WSJT-X/lib/ft8/ldpcsim174_91.f90

program ldpcsim174_91
! End to end test of the (174,91)/crc14 encoder and decoder.
use crc
use packjt77

integer, parameter:: N=174, K=91, M=N-K
character*37 msg,msgsent,msgreceived
character*77 c77
character*8 arg
character*6 grid
character*96 tmpchar
integer*1, allocatable ::  codeword(:), decoded(:), message(:)
integer*1 msgbits(77)
integer*1 message77(77)
integer*1 apmask(N), cw(N)
integer nerrtot(0:N),nerrdec(0:N)
real*8, allocatable ::  rxdata(:)
real, allocatable :: llr(:)

nerrtot=0
nerrdec=0

nargs=iargc()
if(nargs.ne.4) then
   print*,'Usage: ldpcsim  niter  ndepth  #trials   s '
   print*,'eg:    ldpcsim    10     2      1000    0.84'
   print*,'belief propagation iterations: niter, ordered-statistics depth: ndepth'
   print*,'If s is negative, then value is ignored and sigma is calculated from SNR.'
   return
endif
call getarg(1,arg)
read(arg,*) max_iterations 
call getarg(2,arg)
read(arg,*) ndepth 
call getarg(3,arg)
read(arg,*) ntrials 
call getarg(4,arg)
read(arg,*) s

! scale Eb/No for a (174,91) code
rate=real(K)/real(N)

write(*,*) "rate: ",rate
write(*,*) "niter= ",max_iterations," s= ",s

allocate ( codeword(N), decoded(K), message(K) )
allocate ( rxdata(N), llr(N) )

!  msg="K1JT K9AN EN50"
  msg="G4WJS K9AN EN50"
  i3=0
  n3=1
  call pack77(msg,i3,n3,c77) !Pack into 12 6-bit bytes
  call unpack77(c77,msgsent) !Unpack to get msgsent
  write(*,*) "message sent ",msgsent

  read(c77,'(77i1)') msgbits(1:77)

  write(*,*) 'message'
  write(*,'(a71,1x,a3,1x,a3)') c77(1:71),c77(72:74),c77(75:77)

  call encode174_91(msgbits,codeword)

  call init_random_seed()

  write(*,*) 'codeword' 
  write(*,'(22(8i1,1x))') codeword

write(*,*) "Eb/N0   SNR2500   ngood  nundetected  sigma  psymerr"
do idb = 20,-10,-1 
!do idb = 0,0,-1 
  db=idb/2.0-1.0
  sigma=1/sqrt( 2*rate*(10**(db/10.0)) )
  ngood=0
  nue=0
  nsumerr=0

  do itrial=1, ntrials
! Create a realization of a noisy received word
    do i=1,N
      rxdata(i) = 2.0*codeword(i)-1.0 + sigma*gran()
    enddo
    nerr=0
    do i=1,N
      if( rxdata(i)*(2*codeword(i)-1.0) .lt. 0 ) nerr=nerr+1
    enddo
    if(nerr.ge.1) nerrtot(nerr)=nerrtot(nerr)+1

    rxav=sum(rxdata)/N
    rx2av=sum(rxdata*rxdata)/N
    rxsig=sqrt(rx2av-rxav*rxav)
    rxdata=rxdata/rxsig
    if( s .lt. 0 ) then
      ss=sigma
    else 
      ss=s
    endif

    llr=2.0*rxdata/(ss*ss)
    nap=0 ! number of AP bits
    llr(1:nap)=5*(2.0*msgbits(1:nap)-1.0)
    apmask=0
    apmask(1:nap)=1

! max_iterations is max number of belief propagation iterations
    call bpdecode174_91(llr, apmask, max_iterations, message77, cw, nharderrors,niterations)
    if( ndepth .ge. 0 .and. nharderrors .lt. 0 ) call osd174_91(llr, apmask, ndepth, message77, cw,  nharderrors, dmin)
! If the decoder finds a valid codeword, nharderrors will be .ge. 0.
    if( nharderrors .ge. 0 ) then
      call extractmessage77(message77,msgreceived)
      nhw=count(cw.ne.codeword)
      if(nhw.eq.0) then ! this is a good decode
         ngood=ngood+1
         nerrdec(nerr)=nerrdec(nerr)+1
      else
         nue=nue+1
      endif
    endif
    nsumerr=nsumerr+nerr
  enddo

  baud=12000/1920
  snr2500=db+10.0*log10((baud/2500.0))
  pberr=real(nsumerr)/(real(ntrials*N))
  write(*,"(f4.1,4x,f5.1,1x,i8,1x,i8,8x,f5.2,8x,e10.3)") db,SNR2500,ngood,nue,ss,pberr

enddo

open(unit=23,file='nerrhisto.dat',status='unknown')
do i=1,174
  write(23,'(i4,2x,i10,i10,f10.2)') i,nerrdec(i),nerrtot(i),real(nerrdec(i))/real(nerrtot(i)+1e-10)
enddo
close(23)

end program ldpcsim174_91