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https://github.com/saitohirga/WSJT-X.git
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9ae479e9d9
2. osd codeword selected based on correlation discrepancy instead of Hamming dist (improves sensitivity) 3. trap zero-valued spectrum values caused by large dt. 4. trap all-zero codeword 4. both decoders return number of hard errors 5. osd174 returns correlation discrepancy (rejection threshold still needs to be tuned). 6. both decoders return the codeword with bits in as-transmitted order, for subtraction. git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@7735 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
239 lines
6.9 KiB
Fortran
239 lines
6.9 KiB
Fortran
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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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(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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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.4) then
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print*,'Usage: ldpcsim niter norder #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 order: norder'
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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,*) norder
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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) !Pack into 12 6-bit bytes
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call unpackmsg(i4Msg6BitWords,msgsent) !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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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(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)
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if( norder .ge. 0 .and. nharderrors .lt. 0 ) call osd174(llr, norder, decoded, cw, nharderrors)
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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,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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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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baud=12000/2048
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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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