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136 lines
3.4 KiB
Fortran
136 lines
3.4 KiB
Fortran
program ldpcsim174_91
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! End to end test of the (174,91)/crc14 encoder and decoder.
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use crc
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use packjt77
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integer, parameter:: N=174, K=91, M=N-K
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character*37 msg,msgsent,msgreceived
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character*77 c77
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character*8 arg
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character*6 grid
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character*96 tmpchar
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integer*1, allocatable :: codeword(:), decoded(:), message(:)
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integer*1 msgbits(77)
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integer*1 message77(77)
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integer*1 apmask(N), cw(N)
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integer nerrtot(0:N),nerrdec(0:N)
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real*8, allocatable :: rxdata(:)
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real, allocatable :: llr(:)
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nerrtot=0
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nerrdec=0
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nargs=iargc()
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if(nargs.ne.4) then
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print*,'Usage: ldpcsim niter ndepth #trials s '
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print*,'eg: ldpcsim 10 2 1000 0.84'
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print*,'belief propagation iterations: niter, ordered-statistics depth: ndepth'
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print*,'If s is negative, then value is ignored and sigma is calculated from SNR.'
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return
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endif
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call getarg(1,arg)
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read(arg,*) max_iterations
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call getarg(2,arg)
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read(arg,*) ndepth
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call getarg(3,arg)
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read(arg,*) ntrials
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call getarg(4,arg)
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read(arg,*) s
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! scale Eb/No for a (174,91) code
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rate=real(K)/real(N)
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write(*,*) "rate: ",rate
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write(*,*) "niter= ",max_iterations," s= ",s
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allocate ( codeword(N), decoded(K), message(K) )
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allocate ( rxdata(N), llr(N) )
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! msg="K1JT K9AN EN50"
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msg="G4WJS K9AN EN50"
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i3=0
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n3=1
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call pack77(msg,i3,n3,c77) !Pack into 12 6-bit bytes
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call unpack77(c77,msgsent) !Unpack to get msgsent
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write(*,*) "message sent ",msgsent
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read(c77,'(77i1)') msgbits(1:77)
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write(*,*) 'message'
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write(*,'(a71,1x,a3,1x,a3)') c77(1:71),c77(72:74),c77(75:77)
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call encode174_91(msgbits,codeword)
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call init_random_seed()
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write(*,*) 'codeword'
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write(*,'(22(8i1,1x))') codeword
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write(*,*) "Eb/N0 SNR2500 ngood nundetected sigma psymerr"
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do idb = 20,-10,-1
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!do idb = 0,0,-1
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db=idb/2.0-1.0
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sigma=1/sqrt( 2*rate*(10**(db/10.0)) )
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ngood=0
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nue=0
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nsumerr=0
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do itrial=1, ntrials
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! Create a realization of a noisy received word
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do i=1,N
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rxdata(i) = 2.0*codeword(i)-1.0 + sigma*gran()
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enddo
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nerr=0
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do i=1,N
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if( rxdata(i)*(2*codeword(i)-1.0) .lt. 0 ) nerr=nerr+1
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enddo
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if(nerr.ge.1) nerrtot(nerr)=nerrtot(nerr)+1
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rxav=sum(rxdata)/N
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rx2av=sum(rxdata*rxdata)/N
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rxsig=sqrt(rx2av-rxav*rxav)
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rxdata=rxdata/rxsig
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if( s .lt. 0 ) then
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ss=sigma
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else
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ss=s
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endif
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llr=2.0*rxdata/(ss*ss)
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nap=0 ! number of AP bits
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llr(1:nap)=5*(2.0*msgbits(1:nap)-1.0)
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apmask=0
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apmask(1:nap)=1
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! max_iterations is max number of belief propagation iterations
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call bpdecode174_91(llr, apmask, max_iterations, message77, cw, nharderrors,niterations)
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if( ndepth .ge. 0 .and. nharderrors .lt. 0 ) call osd174_91(llr, apmask, ndepth, message77, cw, nharderrors, dmin)
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! If the decoder finds a valid codeword, nharderrors will be .ge. 0.
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if( nharderrors .ge. 0 ) then
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call extractmessage77(message77,msgreceived)
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nhw=count(cw.ne.codeword)
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if(nhw.eq.0) then ! this is a good decode
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ngood=ngood+1
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nerrdec(nerr)=nerrdec(nerr)+1
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else
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nue=nue+1
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endif
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endif
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nsumerr=nsumerr+nerr
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enddo
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baud=12000/1920
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snr2500=db+10.0*log10((baud/2500.0))
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pberr=real(nsumerr)/(real(ntrials*N))
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write(*,"(f4.1,4x,f5.1,1x,i8,1x,i8,8x,f5.2,8x,e10.3)") db,SNR2500,ngood,nue,ss,pberr
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enddo
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open(unit=23,file='nerrhisto.dat',status='unknown')
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do i=1,174
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write(23,'(i4,2x,i10,i10,f10.2)') i,nerrdec(i),nerrtot(i),real(nerrdec(i))/real(nerrtot(i)+1e-10)
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enddo
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close(23)
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end program ldpcsim174_91
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