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https://github.com/saitohirga/WSJT-X.git
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164 lines
4.8 KiB
Fortran
164 lines
4.8 KiB
Fortran
program ldpcsim174_74
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! End-to-end test of the (174,74)/crc24 encoder and decoders.
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use crc
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use packjt77
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parameter(N=174, K=74, M=N-K)
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character*8 arg
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character*37 msg0,msg
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character*77 c77
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character*50 cmsg
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character*24 c24
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integer*1 msgbits(74)
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integer*1 apmask(174)
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integer*1 cw(174)
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integer*1 codeword(N),message(50)
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integer ncrc24
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integer nerrtot(174),nerrdec(174),nmpcbad(74)
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real rxdata(N),llr(N)
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real dllr(174),llrd(174)
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logical first,unpk77_success
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data first/.true./
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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.5 .and. nargs.ne.6) then
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print*,'Usage: ldpcsim niter ndeep #trials s K [msg]'
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print*,'e.g. ldpcsim174_74 20 5 1000 0.85 64 "K9AN EN50 37"'
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print*,'s : if negative, then value is ignored and sigma is calculated from SNR.'
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print*,'niter: is the number of BP iterations.'
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print*,'ndeep: -1 is BP only, ndeep>=0 is OSD order'
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print*,'K :is the number of message+CRC bits and must be in the range [50,74]'
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print*,'WSPR-format message is optional'
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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,*) ndeep
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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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call getarg(5,arg)
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read(arg,*) Keff
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msg0='K9AN EN50 37 '
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if(nargs.eq.6) call getarg(6,msg0)
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call pack77(msg0,i3,n3,c77)
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cmsg=c77(1:50)
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rate=real(Keff)/real(N)
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write(*,*) "code rate: ",rate
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write(*,*) "niter : ",max_iterations
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write(*,*) "ndeep : ",ndeep
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write(*,*) "s : ",s
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write(*,*) "K : ",Keff
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msgbits=0
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read(cmsg,'(50i1)') msgbits(1:50)
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write(*,*) 'message'
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write(*,'(74i1)') msgbits
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call get_crc24(msgbits,ncrc24)
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write(c24,'(b24.24)') ncrc24
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read(c24,'(24i1)') msgbits(51:74)
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call encode174_74(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(*,'(50i1,1x,24i1,1x,100i1)') codeword
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write(*,*) "Eb/N0 Es/N0 ngood nundetected sigma symbol error rate"
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do idb = 8,-3,-1
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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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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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rxdata(i) = 2.0*codeword(i)-1.0 + sigma*gran()
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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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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 bpdecode174_74(llr,apmask,max_iterations,message,cw,nharderror,niterations)
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dmin=0.0
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if( (nharderror .lt. 0) .and. (ndeep .ge. 0) ) then
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call osd174_74(llr, Keff, apmask, ndeep, message, cw, nharderror, dmin)
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endif
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if(nharderror.ge.0) then
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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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if(n2err.eq.0) then
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ngood=ngood+1
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else
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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(200.0/116.0/2500.0)
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esn0=db+10*log10(rate)
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pberr=real(nberr)/(real(ntrials*N))
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write(*,"(f4.1,4x,f5.1,1x,i8,1x,i8,8x,f5.2,8x,e10.3)") db,esn0,ngood,nue,ss,pberr
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if(first) then
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write(c77,'(50i1)') message
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c77(51:77)='000000000000000000000110000'
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call unpack77(c77,0,msg,unpk77_success)
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if(unpk77_success) then
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write(*,1100) msg(1:14)
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1100 format('Decoded message: ',a14)
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else
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print*,'Error unpacking message'
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endif
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first=.false.
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endif
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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=1,68
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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_74
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