Research On Parameter Estimation And Blind Demodulation Of Noncooperative CPM Signals

In the face of the increasingly complex electromagnetic environment in the space and tense spectrum resources,it is imperative to find a modulation scheme that has high spectrum efficiency and strong immunity of interference.CPM is an abbreviation of continuous phase modulation.As a non-linear modulation type with constant envelope and consistant phase,CPM attracts more and more attention because of its excellent spectrum and power efficiency.At present,CPM is mainly used in civil Communications and military confrontation.Noncooperative communication means that the receiver does not know the modulation information of transmitter and needs to estimate the parameters of the received signal.Likewise,the demodulator must also use non-coherent demodulation.Due to the large number of CPM signal parameters,the characteristics of CPM signals obtained by different modulation parameters are quite different.Therefore,it is extremely difficult to accurately estimate and correctly demodulate the main modulation parameters of the CPM signal under the non-cooperative communication mode.First of all,it is began with a systematic exposition of the mathematical modeling of CPM signals and the PAM linear decomposition process.On this basis,analyse deeply CPM signal phase characteristics and spectral characteristics and the impact of different parameters.Secondly,according to the CPM signal procedure under non-cooperative communication,it is introduced the main parameters in detail.For the modulation index,the commonly method is a estimation algorithm based on the first-order cyclostationarity,but the algorithm has its limitations and does not apply to the CPM signal whose pulse type is Gaussian.In order to expand the scope of application,It is presented an optimized joint estimation algorithm makes it possible to apply both rectangular and raised cosine pulses and still valid for Gaussian shaped pulses.for the modulation order,an identification algorithm based on cyclic spectrum is introduced,according to the number of discrete spectral lines in the cross section of the cyclic spectrum,realized the modulation order identification.For the correlation length,an estimation algorithm based on average autocorrelation function is adopted,according to the number of symbols whose average autocorrelation function is not zero in the CPM signal to achieve the estimation of the correlation length.For the pulse type,the identification algorithm based on ring statistics and support vector machine is adopted.The main idea of this algorithm is to construct the ring statistics,calculate different classification features and input them into SVM to realize the pulse type estimation.Finally,it is mainly introduced the non-coherent grid demodulation algorithm in the blind demodulation of CPM signal.The algorithm can resist the primary phase by introducing a phase rotation grid.By introducing coupled transitions between adjacent phase states,The algorithm eliminates the influence of frequency offset on demodulation.