55 lines
1.5 KiB
Fortran
55 lines
1.5 KiB
Fortran
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program bodide
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! Compute probability of word error for a bounded distance decoder.
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! Hardwired for non-coherent 64-FSK and the JT65 RS (63,12) code on GF(64).
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!
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! Let ps be symbol error probability.
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! The probability of getting an error pattern with e symbol errors is:
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! ps^e * (1-ps)*(n-e)
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! The number of error patterns with e errors is binomial(63,e)
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! Overall probability of getting a word with e errors is:
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! P(e)= binomial(63,e)* ps^e * (1-ps)*(n-e)
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! Probability that word is correct is P(0 to 25 errors) = sum{e=0}^{25} P(e)
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! Probability that word is wrong is 1-P(0 to 25 errors)
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! P_word_error=1-( sum_{e=0}^{t} P(e) )
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!
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implicit real*16 (a-h,o-z)
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integer*8 binomial
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integer x,s,XX,NN,M
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character arg*8
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nargs=iargc()
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if(nargs.ne.1) then
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print*,'Probability of word error for noncoherent 64-FSK with bounded distance decoding'
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print*,'Usage: bounded_distance D'
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print*,'Example: bounded_distance 25'
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go to 999
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endif
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call getarg(1,arg)
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read(arg,*) nt
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M=64
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write(*,1012)
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1012 format('Es/No P(word error)'/ &
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'----------------------')
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do isnr=0,40
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esno=10**(isnr/2.0/10.0)
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hsum=0.d0
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do k=1,M-1
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h=binomial(M-1,k)
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h=h*((-1)**(k+1))/(k+1)
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h=h*exp(-esno*k/(k+1))
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hsum=hsum + h
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enddo
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ps=hsum
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hsum=0.d0
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do i=0,nt
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h=binomial(63,i)
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h=h*ps**i
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h=h*(1-ps)**(63-i)
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hsum=hsum+h
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enddo
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pw=1-hsum
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write(*,'(f4.1,4x,e10.4,4x,e10.4)') isnr/2.0, ps, pw
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enddo
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999 end program bodide
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