【作者】 李辉；

【导师】 宋耀良；

【作者基本信息】 南京理工大学 ， 信息与通信工程， 2008， 博士

【摘要】 超宽带混沌信号由于频谱宽阔,用于通信具有高速率、高保密性、低截获率、有很好的抗多径衰落等优点,是解决通信速率、安全和干扰问题的理想信号。本文围绕着超宽带混沌信号的产生、超宽带混沌通信系统的构建、调制方式和多址方式等方面,对超宽带混沌通信几个关键性技术进行了系统地研究。主要内容包括如下几个方面:1.在简要论述了混沌系统的特点、分类、研究方法和混沌信号的描述方法的基础上,着重讨论了离散和连续混沌信号的产生方法以及混沌系统的同步理论。针对超宽带视频混沌信号产生的难题,对数字混沌驱动级联Colpitts振荡电路的方法进行了改进,产生了具有宽阔平坦的类噪声频谱、满足超宽带定义的混沌信号,并验证了电路同步的鲁棒性。2.分类研究了常见的相干和非相干解调混沌通信系统,重点讨论了混沌差分键控(DCSK)和调频混沌差分键控(FM-DCSK)系统。考虑到解调模板中的噪声分量是影响FM-DCSK超宽带系统性能的一个重要因素,提出了FM-DCSK的一种改进方案。从理论上分析了系统在加性高斯白噪声信道中误码率的解析式,结果表明改进的系统比改进前对同步的要求降低,而且可以有效地降低解调模板和数据段中的噪声分量。3.由于常见的DCSK多址方案存在以下两个问题:首先所有用户共享同一时隙,只能利用混沌信号的低互相关性来降低多址干扰;其次发送的参考信号和数据信号并不相同或相反,破坏了DCSK系统的良好抗多径性。重点研究了各种DCSK系统的多址实现方案,提出了DCSK系统一种新的跳时多址方式。该方式给每个用户分配不同的伪随机跳时码,根据跳时码参考信号和数据信号进行相同量的跳时。从理论上分析了多址系统在加性高斯白噪声信道中的误码率解析式。分析和仿真结果表明该方式可以很好地解决上述两个问题,并且调整参数可以获得更低的误码率。4.针对跳时脉位调制(TH-PPM)的超宽带系统信号离散功率谱分量集中、易引起多址干扰的缺点,引入了基于Tent映射的混沌脉位调制(CPPM)UWB系统。从理论上推导了其信号的功率谱密度表达式。分析和仿真表明UWB系统CPPM方式可以获得更均匀的功率谱,其离散谱密度明显低于TH-PPM,从而能减少对其它通信系统的干扰、具有更低截获概率和高保密性。5.为了进一步提高混沌通信系统的速率,根据宽带混沌信号极低的互相关特性,提出利用产生的超宽带混沌信号作为载波,构建了多路并行传输的超宽带系统,仿真表明系统在较高的传输速率下具有较低的误码率。6.讨论了UWB FM-DCSK系统和UWB多比特FM-DCSK系统的结构和信号形式,分析了在多径信道下两系统的误码率解析式,结果表明两系统在多径信道下具有良好的性能。给出了UWB FM-DCSK系统在超宽带信道模型下的仿真。提出了一种超宽带频分复用混沌差分键控(FDM-DCSK)系统,从理论上分析了系统在加性高斯白噪声信道中误码率的解析式,仿真表明在相同的误码率条件下,FDM-DCSK比DCSK系统信噪比降低3到4dB,而且具有更高的传输速率。更多还原

【Abstract】 Ultra wideband (UWB) chaotic signal has a broad spectrum, so it has lowprobability of interception, high communication rate, high security and strong anti-multipath characteristics in communications. It is an ideal signal to resolve the rate, security and interference problems for communication system. Focus on the problems of UWB chaotic signal’s generation, UWB chaotic communication system’s construction, modulation mode and multiple-access mode, some key techniques in the UWB chaotic communications were discussed in this dissertation. Main contents of the dissertation include following aspects:1. The characteristics, classifications and research methods of the chaotic systems, the description of chaotic signal were discussed. The discrete, continuous chaotic generating method and chaotic synchronization were emphasized. Aiming at the difficulty of UWB chaotic signal generation in video frequency, a chaotic signal generation circuit using cascading Colpitts circuits with digital chaotic driving was improved. The generated chaotic signal has a broad and flat frequency spectrum and is satisfied with the definition of UWB of FCC. The robust synchronization method was validated.2. The common coherent and incoherent demodulation chaotic communication system was researched. The emphases were put on Differential Chaos-Shift-Keying (DCSK) and Frequency Modulated Differential Chaos-Shift-Keying (FM-DCSK). Considering that the noise in demodulated template has an important influence on the FM-DCSK UWB system’s performance, an improved scheme was put forward. In AWGN channel the system’s bit error rate (BER) was obtained in theory. The result shows that compared to unimproved system, the improved system has lower standard for synchronization and can effectively reduce the noise in demodulation template and symbol.3. The common multiple-access schemes for DCSK have two disadvantages. Firstly, all users share the same slot, the only way to decrease multiple-access interference is utilizing the low correlativity of chaotic signal. Secondly, the transmitted signals for reference and symbol are not same or reverse, so the strong anti-multipath character is destroyed. Some multiple-access schemes for DCSK system were researched. A novel time-hopping multiple-access scheme for DCSK system was put forward. It assigns different PN time-hopping codes to different users. The signals for reference and symbol in a frame have the same time-hopping value. In AWGN channel the system’s bit error rate was obtained in theory. Analysis and simulation show that time-hopping multiple-access scheme can overcome above two disadvantages and has lower bit error rate by adjusting parameter.4. Using Time-Hopping pulse position modulation (TH-PPM), an UWB system has some disadvantages that the discrete power spectral density (PSD) is centralized and may arouse multiple-access interference. An UWB system utilizing chaotic pulse position modulation (CPPM) based on Tent map was introduced. The PSD of CPPM signal was deduced in theory. Analysis and simulation show that, for UWB system, CPPM can obtain more even PSD, its discrete PSD is smaller than TH-PPM’s. Therefore it has less interference on other communication systems, lower probability of detection and higher security.5. For increasing chaotic communication rate, based on the low cross-correlation of wide band chaotic signal, a multiplexing ultra-wide band system based on generated UWB chaotic carrier was put forward. Simulations show that the system has low BER in high communication rate.6. The frame and signal formation of the UWB FM-DCSK system and UWB many bits FM-DCSK system were analyzed. In the multipath channel the two systems’ BER were obtained in theory. The result shows that the two systems have good performance in the mutipath channel. Simulations on UWB FM-DCSK system were made in UWB channel model. An UWB FDM-DCSK system was proposed. In AWGN channel the system’s BER was obtained in theory. Simulations show that compared with DCSK system, in the same BER it can decline signal-to-noise ratio (SNR) about 3 to 4dB and reach higher communication rate.更多还原