Pulse doppler coherent method and system for snr enhancement

Abstract

A method and system for SNR enhancement in pulse-Doppler coherent target detection. In accordance with the method of the invention, complex signals are obtained for each of two or more sub-intervals of the time-on-target interval, allowing simultaneous range and Doppler measurements. A coherent integration is then performed on the signals to generate complex-valued folded matrices. The folded matrices are unfolded and target detection is then performed in a process involving one or more of the unfolded matrices. A pulse-Doppler coherent system is also provided configured for target detection by the method of the invention.

1 . A method for target detection in a pulse-Doppler coherent system, allowing simultaneous measurements of the target range and Doppler parameters, comprising coherent integration of the signal over the entire time-on-target interval consisting of two or more portions of time differing by at least one parameter of the wave form, the method comprising:
 a) transmitting a signal generated by a transmitter;   b) receiving the signal being reflected by a target and converting the received signal into a complex signal; performing coherent integration of said complex signal over each of said two or more portions of time, said portions serving as coherent processing intervals (CPIs), thus obtaining complex matrices each corresponding to respective CPI;   c) unfolding said complex matrices;   d) generating new complex matrices by complex value interpolation of the complex matrices obtained in step (c);   e) generating phase-corrected matrices by performing a phase correction on each of the new complex matrices obtained in step (d);   f) performing coherent integration of the phase-corrected matrices obtained in step (e) and calculating a corresponding real-valued matrix;   g) performing target detection involving said real-valued matrix.   
     
     
         2 . The method according to  claim 1  wherein
 a) the parameter of the waveform differing the portions of time is pulse repetition frequency (PRF) characterizing respective CPI; 
 b) the obtained complex signals are characterized as x nm   (l) =x (l) (tnm), where l=1 to L is a PRF index, L is a number of PRFs used, n is a pulse number in the signal, m is a range gate, and t n,m  is a sampling time of the signal of the range gate m of the pulse n; 
 c) the complex matrices X l  for l=1 to L are generated by performing coherent integration of the signals x nm   (l) ; a 
 d) the complex unfolded matrices X k′m′   (l) , are provided by unfolding the matrices X l  for l=0 to L−1. 
 
     
     
         3 . The method according to  claim 1 , wherein performing coherent integration comprises calculating a discrete Fourier transform on one or more of the signals x nm   (l)  to generate one or more signals 
       
         
           
             
               
                 
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       where k is an index of the Doppler frequency, K is the number of Doppler frequencies, N is the number of pulses in the signal, w n  is a weighting factor and M (l)  is the number of range gates of the PRF  1 . 
     
     
         4 . The method according to  claim 2 , wherein unfolding the matrices X l  comprises:
 a) defining X k′,m′   (l)  for values of m′ for which R min <mRG<R max , where [R min ,R max ] is a predetermined detection region of interest, and for values of k′ for which D min <k′·PRF/K<D max , where [D min ,D max ,] is a predetermined region of Doppler frequencies of interest, by setting X k′m′   (l) =X km   (l) , where k=k′ mod K, and m=m′ mod M.   
     
     
         5 . The method according to  claim 4 , wherein unfolding the matrices X l  comprises resampling the matrices X l . 
     
     
         6 . The method according to  claim 5 , wherein resampling the matrices X l  comprises defining, for each pair of indices k′m′, new indices p and q by:
 b) dividing the interval of interest [R min , R max ] into one or more subintervals of a predetermined length Δr; 
 c) determining a value of p from among all values of p for which 0≦pΔr≦R max −R min ) such that R p =R min +p·Δr is closest to the range represented by the range gate m; 
 d) dividing the interval [D min ,D max ] into one or more subintervals of a predetermined length Δq; and 
 e) determining a value of q from among all integral values of q for which 0≦qΔq≦D max −D min  such that D q =D min +q·Δq is closest to k. 
 
     
     
         7 . The method according to  claim 6 , further comprising generating one or more matrices XI (l)  where XI p,q   (l)  is obtained by interpolation of one or more values of X k′,m′   (l)  for indices k′m′ in a neighborhood of the indices p q. 
     
     
         8 . The method according to  claim 7 , further comprising performing a Doppler compensation on one or more of the matrices XI (l) . 
     
     
         9 . The method according to  claim 8 , wherein performing the Doppler compensation includes calculating matrices Y (l)  defined by Y km   (l) =XI km   (l) ·e −2πj·D     q     ·t     0       (l)   . 
     
     
         10 . The method according to  claim 9 , wherein performing target detection comprises:
 f) calculating a real-valued matrix A where   
       
         
           
             
               
                 
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 g) determining, for each of one or more pairs of indices, whether the value of A p,q  is greater than or equal to a predetermined threshold T, a target being detected at the location having the associated indices p,q if the value of A p,q  is greater than or equal to T, and a target not being detected at the location having the associated indices p,q if the value of A p,q  is not greater than or equal to T. 
 
     
     
         11 . A pulse-Doppler coherent system configured for target detection by the method of  claim 1 . 
     
     
         12 . A pulse-Doppler coherent system configured for target detection and comprising:
 a) a transmitter for generating and transmitting signals, said signals characterized by their PRF, said signals impinging on a target;   b) a receiver configured to obtain the signals reflected by the target and to convert the received signals into complex signals, said signals corresponding to each of two or more CPIs within a time-on-target interval, wherein each of said CPIs are characterized by waveforms different in at least one parameter;   c) a Fast Fourier Transform (FFT) unit, for providing a coherent integration of said signals, the output of said FFT unit is a sequence of CPI spectra for each PRF;   d) a plurality of CPI memories for storing the respective CPI spectra for a specific PRF;   e) a plurality of interpolation units for providing a complex value interpolation of the output of said FFT unit;   f) a plurality of unfolding units for unfolding the output of said FFT unit;   g) a phase correction unit for phase-correcting the results of the interpolation;   h) a summation unit for performing a coherent integration of the results of the phase correction and calculating corresponding real values;   i) a decision unit for providing a target decision.   
     
     
         13 . A computer program product comprising at least one computer readable medium having computer-executable instructions for performing the steps of the method of  claim 1  when run on a computer. 
     
     
         14 . A computer program product as claimed in  claim 13  embodied on a computer readable medium.