235 lines
6.9 KiB
Plaintext
235 lines
6.9 KiB
Plaintext
program ldpcsim174
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! End to end test of the (174,75)/crc12 encoder and decoder.
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use crc
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use packjt
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character*22 msg,msgsent,msgreceived
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character*8 arg
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character*6 grid
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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(87)
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integer*1 apmask(174), cw(174)
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integer*2 checksum
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integer*4 i4Msg6BitWords(13)
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integer colorder(174)
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integer nerrtot(174),nerrdec(174),nmpcbad(87)
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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/ &
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0, 1, 2, 3, 30, 4, 5, 6, 7, 8, 9, 10, 11, 32, 12, 40, 13, 14, 15, 16,&
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17, 18, 37, 45, 29, 19, 20, 21, 41, 22, 42, 31, 33, 34, 44, 35, 47, 51, 50, 43,&
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36, 52, 63, 46, 25, 55, 27, 24, 23, 53, 39, 49, 59, 38, 48, 61, 60, 57, 28, 62,&
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56, 58, 65, 66, 26, 70, 64, 69, 68, 67, 74, 71, 54, 76, 72, 75, 78, 77, 80, 79,&
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73, 83, 84, 81, 82, 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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120,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138,139,&
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140,141,142,143,144,145,146,147,148,149,150,151,152,153,154,155,156,157,158,159,&
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160,161,162,163,164,165,166,167,168,169,170,171,172,173/
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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.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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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=174
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K=87
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! scale Eb/No for a (174,87) 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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call packmsg(msg,i4Msg6BitWords,itype,.false.) !Pack into 12 6-bit bytes
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call unpackmsg(i4Msg6BitWords,msgsent,.false.,grid) !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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! K=87, For now:
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! msgbits(1:72) JT message bits
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! msgbits(73:75) 3 free message bits (set to 0)
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! msgbits(76:87) CRC12
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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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msgbits(73:75)=0 ! the three extra message bits go here
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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(75+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(79+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 encode174(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(*,'(22(8i1,1x))') codeword
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write(*,*) "Es/N0 SNR2500 ngood nundetected nbadcrc sigma"
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do idb = 20,-10,-1
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!do idb = -3,-3,-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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if(nerr.ge.1) 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(174-87+1:174-87+nap)+1)=5*(2.0*msgbits(1:nap)-1.0)
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apmask=0
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apmask(colorder(174-87+1:174-87+nap)+1)=1
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! max_iterations is max number of belief propagation iterations
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call bpdecode174(llr, apmask, max_iterations, decoded, cw, nharderrors,niterations)
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if( ndepth .ge. 0 .and. nharderrors .lt. 0 ) call osd174(llr, apmask, ndepth, decoded, 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 extractmessage174(decoded,msgreceived,ncrcflag)
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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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if(nerrmpc.ge.1) 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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if(nerr.ge.1) 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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baud=12000/1920
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snr2500=db+10.0*log10((baud/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=1,174
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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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open(unit=25,file='nmpcbad.dat',status='unknown')
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do i=1,87
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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 ldpcsim174
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