Key Technology Research On Estimation Of TDOA And FDOA For Frequency-Hopping Signals

Without a priori knowledge of the signal parameters,it is more difficult to process the passive received signals because it needs extra parameter estimations.As one of the passive positioning methods,localization with time difference of arrival(TDOA)and frequency difference of arrival(FDOA)can realize high-precision positioning with fewer sensors,so it is necessary to study the joint TDOA/FDOA estimation method.It has shown that the performance of the coherent accumulation method is better than the incoherent method.Because the frequency-hopping(FH)pulse has high security,it is widely used in military and communication fields,which has high time resolution due to a relatively large bandwidth.However,its hopping carrier frequency of individual pulse increases the difficulty of coherent accumulation.As for the Linear Frequency Modulation(LFM)pulses with the high resolution and low intercept rate,it is important to estimate TDOA/FDOA to localize LFM emitters.Therefore,this paper studies the coherent TDOA/FDOA estimation method on FH pulse train,especially on FH-LFM pulse train.The main work of this research can be summarized as follows:Firstly,it needs to estimate all the parameters used for estimating the TDOA/FDOA between the two FH received signals in passive system.For some common waveforms with hopping carrier frequency,including unmodulated pulse train,phase encoding pulse train and LFM pulse train,flowcharts of parameter estimation processing are proposed.Then,the TDOA/FDOA estimation algorithms are studied.To realize the coherent TDOA/FDOA estimation of the passive received FH signals,the Coherent Modified Cross Ambiguity Function(CMCAF)method is combined with parameter estimation before so the application of CMCAF in passive receivers is presented.To enhance the efficiency in light of the heavy computation problem of the two-dimensional search of CMCAF,this paper presents two fast algorithms based on Fast Fourier Transform(FFT)and Chirp-Z Transform(CZT),respectively,and analyzes their computational quantities.The simulations prove that the algorithm based on CZT is more efficient than the other one,while it has high estimation performance.In addition,when the CMCAF is used to estimate FDOA,the ambiguity may be occurred.In this paper,a high-precision unambiguity algorithm is proposed.The difference of TDOA is employed to calculate the numbers of FDOA ambiguity to correct the FDOA estimation.Simulation experiments are conducted to prove that the estimation accuracy of this method is higher than the method that uses the difference of TDOA only.Finally,the sampling rate must be not lower than the total bandwidth when the CMCAF method is used so that the data amount is too large.A Maximum Likelihood Indirect Estimation(MLIE)algorithm on coherent FH-LFM pulse train is presented,which can obtain high performance and the sampling rate do not have to be as high as the total bandwidth.For single receiver,the time of arrival(TOA)and the frequency of arrival(FOA)estimation are firstly obtained based on the MLE,and then the TDOA/FDOA estimation is obtained indirectly.The Cramer-Rao Lower Bound(CRLB)of the TOA/FOA estimation on coherent FH-LFM pulse train is also derived in detail to evaluate estimation performance.It is proved by theory and simulations that the hopping mode of carrier frequency has an impact on CRLB and estimation performance.In addition,because of the huge computational load of the three-dimensional search of the likelihood function,this paper proposes a fast algorithm based on CZT.With the calculation amount analysis and simulation experiments,it is shown that the fast algorithm greatly reduces the computational amount,and its performance is compared with other algorithms to verify its superiority.According to comparison between CMCAF method and MLIE method,it is shown that the MLIE method is more efficient.