solving simple nrzi python decoding. 0 bit means no changed occurred but 1 bit means a change occurred in digital signal sequence.
"_": low signal
'¯': high signal
"|": pipe signal( pipe leads to change of signal and itself pipe is not recorded)
given input: _ | ¯ | _ _ _ | ¯ | _| ¯ ¯ ¯
output: 011000110100
my code:
def nrzi(signal: str) -> str:
res = ''
prev = '_'
for i in range(len(signal)):
cur = signal[i]
prev = signal[i-1]
#signal same as prev - no change
if (prev == cur == '_') or (prev == cur == '¯'):
res += '0'
#signal changed cuz prev is pipe
elif prev == '|' and cur == '_':
res += '0'
elif prev == '|' and cur == '¯':
res += '1'
return ''.join(res)
signal = "_|¯|____|¯|__|¯¯¯"
result = nrzi(signal)
print(result)
it produces
10000100100 vs correct 011000110100
whats wrong?
you had two problem in your code
first:
at the first time looping through the for loop you are getting the last result with the signal[i-1] this means at the first you will be getting the _- which means +1 this is happening because python is looking at the if statements and none of them declare anything about the _- so python uses the last statement which is the +1.
second:
is your if statement going from your output that you expect you want to get 1 every time you have |_ so I changed it to look like this:
elif prev == '|' and cur == '_':
res += '1'
The code now looks like this and the output is: 011000110100:
def nrzi(signal: str) -> str:
res = ''
prev = '_'
for i in range(len(signal)):
cur = signal[i]
prev = [signal[i], signal[i-1]] [i >= 1]
#signal same as prev - no change
if (prev == cur == '_') or (prev == cur == '¯'):
res += '0'
#signal changed cuz prev is pipe
elif prev == '|' and cur == '_':
res += '1'
elif prev == '|' and cur == '¯':
res += '1'
return ''.join(res)
signal = "_|¯|____|¯|__|¯¯¯"
result = nrzi(signal)
print(result)