【作者】 付江志；

【导师】 郭黎利；

【作者基本信息】 哈尔滨工程大学 ， 通信与信息系统， 2010， 博士

【摘要】 测控通信系统在航空、航天领域的广泛应用,使其由普通的通信系统扩展到具有遥控、遥测、跟踪等多种功能。直接序列扩频技术由于具有功率谱密度低、信号隐蔽性好、距离分辨率高、多址通信能力强、抗干扰/噪声能力强等特点,成为现代测控系统最常用的通信体制。直接序列扩频系统本身所固有的扩频增益可以抑制信道中有意或无意的干扰,但是由于频率资源有限,当遇到大功率窄带干扰或干扰信号中心频率与直扩信号中心频率近似时,单纯依靠增大扩频增益并不能进行有效抑制。因此研究如何在恶劣的环境下提高测控系统的抗窄带干扰能力具有重要意义。目前对于窄带干扰的抑制主要体现在干扰消除和干扰规避两个方面。其中干扰消除的实现是以计算量的增加或信号能量损失为代价的,而干扰规避是以系统复杂度的增加来达到抑制干扰而不降低通信质量的。根据测控系统的特点,本文主要对干扰规避技术进行研究。以往的规避技术主要集中在时域、空域和频域,并没有利用到扩频序列的码域特性。本文首次对根据序列码域特性实现干扰规避的技术进行研究,即通过设计具有不同频谱结构的扩频序列,采用不同的通信方式使直扩测控系统实现对窄带干扰的规避。首先,本文通过对m-W (m-Walsh)复合序列的研究,得出了不同m-W复合序列信号频谱变化的规律。在对二进制扩频序列信号研究的基础上,根据复合序列的生成方式和相关特性,以及m序列和Walsh序列的特点,研究了m-W复合序列的频谱结构,总结出m-W复合序列具有频谱可控的特性,为直扩系统利用码域特性实现窄带干扰的规避提供理论基础。其次,针对高斯信道中存在的少数窄带干扰,提出了通过使用不同的m-W复合序列实现对窄带干扰规避的方法。该方法是在确定窄带干扰频率位置的情况下,通过设计m-W复合序列作为扩频序列,使受窄带干扰影响的信号能量最小,达到对窄带干扰规避的效果。实验仿真表明,利用m-W复合序列的规避技术可有效降低干扰对信号的影响,实现了对窄带干扰的抑制。然后,针对高斯信道中的固定式窄带干扰和时变或多频干扰,提出了自适应跳码直扩抗干扰方法。该方法将m-W复合序列与跳码直扩技术相结合,使直扩信号具有DS-FH特性,并利用链路质量分析和序列更换算法,使直扩系统具有自适应规避窄带干扰的能力。实验仿真表明,对于固定式窄带干扰、时变或多频干扰,采用自适应方式的跳码直扩系统具有很强的抗干扰能力。再次,针对高斯信道中的瞄准式窄带干扰,提出了基于码域特性的频率分集抗窄带干扰方法。该方法将m-W复合序列与正交多码扩频技术相结合,利用不同的m-W复合序列在频域具有不同频谱结构的特点,对相同的信息使用不同m-W复合序列进行多路并行扩频,得到频率分集的效果,进一步利用分集合并技术提高系统的抗窄带干扰能力。实验仿真表明,当瞄准式窄带干扰影响部分频率时,通过对分集的多路信息进行适当合并,可有效提高系统的抗干扰能力。最后,对于速率较高且频带受限的测控系统,在信道中窄带干扰较多,可用于规避干扰的m-W复合序列较少的情况下,提出了基于m-W复合序列的多进制(M-ary)正交扩频技术。本文在传统M-ary正交扩频的基础上,将m-W复合序列与其相结合,产生新的M-ary正交扩频方式,重点对其结构特点、传输效率、高斯信道下的误码率和抗窄带干扰能力进行了研究。理论分析和实验仿真表明,相比于传统M-ary扩频技术,基于复合序列的M-ary正交扩频技术可在传输效率或系统复杂度方面具有明显优势,进一步通过采用m-W复合序列的规避技术,可使M-ary扩频系统的抗窄带干扰能力大大提高。更多还原

