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) 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 -12" i3=0 n3=1 call pack77(msg,i3,n3,c77) call unpack77(c77,msgsent) 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) 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