【作者】 周家喜；

【导师】 徐佩霞；

【作者基本信息】 中国科学技术大学 ， 通信与信息系统， 2009， 博士

【摘要】 非协作通信是一种非授权接入通信模式。接收端在不影响协作通信双方正常通信的前提下利用现代信号处理技术完成对接收信号的解调工作。在非协作通信中,接收方无法已知发送方调制信号的任何参数,要能在非授权接入的情况下正确解调出有用信息,必须采用盲解调技术。连续相位调制(CPM)是一种相位连续、包络恒定的调制方式,具有很高的频谱利用率和功率利用率,在现代移动通信和卫星通信中获得了广泛的应用,是近几年非协作通信中颇受重视的一种调制方式。因为CPM是一种非线性调制方式,所以一些线性调制信号的处理方法不能应用于CPM信号。CPM信号是一个庞大的家族,随着调制指数、频率成形脉冲等调制参数的不同,生成的信号具有不同的性质,这也给非协作通信中CPM信号的盲解调提出了挑战。因此对非协作通信中CPM信号盲解调关键技术的研究具有重要的理论意义和实用价值。本文以单载波传输体制下的CPM信号为对象,以非协作数字通信为背景,以实现CPM信号的盲解调为目标,对CPM信号的参数盲估计算法和信号盲解调算法进行了深入的分析和研究。主要的工作是对CPM信号的自相关特性和循环平稳性与调制参数之间的内在联系进行了理论分析,分别提出了一种调制阶数盲识别算法和频率成形脉冲盲估计算法,然后在实现调制参数盲估计的基础上提出了一种基于复合网格的CPM信号非相干解调算法,并对各个算法的性能进行了理论分析和计算机仿真。最后,提出了一种CPM信号的盲解调器结构,并将该盲解调器应用于实际通信侦察系统中,实现了对实际的卫星通信CPM信号的盲解调。本文的主要研究内容和贡献有:1、对现有的调制识别方法进行了分析与总结,讨论了这些算法在运用于CPM信号的调制阶数盲识别时存在的局限性。深入分析了多进制CPM信号循环谱密度函数与信号调制参数之间的内在联系,在此基础上提出了一种基于信号循环平稳性的CPM信号调制阶数盲识别算法,实现了任意调制指数和频率成形脉冲的CPM信号调制阶数的盲识别。理论分析与计算机仿真结果表明,该算法具有较高的正确识别率,并且受高斯噪声影响较小,实现简单,具有实用意义。2、深入分析了CPM信号调制参数与自相关函数之间的内在联系,在此基础上提出了一种频率成形脉冲的盲估计算法。该算法利用之前提出的调制阶数盲识别算法识别出的调制阶数信息,能够在任意调制指数下有效估计出频率成形脉冲,为CPM信号的盲解调奠定了基础。理论分析与计算机仿真结果表明,该算法实现简单,估计精度较高。3、提出了一种CPM信号复合网格图的数学模型。将CPM信号的基本网格图和相位旋转网格图交叉合并组成复合网格图,降低接收信号初始相位对解调的影响;在复合网格图的各个单元网格之间引入状态耦合转移,实现对接收CPM信号中多普勒频移的有效跟踪。在此基础上提出了一种基于复合网格的CPM信号非相干解调算法。理论分析与仿真表明,当采用四个以上单元网格时,该非相干解调算法性能非常接近最佳接收机的解调性能,且具有较好的抗初相和频偏跟踪性能,对于非协作通信中CPM信号盲解调具有重要实用意义。4、在实现调制参数的盲估计和对复合网格解调算法研究的基础上,综合考虑实际系统中各个调制参数的盲估计顺序,设计了一种非协作通信中CPM信号盲解调器结构。该解调器采用前馈结构,易于硬件实现,并且具有良好的解调性能。5、论文通过实际的卫星通信信号对提出的CPM信号盲解调器进行了验证。结果表明,本文提出的盲解调器可以正确实现实际卫星通信信号的调制参数盲估计和解调,并且解调后反向重建的信号与接收信号一致。更多还原

