subroutine sync4d(cd0,i0,ctwk,itwk,sync) ! Compute sync power for a complex, downsampled FT4 signal. include 'ft4_params.f90' parameter(NP=NMAX/NDOWN,NSS=NSPS/NDOWN) complex cd0(0:NP-1) complex csync(4*NSS) complex csync2(4*NSS) complex ctwk(4*NSS) complex z1,z2,z3,z4 logical first integer icos4(0:3) data icos4/0,1,3,2/ data first/.true./ save first,twopi,csync p(z1)=real(z1)**2 + aimag(z1)**2 !Statement function for power if( first ) then twopi=8.0*atan(1.0) k=1 phi=0.0 do i=0,3 dphi=twopi*icos4(i)/real(NSS) do j=1,NSS csync(k)=cmplx(cos(phi),sin(phi)) phi=mod(phi+dphi,twopi) k=k+1 enddo enddo first=.false. endif sync=0 i1=i0 !four Costas arrays i2=i0+33*NSS-1 i3=i0+66*NSS-1 i4=i0+99*NSS-1 csync2=csync if(itwk.eq.1) csync2=ctwk*csync2 !Tweak the frequency if(i1.ge.0 .and. i1+4*NSS-1.le.NP-1) z1=sum(cd0(i1:i1+4*NSS-1)*conjg(csync2)) if(i2.ge.0 .and. i2+4*NSS-1.le.NP-1) z2=sum(cd0(i2:i2+4*NSS-1)*conjg(csync2)) if(i3.ge.0 .and. i3+4*NSS-1.le.NP-1) z3=sum(cd0(i3:i3+4*NSS-1)*conjg(csync2)) if(i4.ge.0 .and. i4+4*NSS-1.le.NP-1) z4=sum(cd0(i4:i4+4*NSS-1)*conjg(csync2)) sync = sync + p(z1) + p(z2) + p(z3) + p(z4) return end subroutine sync4d