mirror of https://github.com/saitohirga/WSJT-X.git
138 lines
3.3 KiB
Fortran
138 lines
3.3 KiB
Fortran
program ldpcsim
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use, intrinsic :: iso_c_binding
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use hashing
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use packjt
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character*22 msg,msgsent,msgreceived
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character*80 prefix
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character*85 pchk_file,gen_file
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character*8 arg
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integer*1, allocatable :: codeword(:), decoded(:), message(:)
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real*8, allocatable :: lratio(:), rxdata(:)
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integer ihash
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nargs=iargc()
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if(nargs.ne.7) then
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print*,'Usage: ldpcsim <pchk file prefix > N K niter ndither #trials s '
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print*,'eg: ldpcsim "/pathto/peg-32-16-reg3" 32 16 10 1 1000 0.75'
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return
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endif
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call getarg(1,prefix)
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call getarg(2,arg)
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read(arg,*) N
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call getarg(3,arg)
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read(arg,*) K
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call getarg(4,arg)
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read(arg,*) max_iterations
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call getarg(5,arg)
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read(arg,*) max_dither
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call getarg(6,arg)
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read(arg,*) ntrials
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call getarg(7,arg)
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read(arg,*) s
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pchk_file=trim(prefix)//".pchk"
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gen_file=trim(prefix)//".gen"
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rate=real(K)/real(N)
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write(*,*) "rate: ",rate
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! don't count hash bits as data bits
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!rate=5.0/real(N)
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write(*,*) "pchk file: ",pchk_file
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write(*,*) "niter= ",max_iterations," ndither= ",max_dither," s= ",s
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allocate ( codeword(N), decoded(K), message(K) )
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allocate ( lratio(N), rxdata(N) )
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call init_ldpc(trim(pchk_file)//char(0),trim(gen_file)//char(0))
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msg="K9AN K1JT RRR"
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irpt=62
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call hash(msg,22,ihash)
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ihash=iand(ihash,1023) !10-bit hash
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ig=64*ihash + irpt !6-bit report
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write(*,*) irpt,ihash,ig
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do i=1,16
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message(i)=iand(1,ishft(ig,1-i))
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enddo
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call ldpc_encode(message,codeword)
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call init_random_seed()
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write(*,*) "Eb/N0 ngood nundetected nbadhash"
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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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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)-0.5) + sigma*gran()
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!write(*,*) i,gran()
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enddo
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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 .le. 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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do i=1,N
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lratio(i)=exp(2.0*rxdata(i)/(ss*ss))
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enddo
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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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! 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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nueflag=0
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nhashflag=0
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imsg=0
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do i=1,16
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imsg=ishft(imsg,1)+iand(1,decoded(17-i))
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enddo
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nrxrpt=iand(imsg,63)
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nrxhash=(imsg-nrxrpt)/64
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if( nrxhash .ne. ihash ) then
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nbadhash=nbadhash+1
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nhashflag=1
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endif
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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( message(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. 0 .and. nueflag .eq. 0 ) then
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ngood=ngood+1
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else if( nhashflag .eq. 0 .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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write(*,"(f4.1,1x,i8,1x,i8,1x,i8)") db,ngood,nue,nbadhash
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enddo
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end program ldpcsim
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