【Abstract】 Non-cooperative communication is an unauthorized accessing communication mode.The receiver demodulates the received signal by the modern signal processing technology which does not affect the user in common cooperative communication.In non-cooperative communication,the modulation parameters of sending signal is unknown for receiver.The blind signal processing technology must be used,if the receiver wants to demodulate the signal under unauthorized accessing mode.Continuous phase modulation(CPM) is an excellent digital modulation scheme with continuity phase and constant modulus.It is used widely in mobile and satellite communications thanks to its attractive spectral and power efficiency.In recent years, much attention is paid to it in non-cooperative communication system.Much signal processing methods which are used in liner modulation can’t be used in CPM because it is a non-liner modulation scheme.CPM signals are a huge family.The signals which are generated by different modulation index and frequency shaping pulse have different property that pose a challenge to the signal demodulation in non-cooperative communication system.So the study of key technologies of blind demodulation of CPM signals in non-cooperative communication has important theoretical significance and practical value.In this dissertation,the blind estimation algorithms of modulation parameters and demodulation algorithms of CPM signals are deeply studied,to demodulate the CPM signals in single carrier no-cooperative communication systems.The main work of this dissertation is that,a blind identification algorithm of modulation order which is based on the study of the cyclostationarity of CPM signals and a blind estimation algorithm of frequency shaping pulse which is based on the study of the relationship of modulation parameters and auto-correlation are proposed.Then a non-coherent demodulation algorithm based on composite trellis processing is proposed after the modulation parameters are estimated blindly.The performance of all algorithms is provided by theoretical analysis and computer simulation.At last,a structure of blind demodulator is proposed and used in practical satellite communication system.The main research content and contribution of this dissertation are listed as follows.1、Existing modulation classification algorithms are analyzed and summarized and the limitations of the applying these algorithms in the blind identification of modulation order of CPM signals are discussed.Then a novel blind identification algorithm of Modulation Order based on cyclostationarity is developed under the in-depth study on the internal relationship of the Modulation Order and the cyclic-spectrum density of M-order CPM-signal.The proposed algorithm can be suitable for CPM-signal with any arbitrary modulation index and frequency shaping pulse.The theoretical analysis and computer simulation show that the algorithm has the ability to provide a good identification of Modulation Order.In addition,it is less affected by Gaussian noise and easy implementation.2、A blind estimation algorithm of frequency-shaping pulse is developed under the in-depth study on the internal relationship of the modulation parameters and the auto-correlation function of CPM-signal.Using the modulation order which is estimated before,the algorithm which provides the theoretical foundation and the feasibility of the blind demodulation of CPM-signal has the ability to provide a good estimation of frequency shaping pulse of CPM-signal with any arbitrary modulation index.The theoretical analysis and computer simulation show that the algorithm facilitates hardware implementation and has high estimation accuracy.3、Mathematical model of composite trellis diagram of CPM signals is proposed.The influence of the initial phase is reduced by combining root trellis diagram and multiple component trellis diagrams which are each a phase-displaced version of a root trellis diagram.The tracking of Doppler frequency shifting is achieved by importing state coupling transitions between component trellis diagrams of composite trellis diagram.On this basis,a non-coherent demodulation algorithm based on composite trellis processing is proposed.The theoretical analysis and computer simulation show:the performance of the algorithm approximates coherent demodulation perfectly when the number of component trellis diagram is greater than four;the algorithm can trace the original phase and Doppler frequency shifting effectively and is more appropriate to the situation of blind detection when carrier recovery is difficult.4、A structure of blind demodulator is proposed on the basis of the research of blind estimation of modulation parameters and demodulation algorithm which is based on composite trellis technology,which also consider the estimation order of modulation parameters in practical communication system.The demodulator using feed-forward structure and is easy hardware implementation.Also it has good demodulation performance.5、The demodulator is verified by the satellite communication signal which is intercepted practically.The result shows that the blind demodulator which is proposed in this dissertation can demodulate the practical signal correctly,and the reversed reconstruction signal after demodulation is the same as the receiving signal.更多还原