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program ldpcsim
use, intrinsic :: iso_c_binding
use hashing
use packjt
character*22 msg,msgsent,msgreceived
character*8 arg
integer*1, allocatable :: codeword(:), decoded(:), message(:)
real*8, allocatable :: rxdata(:), rxavgd(:)
real, allocatable :: llr(:)
integer ihash
integer*1 hardbits(32)
nargs=iargc()
if(nargs.ne.4) then
print*,'Usage: ldpcsim niter navg #trials s '
print*,'eg: ldpcsim 10 1 1000 0.75'
return
endif
call getarg(1,arg)
read(arg,*) max_iterations
call getarg(2,arg)
read(arg,*) navg
call getarg(3,arg)
read(arg,*) ntrials
call getarg(4,arg)
read(arg,*) s
K=16
N=32
!rate=real(K)/real(N)
! don't count hash bits as data bits
rate=4.0/real(N)
write(*,*) "rate: ",rate
write(*,*) "niter= ",max_iterations,"navg= ",navg," s= ",s
allocate ( codeword(N), decoded(K), message(K) )
allocate ( rxdata(N), rxavgd(N), llr(N) )
msg="K1JT K9AN"
call fmtmsg(msg,iz)
call hash(msg,22,ihash)
irpt=14
ihash=iand(ihash,4095) !12-bit hash
ig=16*ihash + irpt !4-bit report
write(*,*) irpt,ihash,ig
do i=1,16
message(i)=iand(1,ishft(ig,1-i))
enddo
write(*,'(16i1)') message
call encode_msk40(message,codeword)
write(*,'(32i1)') codeword
call init_random_seed()
write(*,*) "Eb/N0 SNR2500 ngood nundetected nbadhash"
do idb = 0, 30
db=idb/2.0
sigma=1/sqrt( 2*rate*(10**(db/10.0)) )
ngood=0
nue=0
nbadhash=0
itsum=0
do itrial=1, ntrials
rxavgd=0d0
do iav=1,navg
call sgran()
! Create a realization of a noisy received word
do i=1,N
rxdata(i) = 2.0*codeword(i)-1.0 + sigma*gran()
enddo
rxavgd=rxavgd+rxdata
enddo
rxdata=rxavgd
! Correct signal normalization is important for this decoder.
rxav=sum(rxdata)/N
rx2av=sum(rxdata*rxdata)/N
rxsig=sqrt(rx2av-rxav*rxav)
rxdata=rxdata/rxsig
if( s .le. 0 ) then
ss=sigma
else
ss=s
endif
llr=2.0*rxdata/(ss*ss)
call bpdecode40(llr, max_iterations, decoded, niterations)
! If the decoder finds a valid codeword, niterations will be .ge. 0.
if( niterations .ge. 0 ) then
nueflag=0
nhashflag=0
imsg=0
do i=1,16
imsg=ishft(imsg,1)+iand(1,decoded(17-i))
enddo
nrxrpt=iand(imsg,15)
nrxhash=(imsg-nrxrpt)/16
if( nrxhash .ne. ihash ) then
nbadhash=nbadhash+1
nhashflag=1
endif
! Check the message plus hash against what was sent.
do i=1,K
if( message(i) .ne. decoded(i) ) then
nueflag=1
endif
enddo
if( nhashflag .eq. 0 .and. nueflag .eq. 0 ) then
ngood=ngood+1
itsum=itsum+niterations
else if( nhashflag .eq. 0 .and. nueflag .eq. 1 ) then
nue=nue+1;
endif
else
hardbits=0
where(llr .gt. 0) hardbits=1
! write(*,'(32i1)') hardbits
! write(*,'(32i1)') codeword
isum=0
do i=1,32
if( hardbits(i) .ne. codeword(i) ) isum=isum+1
enddo
! write(*,*) 'number of errors ',isum
endif
enddo
avits=real(itsum)/real(ngood+0.1)
snr2500=db-10.0
write(*,"(f4.1,4x,f5.1,1x,i8,1x,i8,1x,i8,1x,f8.2,1x,f8.1)") db,snr2500,ngood,nue,nbadhash,ss,avits
enddo
end program ldpcsim
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