WSJT-X/lib/fsk4hf/ldpcsim174_74.f90

163 lines
4.8 KiB
Fortran

program ldpcsim174_74
! End-to-end test of the (174,74)/crc24 encoder and decoders.
use packjt77
parameter(N=174, K=74, M=N-K)
character*8 arg
character*37 msg0,msg
character*77 c77
character*50 cmsg
character*24 c24
integer*1 msgbits(74)
integer*1 apmask(174)
integer*1 cw(174)
integer*1 codeword(N),message(50)
integer ncrc24
integer nerrtot(174),nerrdec(174),nmpcbad(74)
real rxdata(N),llr(N)
real dllr(174),llrd(174)
logical first,unpk77_success
data first/.true./
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.5 .and. nargs.ne.6) then
print*,'Usage: ldpcsim niter ndeep #trials s K [msg]'
print*,'e.g. ldpcsim174_74 20 5 1000 0.85 64 "K9AN EN50 37"'
print*,'s : if negative, then value is ignored and sigma is calculated from SNR.'
print*,'niter: is the number of BP iterations.'
print*,'ndeep: -1 is BP only, ndeep>=0 is OSD order'
print*,'K :is the number of message+CRC bits and must be in the range [50,74]'
print*,'WSPR-format message is optional'
return
endif
call getarg(1,arg)
read(arg,*) max_iterations
call getarg(2,arg)
read(arg,*) ndeep
call getarg(3,arg)
read(arg,*) ntrials
call getarg(4,arg)
read(arg,*) s
call getarg(5,arg)
read(arg,*) Keff
msg0='K9AN EN50 37 '
if(nargs.eq.6) call getarg(6,msg0)
call pack77(msg0,i3,n3,c77)
cmsg=c77(1:50)
rate=real(Keff)/real(N)
write(*,*) "code rate: ",rate
write(*,*) "niter : ",max_iterations
write(*,*) "ndeep : ",ndeep
write(*,*) "s : ",s
write(*,*) "K : ",Keff
msgbits=0
read(cmsg,'(50i1)') msgbits(1:50)
write(*,*) 'message'
write(*,'(74i1)') msgbits
call get_crc24(msgbits,74,ncrc24)
write(c24,'(b24.24)') ncrc24
read(c24,'(24i1)') msgbits(51:74)
call encode174_74(msgbits,codeword)
call init_random_seed()
call sgran()
write(*,*) 'codeword'
write(*,'(50i1,1x,24i1,1x,100i1)') codeword
write(*,*) "Eb/N0 Es/N0 ngood nundetected sigma symbol error rate"
do idb = 8,-3,-1
db=idb/2.0-1.0
sigma=1/sqrt( 2*rate*(10**(db/10.0)) ) ! to make db represent Eb/No
! sigma=1/sqrt( 2*(10**(db/10.0)) ) ! db represents Es/No
ngood=0
nue=0
nberr=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
nberr=nberr+nerr
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)
apmask=0
! max_iterations is max number of belief propagation iterations
call bpdecode174_74(llr,apmask,max_iterations,message,cw,nharderror,niterations)
dmin=0.0
if( (nharderror .lt. 0) .and. (ndeep .ge. 0) ) then
call osd174_74(llr, Keff, apmask, ndeep, message, cw, nharderror, dmin)
endif
if(nharderror.ge.0) then
n2err=0
do i=1,N
if( cw(i)*(2*codeword(i)-1.0) .lt. 0 ) n2err=n2err+1
enddo
if(n2err.eq.0) then
ngood=ngood+1
else
nue=nue+1
endif
endif
enddo
! snr2500=db+10*log10(200.0/116.0/2500.0)
esn0=db+10*log10(rate)
pberr=real(nberr)/(real(ntrials*N))
write(*,"(f4.1,4x,f5.1,1x,i8,1x,i8,8x,f5.2,8x,e10.3)") db,esn0,ngood,nue,ss,pberr
if(first) then
write(c77,'(50i1)') message
c77(51:77)='000000000000000000000110000'
call unpack77(c77,0,msg,unpk77_success)
if(unpk77_success) then
write(*,1100) msg(1:14)
1100 format('Decoded message: ',a14)
else
print*,'Error unpacking message'
endif
first=.false.
endif
enddo
open(unit=23,file='nerrhisto.dat',status='unknown')
do i=1,120
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=1,68
write(25,'(i4,2x,i10)') i,nmpcbad(i)
enddo
close(25)
end program ldpcsim174_74