96 lines
2.6 KiB
Plaintext
96 lines
2.6 KiB
Plaintext
subroutine xcor4(s2,ipk,nsteps,nsym,lag1,lag2,ich,mode4,ccf,ccf0, &
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lagpk,flip)
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! Computes ccf of the 4_FSK spectral array s2 and the pseudo-random
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! array pr2. Returns peak of CCF and the lag at which peak occurs.
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! The CCF peak may be either positive or negative, with negative
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! implying the "OOO" message.
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parameter (NHMAX=1260) !Max length of power spectra
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parameter (NSMAX=525) !Max number of half-symbol steps
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real s2(NHMAX,NSMAX) !2d spectrum, stepped by half-symbols
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real a(NSMAX)
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real ccf(-5:540)
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integer nch(7)
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integer npr2(207)
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real pr2(207)
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logical first
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data lagmin/0/ !Silence compiler warning
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data first/.true./
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data npr2/ &
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0,0,0,0,1,1,0,0,0,1,1,0,1,1,0,0,1,0,1,0,0,0,0,0,0,0,1,1,0,0, &
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0,0,0,0,0,0,0,0,0,0,1,0,1,1,0,1,1,0,1,0,1,1,1,1,1,0,1,0,0,0, &
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1,0,0,1,0,0,1,1,1,1,1,0,0,0,1,0,1,0,0,0,1,1,1,1,0,1,1,0,0,1, &
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0,0,0,1,1,0,1,0,1,0,1,0,1,0,1,1,1,1,1,0,1,0,1,0,1,1,0,1,0,1, &
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0,1,1,1,0,0,1,0,1,1,0,1,1,1,1,0,0,0,0,1,1,0,1,1,0,0,0,1,1,1, &
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0,1,1,1,0,1,1,1,0,0,1,0,0,0,1,1,0,1,1,0,0,1,0,0,0,1,1,1,1,1, &
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1,0,0,1,1,0,0,0,0,1,1,0,0,0,1,0,1,1,0,1,1,1,1,0,1,0,1/
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data nch/1,2,4,9,18,36,72/
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save
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if(first) then
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do i=1,207
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pr2(i)=2*npr2(i)-1
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enddo
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first=.false.
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endif
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ccfmax=0.
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ccfmin=0.
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nw=nch(ich)
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do j=1,nsteps
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n=2*mode4
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if(mode4.eq.1) then
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a(j)=max(s2(ipk+n,j),s2(ipk+3*n,j)) - max(s2(ipk ,j),s2(ipk+2*n,j))
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else
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kz=max(1,nw/2)
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ss0=0.
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ss1=0.
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ss2=0.
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ss3=0.
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wsum=0.
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do k=-kz+1,kz-1
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w=float(kz-iabs(k))/nw
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wsum=wsum+w
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ss0=ss0 + w*s2(ipk +k,j)
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ss1=ss1 + w*s2(ipk+ n+k,j)
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ss2=ss2 + w*s2(ipk+2*n+k,j)
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ss3=ss3 + w*s2(ipk+3*n+k,j)
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enddo
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a(j)=(max(ss1,ss3) - max(ss0,ss2))/sqrt(wsum)
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endif
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enddo
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do lag=lag1,lag2
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x=0.
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do i=1,nsym
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j=2*i-1+lag
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if(j.ge.1 .and. j.le.nsteps) x=x+a(j)*pr2(i)
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enddo
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ccf(lag)=2*x !The 2 is for plotting scale
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if(ccf(lag).gt.ccfmax) then
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ccfmax=ccf(lag)
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lagpk=lag
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endif
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if(ccf(lag).lt.ccfmin) then
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ccfmin=ccf(lag)
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lagmin=lag
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endif
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enddo
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ccf0=ccfmax
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flip=1.0
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if(-ccfmin.gt.ccfmax) then
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do lag=lag1,lag2
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ccf(lag)=-ccf(lag)
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enddo
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lagpk=lagmin
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ccf0=-ccfmin
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flip=-1.0
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endif
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return
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end subroutine xcor4
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