数字通信系统中的混沌调制解调

由于具有类噪声的宽带功率谱,在当今的宽带数字通信系统中,利用混沌信号进行调制解调正受到越来越多的瞩目。分析了混沌调制解调的原理,在此基础上介绍了现有的几种混沌调制技术：CSK、COOK、DCSK及FM－DCSK,并根据实际情况介绍了相应的非相干解调方式。最后,归纳了混沌调制解调技术中存在的问题及发展的方向。     

Performance Monitoring of Digital Communication Systems Using Extreme-Value Theory

Extreme-value theory has been suggested by various investigators as an efficient tool for use in monitoring the performance of digital communication systems. One drawback to such a procedure is that it requires learning periods to estimate certain parameters of the extremal distributions. Clearly, whenever an update of the estimates is needed, transmission of information must temporarily cease since a new learning period must begin. To avoid this problem, a technique is proposed for obtaining estimates of the parameters when the learning period is eliminated (i.e., estimates are obtained using noisy samples), and these parameter estimates are in turn used to estimate the probability of error of the communication system. The accuracy of this procedure is tested by computer simulation, and it is indicated how one can verify (in a statistical sense) whether or not this technique is appropriate for any given system.     

Performance of Chaos-Based Digital Communication Systems in the Presence of a Pulsed-Noise Jammer

Chaos-based communication systems are known to offer advantages that are shared by spread-spectrum communications. One important aspect of the performance of any spread-spectrum communication system is the ability to resist jamming. In this paper, an analysis of the antijamming performance of a coherent chaos shift keying system under the influence of a common pulsed-noise jammer is presented. Two types of pulsed-noise jammers, slowly switching and fast switching jammers, are considered in our studies. The performance is evaluated in terms of the bit error rate (BER) under different levels of noise power, jamming power, spreading factor, and duty factor. The maximum (worst-case) BERs are also obtained analytically for the case where the jammer is slowly switching. Computer simulations are performed to verify the analytical results. Finally, the BERs are compared with those of a conventional direct-sequence spread-spectrum communication system.     

一种新的混沌数字保密通信实现方案

针对差分混沌键控（DCSK）的保密性低,数据传输速率不高等缺点,这里设计并研究了一种新的混沌键控调制方式—调频相关延迟键控（FM-CDSK）通信方案,该方案同时兼具CDSK和FM-DCSK的优点。通过仿真分析验证了该系统在数据传输速率和保密性等方面较DCSK和CDSK都有所提高,传输速率更是比原有键控方式提高了2倍,并且利用该混沌调制方式很好的实现了图像信号的保密传输,验证了该系统在数字保密通信中的可实现性。     

The Overlapping Problem and Performance Degradation of Mobile Digital Communication Systems

The expansion in the use of land mobile communications have led to a state of congestion in that portion of the radio spectrum allocated to the land mobile service. Digital communication is one of the methods that can be applied to improve spectrum utilization. In a typical digital communication system, messages are not queued and all overlapped messages have to be retransmitted. That overlapping phenomenon has a negative impact on the performance of the system. The behavior of various determinants of system performance (like probability distribution of waiting time and the load that saturates the channel capacity) are studied in detail. A simulation model was developed to simulate four basic design approaches. It was found that a combination of randomizer (for automatic retransmission) and an inhibit signal has no significant payoff and that each one of these features is superior to a commonly used method of automatic retransmission with constant delay. The relative merits of each design is studied as a function of the load on the channel.     

On the Performance of Digital Communication Systems With Bandpass Limiters--Part II: Two-Link System

This paper examines the performance of a two-link digital communication system operating in the presence of Gaussian noise on both links when bandpass limiters are inserted into the system. The product of the signal time duration and the noise bandwidth for the systems under consideration is small. It is concluded that under certain conditions, the presence of a limiter can improve the performance of the system. Also, a simplification of previous work is presented when an infinite clipper is introduced at baseband in the detector.     

数字化接收机极限性能指标的研究

等效噪声温度高达数十万度的A／D模块，引起了数字接收机性能的深刻变化。在接收机中，不能简单地将它当成一般有源器件处理。文中论证了数字化后雷达接收机所能达到的灵敏度、瞬时动态范围极限性能指标，推导出设计公式和曲线，给出实验验证结果。结果和概念澄清了一些流行的模糊认识，对数字接收机的增益、灵敏度、瞬时动态范围的设计和调试，可按给出的公式、曲线精确地获得。     

Efficiency of Digital Synchronous Communication Systems

A novel criterion for digital synchronous communication system efficiency estimation is defined. All system attributes such as bit error probability, coding efficiency, initial system synchronization time, efficiency of detection of timing anomalies and system sync recovery, reliability of the lock indication, and the amount of redundancy insertion in the data stream for synchronization and error-correcting coding purposes are included in a single parameter called "system efficiency." The expression for this parameter is derived under the assumption of signal ergodicity and steady-state system operation. In its final form, this parameter seems obvious almost by inspection. Even so, until now, it has not been used in the analysis of communication system efficiency. The analysis of this parameter for several different systems is presented as an illustration.     

