WSJT-X/lib/ft8/ldpcsim174_91.f90

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Fortran
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program ldpcsim174_91
! End to end test of the (174,91)/crc14 encoder and decoder.
use crc
use packjt
integer, parameter:: N=174, K=91, M=N-K
character*22 msg,msgsent,msgreceived
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*4 i4Msg6BitWords(13)
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"
call packmsg(msg,i4Msg6BitWords,itype,.false.) !Pack into 12 6-bit bytes
call unpackmsg(i4Msg6BitWords,msgsent,.false.,grid) !Unpack to get msgsent
write(*,*) "message sent ",msgsent
tmpchar=' '
write(tmpchar,'(12b6.6)') i4Msg6BitWords(1:12)
tmpchar(73:77)='00000' !i5bit
read(tmpchar,'(77i1)') msgbits(1:77)
write(*,*) 'message'
write(*,'(28i1,1x,28i1,1x,16i1,1x,5i1)') msgbits
! msgbits is the 77-bit message, codeword is 174 bits
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