2017-06-27 15:44:12 -04:00
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subroutine ft8b(s,f1,xdt,nharderrors,dmin,nbadcrc,message)
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2017-06-19 16:15:43 -04:00
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include 'ft8_params.f90'
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parameter(NRECENT=10)
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character*12 recent_calls(NRECENT)
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character message*22,datetime*13
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real s(NH1,NHSYM)
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real s1(0:7,ND)
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real ps(0:7)
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real rxdata(3*ND),llr(3*ND) !Soft symbols
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real candidate(3,100)
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integer*1 decoded(KK),apmask(3*ND),cw(3*ND)
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max_iterations=40
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norder=2
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tstep=0.5*NSPS/12000.0
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df=12000.0/NFFT1
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2017-06-27 15:44:12 -04:00
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i0=nint(f1/df)
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j0=nint(xdt/tstep)
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2017-06-19 16:15:43 -04:00
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2017-06-27 15:44:12 -04:00
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j=0
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ia=i0
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ib=i0+14
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do k=1,NN
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if(k.le.7) cycle
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if(k.ge.37 .and. k.le.43) cycle
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if(k.gt.72) cycle
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n=j0+2*(k-1)+1
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if(n.lt.1) cycle
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j=j+1
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s1(0:7,j)=s(ia:ib:2,n)
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enddo
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do j=1,ND
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ps=s1(0:7,j)
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where (ps.gt.0.0) ps=log(ps)
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r1=max(ps(1),ps(3),ps(5),ps(7))-max(ps(0),ps(2),ps(4),ps(6))
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r2=max(ps(2),ps(3),ps(6),ps(7))-max(ps(0),ps(1),ps(4),ps(5))
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r4=max(ps(4),ps(5),ps(6),ps(7))-max(ps(0),ps(1),ps(2),ps(3))
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rxdata(3*j-2)=r4
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rxdata(3*j-1)=r2
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rxdata(3*j)=r1
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enddo
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2017-06-23 10:14:09 -04:00
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2017-06-27 15:44:12 -04:00
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rxav=sum(rxdata)/(3.0*ND)
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rx2av=sum(rxdata*rxdata)/(3.0*ND)
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var=rx2av-rxav*rxav
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if( var .gt. 0.0 ) then
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rxsig=sqrt(var)
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else
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rxsig=sqrt(rx2av)
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endif
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rxdata=rxdata/rxsig
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ss=0.84
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llr=2.0*rxdata/(ss*ss)
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apmask=0
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cw=0
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2017-06-23 10:14:09 -04:00
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! cw will be needed for subtraction.
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! dmin is the correlation discrepancy of a returned codeword - it is
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! used to select the best codeword within osd174.
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2017-06-27 15:44:12 -04:00
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call bpdecode174(llr,apmask,max_iterations,decoded,cw,nharderrors)
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dmin=0.0
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if(nharderrors.lt.0) then
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call osd174(llr,norder,decoded,cw,nharderrors,dmin)
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2017-06-23 10:14:09 -04:00
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! This threshold needs to be tuned. 99.0 should pass everything.
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2017-06-27 15:44:12 -04:00
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if( dmin .gt. 99.0 ) nharderrors=-1
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endif
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nbadcrc=1
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message=' '
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if(count(cw.eq.0).eq.174) go to 900 !Reject the all-zero codeword
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if(nharderrors.ge.0) call chkcrc12a(decoded,nbadcrc)
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if(nbadcrc.eq.0) then
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call extractmessage174(decoded,message,ncrcflag,recent_calls,nrecent)
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! write(*,1112) datetime(8:13),nsnr,xdt,nint(f1),message
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!1112 format(a6,i4,f5.1,i5," ~ ",a22)
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endif
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900 continue
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2017-06-19 16:15:43 -04:00
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return
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end subroutine ft8b
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