多径衰落信道中M进制直接序列扩频系统RAKE接收机性能分析

本文分析了存在码片定时误差和载波相位估计误差情况下,采用BPSK调制的M进制正交码直接序列扩频信号在多径衰落信道下的RAKE接收机性能.分别讨论了不使用分集和采用选择式合并、等增益合并和最大比合并三种分集合并策略时接收信号的误码率,并推导出相应的近似计算方法.文章最后在此基础上分析了不同的分集合并办法、码片定时误差和载波相位误差对系统性能的影响.     

Direct-Sequence Spread Spectrum with DPSK Modulation and Diversity for Indoor Wireless Communications

Direct-sequence spread spectrum with differential phase shift-keying (DPSK) modulation and code-division multiple-access is a promising approach for wireless communications in an indoor environment, which is characterized in this paper by a Rayleigh-fading multipath channel. In this study, we consider two specific channel models having different path-delay distributions and average path power profiles. A star configuration, in which each user exercises average power control in transmitting to a central station, is the basic communication unit, which could be one cell in a cellular hierarchy. We obtain the performance of a single link between a user and its receiver in the central station, and consider two types of diversity, selection diversity and predetection combining to exploit the multipath. A similar system with coherent PSK (CPSK) modulation has been studied previously for one of the channel models considered here. For the same channel model, we show that the irreducible error probability with selection diversity is about half an order of magnitude higher when DPSK is used instead of CPSK. With predetection combining, the performance improves significantly in comparison with selection diversity as the diversity order increases. DPSK modulation with predetection combining is akin to coherent PSK with optimal maximal-ratio combining, but is simpler to implement. The performance with selection diversity for a second channel model, which is based on measurements in an office building, is not significantly different. This indicates that the spreadspectrum approach is rather robust to the path-delay distribution and average path-power profile.     

预编码——差错控制编码的一种新方法

文章首先介绍了Ａ．Ｓ．Ｋｈａｙｒａｌｌａｈ提出的对差错控制码进行预编码的基本思想，然后指出了预编码理论与实践上的意义。     

Rayleigh衰落信道下编码多进制直接序列扩频通信系统的性能分析

分析了一种采用RS(n,k)编码的在MSK调制方式下基于循环移位的M进制直接序列扩频通信系统在Rayleigh衰落信道中的性能,给出了准确的误码率公式.通过SPW软件仿真给出了该系统在Rayleigh衰落环境下的性能曲线.仿真得到的误码率与公式推导的结果完全吻合.     

基于ICR的任意传输速率扩频通信系统

介绍了一个基于ICR的任意传输速率（最高可达11Mbit/s）扩频通信系统的设计和实现过程，分析了802．11b标准中直接序列扩频系统的处理措施，详细描述了如何实现任意速度传输，以及ICR的工作过程。     

扩频通信新方向--自编码扩频

扩频通信是把信息的频谱展宽进行传输的技术 ,而目前我们采用的PN序列具有周期性 ,为了寻找一种扩频码具有真正的随机性 ,并具有较强的抗干扰和信息保密能力的扩频通信技术 ,人们提出了自编码扩频的概念 ,本文介绍了其原理和相关的关键技术     

基于纠错编码和扩频调制的彩色图像水印算法

提出一种基于纠错编码和码分多址(CDMA)的彩色图像水印算法,先后将秘密信息进行Arnold置乱,纠错编码,扩频调制.提取宿主图像的绿色分量,对其进行离散余弦变换,将预处理的水印嵌入到变换后的部分中频区域.水印提取部分,首先对待测图像的绿色分量做离散余弦变换,其次提取中频部分的水印信息,将提取的值和由密钥得到的Gold...     

扩频通信中扩频水印的嵌入方法

本文提出了一种基于多码扩频(MC-DSSS)技术的数字水印嵌入方法,即利用扩频码的正交性将扩频水印嵌入到扩频通信信号中。理论分析和仿真结果表明,此种方法嵌入的水印具有很多优点,如透明性、鲁棒性和可靠性等,并具有良好的抗干扰性能。     

基于混沌的扩频通信

针对混沌信号具有的随机性、宽带性、似噪声以及对初始条件的极端敏感性的特点，本文用混沌序列取代扩频通信系统中的伪随机码，在提出并实现一种混沌网络同步化法的基础上，实现了语音、文字和图像的码分多址的扩频通信。用Ｌｏｒｅｎｚ混沌系统对同步和通信的仿真结果表明了本文所述方法的有效性和可靠性。进一步指出了这种通信方式具有简便性和自然的保密性的优点。     

并行组合扩频通信扩频序列的优选

并行组合扩频通信相对传统扩频通信具有更高效,更安全的优势。但是由于并行通道间存在互干扰,降低了系统的传输可靠性。为了提高并行组合扩频通信系统的性能,需要从备选的扩频序列中优选出合适的扩频序列来组成扩频序列集用于信息映射。通过分析并行组合扩频通信的通信原理,从减小接收端各支路互相关干扰的角度提出了一种扩频序列的优选方法。仿真结果表明,采用该方法能够有效地降低系统的误码率,提高系统的可靠性。     

The Spread Spectrum Concept

This paper describes an idealized spread-spectrum communication system. The processing gain concept is developed as a measure of a well-designed system's robust performance against independent wide-sense stationary interference. Multipath and repeater jammer rejection, partial correlation problems, and security requirements are related to spread-spectrum code properties.     

