Research On Blind Demodulation Method Of MPSK/MAPSK Signal

In digital communication,electronic reconnaissance often acquires information by blind demodulation of intercepted signals.As a key technology of non-cooperative signal processing,blind demodulation methods include parameter estimation,modulation identification,symbol synchronization and carrier synchronization,and blind equalization.In this thesis,the general blind demodulation method of MPSK and MAPSK signals is studied.Based on the in-depth study of the principle of blind demodulation algorithm,the performance simulation of the algorithm is completed.The main work of this thesis includes:First of all,carrier frequency and symbol rate need to be known in demodulation.For non-cooperative reconnaissance,there is no prior information of these parameters,so the value of the parameters must be estimated to facilitate identification and demodulation.In this paper,Welch power spectrum based frequency centring method is used to estimate the carrier frequency of the two kinds of signals,and compared with traditional frequency centring method.In the problem of symbolic rate estimation,the improved envelope spectrum method based on CZT method is adopted in this thesis,and its performance is compared with that of traditional envelope spectrum method.Then,the signal characteristics of MPSK and MAPSK were analyzed.In this paper,the modulation recognition between and within classes of signals was completed by combining spectral line features and high-order cumulant method,and the recognition accuracy of signal sets reached 90% at SNR around 7d B.Then,in the actual communication process,there is an unknown time delay in signal propagation,which leads to the difficulty in alignment with the optimal sampling point of each symbol,thus resulting in an increase in the bit error rate of the system,and this task requires symbol synchronization to complete.For MPSK and MAPSK symbol synchronization problems,in the existing symbol synchronization algorithm based on the research,in order to be able to avoid a multilevel signal APSK signal passing zero detection not,existing for MPSK multilevel Gardner,promote to MAPSK symbol synchronization algorithm,through theoretical derivation and simulation analysis proves the validity of the algorithm for MAPSK,the symbol synchronization algorithm can effectively reduce the MAPSK multilevel symbol synchronization signal timing error,the decimal interval curve more smooth.Then,the carrier synchronization of MPSK and MAPSK signals is integrated.In this thesis,the unified Costas ring structure is adopted to study and design the phase discrimination algorithm of all kinds of signals.After that,the performance of blind demodulation error code is simulated and analyzed.The loss of error code performance is about 1?2d B compared with the theoretical error rate.Finally,in view of the blind equalization of MPSK and MAPSK,this paper adopts the double-mode algorithm of CMA+DDLMS to carry out the blind equalization of signals,and compares it with the CMA method.The equilibrium steady-state error of the two-mode method is smaller while the convergence speed is ensured.