直扩信号码序列恢复算法及系统性能仿真研究

【作者】 郭林；

【导师】 吕明；

【作者基本信息】 电子科技大学 ， 信号与信息处理， 2009， 硕士

【摘要】 直扩信号由于具有工作信噪比低、强抗干扰性、低截获概率、能够抑制多径效应等优点,已经在军事和民用通信领域得到广泛应用。因而与之对应的直扩通信对抗技术也成为通信对抗领域急需解决的研究主题。直扩通信对抗包括直扩信号的盲检测、参数估计和扩频码序列恢复等内容。在检测到直扩信号和估计出直扩信号的参数后,要恢复原始信息,就需要恢复出扩频码序列,因而对直扩信号PN码序列的估计研究就具有迫切性和重要意义。本文正是针对上述问题,以恢复扩频码序列为主要研究对象,对码序列恢复方法做了创新性和探索性研究,核心工作和创新点主要体现在以下几个方面:1.建立了同步和非同步的基带信号模型,介绍了码序列估计及解扩的两种方案,研究了基于主特征向量的码序列恢复原理,对基于特征值分解的码序列恢复算法进行了计算机仿真实验。2.研究了码同步技术,包括延迟相乘法和改进滑动窗法,重点研究的是改进滑动窗法进行码同步,结合码序列恢复算法对同步和非同步情况做了大量仿真。3.研究了短码调制直扩信号的码序列恢复算法,包括基于神经网络的码序列恢复算法、基于投影逼近子空间跟踪的码序列恢复算法、基于新息准则的神经网络码序列恢复算法。通过大量的计算机仿真实验,分析了在同步和非同步两种信号模型下算法的可行性,比较了算法在恢复码序列的相关性和收敛性方面的性能。4.针对更低信噪比下的直扩信号码序列恢复问题,研究了利用小波去噪的方法先将直扩信号进行预处理,然后再进行码序列的恢复,进行了去噪前后的比较。5.研究了基于快速逼近功率迭代的码序列恢复算法,该算法通过迭代,快速提取主特征向量,实现码序列的恢复。大量的仿真和算法分析表明,该算法能够在低信噪比下,迅速提取出主特征向量,使码序列恢复能够实时实现。6.针对长码调制直扩信号码序列恢复问题,研究了基于分段的码序列恢复方法,大量的仿真表明该方法能使码序列恢复算法工作在较低的信噪比下,而且性能也能达到一定的要求。7.研究了DSSS/BPSK信号参数估计的基本方法,建立了对DSSS/BPSK信号进行检测、参数估计和码序列恢复的联合处理系统,并对系统进行仿真和分析。更多还原

【Abstract】 Direct sequence spreading spectrum signal has been widely used both in military and commercial telecommunication area, owing to the ability of working at low signal-to-noise ratio (SNR), strong anti-jamming, lower probability interception and mitigating the effects of multi-path fading effects. So the DSSS communication antagonism technology becomes an urgent research topic in the communication field. The blind detection, parameters estimation and recovery of spreading sequences are the main contents of DSSS communication antagonism. After having estimated some signal parameters, it need to recover the spreading sequences before de-spreading the DSSS signal and recovering the primitive information. Therefore the research on blind estimation of PN sequences shows the vital urgency and significance at present. This paper focuses on the blind code synchronization approach and the spreading sequences estimation algorithm. In this thesis, the spreading sequence restoration has been analyzed. The methods of code sequences restoration are explored and investigated, and the key work and innovations of the thesis mainly include:1. Set up the synchronous and non-synchronized base-band signal model, introduced the two programs of code sequence estimation and despreading, researched the principle of restoring the code sequence based on the principal eigenvector and computer simulation based on eigen-value decomposition algorithm.2. Studied the code synchronization technology, including delayed multiplication and modified sliding window, modified sliding window method is researched for code synchronization, combining algorithm of restoring code sequence a lot of simulations are done in synchronous and non-synchronous cases.3. Studied the code sequences restoration algorithm of the short-code modulation DSSS signal, including code sequences restoration algorithm based on neural network algorithm, code sequences restoration algorithm based on the projection approximation subspace tracking, code sequences restoration algorithm based on neural network by a novel information criterion. Through many computer simulation experiments, analysis of the feasibility of algorithms in the synchronous and asynchronous two signal models,the relevance of sequences and convergence performance are compared by the algorithms.4. For the problem of code sequences restoration in the lower SNR DSSS signal, researched pre-processing of DSSS signal by the use of wavelet denoising method, then we will proceed to restore code sequences and compare before and after denoising.5. Researched the code sequences restoration algorithm based on fast approximated power iteration, rapid extraction of the principal eigenvector achieves recovery of PN code sequences. Many simulation and algorithm analysis show that the algorithm can quickly extract the principal eigenvector at low SNR, so that spreading sequences can restore real-time implementation.6. For the problem of code sequence restoration of long-code modulation DSSS signal, researched the recovery method based on the subsection technique, many simulations show that this method can restore the code sequences at low SNR, and the performance can also achieve the request.7. Studied the basic ways of parameter estimation in the DSSS/BPSK signal, builded on the union processing system including the DSSS/BPSK signal detection, parameter estimation and code sequences restoration, and a lot of simulation and analysis are done for this system.更多还原