How to count changes in binary transmission through channel

Have a transmitter that transmits 100000 random binary bits through a noisy channel. Is there a function I can use to figure out how many of the bits received have changed? Thanks

Answer 1

[Sven]

Hmmm... does this answer your question, Will?

originalBits = rand(1,100000)>0.5;
returnedBits = transmitSignal(originalBits);
changedBits = xor(originalBits, returnedBits);
errorCount = nnz(changedBits);
errorRatio = errorCount / length(originalBits);

Obviously you need to have the function "transmitSignal", or some other way to get the original signal and the signal that was received into memory. Once you have these two variables, the "xor" command just returns whether a bit had changed or not. Let us know if your question is more specific than this.

As an example, maybe you just want to simulate errors by randomly changing some bits:

bitsToChange = rand(size(originalBits))>0.95;
returnedBits = originalBits;
returnedBits(bitsToChange) = ~returnedBits(bitsToChange);
changedBits = originalBits ~= returnedBits;
errorCount = nnz(changedBits);
errorRatio = errorCount / length(originalBits);

[Walter Roberson]

The changedBits = xor(originalBits, returnedBits)

line could also be expressed as

changedBits = originalBits ~= returnedBits;

if you find that easier to understand -- or if your "bits" do not happen to have the values 0 and 1 (e.g, the +3 and -3 of your previous question.)

[Sven]

@Walter: How dare you consistently follow up my answers with more correct or simple improvements?

[Sven]

@Will: Walter's right (regardless of how much I resent it) - I'll change the second part of my example to use ~= and keep the first part as xor()