提高混沌同步通信系统传输效率的方法

本文讨论了混沌同步数字通信系统的传 输效率,考察了驱动信号取样周期对同步性能的影响,适当选取取样周期,可减少驱动信号的数据量。由于传输效率与系统设计有关,本文提出一种利用时空混沌同步的加密通信方案,该方案将时空混沌信号用作加密密钥,每个驱动信号样本可使时空系统同时产生多个密钥, 对多个消息数据进行加密,从而有效地提高了数据传输效率,为实现语音信号在计算机网上的加密实时传输提供了一条新的途径。     

耦合混沌同步和多路保密通信

本文针对混沌系统在通信中具有理想的保密作用，讨论了离散多振子耦合混沌系统的特性和两个耦合混沌系统的同步行为，结果表明，两个耦全合混沌系统通过简单调制能很快同步，并且具有通信保密性和多路传输特性。     

基于脉冲分集理论的雷达波形数字水印抗DRFM干扰技术

数字射频存储(Digital Radio Frequency Memory, DRFM)欺骗式干扰的发展越来越成熟,然而,相应的抗干扰技术效果尚显不足。本文基于脉冲分集理论提出了一种抗数字存储欺骗式干扰的方法,首先利用不同的随机数对发射信号脉冲包络进行编码调制;接收处理时,根据编码规则,通过判断回波与发射信号携带的随机数是否相同,从而识别真假回波,进一步进行抗干扰处理,最终达到抑制干扰的目的。仿真结果并与典型的调频率捷变的方法进行比较。仿真结果表明,新算法的抗干扰性能较典型的调频率捷变的算法有明显提升。      

混沌扩谱CDMA的系统模型及其性能分析

混沌序列在具有很好随机性的同时,一些序列还具有KroneckerDelta自相关和近似正交的互相关特点,因此被认为是实现直序扩谱CDMA系统较理想的扩谱序列之一,成为近年来研究的热点。文中从异步DS-CDMA系统的模型入手,分析影响CDMA系统性能的关键问题,说明混沌扩谱CDMA系统的性能优点。为了实现混沌扩谱CDMA系统的数值仿真与性能验证,以切比雪夫映射产生的混沌序列为例进行混沌扩谱CDMA系统的性能分析,并与基于Gold和Kasami两种序列的传统DS-CDMA系统进行比较。     

数字光纤通信系统的建模

介绍了对新研制的光纤通信系统进行计算机仿真所需建立的各模块的数学模型，包括ＬＤ驱动电路、光源调制模块、光纤传输模块和光接收机模块等，以及在建立数学模型的过程中应综合考虑的多种因素，如激光器的寄生效应、啁啾、色散及各种噪声等等。     

混沌在数字通信中的应用

随着对混沌理论的深入研究,混沌具有的优良特性必然被人们所认识,并应用到实际工程中来。短短十几年,混沌通信系统得到了充分的发展,目前正从理论分析向实用化转变。混沌通信系统是传统通信系统的扩展,同样可以分为相干通信和非相干通信两大类。文中着重对相干、非相干混沌数字通信系统进行介绍和评价,指出混沌数字通信系统亟待解决的若干问题,最后对混沌在传统通信系统中应用的前景进行了展望。     

Error Probability of Asynchronous Spread Spectrum Multiple Access Communication Systems

Several approaches for the evaluation of upper and lower bounds on error probability of asynchronous spread spectrum multiple access communication systems are presented. These bounds are obtained by utilizing an isomorphism theorem in the theory of moment spaces. From this theorem, we generate closed, compact, and convex bodies, where one of the coordinates represents error probability, while the other coordinate represents a generalized moment of the multiple access interference random variable. Derivations for the second moment, fourth moment, single exponential moment, and multiple exponential moment are given in terms of the partial cross correlations of the codes used in the system. Error bounds based on the use of these moments are obtained. By using a sufficient number of terms in the multiple exponential moment, upper and lower error bounds can be made arbitrarily tight. In that case, the error probability equals the multiple exponential moment of the multiple access interference random variable. An example using partial cross correlations based on codes generated from Gold's method is presented.     

基于混沌序列的相干OCDMA系统性能分析

文章把二进制的双极性混沌序列应用到两个相干光码分多址(OCDMA)系统中,推导了信噪比和误码率的表达式,仿真分析了误码率随用户数的变化曲线,并和使用Gold序列的同一方案进行了比较,研究结果表明基于混沌序列的系统有较低的误码率和较高的安全性.     

RS Codes with Filtered-OFDM: A Waveform Contender for 5G Mobile Communication Systems

In recent years, the proportion of elderly population in various countries has gradually increased. Increasing with age, it can entail illness. When these diseases are sudden, the elderly often die because there is no immediate treatment. Elderly care has become an important issue. According to this issue, we want to monitor the physiological data of the elderly, such as heartbeat, blood pressure, etc., through wearable devices. Once an abnormal condition is detected, the wearable device can be used to immediately request treatment from a nearby clinic or hospital. In order to improve the network quality of this service, we use the architecture of the mobile edge computing. The mobile edge computing provides features such as immediacy, low latency, proximity etc. However, the process of data transmission on the mobile edge computing has the risk of being stolen and identity authentication is also an important issue. Therefore, we propose a secure protocol based on cryptography to protect personal information with lightweight authentication. The proposed scheme aims to achieve mutual authentication, non-repudiation, integrity, user privacy, and defend against known attacks.

     

一种利用数字信道实现混沌保密通信方法

该文基于混沌保密通信系统特点,提出利用标准数字信道传输发送信号。分析结果表明,该方法方便灵活,性能可靠。     

一种简易数字波形存储器的实现

给出了采用类似DMA的设计思路以及使用双口RAM、快速逻辑电路和CPU(AT89C51)组成的数字波形存储系统的整体电路 ,从而解决了波形数据的快速采集和输出显示问题