239 lines
6.8 KiB
Plaintext
239 lines
6.8 KiB
Plaintext
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program ldpcsim120
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! End to end test of the (120,60)/crc10 encoder and decoder.
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use crc
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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(9)
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integer*1, target:: i1Dec8BitBytes(9)
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integer*1 msgbits(60)
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integer*1 apmask(120)
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integer*1 cw(120)
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integer*2 checksum
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integer colorder(120)
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integer nerrtot(120),nerrdec(120),nmpcbad(60)
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logical checksumok,fsk,bpsk
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real*8, allocatable :: rxdata(:)
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real, allocatable :: llr(:)
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real dllr(120),llrd(120)
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data colorder/ &
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0,1,2,21,3,4,5,6,7,8,20,10,9,11,12,23,13,28,14,31, &
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15,16,22,26,17,30,18,29,25,32,41,34,19,33,27,36,38,43,42,24, &
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37,39,45,40,35,44,47,46,50,51,53,48,52,56,54,57,55,49,58,61, &
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60,59,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79, &
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80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99, &
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100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119/
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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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nmpcbad=0 ! Used to collect the number of errors in the message+crc part of the codeword
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nargs=iargc()
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if(nargs.ne.3) then
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print*,'Usage: ldpcsim niter #trials s '
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print*,'eg: ldpcsim 10 1000 0.84'
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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,*) ntrials
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call getarg(3,arg)
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read(arg,*) s
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fsk=.false.
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bpsk=.true.
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! don't count crc bits as data bits
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N=120
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K=60
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! scale Eb/No for a (120,50) code
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rate=real(50)/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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! The message should be packed into the first 7 bytes
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i1Msg8BitBytes(1:6)=85
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i1Msg8BitBytes(7)=64
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! The CRC will be put into the last 2 bytes
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i1Msg8BitBytes(8:9)=0
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checksum = crc10 (c_loc (i1Msg8BitBytes), 9)
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! For reference, the next 3 lines show how to check the CRC
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i1Msg8BitBytes(8)=checksum/256
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i1Msg8BitBytes(9)=iand (checksum,255)
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checksumok = crc10_check(c_loc (i1Msg8BitBytes), 9)
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if( checksumok ) write(*,*) 'Good checksum'
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write(*,*) i1Msg8BitBytes(1:9)
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mbit=0
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do i=1, 7
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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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i1=i1Msg8BitBytes(8) ! First 2 bits of crc10 are LSB of this byte
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do ibit=1,2
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msgbits(50+ibit)=iand(1,ishft(i1,ibit-2))
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enddo
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i1=i1Msg8BitBytes(9) ! Now shift in last 8 bits of the CRC
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do ibit=1,8
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msgbits(52+ibit)=iand(1,ishft(i1,ibit-8))
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enddo
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write(*,*) 'message'
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write(*,'(9(8i1,1x))') msgbits
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call encode120(msgbits,codeword)
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call init_random_seed()
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call sgran()
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write(*,*) 'codeword'
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write(*,'(15(8i1,1x))') codeword
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write(*,*) "Es/N0 SNR2500 ngood nundetected nbadcrc sigma"
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do idb = -10, 24
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db=idb/2.0-1.0
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! sigma=1/sqrt( 2*rate*(10**(db/10.0)) ) ! to make db represent Eb/No
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sigma=1/sqrt( 2*(10**(db/10.0)) ) ! db represents Es/No
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ngood=0
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nue=0
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nbadcrc=0
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nberr=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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if( bpsk ) then
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rxdata(i) = 2.0*codeword(i)-1.0 + sigma*gran()
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elseif( fsk ) then
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if( codeword(i) .eq. 1 ) then
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r1=(1.0 + sigma*gran())**2 + (sigma*gran())**2
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r2=(sigma*gran())**2 + (sigma*gran())**2
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elseif( codeword(i) .eq. 0 ) then
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r2=(1.0 + sigma*gran())**2 + (sigma*gran())**2
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r1=(sigma*gran())**2 + (sigma*gran())**2
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endif
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rxdata(i)=0.35*(sqrt(r1)-sqrt(r2))
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! rxdata(i)=0.35*(exp(r1)-exp(r2))
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! rxdata(i)=0.12*(log(r1)-log(r2))
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endif
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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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nerrtot(nerr)=nerrtot(nerr)+1
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nberr=nberr+nerr
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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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apmask=0
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! max_iterations is max number of belief propagation iterations
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call bpdecode120(llr, apmask, max_iterations, decoded, niterations, cw)
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n2err=0
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do i=1,N
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if( cw(i)*(2*codeword(i)-1.0) .lt. 0 ) n2err=n2err+1
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enddo
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!write(*,*) nerr,niterations,n2err
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damp=0.75
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ndither=0
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if( niterations .lt. 0 ) then
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do i=1, ndither
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do in=1,N
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dllr(in)=damp*gran()
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enddo
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llrd=llr+dllr
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call bpdecode120(llrd, apmask, max_iterations, decoded, niterations, cw)
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if( niterations .ge. 0 ) exit
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enddo
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endif
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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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! Check the CRC
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do ibyte=1,6
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itmp=0
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do ibit=1,8
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itmp=ishft(itmp,1)+iand(1,decoded((ibyte-1)*8+ibit))
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enddo
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i1Dec8BitBytes(ibyte)=itmp
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enddo
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i1Dec8BitBytes(7)=decoded(49)*128+decoded(50)*64
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! Need to pack the received crc into bytes 8 and 9 for crc10_check
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i1Dec8BitBytes(8)=decoded(51)*2+decoded(52)
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i1Dec8BitBytes(9)=decoded(53)*128+decoded(54)*64+decoded(55)*32+decoded(56)*16
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i1Dec8BitBytes(9)=i1Dec8BitBytes(9)+decoded(57)*8+decoded(58)*4+decoded(59)*2+decoded(60)*1
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ncrcflag=0
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if( crc10_check( c_loc( i1Dec8BitBytes ), 9 ) ) ncrcflag=1
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if( ncrcflag .ne. 1 ) then
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nbadcrc=nbadcrc+1
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endif
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nueflag=0
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nerrmpc=0
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do i=1,K ! find number of errors in message+crc part of codeword
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if( msgbits(i) .ne. decoded(i) ) then
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nueflag=1
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nerrmpc=nerrmpc+1
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endif
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enddo
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nmpcbad(nerrmpc)=nmpcbad(nerrmpc)+1 ! This histogram should inform our selection of CRC poly
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if( ncrcflag .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( ncrcflag .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+10*log10(0.4166/2500.0)
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pberr=real(nberr)/(real(ntrials*N))
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write(*,"(f4.1,4x,f5.1,1x,i8,1x,i8,1x,i8,8x,f5.2,8x,e10.3)") db,snr2500,ngood,nue,nbadcrc,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=1,120
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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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open(unit=25,file='nmpcbad.dat',status='unknown')
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do i=1,60
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write(25,'(i4,2x,i10)') i,nmpcbad(i)
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enddo
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close(25)
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end program ldpcsim120
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