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https://github.com/saitohirga/WSJT-X.git
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535c02d900
By cascading the full 24-bit crc generator matrix with the (240,74) LDPC code generator, create a (240,50) generator that is used to decode with approximately 1 dB better sensitivity than the (240,64) with 14-bit CRC approach that is normally used. This approach treats the CRC bits as additional parity bits and provides no means for identifying incorrect codewords. All codewords on the list generated by the OSD algorithm have CRCs that match the CRC of the message payload. Codewords are validated by unpacking the message and comparing the unpacked message with the list of stored callsign/grid pairs stored in the fst4w_calls.txt file.
126 lines
3.5 KiB
Fortran
126 lines
3.5 KiB
Fortran
program ldpcsim240_74
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! End-to-end test of the (240,74)/crc24 encoder and decoders.
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use packjt77
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parameter(N=240, K=74, M=N-K)
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character*8 arg
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character*37 msg0,msg
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character*77 c77
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character*24 c24
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integer*1 msgbits(74)
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integer*1 apmask(240)
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integer*1 cw(240)
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integer*1 codeword(N),message74(74)
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integer ncrc24
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real rxdata(N),llr(N)
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logical first,unpk77_success
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data first/.true./
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nargs=iargc()
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if(nargs.ne.5 .and. nargs.ne.6) then
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print*,'Usage: ldpcsim niter ndeep #trials s K [msg]'
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print*,'e.g. ldpcsim240_74 20 5 1000 0.85 64 "K9AN K1JT FN20"'
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print*,'s : if negative, then value is ignored and sigma is calculated from SNR.'
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print*,'niter: is the number of BP iterations.'
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print*,'ndeep: -1 is BP only, ndeep>=0 is OSD order'
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print*,'K :is the number of message+CRC bits and must be in the range [50,74]'
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print*,'WSPR-format message is optional'
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return
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endif
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call getarg(1,arg)
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read(arg,*) max_iterations
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call getarg(2,arg)
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read(arg,*) norder
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call getarg(3,arg)
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read(arg,*) ntrials
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call getarg(4,arg)
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read(arg,*) s
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call getarg(5,arg)
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read(arg,*) Keff
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msg0='K9AN K1JT FN20 '
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if(nargs.eq.6) call getarg(6,msg0)
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call pack77(msg0,i3,n3,c77)
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rate=real(Keff)/real(N)
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write(*,*) "code rate: ",rate
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write(*,*) "niter : ",max_iterations
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write(*,*) "norder : ",norder
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write(*,*) "s : ",s
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write(*,*) "K : ",Keff
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msgbits=0
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read(c77,'(50i1)') msgbits(1:50)
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write(*,*) 'message'
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write(*,'(50i1)') msgbits(1:50)
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call get_crc24(msgbits,74,ncrc24)
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write(c24,'(b24.24)') ncrc24
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read(c24,'(24i1)') msgbits(51:74)
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write(*,'(24i1)') msgbits(51:74)
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write(*,*) 'message with crc24'
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write(*,'(74i1)') msgbits(1:74)
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call encode240_74(msgbits,codeword)
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call init_random_seed()
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call sgran()
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write(*,*) 'codeword'
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write(*,'(77i1,1x,24i1,1x,73i1)') codeword
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write(*,*) "Eb/N0 Es/N0 ngood nundetected sigma symbol error rate"
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do idb = 8,-3,-1
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db=idb/2.0-1.0
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sigma=1/sqrt( 2*rate*(10**(db/10.0)) ) ! to make db represent Eb/No
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! sigma=1/sqrt( 2*(10**(db/10.0)) ) ! db represents Es/No
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ngood=0
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nue=0
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nberr=0
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do itrial=1, ntrials
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! Create a realization of a noisy received word
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do i=1,N
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rxdata(i) = 2.0*codeword(i)-1.0 + sigma*gran()
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enddo
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nerr=0
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do i=1,N
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if( rxdata(i)*(2*codeword(i)-1.0) .lt. 0 ) nerr=nerr+1
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enddo
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nberr=nberr+nerr
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rxav=sum(rxdata)/N
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rx2av=sum(rxdata*rxdata)/N
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rxsig=sqrt(rx2av-rxav*rxav)
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rxdata=rxdata/rxsig
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if( s .lt. 0 ) then
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ss=sigma
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else
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ss=s
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endif
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llr=2.0*rxdata/(ss*ss)
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apmask=0
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dmin=0.0
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maxosd=2
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call decode240_74(llr, Keff, maxosd, norder, apmask, message74, cw, ntype, nharderror, dmin)
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if(nharderror.ge.0) then
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n2err=0
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do i=1,N
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if( cw(i).ne.codeword(i) ) n2err=n2err+1
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enddo
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if(n2err.eq.0) then
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ngood=ngood+1
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else
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nue=nue+1
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endif
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endif
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enddo
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! snr2500=db+10*log10(200.0/116.0/2500.0)
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esn0=db+10*log10(rate)
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pberr=real(nberr)/(real(ntrials*N))
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write(*,"(f4.1,4x,f5.1,1x,i8,1x,i8,8x,e10.3)") db,esn0,ngood,nue,pberr
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enddo
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end program ldpcsim240_74
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