170 lines
4.9 KiB
Plaintext
170 lines
4.9 KiB
Plaintext
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subroutine msk40decodeframe(c,mycall,hiscall,xsnr,bswl,nhasharray, &
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recent_calls,nrecent,msgreceived,nsuccess)
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! use timer_module, only: timer
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parameter (NSPM=240)
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character*4 rpt(0:15)
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character*6 mycall,hiscall,mycall0,hiscall0
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character*22 hashmsg,msgreceived
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character*12 recent_calls(nrecent)
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complex cb(42)
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complex cfac,cca
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complex c(NSPM)
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integer*1 cw(32)
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integer*1 decoded(16)
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integer s8r(8),hardbits(40)
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integer nhasharray(nrecent,nrecent)
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real*8 dt, fs, pi, twopi
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real cbi(42),cbq(42)
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real pp(12)
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real softbits(40)
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real llr(32)
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logical first
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logical*1 bswl
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data first/.true./
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data s8r/1,0,1,1,0,0,0,1/
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data mycall0/'dummy'/,hiscall0/'dummy'/
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data rpt/"-03 ","+00 ","+03 ","+06 ","+10 ","+13 ","+16 ", &
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"R-03","R+00","R+03","R+06","R+10","R+13","R+16", &
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"RRR ","73 "/
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save first,cb,fs,pi,twopi,dt,s8r,pp,rpt,mycall0,hiscall0,ihash
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if(first) then
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! define half-sine pulse and raised-cosine edge window
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pi=4d0*datan(1d0)
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twopi=8d0*datan(1d0)
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fs=12000.0
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dt=1.0/fs
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do i=1,12
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angle=(i-1)*pi/12.0
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pp(i)=sin(angle)
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enddo
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! define the sync word waveforms
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s8r=2*s8r-1
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cbq(1:6)=pp(7:12)*s8r(1)
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cbq(7:18)=pp*s8r(3)
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cbq(19:30)=pp*s8r(5)
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cbq(31:42)=pp*s8r(7)
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cbi(1:12)=pp*s8r(2)
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cbi(13:24)=pp*s8r(4)
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cbi(25:36)=pp*s8r(6)
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cbi(37:42)=pp(1:6)*s8r(8)
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cb=cmplx(cbi,cbq)
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first=.false.
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endif
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if(mycall.ne.mycall0 .or. hiscall.ne.hiscall0) then
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hashmsg=trim(mycall)//' '//trim(hiscall)
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if( hashmsg .ne. ' ' .and. hiscall .ne. '' ) then ! protect against blank mycall/hiscall
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call fmtmsg(hashmsg,iz)
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call hash(hashmsg,22,ihash)
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ihash=iand(ihash,4095)
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else
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ihash=9999 ! so that it can never match a received hash
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endif
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mycall0=mycall
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hiscall0=hiscall
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endif
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nsuccess=0
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msgreceived=' '
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! Estimate carrier phase.
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cca=sum(c(1:1+41)*conjg(cb))
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phase0=atan2(imag(cca),real(cca))
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! Remove phase error - want constellation rotated so that sample points lie on I/Q axes
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cfac=cmplx(cos(phase0),sin(phase0))
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c=c*conjg(cfac)
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! Matched filter.
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softbits(1)=sum(imag(c(1:6))*pp(7:12))+sum(imag(c(NSPM-5:NSPM))*pp(1:6))
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softbits(2)=sum(real(c(1:12))*pp)
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do i=2,20
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softbits(2*i-1)=sum(imag(c(1+(i-1)*12-6:1+(i-1)*12+5))*pp)
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softbits(2*i)=sum(real(c(7+(i-1)*12-6:7+(i-1)*12+5))*pp)
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enddo
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! Sync word hard error weight is used to reject frames that
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! are unlikely to decode.
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hardbits=0
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do i=1,40
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if( softbits(i) .ge. 0.0 ) then
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hardbits(i)=1
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endif
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enddo
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nbadsync1=(8-sum( (2*hardbits(1:8)-1)*s8r ) )/2
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nbadsync=nbadsync1
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if( nbadsync .gt. 3 ) then
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return
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endif
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! Normalize the softsymbols before submitting to decoder.
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sav=sum(softbits)/40
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s2av=sum(softbits*softbits)/40
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ssig=sqrt(s2av-sav*sav)
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softbits=softbits/ssig
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sigma=0.75
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! if(xsnr.lt.0.0) sigma=0.75-0.0875*xsnr
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if(xsnr.lt.0.0) sigma=0.75-0.11*xsnr
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llr(1:32)=softbits(9:40)
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llr=2.0*llr/(sigma*sigma)
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max_iterations=5
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call bpdecode40(llr,max_iterations,decoded,niterations)
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if( niterations .ge. 0.0 ) then
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call encode_msk40(decoded,cw)
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nhammd=0
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cord=0.0
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do i=1,32
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if( cw(i) .ne. hardbits(i+8) ) then
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nhammd=nhammd+1
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cord=cord+abs(softbits(i+8))
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endif
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enddo
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imsg=0
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do i=1,16
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imsg=ishft(imsg,1)+iand(1,decoded(17-i))
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enddo
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nrxrpt=iand(imsg,15)
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nrxhash=(imsg-nrxrpt)/16
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if(nhammd.le.4 .and. cord .lt. 0.65 .and. &
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nrxhash.eq.ihash .and. nrxrpt.ge.7) then
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!write(*,*) 'decodeframe 1',nbadsync,nhammd,cord,nrxhash,nrxrpt,ihash,xsnr,sigma
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nsuccess=1
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write(msgreceived,'(a1,a,1x,a,a1,1x,a4)') "<",trim(mycall), &
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trim(hiscall),">",rpt(nrxrpt)
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return
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elseif(bswl .and. nhammd.le.4 .and. cord.lt.0.65 .and. nrxrpt.ge.7 ) then
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do i=1,nrecent
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do j=i+1,nrecent
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if( nrxhash .eq. nhasharray(i,j) ) then
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nsuccess=2
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write(msgreceived,'(a1,a,1x,a,a1,1x,a4)') "<",trim(recent_calls(i)), &
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trim(recent_calls(j)),">",rpt(nrxrpt)
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!write(*,*) 'decodeframe 2',nbadsync,nhammd,cord,nrxhash,nrxrpt,ihash,xsnr,sigma
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elseif( nrxhash .eq. nhasharray(j,i) ) then
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nsuccess=2
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write(msgreceived,'(a1,a,1x,a,a1,1x,a4)') "<",trim(recent_calls(j)), &
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trim(recent_calls(i)),">",rpt(nrxrpt)
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!write(*,*) 'decodeframe 3',nbadsync,nhammd,cord,nrxhash,nrxrpt,ihash,xsnr,sigma
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endif
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enddo
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enddo
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if(nsuccess.eq.0) then
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nsuccess=3
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!write(*,*) 'decodeframe 4',bswl,nbadsync,nhammd,cord,nrxhash,nrxrpt,ihash,xsnr,sigma,nsuccess
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write(msgreceived,'(a1,i4.4,a1,1x,a4)') "<",nrxhash,">",rpt(nrxrpt)
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endif
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endif
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endif
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return
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end subroutine msk40decodeframe
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