305 lines
7.9 KiB
Plaintext
305 lines
7.9 KiB
Plaintext
subroutine syncmsk(cdat,npts,jpk,ipk,idf,rmax,snr,metric,decoded)
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! Attempt synchronization, and if successful decode using Viterbi algorithm.
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use iso_c_binding, only: c_loc,c_size_t
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use packjt
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use hashing
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use timer_module, only: timer
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parameter (NSPM=1404,NSAVE=2000)
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complex cdat(npts) !Analytic signal
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complex cb(66) !Complex waveform for Barker-11 code
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complex cd(0:11,0:3)
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complex c(0:NSPM-1) !Complex data for one message length
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complex c2(0:NSPM-1)
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complex cb3(1:NSPM,3)
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real r(12000)
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real rdat(12000)
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real ss1(12000)
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real symbol(234)
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real rdata(198)
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real rd2(198)
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real rsave(NSAVE)
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real xp(29)
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complex z,z0,z1,z2,z3,cfac
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integer*1 e1(198)
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integer*1, target :: d8(13)
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integer*1 i1hash(4)
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integer*1 i1
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integer*4 i4Msg6BitWords(12) !72-bit message as 6-bit words
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integer mettab(0:255,0:1) !Metric table for BPSK modulation
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integer ipksave(NSAVE)
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integer jpksave(NSAVE)
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integer indx(NSAVE)
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integer b11(11) !Barker-11 code
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character*22 decoded
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character*72 c72
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logical first
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equivalence (i1,i4)
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equivalence (ihash,i1hash)
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data xp/0.500000, 0.401241, 0.309897, 0.231832, 0.168095, &
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0.119704, 0.083523, 0.057387, 0.039215, 0.026890, &
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0.018084, 0.012184, 0.008196, 0.005475, 0.003808, &
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0.002481, 0.001710, 0.001052, 0.000789, 0.000469, &
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0.000329, 0.000225, 0.000187, 0.000086, 0.000063, &
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0.000017, 0.000091, 0.000032, 0.000045/
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data first/.true./
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data b11/1,1,1,0,0,0,1,0,0,1,0/
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save first,cb,cd,twopi,dt,f0,f1,mettab
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phi=0.
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if(first) then
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! Get the metric table
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bias=0.0
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scale=20.0
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xln2=log(2.0)
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mettab=0
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do i=128,156
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x0=log(max(0.001,2.0*xp(i-127)))/xln2
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x1=log(max(0.001,2.0*(1.0-xp(i-127))))/xln2
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mettab(i,0)=nint(scale*(x0-bias))
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mettab(i,1)=nint(scale*(x1-bias))
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mettab(256-i,0)=mettab(i,1)
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mettab(256-i,1)=mettab(i,0)
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enddo
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do i=157,255
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mettab(i,0)=mettab(156,0)
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mettab(i,1)=mettab(156,1)
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mettab(256-i,0)=mettab(i,1)
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mettab(256-i,1)=mettab(i,0)
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enddo
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j=0
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twopi=8.0*atan(1.0)
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dt=1.0/12000.0
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f0=1000.0
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f1=2000.0
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dphi=0
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do i=1,11
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if(b11(i).eq.0) dphi=twopi*f0*dt
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if(b11(i).eq.1) dphi=twopi*f1*dt
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do n=1,6
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j=j+1
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phi=phi+dphi
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cb(j)=cmplx(cos(phi),sin(phi))
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enddo
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enddo
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cb3=0.
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cb3(1:66,1)=cb
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cb3(283:348,1)=cb
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cb3(769:834,1)=cb
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cb3(1:66,2)=cb
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cb3(487:552,2)=cb
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cb3(1123:1188,2)=cb
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cb3(1:66,3)=cb
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cb3(637:702,3)=cb
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cb3(919:984,3)=cb
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phi=0.
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do n=0,3
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k=-1
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dphi=twopi*f0*dt
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if(n.ge.2) dphi=twopi*f1*dt
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do i=0,5
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k=k+1
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phi=phi+dphi
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if(phi.gt.twopi) phi=phi-twopi
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cd(k,n)=cmplx(cos(phi),sin(phi))
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enddo
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dphi=twopi*f0*dt
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if(mod(n,2).eq.1) dphi=twopi*f1*dt
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do i=6,11
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k=k+1
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phi=phi+dphi
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if(phi.gt.twopi) phi=phi-twopi
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cd(k,n)=cmplx(cos(phi),sin(phi))
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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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nfft=NSPM
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jz=npts-nfft
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decoded=" "
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ipk=0
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jpk=0
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metric=-9999
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r=0.
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call timer('sync1 ',0)
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do j=1,jz !Find the Barker-11 sync vectors
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z=0.
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ss=0.
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do i=1,66
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ss=ss + real(cdat(j+i-1))**2 + aimag(cdat(j+i-1))**2
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z=z + cdat(j+i-1)*conjg(cb(i)) !Signal matching Barker 11
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enddo
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ss=sqrt(ss/66.0)*66.0
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r(j)=abs(z)/(0.908*ss) !Goodness-of-fit to Barker 11
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ss1(j)=ss
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enddo
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call timer('sync1 ',1)
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call timer('sync2 ',0)
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jz=npts-nfft
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rmax=0.
