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Added real-world likelihood normalization that doesn't require SNR estimate.

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git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@6500 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
This commit is contained in:
Steven Franke 2016-02-27 06:20:08 +00:00
parent a7e1e8ee75
commit 88e84d18e9
1 changed files with 19 additions and 7 deletions
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26
lib/ldpc/msksim.f90
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@ -3,15 +3,16 @@ program msksim
use, intrinsic :: iso_c_binding
parameter (N=128, M=48, K=80) ! M and N are global variables on the C side.
integer(1) message(1:K)
integer(1) codeword(1:N)
integer(1) decoded(1:K)
real*8 lratio(N)
character(50) pchk_file,gen_file
integer(1) codeword(1:N), decoded(1:K), message(1:K)
real*8 lratio(N), rxdata(N)
! To change to a different code, edit the following 3 lines.
pchk_file="./jtmode_codes/ldpc-128-80-sf13.pchk"
gen_file="./jtmode_codes/ldpc-128-80-sf13.gen"
rate=real(K)/real(N)
call init_ldpc(trim(pchk_file)//char(0),trim(gen_file)//char(0))
message(1:40)=1
@ -20,7 +21,6 @@ call ldpc_encode(message,codeword)
max_iterations=10
ntrials=1000000
rate=real(K)/real(N)
write(*,*) "Eb/N0 ngood nundetected"
do idb = 0, 11
@ -33,8 +33,20 @@ do idb = 0, 11
do itrial=1, ntrials
do i=1,N
rxdata = 2.0*(codeword(i)-0.5) + sigma*gran()
lratio(i)=exp(2.0*rxdata/(sigma*sigma))
rxdata(i) = 2.0*(codeword(i)-0.5) + sigma*gran()
enddo
! correct signal normalization is important for this decoder.
rxav=sum(rxdata)/N
rx2av=sum(rxdata*rxdata)/N
rxsig=sqrt(rx2av-rxav*rxav)
rxdata=rxdata/rxsig
! s can be tuned to trade a few tenth's dB of threshold
! for an order of magnitude in UER
do i=1,N
s=0.75
lratio(i)=exp(2.0*rxdata(i)/(s*s))
enddo
call ldpc_decode(lratio, decoded, max_iterations, niterations)