Research On Key Techniques In Blind Demodulation Of CPM-signal In Non-Cooperative Communication

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.