【Abstract】 As tracking telemetry & command (TT & C) system is widely used in aeronautics and astronautics, it is extended from a common communication system to an advanced one comprising functions of remote control, telemetry and tracking. At the same time, direct spread sequence spectrum (DSSS) technology has become the most popular communication mechanism in modern TT & C system because of its low power spectrum density, well-concealed signals, high range resolution, strong capacity of multi-address communication, as well as remarkable anti-jamming and anti-noise abilities. A system applying DSSS has inherent spreading gain that may help resisting intentional or unintentional interference in channels. When such a system suffers high-power narrowband interference(NBI) or when central frequency of interference signals gets close to central frequency of DSSS signals, however, the simple way of enlarging spreading gain cannot resist all interferences due to limited frequency resource. Therefore, it is practically necessary to study how to promote the capacity of a TT & C system to resist NBI in atrocious weather.Current ways of resisting interference consist of interference cancellation and interference avoidance. Implementation of interference cancellation is based on the increase in the amount of calculation or the expense of signal energy, while avoiding interference with the increase in system complexity is to achieve interference suppression without reducing communication quality.The thesis focuses on interference avoidance in TT & C system. Because former technologies focuses on time-domain,space-domain and frequency-domain without using sequences characteristics,the thesis puts forward NBI avoidance technologies on the basis of code characteristics for the first time,which avoids NBI through designing spread sequences with different spectrum structures and applying different communication modes. First, the thesis studies m-Walsh composite sequence(m-W CS) and makes out the changing rule of various m-W CS signal spectrums. Based on the research on binary spread sequence spectrum signals, the thesis works over spectrum structures of m-W CS by referring to generation process and correlation features of composite sequence and characteristics of m sequence and Walsh sequence, and makes a conclusion that it is feasible to control spectrums of m-W CS. This preliminary conclusion acts as a theoretical basis on avoiding NBI in a DSSS TT & C system by using code characteristics.Second, the thesis provides a method to avoid weak NBI in Gaussian channels by using various m-W CSs. Specific implementation steps of the method are positioning NBI in frequency-domain, designing m-W CS as spread sequence spectrum, and minimizing energy of the signals suffering NBI. In this way NBI can be avoided. Simulation experiment result shows this avoidance technology that makes use of m-W CS can mitigate the effect on signals due to interference.Third, the thesis puts forward an adoptive, code-hopping, DSSS-based anti-jamming approach to cope with time-varying or multi-frequency interference occurred in Gaussian channels. The approach combines m-W CS with code-hopping DSSS technology to offer DS-FH distinctions with DSSS signals, and enables a DSSS system avoiding NBI on a self-adaptation basis through link quality analysis and sequence shift algorithm. Simulation experiment result shows an adaptive, code-hopping DSSS system has strong anti-jamming ability under spot narrowband jamming and time-varying or multi-frequency interference.Fourth, the thesis gives a frequency diversity means to suppress spot NBI in Gaussian channels based on the characteristic of code-domain. This means integrates m-W CS with orthogonal multicode spread spectrum technology, and uses diversified m-W CSs over identical information to realize multi-channel parallel spread spectrum in consideration of the point that different m-W CSs have different spectrum structures in a specific frequency domain. Thus, frequency diversity is realized and diversity combination technologies are used to strengthen the ability of system to resistance against NBI. Simulation experiment result shows this methodology effectively protects the system from interference by incorporating diversity multi-channel information when spot NBI disturbs some frequencies.Fifth, the thesis suggests an m-W composite-sequence-based M-ary orthogonal spread spectrum solution in a high-velocity, limited-band TT & C system in which NBI in channels is strong and the amount of m-W CS used to avoid interference is low. Based on typical M-ary orthogonal spread spectrum, the thesis creates a new M-ary orthogonal spread spectrum mode by amalgamating m-W CS with M-ary orthogonal spread spectrum, and studies structures, transmission efficiency, bit error rate(BER) in Gaussian channels and anti-jamming capacity of the new mode. In accordance with theoretical analysis and simulation experiment result, the amalgamation of CS and M-ary orthogonal spread spectrum overmatches typical M-ary spread spectrum technology with regard to transmission efficiency or system complexity. Furthermore, the convergence of this new mode and the avoidance technology by using m-W CS remarkably enhances the ability of an M-ary spread spectrum system to resist NBI.更多还原