program ldpcsim120 ! End to end test of the (120,60)/crc10 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(9) integer*1, target:: i1Dec8BitBytes(9) integer*1 msgbits(60) integer*1 apmask(120) integer*2 checksum integer colorder(120) integer nerrtot(120),nerrdec(120),nmpcbad(60) logical checksumok,fsk,bpsk real*8, allocatable :: rxdata(:) real, allocatable :: llr(:) data colorder/ & 0,1,2,21,3,4,5,6,7,8,20,10,9,11,12,23,13,28,14,31, & 15,16,22,26,17,30,18,29,25,32,41,34,19,33,27,36,38,43,42,24, & 37,39,45,40,35,44,47,46,50,51,53,48,52,56,54,57,55,49,58,61, & 60,59,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79, & 80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99, & 100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119/ 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=120 K=60 ! scale Eb/No for a (120,50) code rate=real(50)/real(N) write(*,*) "rate: ",rate write(*,*) "niter= ",max_iterations," s= ",s allocate ( codeword(N), decoded(K), message(K) ) allocate ( rxdata(N), llr(N) ) ! The message should be packed into the first 7 bytes i1Msg8BitBytes(1:6)=85 i1Msg8BitBytes(7)=64 ! The CRC will be put into the last 2 bytes i1Msg8BitBytes(8:9)=0 checksum = crc10 (c_loc (i1Msg8BitBytes), 9) ! For reference, the next 3 lines show how to check the CRC i1Msg8BitBytes(8)=checksum/256 i1Msg8BitBytes(9)=iand (checksum,255) checksumok = crc10_check(c_loc (i1Msg8BitBytes), 9) if( checksumok ) write(*,*) 'Good checksum' write(*,*) i1Msg8BitBytes(1:9) mbit=0 do i=1, 7 i1=i1Msg8BitBytes(i) do ibit=1,8 mbit=mbit+1 msgbits(mbit)=iand(1,ishft(i1,ibit-8)) enddo enddo i1=i1Msg8BitBytes(8) ! First 2 bits of crc10 are LSB of this byte do ibit=1,2 msgbits(50+ibit)=iand(1,ishft(i1,ibit-2)) enddo i1=i1Msg8BitBytes(9) ! Now shift in last 8 bits of the CRC do ibit=1,8 msgbits(52+ibit)=iand(1,ishft(i1,ibit-8)) enddo write(*,*) 'message' write(*,'(9(8i1,1x))') msgbits call encode120(msgbits,codeword) call init_random_seed() call sgran() write(*,*) 'codeword' write(*,'(15(8i1,1x))') codeword write(*,*) "Es/N0 SNR2500 ngood nundetected nbadcrc sigma" do idb = -10, 24 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 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) apmask=0 ! max_iterations is max number of belief propagation iterations call bpdecode120(llr, apmask, max_iterations, decoded, niterations) ! If the decoder finds a valid codeword, niterations will be .ge. 0. if( niterations .ge. 0 ) then ! Check the CRC do ibyte=1,6 itmp=0 do ibit=1,8 itmp=ishft(itmp,1)+iand(1,decoded((ibyte-1)*8+ibit)) enddo i1Dec8BitBytes(ibyte)=itmp enddo i1Dec8BitBytes(7)=decoded(49)*128+decoded(50)*64 ! Need to pack the received crc into bytes 8 and 9 for crc10_check i1Dec8BitBytes(8)=decoded(51)*2+decoded(52) i1Dec8BitBytes(9)=decoded(53)*128+decoded(54)*64+decoded(55)*32+decoded(56)*16 i1Dec8BitBytes(9)=i1Dec8BitBytes(9)+decoded(57)*8+decoded(58)*4+decoded(59)*2+decoded(60)*1 ncrcflag=0 if( crc10_check( c_loc( i1Dec8BitBytes ), 9 ) ) ncrcflag=1 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 nmpcbad(nerrmpc)=nmpcbad(nerrmpc)+1 ! This histogram should inform our selection of CRC poly if( ncrcflag .eq. 1 .and. nueflag .eq. 0 ) then ngood=ngood+1 nerrdec(nerr)=nerrdec(nerr)+1 else if( ncrcflag .eq. 1 .and. nueflag .eq. 1 ) then nue=nue+1; endif endif enddo snr2500=db+10*log10(0.4166/2500.0) 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=1,120 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=1,60 write(25,'(i4,2x,i10)') i,nmpcbad(i) enddo close(25) end program ldpcsim120