77 lines
1.6 KiB
Plaintext
77 lines
1.6 KiB
Plaintext
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program msksim
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use, intrinsic :: iso_c_binding
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! To change to a new code, edit the following line and the filenames
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! that contain the parity check and generator matrices.
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parameter (N=198, M=126, K=72) ! M and N are global variables on the C side.
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character(50) pchk_file,gen_file
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integer(1) codeword(1:N), decoded(1:K), message(1:K)
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real*8 lratio(N), rxdata(N)
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pchk_file="./jtmode_codes/peg-198-72-irreg-8x3-2x4.pchk"
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gen_file="./jtmode_codes/peg-198-72-irreg-8x3-2x4.gen"
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rate=real(K)/real(N)
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call init_ldpc(trim(pchk_file)//char(0),trim(gen_file)//char(0))
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message(1:K/2)=1
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message((K/2+1):K)=0
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call ldpc_encode(message,codeword)
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max_iterations=50
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ntrials=1000000
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write(*,*) "Eb/N0 ngood nundetected"
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do idb = 0, 11
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db=idb/2.0-0.5
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sigma=1/sqrt( 2*rate*(10**(db/10.0)) )
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ngood=0
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nue=0
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do itrial=1, ntrials
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do i=1,N
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rxdata(i) = 2.0*(codeword(i)-0.5) + sigma*gran()
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enddo
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! correct signal normalization is important for this decoder.
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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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! s can be tuned to trade a few tenth's dB of threshold
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! for an order of magnitude in UER
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do i=1,N
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s=0.75
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lratio(i)=exp(2.0*rxdata(i)/(s*s))
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enddo
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call ldpc_decode(lratio, decoded, max_iterations, niterations)
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if( niterations .ge. 0 ) then
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nueflag=0
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do i=1,K
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if( message(i) .ne. decoded(i) ) then
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nueflag=1
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endif
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enddo
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if( nueflag .eq. 1 ) then
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nue=nue+1
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else
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ngood=ngood+1;
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endif
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endif
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enddo
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write(*,"(f4.1,1x,i8,1x,i8)") db,ngood,nue
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enddo
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end program msksim
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