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.     

个人通信中的扩频技术

在个人通信中,必然会遇到频谱共享、通信安全、传播环境和多径干扰等复杂技术难题,而扩频通信技术是同时解决这些问题又可提供多种信息服务的良策。本文主要讨论扩频技术基础以及扩频技术在个人通信中的应用。     

扩频通信的频谱相关检测方法

基于周期平稳信号特征和频谱相关密度，本文提出了利用频谱相关处理检测扩频通信信号的频谱相关检测方法。这种方法的检测性能常规经典方法，并有更好的抗噪声和干扰的能力。     

小波在扩频通信中的应用

本文描述了基于正交小波函数族的多址通信原理,并提出了一种多速率正交小波调制方法,用具有不同伸缩尺度的小波函数对不同信道中的码流进行编码,可以达到扩展信息序列频谱的目的,因此这一多址技术具有很好的抗干扰性能,本文还讨论了这一多址方式的其它特点,并针对信道容量不平等问题提出了一些解决办法。     

揭开隐藏在扩谱通信中的秘密

抗干扰、跳频数字无线电系统技术正在迅速发展,军队正努力跟上新的检测技术和截获技术。     

混合DS－SFH扩频多址通信系统采用RS码的性能界限的分析

本文推导了混合直接序列和慢跳频扩频多址通信系统，在Ｒｉｃｉａｎ和Ｒａｙｌｅｉｇｈ多径衰落信道中，采用ＲＳ编码和非相干ＤＰＳＫ、ＦＳＫ调制的系统性能界限，提出了利用探测多径干扰和多址干扰是否存在的信道信息的ＲＳ译码新算法。     

Fast Acquisition Scheme of the Spread Spectrum Signals for Satellite Communications

Journal of Communications Technology and Electronics - A four-channel parallel acquisition scheme combining partial matched filters and fast Fourier transforms (PMF-FFT) is proposed for the fast...     

Digital Whitening Techniques for Improving Spread Spectrum Communications Performance in the Presence of Narrowband Jamming and Interference

Narrowband jamming and interference due to other users in spread spectrum communication systems can be effectively suppressed by using digital whitening. As a result, an impressive improvement in receiver performance can be obtained. The digital whitening is accomplished using a transversal filter whose coefficients are selected by either a Wiener algorithm or a maximum entropy algorithm. Filters obtained by use of these algorithms are evaluated for various jamming and signaling conditions and are found to exhibit comparable performance over a wide range of input signal-to-noise ratios.     

Spread Spectrum Multiple Access Communications Experiment Through a Satellite

The purpose of this paper is to demonstrate that spread spectrum performance characteristics under different conditions of limiting and audio channel SNR degradation with close separation of carrier frequencies are similar to that of sinusoidal signals. Experiments also show that simultaneous transmission of acceptable spread spectrum and TV signals are feasible.     

Application of Acoustic Surface-Wave Technology to Spread Spectrum Communications

Spread spectrum transmission is being proposed for an increasing number of digital communication, navigation, and RADAR systems. One of the reasons is the simplicity and availability of surface-wave devices (SWD) for performing the necessary signal generation and processing. The properties of spread spectrum signals, the operation of SWD's, and their advantages and limitations when used in communication systems are discussed. Spread spectrum terminology and basic concepts are defined in terms common to both systems engineers and device designers.     

Spread Spectrum and Time Division Multiple Access Satellite Communications

Although time division multiple access (TDMA) satellite communication provides the highest traffic capacity per satellite and offers efficient transmission of a wide variety of services, it suffers from network timing and ranging requirements and message security. On the other hand, spread spectrum multiple access (SSMA) satellite communication is suited for reliable random access and tactical transmission systems. Orthogonal functions such as Rademacher, Haar, and Walsh, or pseudonoise sequence coding of amplitude and phase of the analog message or code division of baseband signals, frequency and time hopping are among the several methods employed for spread spectrum communications. A combination of TDMA and SSMA can be used for asynchronous and reliable transmission of digital or analog signals.     

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.     

