WSJT-X/lib/ldpcsim144.f90

156 lines
4.0 KiB
Fortran
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program ldpcsim
use, intrinsic :: iso_c_binding
use iso_c_binding, only: c_loc,c_size_t
use hashing
use packjt
parameter(NRECENT=10)
character*12 recent_calls(NRECENT)
character*22 msg,msgsent,msgreceived
character*8 arg
integer*1, allocatable :: codeword(:), decoded(:), message(:)
integer*1, target:: i1Msg8BitBytes(10)
integer*1 i1hash(4)
integer*1 msgbits(80)
integer*4 i4Msg6BitWords(13)
integer ihash
real*8, allocatable :: lratio(:), rxdata(:)
real, allocatable :: yy(:), llr(:)
equivalence(ihash,i1hash)
do i=1,NRECENT
recent_calls(i)=' '
enddo
nargs=iargc()
if(nargs.ne.4) then
print*,'Usage: ldpcsim niter ndither #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,*) max_dither
call getarg(3,arg)
read(arg,*) ntrials
call getarg(4,arg)
read(arg,*) s
! don't count hash bits as data bits
N=128
K=72
rate=real(K)/real(N)
write(*,*) "rate: ",rate
write(*,*) "niter= ",max_iterations," ndither= ",max_dither," s= ",s
allocate ( codeword(N), decoded(K), message(K) )
allocate ( lratio(N), rxdata(N), yy(N), llr(N) )
msg="K9AN K1JT EN50"
call packmsg(msg,i4Msg6BitWords,itype) !Pack into 12 6-bit bytes
call unpackmsg(i4Msg6BitWords,msgsent) !Unpack to get msgsent
write(*,*) "message sent ",msgsent
i4=0
ik=0
im=0
do i=1,12
nn=i4Msg6BitWords(i)
do j=1, 6
ik=ik+1
i4=i4+i4+iand(1,ishft(nn,j-6))
i4=iand(i4,255)
if(ik.eq.8) then
im=im+1
! if(i4.gt.127) i4=i4-256
i1Msg8BitBytes(im)=i4
ik=0
endif
enddo
enddo
ihash=nhash(c_loc(i1Msg8BitBytes),int(9,c_size_t),146)
ihash=2*iand(ihash,32767) !Generate the 8-bit hash
i1Msg8BitBytes(10)=i1hash(1) !CRC to byte 10
mbit=0
do i=1, 10
i1=i1Msg8BitBytes(i)
do ibit=1,8
mbit=mbit+1
msgbits(mbit)=iand(1,ishft(i1,ibit-8))
enddo
enddo
call encode_msk144(msgbits,codeword)
call init_random_seed()
write(*,*) "Eb/N0 SNR2500 ngood nundetected nbadhash sigma"
do idb = -6, 14
db=idb/2.0-1.0
sigma=1/sqrt( 2*rate*(10**(db/10.0)) )
ngood=0
nue=0
nbadhash=0
do itrial=1, ntrials
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
! 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
! To match the metric to the channel, s should be set to the noise standard deviation.
! For now, set s to the value that optimizes decode probability near threshold.
! The s parameter can be tuned to trade a few tenth's dB of threshold for an order of
! magnitude in UER
if( s .lt. 0 ) then
ss=sigma
else
ss=s
endif
llr=2.0*rxdata/(ss*ss)
lratio=exp(llr)
yy=rxdata
! max_iterations is max number of belief propagation iterations
! call ldpc_decode(lratio, decoded, max_iterations, niterations, max_dither, ndither)
! call amsdecode(yy, max_iterations, decoded, niterations)
! call bitflipmsk144(rxdata, decoded, niterations)
call bpdecode144(llr, max_iterations, decoded, niterations)
! If the decoder finds a valid codeword, niterations will be .ge. 0.
if( niterations .ge. 0 ) then
call extractmessage144(decoded,msgreceived,nhashflag,recent_calls,nrecent)
if( nhashflag .ne. 1 ) then
nbadhash=nbadhash+1
endif
nueflag=0
! Check the message plus hash against what was sent.
do i=1,K
if( msgbits(i) .ne. decoded(i) ) then
nueflag=1
endif
enddo
if( nhashflag .eq. 1 .and. nueflag .eq. 0 ) then
ngood=ngood+1
else if( nhashflag .eq. 1 .and. nueflag .eq. 1 ) then
nue=nue+1;
endif
endif
enddo
snr2500=db-4.0
write(*,"(f4.1,4x,f5.1,1x,i8,1x,i8,1x,i8,8x,f5.2)") db,snr2500,ngood,nue,nbadhash,ss
enddo
end program ldpcsim