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trellis improvements 

git-svn-id: http://op25.osmocom.org/svn/trunk@33 65a5c917-d112-43f1-993d-58c26a4786be
This commit is contained in:
mossmann 2008-04-16 16:32:03 +00:00
parent a096f35022
commit 39f1f3963f
1 changed files with 20 additions and 5 deletions
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25
python/c4fm-decode.py
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@ -89,6 +89,8 @@ def data_deinterleave(input):
# 1/2 rate trellis decode a sequence of symbols
# TODO: Use soft symbols instead of hard symbols.
def trellis_1_2_decode(input):
if len(input) != 98:
raise NameError('wrong input length for trellis_1_2_decode')
output = []
# state transition table, including constellation to dibit pair mapping
next_words = (
@ -108,15 +110,22 @@ def trellis_1_2_decode(input):
if ((~codeword ^ next_words[state][candidate]) & (1 << bit)) > 0:
similarity[candidate] += 1
# find the dibit that matches all four codeword bits
# TODO: exception handling: at least try the next best match
state = similarity.index(4)
if similarity.count(4) == 1:
state = similarity.index(4)
# otherwise find the dibit that matches three codeword bits
elif similarity.count(3) == 1:
state = similarity.index(3)
print "corrected single trellis error"
else:
raise NameError('ambiguous trellis decoding error')
output.append(state)
return output[:48]
# 3/4 rate trellis decode a sequence of symbols
# TODO: Use soft symbols instead of hard symbols.
def trellis_3_4_decode(input):
# TODO: make way less fake
if len(input) != 98:
raise NameError('wrong input length for trellis_1_2_decode')
output = []
# state transition table, including constellation to dibit pair mapping
next_words = (
@ -140,8 +149,14 @@ def trellis_3_4_decode(input):
if ((~codeword ^ next_words[state][candidate]) & (1 << bit)) > 0:
similarity[candidate] += 1
# find the dibit that matches all four codeword bits
# TODO: exception handling: at least try the next best match
state = similarity.index(4)
if similarity.count(4) == 1:
state = similarity.index(4)
# otherwise find the dibit that matches three codeword bits
elif similarity.count(3) == 1:
state = similarity.index(3)
print "corrected single trellis error"
else:
raise NameError('ambiguous trellis decoding error')
output.append(state)
return tribits_to_integer(output[:48])