2015-11-18 01:28:12 +00:00
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subroutine subtract65(dd,npts,f0,dt)
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! Subtract a jt65 signal
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!
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! Measured signal : dd(t) = a(t)cos(2*pi*f0*t+theta(t))
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! Reference signal : cref(t) = exp( j*(2*pi*f0*t+phi(t)) )
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! Complex amp : cfilt(t) = LPF[ dd(t)*CONJG(cref(t)) ]
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! Subtract : dd(t) = dd(t) - 2*REAL{cref*cfilt}
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use packjt
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2015-12-27 15:40:57 +00:00
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use timer_module, only: timer
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2015-11-18 01:28:12 +00:00
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integer correct(63)
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parameter (NMAX=60*12000) !Samples per 60 s
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parameter (NFILT=1600)
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real*4 dd(NMAX), window(-NFILT/2:NFILT/2)
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complex cref,camp,cfilt,cw
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integer nprc(126)
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real*8 dphi,phi
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logical first
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data nprc/ &
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1,0,0,1,1,0,0,0,1,1,1,1,1,1,0,1,0,1,0,0, &
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0,1,0,1,1,0,0,1,0,0,0,1,1,1,0,0,1,1,1,1, &
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0,1,1,0,1,1,1,1,0,0,0,1,1,0,1,0,1,0,1,1, &
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0,0,1,1,0,1,0,1,0,1,0,0,1,0,0,0,0,0,0,1, &
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1,0,0,0,0,0,0,0,1,1,0,1,0,0,1,0,1,1,0,1, &
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0,1,0,1,0,0,1,1,0,0,1,0,0,1,0,0,0,0,1,1, &
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1,1,1,1,1,1/
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data first/.true./
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common/chansyms65/correct
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common/heap1/cref(NMAX),camp(NMAX),cfilt(NMAX),cw(NMAX)
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save first
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pi=4.0*atan(1.0)
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! Symbol duration is 4096/11025 s.
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! Sample rate is 12000/s, so 12000*(4096/11025)=4458.23 samples/symbol.
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! For now, call it 4458 samples/symbol. Over the message duration, we'll be off
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! by about (4458.23-4458)*126=28.98 samples; 29 samples, or 0.7% of 1 symbol.
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! Could eliminate accumulated error by injecting one extra sample every
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! 5 or so symbols... Maybe try this later.
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nstart=dt*12000+1;
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nsym=126
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ns=4458
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nref=nsym*ns
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nend=nstart+nref-1
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phi=0.0
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iref=1
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ind=1
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isym=1
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call timer('subtr_1 ',0)
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do k=1,nsym
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if( nprc(k) .eq. 1 ) then
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omega=2*pi*f0
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else
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omega=2*pi*(f0+2.6917*(correct(isym)+2))
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isym=isym+1
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endif
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dphi=omega/12000.0
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do i=1,ns
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cref(ind)=cexp(cmplx(0.0,phi))
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phi=modulo(phi+dphi,2*pi)
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id=nstart-1+ind
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if(id.ge.1) camp(ind)=dd(id)*conjg(cref(ind))
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ind=ind+1
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enddo
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enddo
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call timer('subtr_1 ',1)
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call timer('subtr_2 ',0)
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! Smoothing filter: do the convolution by means of FFTs. Ignore end-around
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! cyclic effects for now.
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nfft=564480
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if(first) then
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! Create and normalize the filter
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sum=0.0
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do j=-NFILT/2,NFILT/2
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window(j)=cos(pi*j/NFILT)**2
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sum=sum+window(j)
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enddo
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cw=0.
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do i=-NFILT/2,NFILT/2
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j=i+1
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if(j.lt.1) j=j+nfft
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cw(j)=window(i)/sum
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enddo
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call four2a(cw,nfft,1,-1,1)
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first=.false.
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endif
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nz=561708
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cfilt(1:nz)=camp(1:nz)
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cfilt(nz+1:nfft)=0.
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call four2a(cfilt,nfft,1,-1,1)
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fac=1.0/float(nfft)
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cfilt(1:nfft)=fac*cfilt(1:nfft)*cw(1:nfft)
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call four2a(cfilt,nfft,1,1,1)
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call timer('subtr_2 ',1)
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! Subtract the reconstructed signal
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call timer('subtr_3 ',0)
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do i=1,nref
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j=nstart+i-1
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if(j.ge.1 .and. j.le.npts) dd(j)=dd(j)-2*REAL(cfilt(i)*cref(i))
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enddo
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call timer('subtr_3 ',1)
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return
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end subroutine subtract65
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