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55 lines
1.6 KiB
Fortran
55 lines
1.6 KiB
Fortran
subroutine sync4d(cd0,i0,ctwk,itwk,sync)
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! Compute sync power for a complex, downsampled FT4 signal.
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! 20 samples per symbol
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include 'ft4_params.f90'
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parameter(NP=NMAX/16)
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complex cd0(0:NP-1)
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complex csync(80)
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complex csync2(80)
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complex ctwk(80)
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complex z1,z2,z3
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logical first
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integer icos4(0:3)
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data icos4/0,1,3,2/
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data first/.true./
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save first,twopi,fs2,dt2,taus,baud,csync
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p(z1)=real(z1)**2 + aimag(z1)**2 !Statement function for power
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! Set some constants and compute the csync array.
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if( first ) then
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twopi=8.0*atan(1.0)
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fs2=12000.0/NDOWN !Sample rate after downsampling
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dt2=1/fs2 !Corresponding sample interval
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taus=20*dt2 !Symbol duration
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baud=1.0/taus !Keying rate
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k=1
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phi=0.0
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do i=0,3
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! dphi=(twopi/2.0)*(2*icos4(i)-3)*baud*dt2
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dphi=twopi*icos4(i)*baud*dt2
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do j=1,20
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csync(k)=cmplx(cos(phi),sin(phi)) !Waveform for 7x7 Costas array
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phi=mod(phi+dphi,twopi)
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k=k+1
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enddo
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enddo
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first=.false.
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endif
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sync=0
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i1=i0 !three Costas arrays
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i2=i0+36*20-1
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i3=i0+72*20-1
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csync2=csync
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if(itwk.eq.1) csync2=ctwk*csync2 !Tweak the frequency
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if(i1.ge.0 .and. i1+79.le.NP-1) z1=sum(cd0(i1:i1+79)*conjg(csync2))
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if(i2.ge.0 .and. i2+79.le.NP-1) z2=sum(cd0(i2:i2+79)*conjg(csync2))
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if(i3.ge.0 .and. i3+79.le.NP-1) z3=sum(cd0(i3:i3+79)*conjg(csync2))
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sync = sync + p(z1) + p(z2) + p(z3)
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return
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end subroutine sync4d
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