75 lines
2.4 KiB
Plaintext
75 lines
2.4 KiB
Plaintext
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subroutine getfc2(c,csync,fc1,fc2,fc3)
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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 cs(0:NZ-1) !For computing spectrum
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complex csync(0:NZ-1) !Sync symbols only, from cbb
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real a(5)
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fs=12000.0/72.0
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df=fs/NZ
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baud=fs/NSPS
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a(1)=-fc1
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a(2:5)=0.
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call twkfreq1(c,NZ,fs,a,cs) !Mix down by fc1
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! Filter, square, then FFT to get refined carrier frequency fc2.
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call four2a(cs,NZ,1,-1,1) !To freq domain
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ia=nint(0.75*baud/df)
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cs(ia:NZ-1-ia)=0. !Save only freqs around fc1
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call four2a(cs,NZ,1,1,1) !Back to time domain
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cs=cs/NZ
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cs=cs*cs !Square the data
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call four2a(cs,NZ,1,-1,1) !Compute squared spectrum
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! Find two peaks separated by baud
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pmax=0.
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fc2=0.
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ic=nint(baud/df)
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ja=nint(0.5*baud/df)
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do j=-ja,ja
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f2=j*df
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ia=nint((f2-0.5*baud)/df)
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if(ia.lt.0) ia=ia+NZ
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ib=nint((f2+0.5*baud)/df)
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p=real(cs(ia))**2 + aimag(cs(ia))**2 + &
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real(cs(ib))**2 + aimag(cs(ib))**2
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if(p.gt.pmax) then
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pmax=p
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fc2=0.5*f2
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endif
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! write(52,1200) f2,p,db(p)
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!1200 format(f10.3,2f15.3)
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enddo
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a(1)=-fc1
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a(2:5)=0.
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call twkfreq1(c,NZ,fs,a,cs) !Mix down by fc1
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cs=cs*conjg(csync)
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call four2a(cs,NZ,1,-1,1) !To freq domain
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pmax=0.
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do i=0,NZ-1
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f=i*df
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if(i.gt.NZ/2) f=(i-NZ)*df
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p=real(cs(i))**2 + aimag(cs(i))**2
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! write(51,3001) f,p,db(p)
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!3001 format(f10.3,e12.3,f10.3)
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if(p.gt.pmax) then
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pmax=p
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fc3=f
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endif
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enddo
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return
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end subroutine getfc2
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