234 lines
6.5 KiB
Fortran
234 lines
6.5 KiB
Fortran
program ldpcsim168
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! End to end test of the (168,84)/crc12 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(11)
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integer*1 msgbits(84)
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integer*1 apmask(168), cw(168)
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integer*2 checksum
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integer*4 i4Msg6BitWords(13)
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integer colorder(168)
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integer nerrtot(168),nerrdec(168),nmpcbad(84)
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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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data colorder/0,1,2,3,28,4,5,6,7,8,9,10,11,34,12,32,13,14,15,16,17, &
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18,36,29,42,31,20,21,41,40,30,38,22,19,47,37,46,35,44,33,49,24, &
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43,51,25,26,27,50,52,57,69,54,55,45,59,58,56,61,60,53,48,23,62, &
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63,64,67,66,65,68,39,70,71,72,74,73,75,76,77,80,81,78,82,79,83, &
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84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104, &
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105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125, &
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126,127,128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,146, &
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147,148,149,150,151,152,153,154,155,156,157,158,159,160,161,162,163,164,165,166,167/
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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=168
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K=84
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! scale Eb/No for a (168,72) code
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rate=real(72)/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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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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i1Msg8BitBytes(10:11)=0
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checksum = crc12 (c_loc (i1Msg8BitBytes), 11)
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! For reference, the next 3 lines show how to check the CRC
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i1Msg8BitBytes(10)=checksum/256
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i1Msg8BitBytes(11)=iand (checksum,255)
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checksumok = crc12_check(c_loc (i1Msg8BitBytes), 11)
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if( checksumok ) write(*,*) 'Good checksum'
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mbit=0
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do i=1, 9
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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(10) ! First 4 bits of crc12 are LSB of this byte
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do ibit=1,4
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msgbits(72+ibit)=iand(1,ishft(i1,ibit-4))
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enddo
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i1=i1Msg8BitBytes(11) ! Now shift in last 8 bits of the CRC
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do ibit=1,8
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msgbits(76+ibit)=iand(1,ishft(i1,ibit-8))
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enddo
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write(*,*) 'message'
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write(*,'(11(8i1,1x))') msgbits
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call encode168(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(*,'(21(8i1,1x))') codeword
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write(*,*) "Es/N0 SNR2500 ngood nundetected nbadcrc sigma"
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do idb = 6,-6,-1
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db=idb/2.0-1.0
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sigma=1/sqrt( 2*(10**(db/10.0)) )
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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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nap=0 ! number of AP bits
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llr(colorder(168-84+1:168-84+nap)+1)=5*(2.0*msgbits(1:nap)-1.0)
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apmask=0
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apmask(colorder(168-84+1:168-84+nap)+1)=1
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! max_iterations is max number of belief propagation iterations
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call bpdecode168(llr, apmask, max_iterations, decoded, niterations)
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! if( niterations .eq. -1 ) then
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! norder=3
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! call osd168(llr, norder, decoded, niterations, cw)
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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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call extractmessage168(decoded,msgreceived,ncrcflag,recent_calls,nrecent)
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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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write(37,*) niterations, ncrcflag, nueflag
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nmpcbad(nerrmpc)=nmpcbad(nerrmpc)+1
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if( ncrcflag .eq. 1 ) then
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if( 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( 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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endif
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enddo
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snr2500=db+10*log10(10.417/2500.0)
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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=1,168
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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=1,84
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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 ldpcsim168
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