59 lines
1.9 KiB
Plaintext
59 lines
1.9 KiB
Plaintext
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subroutine getfc1(c,fc1)
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parameter (KK=84) !Information bits (72 + CRC12)
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parameter (ND=168) !Data symbols: LDPC (168,84), r=1/2
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parameter (NS=65) !Sync symbols (2 x 26 + Barker 13)
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parameter (NR=3) !Ramp up/down
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parameter (NN=NR+NS+ND) !Total symbols (236)
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parameter (NSPS=16) !Samples per MSK symbol (16)
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parameter (N2=2*NSPS) !Samples per OQPSK symbol (32)
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parameter (N13=13*N2) !Samples in central sync vector (416)
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parameter (NZ=NSPS*NN) !Samples in baseband waveform (3760)
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parameter (NFFT1=4*NSPS,NH1=NFFT1/2)
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complex c(0:NZ-1) !Complex waveform
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complex c2(0:NFFT1-1) !Short spectra
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real s(-NH1+1:NH1) !Coarse spectrum
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nspec=NZ/NFFT1
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fs=12000.0/72.0
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df1=fs/NFFT1
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s=0.
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do k=1,nspec
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ia=(k-1)*N2
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ib=ia+N2-1
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c2(0:N2-1)=c(ia:ib)
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c2(N2:)=0.
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call four2a(c2,NFFT1,1,-1,1)
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do i=0,NFFT1-1
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j=i
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if(j.gt.NH1) j=j-NFFT1
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s(j)=s(j) + real(c2(i))**2 + aimag(c2(i))**2
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enddo
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enddo
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! call smo121(s,NFFT1)
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smax=0.
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ipk=0
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fc1=0.
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ia=nint(40.0/df1)
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do i=-ia,ia
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f=i*df1
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if(s(i).gt.smax) then
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smax=s(i)
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ipk=i
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fc1=f
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endif
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! write(51,3001) f,s(i),db(s(i))
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! 3001 format(f10.3,e12.3,f10.3)
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enddo
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! The following is for testing SNR calibration:
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! sp3n=(s(ipk-1)+s(ipk)+s(ipk+1)) !Sig + 3*noise
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! base=(sum(s)-sp3n)/(NFFT1-3.0) !Noise per bin
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! psig=sp3n-3*base !Sig only
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! pnoise=(2500.0/df1)*base !Noise in 2500 Hz
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! xsnrdb=db(psig/pnoise)
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return
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end subroutine getfc1
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