subroutine syncft4(iwave,nfa,nfb,syncmin,nfqso,maxcand,s,candidate, & ncand,sbase) include 'ft4_params.f90' ! Search over +/- 2.5s relative to 0.5s TX start time. parameter (JZ=20) complex cx(0:NH1) real s(NH1,NHSYM) real savg(NH1) real sbase(NH1) real x(NFFT1) real sync2d(NH1,-JZ:JZ) real red(NH1) real candidate0(3,maxcand) real candidate(3,maxcand) real dd(NMAX) integer jpeak(NH1) integer indx(NH1) integer ii(1) integer*2 iwave(NMAX) integer icos4(0:3) data icos4/0,1,3,2/ !Costas 4x4 tone pattern equivalence (x,cx) dd=iwave/1e3 ! Compute symbol spectra, stepping by NSTEP steps. savg=0. tstep=NSTEP/12000.0 df=12000.0/NFFT1 fac=1.0/300.0 do j=1,NHSYM ia=(j-1)*NSTEP + 1 ib=ia+NSPS-1 x(1:NSPS)=fac*dd(ia:ib) x(NSPS+1:)=0. call four2a(x,NFFT1,1,-1,0) !r2c FFT do i=1,NH1 s(i,j)=real(cx(i))**2 + aimag(cx(i))**2 enddo savg=savg + s(1:NH1,j) !Average spectrum enddo call baseline(savg,nfa,nfb,sbase) ia=max(1,nint(nfa/df)) ib=nint(nfb/df) nssy=NSPS/NSTEP ! # steps per symbol nfos=NFFT1/NSPS ! # frequency bin oversampling factor jstrt=0.25/tstep candidate0=0. k=0 do i=ia,ib do j=-JZ,+JZ ta=0. tb=0. tc=0. t0a=0. t0b=0. t0c=0. do n=0,3 m=j+jstrt+nssy*n if(m.ge.1.and.m.le.NHSYM) then ta=ta + s(i+nfos*icos4(n),m) t0a=t0a + sum(s(i:i+nfos*3:nfos,m)) endif tb=tb + s(i+nfos*icos4(n),m+nssy*36) t0b=t0b + sum(s(i:i+nfos*3:nfos,m+nssy*36)) if(m+nssy*72.le.NHSYM) then tc=tc + s(i+nfos*icos4(n),m+nssy*72) t0c=t0c + sum(s(i:i+nfos*3:nfos,m+nssy*72)) endif enddo t=ta+tb+tc t0=t0a+t0b+t0c t0=(t0-t)/3.0 sync_abc=t/t0 t=tb+tc t0=t0b+t0c t0=(t0-t)/3.0 sync_bc=t/t0 sync2d(i,j)=max(sync_abc,sync_bc) enddo enddo red=0. do i=ia,ib ii=maxloc(sync2d(i,-JZ:JZ)) - 1 - JZ j0=ii(1) jpeak(i)=j0 red(i)=sync2d(i,j0) enddo iz=ib-ia+1 call indexx(red(ia:ib),iz,indx) ibase=indx(nint(0.40*iz)) - 1 + ia if(ibase.lt.1) ibase=1 if(ibase.gt.nh1) ibase=nh1 base=red(ibase) red=red/base do i=1,min(maxcand,iz) n=ia + indx(iz+1-i) - 1 if(red(n).lt.syncmin.or.isnan(red(n)).or.k.eq.maxcand) exit k=k+1 ! candidate0(1,k)=n*df+37.5*1.5 candidate0(1,k)=n*df candidate0(2,k)=(jpeak(n)-1)*tstep candidate0(3,k)=red(n) enddo ncand=k ! Put nfqso at top of list, and save only the best of near-dupe freqs. do i=1,ncand if(abs(candidate0(1,i)-nfqso).lt.10.0) candidate0(1,i)=-candidate0(1,i) if(i.ge.2) then do j=1,i-1 fdiff=abs(candidate0(1,i))-abs(candidate0(1,j)) if(abs(fdiff).lt.4.0) then if(candidate0(3,i).ge.candidate0(3,j)) candidate0(3,j)=0. if(candidate0(3,i).lt.candidate0(3,j)) candidate0(3,i)=0. endif enddo endif enddo fac=20.0/maxval(s) s=fac*s ! Sort by sync ! call indexx(candidate0(3,1:ncand),ncand,indx) ! Sort by frequency call indexx(candidate0(1,1:ncand),ncand,indx) k=1 ! do i=ncand,1,-1 do i=1,ncand j=indx(i) ! if( candidate0(3,j) .ge. syncmin .and. candidate0(2,j).ge.-1.5 ) then if( candidate0(3,j) .ge. syncmin ) then candidate(2:3,k)=candidate0(2:3,j) candidate(1,k)=abs(candidate0(1,j)) k=k+1 endif enddo ncand=k-1 return end subroutine syncft4