Binary Symmetric Channel
Section Overview
A binary symmetric channel corrupts a binary signal by reversing
each bit with a fixed probability. Such a channel can be useful for
testing error-control coding.
To model a binary symmetric channel, use the bsc function.
The two input arguments are the binary signal and the probability, p.
To model a binary channel whose statistical description involves
the number of errors per codeword, see the description of randerr in Random Bit Error Patterns.
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Example: Introducing Noise in a Convolutional Code
The example below introduces bit errors in a convolutional code
with probability 0.01.
t = poly2trellis([4 3],[4 5 17;7 4 2]); % Trellis
msg = ones(10000,1); % Data to encode
code = convenc(ones(10000,1),t); % Encode using convolutional code.
[ncode,err] = bsc(code,.01); % Introduce errors in code.
numchanerrs = sum(sum(err)) % Number of channel errors
dcode = vitdec(ncode,t,2,'trunc','hard'); % Decode.
[numsyserrs,ber] = biterr(dcode,msg) % Errors after decoding
The output below shows that the decoder corrects some, but not
all, of the errors that bsc introduced into the
code. Your results might vary because the channel errors are random.
numchanerrs =
158
numsyserrs =
53
ber =
0.0053
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