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78 lines
1.8 KiB
Fortran
78 lines
1.8 KiB
Fortran
subroutine demod64a(s3,nadd,mrsym,mrprob,mr2sym,mr2prob,ntest,nlow)
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! Demodulate the 64-bin spectra for each of 63 symbols in a frame.
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! Parameters
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! nadd number of spectra already summed
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! mrsym most reliable symbol value
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! mr2sym second most likely symbol value
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! mrprob probability that mrsym was the transmitted value
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! mr2prob probability that mr2sym was the transmitted value
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implicit real*8 (a-h,o-z)
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real*4 s3(64,63)
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real*8 fs(64)
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integer mrsym(63),mrprob(63),mr2sym(63),mr2prob(63)
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common/mrscom/ mrs(63),mrs2(63)
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afac=1.1 * float(nadd)**0.64
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scale=255.999
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! Compute average spectral value
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sum=0.
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do j=1,63
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do i=1,64
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sum=sum+s3(i,j)
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enddo
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enddo
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ave=sum/(64.*63.)
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i1=1 !Silence warning
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i2=1
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! Compute probabilities for most reliable symbol values
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do j=1,63
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s1=-1.e30
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fsum=0.
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psum=0.
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do i=1,64
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x=min(afac*s3(i,j)/ave,50.d0)
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fs(i)=exp(x)
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fsum=fsum+fs(i)
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psum=psum + s3(i,j)
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if(s3(i,j).gt.s1) then
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s1=s3(i,j)
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i1=i !Most reliable
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endif
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enddo
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s2=-1.e30
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do i=1,64
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if(i.ne.i1 .and. s3(i,j).gt.s2) then
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s2=s3(i,j)
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i2=i !Second most reliable
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endif
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enddo
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! p1=fs(i1)/fsum !Normalized probabilities
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! p2=fs(i2)/fsum
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p1=s1/psum
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p2=s2/psum
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mrsym(j)=i1-1
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mr2sym(j)=i2-1
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mrprob(j)=scale*p1
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mr2prob(j)=scale*p2
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mrs(j)=i1
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mrs2(j)=i2
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enddo
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sum=0.
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nlow=0
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do j=1,63
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sum=sum+mrprob(j)
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if(mrprob(j).le.5) nlow=nlow+1
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enddo
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! ntest=sum/63
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ntest=sum
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return
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end subroutine demod64a
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