Modulation Recognition And Parameter Estimation Of Signals For Data Communication

The control communication system is an important part of aerospace engineering,and the data communication enables data transmission between the space detector and the ground.This paper mainly studies various characteristics parameters of digital transmission signals used for data communication,and designs the system flow of signal processing,and the modulation identification methods and parameter estimation of the signals.The paper mainly completes modulation identification and parameter estimation of five types of conventional modulation signals including: BPSK,QPSK,UQPSK,GMSK,OQPSK,and eight types of composite modulation signals including: BPSK-PM,QPSK-PM,OQPSK-PM,GMSK-PM,BPSK-FM,QPSK-FM,OQPSK-FM,GMSK-FM.Therefore,the main work of this paper is as follows:Firstly,according to the relevant standard protocols of telemetry and remote control,this paper summarizes the modulation details and parameters of signals,studies the conventional modulation signals' characteristics of square spectrum and quartic spectrum and the composite modulation signals' characteristics of the frequency domain.These works lay a foundation of theoretical analysis for subsequent modulation identification and parameter estimation.In addition,the Welch period spectrum calculated by 262 kpoint FFT operation enables signals is prominent under the background of a large range of symbol rates and low signal-to-noise ratio parameters,that obtaining more than 90% detection accuracy and improving the performance.Then,the composite modulation signal is recognized from the conventional modulation signal by the impulse component in the power spectrum with more than 90% accuracy.So different kinds of signal perform different pre-processing processes in order to improve the performance of subsequent works.Secondly,the characteristics of delay correlation spectrum,instantaneous frequency delay correlation spectrum,instantaneous amplitude spectrum,and higher-order statistics of conventional modulation signals are studied.For the problem of the similarity between UQPSK and BPSK,it can be solved by the number of symbol rate lines in the delay correlation spectrum when the balance factor of UQPSK is less than or equal to 5,and obtaining more than 90% accuracy.At the same time,the similarity with QPSK signal can be solved by the number of symbol rate lines or the characteristic parameters related to the square spectrum.For GMSK and OQPSK signals,the higher-order statistical characteristic parameters can be used to distinguish them when the signal-to-noise ratio is greater than 17 dB.Thus this paper sums up the conventional modulation signals' identification process.Thirdly,this paper classifies the FM composite modulation signals with modulation indices in the range of [2.3,4] by the compactness of the spectral amplitude,and then composite signals with other modulation index range classified by the characteristics of the instantaneous phase power spectrum,so effectively recognizing the PM composite and the FM composite when the signal-to-noise ratio is not less than 7dB.Based on the theory of conventional modulation signal recognition,in-class recognition is performed to complete the recognition of composite modulation signals.Finally,based on the theoretical basis of the signal spectrum,square spectrum,quartic spectrum,and symbol rate correlation spectrum,the estimation methods of the carrier frequency and symbol rate of the conventional modulation signal and the main carrier frequency of the composite modulation signal are summarized.By extracting the inner modulation signal of the composite modulation signal,the sub-carrier frequency and symbol rate are estimated based on the conventional modulation signal.