时空混沌流扩频

针对计算机网络中的保密通信，充分利用时空混沌序列复杂度高、伪随机性好的特点，将时空混沌直接扩频通信与流密码技术相结合，提出时空混沌流扩频通信方案。以单向耦合映象格子时空混沌系统模型为基础，采用驱动-响应同步方法达到时空混沌同步，使用长周期的时空混沌二值序列作为会话密钥对明文信息进行扩频(加／解密)。这种通信方式具有很高的安全性。     

Computer-Aided Spread Spectrum Signal Design

The calculations required in the formulation of surface acoustic wave device signals have been removed from the design process into a large-scale digital computer. The designer is left to trade off application-critical signal characteristics while the computer presents the alternatives and controls fabrication of the interdigital transducers.     

直扩信号跟踪测角技术研究

提出了一种单脉冲双通道体制的直接利用直扩信号跟踪测角的方法:自相关法提取角度误差。利用和差两支路信号的相关性对两支路信号进行相关来提取角度误差信息。对这种跟踪测角方法进行了理论分析、论证,用MATLAB仿真软件对系统进行了仿真研究。结果表明该方案可行。     

Construction of Two-Dimensional Paraunitary Filter Banks Over Fields of Characteristic Two and Their Connections to Error-Control Coding

Filter banks over finite fields have found applications in digital signal processing and error-control coding. One method to design a filter bank is to factor its polyphase matrix into the product of elementary building blocks that are fully parameterized. It has been shown that this factorization is always possible for one-dimensional (1-D) paraunitary filter banks. In this paper, we focus on two-channel two-dimensional (2-D) paraunitary filter banks that are defined over fields of characteristic two. We generalize the 1-D factorization method to this case. Our approach is based on representing a bivariate finite-impulse-response paraunitary matrix as a polynomial in one variable whose coefficients are matrices over the ring of polynomials in the other variable. To perform the factorization, we extend the definition of paraunitariness to the ring of polynomials. We also define two new building blocks in the ring setting. Using these elementary building blocks, we can construct FIR two-channel 2-D paraunitary filter banks over fields of characteristic two. We also present the connection between these 2-D filter banks and 2-D error-correcting codes. We use the synthesis bank of a 2-D filter bank over the finite field to design 2-D lattice-cyclic codes that are able to correct rectangular erasure bursts. The analysis bank of the corresponding 2-D filter bank is used to construct the parity check matrix. The lattice-cyclic property of these codes provides very efficient decoding of erasure bursts for these codes.      

Performance Criteria for Spread Spectrum Communications

The criteria for antijam (AJ) and anti-intercept (AI) systems are described, in terms of the appropriate action taken by the jammer or interceptor. Avoiding pseudonoise (PN) sequences which can be partially or totally predicted is a foremost criteria, especially for AJ, and use of nonlinear feedforward logic (NFFL) with long-period linear maximal sequences appears attractive. A frequency-hopping (FH) system must anticipate a multitone jamming signal, and an error-control code is necessary. A novel method for generating a multitone signal using repeating maximal sequences is described. PN systems must anticipate a tone jammer, and now an errorcontrol code may be needed to assure that sporadic PN sequence correlation with the tone does not reduce the processing gain. Any AI system must anticipate that the interceptor may, if advantageous, integrate his decision energy over many communicator symbols (up to the message length). Now spreading both in frequency and in time may be valuable. Finally, the use of an automatic adaptive data rate is suggested to realize flexibly either AJ or AI objectives.     

自编码扩频通信技术研究

扩展频谱通信是军事保密通信的基本方式，它是采用信息的频谱展宽进行传输的，从而达到抗干扰和信息保密的目的。而目前采用的PN序列具有周期性，为了寻找一种具有真正的随机性扩频码，并具有较强的抗干扰和信息保密能力的扩频通信技术，人们提出了自编码扩频的概念，文中介绍了自编码扩频原理，分析了系统的性能，并且进行了仿真。     

扩频技术及其应用

扩频技术是充分利用有限频谱资源,提高无线信息传输效率的一种新技术,文章介绍了扩频通信工作原理及其系统模型,详细阐述了扩频通信的两种主要技术:直接序列扩频和跳频扩频,解释其工作原理,并将这二者的性能进行比较。另外介绍了扩频与数字水印技术的结合,利用扩频原理的数字水印技术具有很高的健壮性和安全性。     

Combination Sequences for Spread Spectrum Communications

Certain communication systems which employ spread spectrum techniques as a means of supporting multiple users need very long codes to guard against the threat of intentional jamming, but cannot tolerate the lengthy acquisition time which long codes usually require. As a possible solution to this problem, the use of combination sequences has been suggested, and this paper presents some new results, both analytical and numerical, on this technique.     

毫米波谐波混频器扩频技术

文章主要介绍了3mm谐波混频器的设计方法并用于毫米波扩频,对毫米波宽带匹配技术、宽带滤波桥路技术、毫米波电路加工及微组装工艺也作了阐述。毫米波谐波混频器采用波导和带状线混合结构,混频二极管采用梁式引线二极管对,滤波电路采用带状线结构的高低通滤波器。毫米波信号与本振信号的18次谐波混频,输出一个中频信号,通过与安捷仑的8563EC、8566等频谱议的配合使用,达到频谱仪的扩频,也可用于网络分析仪、频率综合器、频率计等仪器的扩频。