Computes theoretical probability of error for a bounded-distance decoder.

git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@6302 ab8295b8-cf94-4d9e-aec4-7959e3be5d79

lib/ftrsd/ftrsd_paper/bodide.f90

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