176 lines
4.5 KiB
Fortran
176 lines
4.5 KiB
Fortran
program ldpcsim
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use, intrinsic :: iso_c_binding
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use iso_c_binding, only: c_loc,c_size_t
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use hashing
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use packjt
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parameter(NRECENT=10)
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character*12 recent_calls(NRECENT)
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character*22 msg,msgsent,msgreceived
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character*8 arg
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integer*1, allocatable :: codeword(:), decoded(:), message(:)
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integer*1, target:: i1Msg8BitBytes(10)
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integer*1 i1hash(4)
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integer*1 msgbits(80)
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integer*4 i4Msg6BitWords(13)
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integer ihash
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integer nerrtot(128),nerrdec(128)
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real*8, allocatable :: lratio(:), rxdata(:), rxavgd(:)
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real, allocatable :: yy(:), llr(:)
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equivalence(ihash,i1hash)
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do i=1,NRECENT
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recent_calls(i)=' '
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enddo
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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 navg #trials s '
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print*,'eg: ldpcsim 10 1 1000 0.75'
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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,*) navg
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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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! don't count hash bits as data bits
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N=128
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K=72
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rate=real(K)/real(N)
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write(*,*) "rate: ",rate
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write(*,*) "niter= ",max_iterations," navg= ",navg," s= ",s
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allocate ( codeword(N), decoded(K), message(K) )
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allocate ( lratio(N), rxdata(N), rxavgd(N), yy(N), llr(N) )
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msg="K9AN K1JT EN50"
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call packmsg(msg,i4Msg6BitWords,itype,.false.) !Pack into 12 6-bit bytes
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call unpackmsg(i4Msg6BitWords,msgsent,.false.,' ') !Unpack to get msgsent
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write(*,*) "message sent ",msgsent
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i4=0
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ik=0
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im=0
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do i=1,12
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nn=i4Msg6BitWords(i)
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do j=1, 6
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ik=ik+1
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i4=i4+i4+iand(1,ishft(nn,j-6))
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i4=iand(i4,255)
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if(ik.eq.8) then
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im=im+1
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! if(i4.gt.127) i4=i4-256
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i1Msg8BitBytes(im)=i4
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ik=0
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endif
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enddo
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enddo
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ihash=nhash(c_loc(i1Msg8BitBytes),int(9,c_size_t),146)
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ihash=2*iand(ihash,32767) !Generate the 8-bit hash
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i1Msg8BitBytes(10)=i1hash(1) !Hash code to byte 10
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mbit=0
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do i=1, 10
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i1=i1Msg8BitBytes(i)
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do ibit=1,8
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mbit=mbit+1
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msgbits(mbit)=iand(1,ishft(i1,ibit-8))
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enddo
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enddo
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call encode_msk144(msgbits,codeword)
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call init_random_seed()
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write(*,*) "Eb/N0 SNR2500 ngood nundetected nbadhash sigma"
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do idb = -6, 14
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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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nbadhash=0
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do itrial=1, ntrials
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rxavgd=0d0
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do iav=1,navg
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call sgran()
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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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rxavgd=rxavgd+rxdata
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enddo
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rxdata=rxavgd
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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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nerrtot(nerr)=nerrtot(nerr)+1
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! Correct signal normalization is important for this decoder.
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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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! To match the metric to the channel, s should be set to the noise standard deviation.
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! For now, set s to the value that optimizes decode probability near threshold.
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! The s parameter can be tuned to trade a few tenth's dB of threshold for an order of
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! magnitude in UER
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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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lratio=exp(llr)
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yy=rxdata
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! max_iterations is max number of belief propagation iterations
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! call ldpc_decode(lratio, decoded, max_iterations, niterations, max_dither, ndither)
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! call amsdecode(yy, max_iterations, decoded, niterations)
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! call bitflipmsk144(rxdata, decoded, niterations)
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call bpdecode144(llr, max_iterations, decoded, niterations)
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! If the decoder finds a valid codeword, niterations will be .ge. 0.
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if( niterations .ge. 0 ) then
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call extractmessage144(decoded,msgreceived,nhashflag,recent_calls,nrecent)
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if( nhashflag .ne. 1 ) then
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nbadhash=nbadhash+1
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endif
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nueflag=0
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! Check the message plus hash against what was sent.
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do i=1,K
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if( msgbits(i) .ne. decoded(i) ) then
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nueflag=1
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endif
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enddo
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if( nhashflag .eq. 1 .and. nueflag .eq. 0 ) then
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ngood=ngood+1
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nerrdec(nerr)=nerrdec(nerr)+1
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else if( nhashflag .eq. 1 .and. nueflag .eq. 1 ) then
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nue=nue+1;
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endif
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endif
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enddo
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snr2500=db-3.5
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write(*,"(f4.1,4x,f5.1,1x,i8,1x,i8,1x,i8,8x,f5.2)") db,snr2500,ngood,nue,nbadhash,ss
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enddo
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open(unit=23,file='nerrhisto.dat',status='unknown')
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do i=1,128
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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 ldpcsim
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