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! n1=35, n2=69, n3=94
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k=0
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do j=1,jz !Find best full-message sync
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if(ss1(j).lt.85.0) cycle
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r1=r(j) + r(j+282) + r(j+768) ! 6*(12+n1) 6*(24+n1+n2)
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r2=r(j) + r(j+486) + r(j+1122) ! 6*(12+n2) 6*(24+n2+n3)
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r3=r(j) + r(j+636) + r(j+918) ! 6*(12+n3) 6*(24+n3+n1)
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if(r1.gt.rmax) then
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rmax=r1
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jpk=j
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ipk=1
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endif
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if(r2.gt.rmax) then
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rmax=r2
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jpk=j
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ipk=2
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endif
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if(r3.gt.rmax) then
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rmax=r3
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jpk=j
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ipk=3
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endif
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rrmax=max(r1,r2,r3)
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if(rrmax.gt.1.9) then
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k=min(k+1,NSAVE)
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if(r1.eq.rrmax) ipksave(k)=1
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if(r2.eq.rrmax) ipksave(k)=2
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if(r3.eq.rrmax) ipksave(k)=3
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jpksave(k)=j
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rsave(k)=rrmax
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endif
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enddo
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call timer('sync2 ',1)
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kmax=k
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call indexx(rsave,kmax,indx)
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call timer('sync3 ',0)
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do kk=1,kmax
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k=indx(kmax+1-kk)
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ipk=ipksave(k)
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jpk=jpksave(k)
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rmax=rsave(k)
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c=conjg(cb3(1:NSPM,ipk))*cdat(jpk:jpk+nfft-1)
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smax=0.
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dfx=0.
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idfbest=0
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do itry=1,25
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idf=itry/2
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if(mod(itry,2).eq.0) idf=-idf
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idf=4*idf
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twk=idf
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call tweak1(c,NSPM,-twk,c2)
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z=sum(c2)
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if(abs(z).gt.smax) then
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dfx=twk
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smax=abs(z)
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phi=atan2(aimag(z),real(z)) !Carrier phase offset
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idfbest=idf
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endif
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enddo
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idf=idfbest
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call tweak1(cdat,npts,-dfx,cdat)
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cfac=cmplx(cos(phi),-sin(phi))
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cdat=cfac*cdat
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sig=0.
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ref=0.
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rdat(1:npts)=cdat
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iz=11
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do k=1,234 !Compute soft symbols
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j=jpk+6*(k-1)
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z0=2.0*dot_product(cdat(j:j+iz),cd(0:iz,0))
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z1=2.0*dot_product(cdat(j:j+iz),cd(0:iz,1))
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z2=2.0*dot_product(cdat(j:j+iz),cd(0:iz,2))
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z3=2.0*dot_product(cdat(j:j+iz),cd(0:iz,3))
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!### Maybe these should be weighted by yellow() ?
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if(j+1404+iz.lt.npts) then
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z0=z0 + dot_product(cdat(j+1404:j+1404+iz),cd(0:iz,0))
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z1=z1 + dot_product(cdat(j+1404:j+1404+iz),cd(0:iz,1))
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z2=z2 + dot_product(cdat(j+1404:j+1404+iz),cd(0:iz,2))
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z3=z3 + dot_product(cdat(j+1404:j+1404+iz),cd(0:iz,3))
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endif
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if(j-1404.ge.1) then
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z0=z0 + dot_product(cdat(j-1404:j-1404+iz),cd(0:iz,0))
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z1=z1 + dot_product(cdat(j-1404:j-1404+iz),cd(0:iz,1))
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z2=z2 + dot_product(cdat(j-1404:j-1404+iz),cd(0:iz,2))
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z3=z3 + dot_product(cdat(j-1404:j-1404+iz),cd(0:iz,3))
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endif
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sym=max(abs(real(z2)),abs(real(z3))) - max(abs(real(z0)),abs(real(z1)))
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if(sym.lt.0.0) then
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phi=atan2(aimag(z0),real(z0))
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sig=sig + real(z0)**2
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ref=ref + aimag(z0)**2
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else
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phi=atan2(aimag(z1),real(z1))
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sig=sig + real(z1)**2
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ref=ref + aimag(z1)**2
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endif
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n=k
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if(ipk.eq.2) n=k+47
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if(ipk.eq.3) n=k+128
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if(n.gt.234) n=n-234
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ibit=0
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if(sym.ge.0) ibit=1
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symbol(n)=sym
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enddo
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snr=db(sig/ref-1.0)
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rdata(1:35)=symbol(12:46)
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rdata(36:104)=symbol(59:127)
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rdata(105:198)=symbol(140:233)
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! Re-order the symbols and make them i*1
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j=0
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do i=1,99
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i4=128+rdata(i) !### Should be nint() ??? ###
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if(i4.gt.255) i4=255
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if(i4.lt.0) i4=0
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j=j+1
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e1(j)=i1
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rd2(j)=rdata(i)
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i4=128+rdata(i+99)
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if(i4.gt.255) i4=255
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if(i4.lt.0) i4=0
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j=j+1
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e1(j)=i1
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rd2(j)=rdata(i+99)
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enddo
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! Decode the message
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nb1=87
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call vit213(e1,nb1,mettab,d8,metric)
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ihash=nhash(c_loc(d8),int(9,c_size_t),146)
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ihash=2*iand(ihash,32767)
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decoded=' '
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if(d8(10).eq.i1hash(2) .and. d8(11).eq.i1hash(1)) then
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write(c72,1012) d8(1:9)
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1012 format(9b8.8)
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read(c72,1014) i4Msg6BitWords
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1014 format(12b6.6)
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call unpackmsg(i4Msg6BitWords,decoded,.false.,' ') !Unpack to get msgsent
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endif
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if(decoded.ne.' ') exit
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enddo
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call timer('sync3 ',1)
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return
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end subroutine syncmsk
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