Research On Single Carrier Blind Synchronization Technology Under Non-cooperative Condition

Different from the cooperative communication system,in the non-cooperative communication system,the receiver can't directly know the various parameter information of the signal at the transmitting end,such as the carrier frequency,modulation mode,symbol rate and so on.Therefore,if we want to realize the correct demodulation of the signal in the non-cooperative communication system,we must adopt the blind demodulation method to obtain all kinds of parameter information from the received signal.The main function of blind demodulation in non-cooperative digital communication system is to process the received signal and recover the baseband signal to obtain information.As an indispensable part of blind demodulation,blind synchronization technology mainly includes timing synchronization(symbol synchronization)and carrier synchronization.In this paper,the timing synchronization and carrier synchronization technology in non-cooperative communication system are studied from the two problems of large symbol rate deviation and frequency deviation.The specific contents and innovations of this paper are as follows:(1)In view of the slow convergence speed of classical timing synchronization algorithm and the poor synchronization performance of existing timing synchronization algorithm for MQAM signal and large symbol rate deviation,Gardner algorithm is improved.On the one hand,it is the improvement of algorithm structure,which is mainly manifested in properly increasing the sampling multiple of the source signal and performing serial to parallel conversion,using two different interpolation filters to perform interpolation function at the same time and subsequent timing error and other functions.The weight distribution of two interpolation filters is determined according to the radius of the constellation convergence position;on the other hand,according to the mathematical relationship between the loop filter and the symbol rate deviation,the symbol rate deviation is calculated and adjusted in real time according to the output of the loop filter until the loop reaches a stable state.Then,the convergence curve,symbol decision error,the mean square value of symbol synchronization error under different symbol rate deviation and the position of symbol are compared and analyzed by simulation tools.The results show that the improved algorithm can make the loop achieve synchronous state in a shorter time,and increase the symbol rate deviation to 10%,at the same time,it has a better synchronization performance.(2)For the carrier synchronization function,in this paper,the classical carrier synchronization methods are introduced and compared.For MQAM signal and carrier recovery system with large frequency offset,the existing Costas ring and general ring method will not only cause large jitter error,but also reduce the allowable frequency offset range as the order of QAM signal increases.In view of the fact that the open-loop estimation method can enlarge the frequency offset range to a certain extent,two kinds of FFT time-frequency transformation based on signal power spectrum and FFT interpolation based on adjacent spectral lines are introduced firstly,and the score analysis is carried out.However,due to the low estimation accuracy of these two methods,this paper proposes to combine DFT with 2_dL points and iterative correction method on the basis of these two methods further improve the estimation accuracy,and analyze the advantages and disadvantages of the three methods,show that the estimation performance of the method is better than the former two.Then combined with the proposed combined error vector amplitude EVM,the estimated frequency offset is searched and iterated to positive and negative directions respectively,and the final frequency offset estimate is calculated according to the EVM minimum value.Finally,the frequency offset estimation of MQAM signal is simulated and analyzed,and the mean square value after iteration is used as the inspection quantity.The analysis shows that the method adopted in this paper can not only improve the estimation accuracy but also realize the carrier synchronization function for the internal frequency deviation within 10%.