WSJT-X/lib/ldpcsim128_90.f90

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3.4 KiB
Fortran
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program ldpcsim128_90
! Simulate the performance of the (128,90) code that is used in
! the second incarnation of MSK144.
use packjt77
integer, parameter:: NRECENT=10, N=128, K=90, M=N-K
character*12 recent_calls(NRECENT)
character*37 msg,msgsent,msgreceived
character*77 c77
character*8 arg
integer*1 codeword(N), message77(77)
integer*1 apmask(N),cw(N)
integer*1 msgbits(77)
integer*4 i4Msg6BitWords(13)
integer nerrtot(0:N),nerrdec(0:N)
logical unpk77_success
real*8 rxdata(N), rxavgd(N)
real llr(N)
do i=1,NRECENT
recent_calls(i)=' '
enddo
nerrtot=0
nerrdec=0
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
rate=real(77)/real(N)
write(*,*) "rate: ",rate
write(*,*) "niter= ",max_iterations," navg= ",navg," s= ",s
msg="K1ABC RR73; W9XYZ <KH1/KH7Z> -12"
i3=0
n3=1
call pack77(msg,i3,n3,c77)
call unpack77(c77,msgsent,unpk77_success)
read(c77,'(77i1)') msgbits
write(*,*) "message sent ",msgsent
write(*,*) 'msgbits'
write(*,'(77i1)') msgbits
! msgbits is the 77-bit message, codeword is 128 bits
call encode_128_90(msgbits,codeword)
! call init_random_seed()
write(*,*) "Eb/N0 SNR2500 ngood nundetected sigma psymerr"
do idb = 14,0,-1
db=idb/2.0-1.0
sigma=1/sqrt( 2*rate*(10**(db/10.0)) )
ngood=0
nue=0
nbadcrc=0
nsumerr=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
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
rxav=sum(rxdata)/N
rx2av=sum(rxdata*rxdata)/N
rxsig=sqrt(rx2av-rxav*rxav)
rxdata=rxdata/rxsig
! 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 bpdecode128_90(llr, apmask, max_iterations, message77, cw, nharderrors, niterations)
! If the decoder finds a valid codeword, nharderrors will be .ge. 0.
if( nharderrors .ge. 0 ) then
write(c77,'(77i1)') message77
call unpack77(c77,msgreceived,unpk77_success)
nhw=count(cw.ne.codeword)
if(nhw.eq.0) then ! this is a good decode
ngood=ngood+1
nerrdec(nerr)=nerrdec(nerr)+1
else ! this is an undetected error
nue=nue+1
endif
endif
nsumerr=nsumerr+nerr
enddo
snr2500=db+10*log10(rate*2000.0/2500.0) ! symbol rate is 2000 s^-1 and ref BW is 2500 Hz.
pberr=real(nsumerr)/real(ntrials*N)
write(*,"(f4.1,4x,f5.1,1x,i8,1x,i8,7x,f5.2,3x,e10.3)") db,snr2500,ngood,nue,ss,pberr
enddo
open(unit=23,file='nerrhisto.dat',status='unknown')
do i=0,N
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 ldpcsim128_90