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 integer nerrtot(128),nerrdec(128) real*8, allocatable :: lratio(:), rxdata(:), rxavgd(:) real, allocatable :: yy(:), llr(:) equivalence(ihash,i1hash) 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 ! don't count hash bits as data bits N=128 K=72 rate=real(K)/real(N) write(*,*) "rate: ",rate write(*,*) "niter= ",max_iterations," navg= ",navg," s= ",s allocate ( codeword(N), decoded(K), message(K) ) allocate ( lratio(N), rxdata(N), rxavgd(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 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 ! 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 nerrdec(nerr)=nerrdec(nerr)+1 else if( nhashflag .eq. 1 .and. nueflag .eq. 1 ) then nue=nue+1; endif endif enddo snr2500=db-3.5 write(*,"(f4.1,4x,f5.1,1x,i8,1x,i8,1x,i8,8x,f5.2)") db,snr2500,ngood,nue,nbadhash,ss enddo open(unit=23,file='nerrhisto.dat',status='unknown') do i=1,128 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 ldpcsim