【作者】 庄陵；

【导师】 曹长修；

【作者基本信息】 重庆大学 ， 控制理论与控制工程， 2009， 博士

【摘要】 随着无线多媒体业务需求的增长,短程高速无线通信已经成为未来通信技术的重要发展方向之一,市场需要一种技术来解决高速网络接入需求与拥挤的频谱资源分配之间的矛盾,超宽带(UWB,ultra-wideband)通信以其速率高、容量大、成本低及功耗小等特点成为备受关注的重要解决方案。目前超宽带技术统一的商用体制标准还没有出台,如果要制定合理的UWB技术规范,必须综合考虑很多技术问题,如调制技术、信道编码技术等。根据美国联邦通信委员会的规定,超宽带室内通信系统可以使用3.1至10.6GHz这个频段,对于脉冲超宽带系统,如果采用不合适的脉冲波形,在数据速率高、情况复杂的无线通信环境中,接收端将难以正常接收信号,无法保证系统的性能,更重要的是其他无线系统的正常工作也会受到干扰。要解决以上问题,在调制技术、发射功率、脉冲波形等方面必须进行综合设计。本文对超宽带系统的调制方法、信号频域分布和脉冲波形设计展开研究,具体工作和取得成果如下:(1)超宽带通信的调制技术研究:首先简略介绍常用于超宽带脉冲无线电的基本脉冲,即高斯脉冲及其各阶导数,给出时频域波形仿真及脉冲序列的一般表达式;其后讨论超宽带脉冲无线电通信数据调制方式,主要是PPM和PAM两种;之后对脉冲无线电通信的多址调制技术,特别是跳时和直接序列扩频技术进行讨论;着重讨论脉冲无线电目前比较热门的TH-PPM、TH-PAM和DS-UWB的调制解调技术,并分别进行发射端建模仿真,给出信号仿真结果;最后简单介绍多频带超宽带调制技术原理,并进行相应发射机仿真实验。(2)典型超宽带脉冲信号功率谱密度表达式推导、频域分析及仿真:首先从随机理论出发,研究随机过程功率谱密度;分析数字基带信号随机特性,得到其本质是周期性平稳随机信号,并将其等效于一阶马尔可夫链,推导出功率谱密度表达式。其后分别分析两种受到业界重视的超宽带信号,即TH-PPM和DS-UWB信号的随机性,得到它们都属于非平稳过程,具有周期平稳随机信号特性,并在该理论基础之上详细推导出各自功率谱密度表达式,填补了相应文献资料上的空白。对于前者的跳时情况,利用概率密度函数描述其随机特性,推导出相应的功率谱密度解析式。对于DS-UWB信号,由于后面分析功率谱密度影响因素的需要,在推导功率谱密度过程中对体现信号随机特性部分的频谱保留了完整形式。随后分析超宽带信号频域分布的影响因素,得到的结论是:对功率谱分布的控制可以通过对已调序列特性、脉冲重复频率和发射脉冲能量谱密度的设计得到实现。其后通过一系列仿真实验对该结论进行了验证。最后,研究超宽带通信系统对窄带系统的干扰,分析影响受扰窄带无线系统功率的因素,得到设计合适的超宽带脉冲信号波形,能够控制干扰、解决共存问题。(3)超宽带脉冲信号波形的优化设计及仿真:首先基于超宽带系统共存问题,介绍系统发射功率掩蔽的有关规定,并运用数值逼近理论提出两种新的符合功率掩蔽要求、可降低超宽带系统对现存无线系统的干扰、具有较高频谱利用率的超宽带脉冲波形设计方法。频率采样脉冲波形设计法源于数值逼近理论插值法,所得脉冲波形有确定解析式;Chebyshev最佳一致逼近脉冲波形设计法属于均匀一致逼近,逼近程度能够利用参数进行限定。并在理论分析基础上针对不同参数进行仿真,实验结果验证了两种方法的有效性。最后对脉冲设计方法进行了总结和比较。更多还原

【Abstract】 The growth of need for wireless multimedia services makes short-range and high-speed become trends of the wireless communication technologies. The market needs technology that can resolve the conflict of high-speed access demand and crowded spectrum resource allocation. Ultra-wideband (UWB) is considered a solution for its characteristics of high speed, large capacity, low cost and low power consumption. At present, its unified commercial standard isn’t yet addressed. To get a reasonable one, a lot of technical issues must be considered, such as modulation, channel coding technology, etc. Federal Communications Commission authorizes to apply UWB technology for communication purposes in the band from 3.1 to 10.6 GHz. For impulse radio ultra-wideband, inappropriate pulse shape will make it difficult to receive signals in the complex wireless communication environment of high data rate, and can’t guarantee the performance. More importantly, the normal work of other wireless systems will be interfered with. To solve this problem, the modulating technique, transmission power, pulse shape, etc. must be designed comprehensively.In this paper, modulation method, spectrum distribution and pulse shape design of ultra-wideband system are studied. The specific dedication is as follows:(1) Research of ultra-wideband modulation technique. First of all, give a brief description of the basic pulse waveform that commonly used in impulse radio ultra-wideband, that is, Gaussian pulse and its derivative. After giving their time-domain and the frequency-domain simulation waveforms, as well as the general expression of the pulse sequence, subsequently data modulation methods are discussed, the main two are PPM and PAM; and also the multiple access modulation techniques, such as time-hopping and direct sequence spread spectrum. Next, TH-PPM, TH-PAM and DS-UWB modulation are modeled and simulated separately, and the simulation results of transmitters are giving. Finally, introduce modulation technique of the multiband-OFDM ultra-wideband, and make the corresponding transmitter simulation.(2) Formula derivation of power spectral density in impulse radio ultra-wideband communication, spectrum analysis and simulation. At first, the power spectral density of stochastic process is discussed, the random features of digital base-band signal are analyzed, and its power spectral density is derived equivalent to a Markov chain. Next, derives the power spectral density of two kinds of popular ultra-wideband pulse signal . Both of them belong to non-stationary process, have cyclostationary random process characteristics, the analysis is done based on it. For the former, because of the complexity of time-hopping, the probability density function is used to describe the random characteristics, and relative derivation followed by the corresponding formula of the power spectral density. For DS-UWB signal, because of the need to analyze the effect factors of power spectral density, analysis is simplified and retains integrity of the corresponding formula. Subsequently, the various factors that distribute to the impact of the power spectral density are analyzed, and the conclusion is that distribution of power spectral density can be controlled by adjust the sequence characteristics, pulse repetition frequency and pulse energy spectral density. Also the theoretical analysis is verified through a series of simulation. Finally, through the study of interference that ultra-wideband communication system to do with narrow-band system, and the analysis of impact factor of narrow-band wireless systems power, the conclusion is that design of ultra-wideband signal power spectral density can limit the interference, which will solve the problem of coexistence.(3) Optimal design of the ultra-wideband pulse waveform. The relevant provisions of UWB transmitter power mask are presented after discussion of UWB system coexistence. On the basis of numerical approximation theory, two novel methods to design the pulse waveform are given, which according with the mask requirements of power, can reduce the interfere of ultra-wideband systems and existing wireless systems and increase the spectrum utilization. The method based on the frequency sampling is taken from the interpolation theory. The method based on the Chebyshev best uniform approximation theory can control the precision of approximation by limiting parameters. And based on the theoretical analysis, several simulations are made with different parameters. Simulation results show the effectiveness of the two methods. Finally, the design methods of UWB pulse are summarized and compared.更多还原