PR-QMF滤波器组在扩频通信中的应用

针对目前常见的FDMA、TDMA、CDMA,介绍了一种新的基于PR-QMF滤波器组的扩频技术.其扩频信号由合成滤波器产生,而分析滤波器则执行解扩过程.文章中简要介绍了该系统模型,并对其性能在AWGN及有正弦干扰情况下利用蒙特卡洛仿真,从而得出结论     

Analytical Description of Self-Interference in Direct Sequence Spread Spectrum Communications

A new analytical statistical model has been developed in order to describe the self-interference that results due to multipath propagation in a BPSK spread spectrum system. Motivation for this work was the fact that the well-known Gaussian approximation that has been extensively used in the past in order to describe such terms is not satisfactory, especially when the probability of error is smaller than10^–2 or 10^–3. The existence of two paths inthe radio channel has been assumed. The amplitude of each path has been assumed as Rayleigh distributed while the arrival time of the second path with respect to the arrival time of the first one has been assumed to be uniformly distributed. The validity of the developed model has been examined by comparing analytical results with results obtained by simulation using Monte Carlo techniques. Results taken from the Gaussian approximation were also compared with the simulation results. It was shown that the developed model describes with great accuracy the pre-mentioned undesirable term. On the contrary, the Gaussian approximation exhibits significant differences when compared to the simulation results. This is also evident by the use of a comparison parameter which is several orders of magnitude smaller for the developed model than for the Gaussian approximation (the smaller this parameter is the better the fit between two groups of data).     

基于空时处理的水声扩频通信

由于海洋干扰严重,水声通信十分困难。扩频通信技术具有良好的抗干扰性能,能够保证在复杂的海洋环境中进行可靠的通信,常被用于水声通信中。水声信道是典型的相干多径信道。沿不同路径到达的信号具有不同的传播时延和到达角,因此接收信号具有时空特性。即接收信号具有时延扩展和角度扩展。多径信号的相干叠加导致接收信号中存在严重的符号间干扰。为了充分利用水声信号的时空聚类特性,该文设计了一个空时处理器,分别对沿每条路径到达的信号进行滤波。结合时空簇的多样性,可以有效提高通信系统的可靠性。提出了一种基于空时聚类处理的水声扩频通信方案。并在仿真和实验中对该通信方案进行了比较和分析,以验证其性能优势。     

扩频通信抗干扰中的时频域信号处理技术

时频分析对非平稳信号具有良好的压缩能力,因而成为扩频通信系统抗干扰的研究热点.综述了近年来时频信号处理技术在扩频通信抗非平稳干扰中的应用,并对该技术的发展趋势作出了展望.     

Chirp扩频通信系统抗噪声性能研究

Chirp扩频被IEEE 802．15．4A列为物理层可选标准之一,正得到越来越多的关注。文中分析了Chirp信号的特点及Chirp—BOK系统的组成和调制解调方式,提出了一种对Chirp扩频的理论研究方法,在高斯白噪声信道下,分析并得到系统误比特率一信噪比公式。误比特率的仿真结果与理论推导公式相吻合,并证明该扩频机制与其他调制方式比较,抗噪声性能有明显的改善。     

Spread Spectrum Performance Analysis in Arbitrary Interference

An important application of spread spectrum modulation is to Provide interference immune communications. Generally, the approach to system performance analysis will assume a host of various interference situations with the hope the results give wide applicability, while, based on the concept and properties of pseudo-random spreading waveforms, it is possible to rid the analysis of artificial or restricting interference assumptions and obtain completely general performance bounds.     

Optimization of Coded Spread Spectrum System Performance

Error correction coding techniques significantly improve performance of spread spectrum communication systems in environments containing jamming, multipath, and unregulated multiple access. This paper investigates the optimization of spread spectrum system performance for time-varying unknown interference. Noncoherent frequency hopping (FH) spread spectrum modulation, and hybrid FH-PN incorporating a direct sequence PN modulation on each hopped frequency are studied. For FH or FH-PN, the data modulations considered are differential phase-shift-keying (DPSK), differential quadriphase-quadriphase-shift-keying (DQPSK), and multiple-frequency-multiple-frequency-shift-keying (MFSK). Both block and convolutional error correction coding techniques are studied as a means of improving the spread spectrum performance.