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) !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 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