important in wireless communication. This study shows a comparison of two recent modified techniques of differential evolution (DE) with the help of engineering design problems and application of that modified DE, considering the better one, in wireless communication to optimize logistic map based spreading code. A comparative study of properties of both optimized and non-optimized spreading code is also discussed in this paper. The performance of the optimized spreading code is also evaluated with the help of bit error rate (BER) by applying it in static and dynamic direct sequence spread spectrum system (DSSS). The performance of the proposed technique (optimized dynamic logistic map code based DSSS) displays better results than non-optimized spreading code and orthogonal spreading code considering BER. Static optimization is improved by 40% than non-optimized static, dynamic optimization is improved by 70% than static optimization but orthogonal is showing 33% improvement comparing to static optimization and dynamic optimization is improved by 56% than orthogonal one. Therefore, the proposed method can be efficiently applied in the wireless communication system.

     

一种改进的基于Web的移动代理的设计

移动代理系统的特点是移动性,自治性和智能性。在移动代理技术拥有完整性保护后,移动代理就可以免于被恶意的主机和其他代理攻击。传统的移动代理是由固定的代码段组成的,提出了一种改进的移动代理方法(MMA),这种方法可以在执行需求时动态添加新的代理代码模块,也可以删除冗余的代码模块。在基于Web的系统中这种方法比传统的静态方法更加灵活有效。     

Rank-2-Optimal Adaptive Design of Binary Spreading Codes

Over the real/complex field, the spreading code that maximizes the signal-to-interference-plus-noise ratio (SINR) at the output of the maximum-SINR linear filter is the minimum-eigenvalue eigenvector of the interference autocovariance matrix. In the context of binary spreading codes, the maximization problem is NP-hard with complexity exponential in the code length. A new method for the optimization of binary spreading codes under a rank-2 approximation of the inverse interference autocovariance matrix is presented where the rank-2-optimal binary code is obtained in lower than quadratic complexity. Significant SINR performance improvement is demonstrated over the common binary hard-limited eigenvector design which is shown to be equivalent to the rank-1-optimal solution.     

RS(63,45)编译码器的设计与FPGA实现

里德-索罗门(RS)编码是一类具有很强纠错能力的多进制BCH编码,它不但可以纠正随机错误,也能纠正突发错误。首先介绍了伽罗华域加法器和乘法器的设计,然后详细地阐述了RS(63,45)编译码器各模块的设计原理。对编译码器各模块先用Matlab进行设计,验证设计的正确性,再对译码器模块进行纠错性能测试。时序仿真结果表明,该译码器能实现最大的纠错能力。设计的编译码器能运用到实际的无线通信系统中去。     

Inter-Group Complementary Codes for Interference-Resistant CDMA Wireless Communications

Spreading code plays an extremely important role on the overall performance of a CDMA system. The correlation properties and available number of spreading codes determine the interference-resist capability as well as system capacity. In this paper, we analyze the characteristics and limitations of traditional and recently reported spreading codes. Based on the analysis, we propose a new code design approach which will be used to generate inter-group complementary (IGC) codes. The correlation functions of the IGC codes possess definite and bi-valued interference-free windows. In addition, a corresponding code assignment algorithm and spreading scheme will be introduced to take advantage of the desirable properties of the IGC codes for their applications in CDMA systems. Both theoretical analysis and simulation results show that an IGC-CDMA system is interference-resistant and capable to offer a high spectral efficiency if compared with the ones based on other spreading codes.     

基于STM32的传感器接口模块的设计

基于STM32实现了电流型、电压型以及数字IO型传感器接口模块;进行了接口模块的软件设计,说明了详细的固件代码设计.除传统串口外,提供以太网接口,嵌入UDP协议,提供后期开发的便利接口.