WSJT-X/lib/fsk4hf/ldpcsim168.f90

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Fortran
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program ldpcsim168
! End to end test of the (168,84)/crc12 encoder and decoder.
use crc
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(11)
integer*1 msgbits(84)
integer*1 apmask(168), cw(168)
integer*2 checksum
integer*4 i4Msg6BitWords(13)
integer colorder(168)
integer nerrtot(168),nerrdec(168),nmpcbad(84)
logical checksumok,fsk,bpsk
real*8, allocatable :: rxdata(:)
real, allocatable :: llr(:)
data colorder/0,1,2,3,28,4,5,6,7,8,9,10,11,34,12,32,13,14,15,16,17, &
18,36,29,42,31,20,21,41,40,30,38,22,19,47,37,46,35,44,33,49,24, &
43,51,25,26,27,50,52,57,69,54,55,45,59,58,56,61,60,53,48,23,62, &
63,64,67,66,65,68,39,70,71,72,74,73,75,76,77,80,81,78,82,79,83, &
84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104, &
105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125, &
126,127,128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,146, &
147,148,149,150,151,152,153,154,155,156,157,158,159,160,161,162,163,164,165,166,167/
do i=1,NRECENT
recent_calls(i)=' '
enddo
nerrtot=0
nerrdec=0
nmpcbad=0 ! Used to collect the number of errors in the message+crc part of the codeword
nargs=iargc()
if(nargs.ne.3) then
print*,'Usage: ldpcsim niter #trials s '
print*,'eg: ldpcsim 10 1000 0.84'
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,*) ntrials
call getarg(3,arg)
read(arg,*) s
fsk=.false.
bpsk=.true.
! don't count crc bits as data bits
N=168
K=84
! scale Eb/No for a (168,72) code
rate=real(72)/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.,'') !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
i1Msg8BitBytes(10:11)=0
checksum = crc12 (c_loc (i1Msg8BitBytes), 11)
! For reference, the next 3 lines show how to check the CRC
i1Msg8BitBytes(10)=checksum/256
i1Msg8BitBytes(11)=iand (checksum,255)
checksumok = crc12_check(c_loc (i1Msg8BitBytes), 11)
if( checksumok ) write(*,*) 'Good checksum'
mbit=0
do i=1, 9
i1=i1Msg8BitBytes(i)
do ibit=1,8
mbit=mbit+1
msgbits(mbit)=iand(1,ishft(i1,ibit-8))
enddo
enddo
i1=i1Msg8BitBytes(10) ! First 4 bits of crc12 are LSB of this byte
do ibit=1,4
msgbits(72+ibit)=iand(1,ishft(i1,ibit-4))
enddo
i1=i1Msg8BitBytes(11) ! Now shift in last 8 bits of the CRC
do ibit=1,8
msgbits(76+ibit)=iand(1,ishft(i1,ibit-8))
enddo
write(*,*) 'message'
write(*,'(11(8i1,1x))') msgbits
call encode168(msgbits,codeword)
call init_random_seed()
call sgran()
write(*,*) 'codeword'
write(*,'(21(8i1,1x))') codeword
write(*,*) "Es/N0 SNR2500 ngood nundetected nbadcrc sigma"
do idb = 6,-6,-1
db=idb/2.0-1.0
sigma=1/sqrt( 2*(10**(db/10.0)) )
ngood=0
nue=0
nbadcrc=0
nberr=0
do itrial=1, ntrials
! Create a realization of a noisy received word
do i=1,N
if( bpsk ) then
rxdata(i) = 2.0*codeword(i)-1.0 + sigma*gran()
elseif( fsk ) then
if( codeword(i) .eq. 1 ) then
r1=(1.0 + sigma*gran())**2 + (sigma*gran())**2
r2=(sigma*gran())**2 + (sigma*gran())**2
elseif( codeword(i) .eq. 0 ) then
r2=(1.0 + sigma*gran())**2 + (sigma*gran())**2
r1=(sigma*gran())**2 + (sigma*gran())**2
endif
rxdata(i)=0.35*(sqrt(r1)-sqrt(r2))
! rxdata(i)=0.35*(exp(r1)-exp(r2))
! rxdata(i)=0.12*(log(r1)-log(r2))
endif
enddo
nerr=0
do i=1,N
if( rxdata(i)*(2*codeword(i)-1.0) .lt. 0 ) nerr=nerr+1
enddo
nerrtot(nerr)=nerrtot(nerr)+1
nberr=nberr+nerr
! 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)
nap=0 ! number of AP bits
llr(colorder(168-84+1:168-84+nap)+1)=5*(2.0*msgbits(1:nap)-1.0)
apmask=0
apmask(colorder(168-84+1:168-84+nap)+1)=1
! max_iterations is max number of belief propagation iterations
call bpdecode168(llr, apmask, max_iterations, decoded, niterations)
! if( niterations .eq. -1 ) then
! norder=3
! call osd168(llr, norder, decoded, niterations, cw)
! endif
! If the decoder finds a valid codeword, niterations will be .ge. 0.
if( niterations .ge. 0 ) then
call extractmessage168(decoded,msgreceived,ncrcflag,recent_calls,nrecent)
if( ncrcflag .ne. 1 ) then
nbadcrc=nbadcrc+1
endif
nueflag=0
nerrmpc=0
do i=1,K ! find number of errors in message+crc part of codeword
if( msgbits(i) .ne. decoded(i) ) then
nueflag=1
nerrmpc=nerrmpc+1
endif
enddo
write(37,*) niterations, ncrcflag, nueflag
nmpcbad(nerrmpc)=nmpcbad(nerrmpc)+1
if( ncrcflag .eq. 1 ) then
if( nueflag .eq. 0 ) then
ngood=ngood+1
nerrdec(nerr)=nerrdec(nerr)+1
else if( nueflag .eq. 1 ) then
nue=nue+1;
endif
endif
endif
enddo
snr2500=db+10*log10(10.417/2500.0)
pberr=real(nberr)/(real(ntrials*N))
write(*,"(f4.1,4x,f5.1,1x,i8,1x,i8,1x,i8,8x,f5.2,8x,e10.3)") db,snr2500,ngood,nue,nbadcrc,ss,pberr
enddo
open(unit=23,file='nerrhisto.dat',status='unknown')
do i=1,168
write(23,'(i4,2x,i10,i10,f10.2)') i,nerrdec(i),nerrtot(i),real(nerrdec(i))/real(nerrtot(i)+1e-10)
enddo
close(23)
open(unit=25,file='nmpcbad.dat',status='unknown')
do i=1,84
write(25,'(i4,2x,i10)') i,nmpcbad(i)
enddo
close(25)
end program ldpcsim168