Binary Number Transmitter

I need to create a transmitter that generates 100000 binary bits encoded as +/-3 volts using rand() but it doesn't seem to recognize the if just goes to the else. I know its something dumb any help would be appreciated I have:

x = rand(1,100000)
bit=(x>.5)
if bit==0
    bit = bit-3
else x == 1
    bit = bit+3
end

Answer 1

[Sven]

The "if" statement is only executed once, however you have 100000 elements. Essentially, if any elements in a vector are false, the "if" statement will return false. That's why you never enter the "true" portion of the if statement. Here's what I think you were trying:

x = rand(1,100000)
bit = double(x>.5);
bit(bit==0) = -3;
bit(bit==1) = 3;

Or, in a single line statement:

bit = (rand(1,100000)>0.5)*6 - 3;

[Walter Roberson]

The single-line statement will work, but the separate statements will not work in the form stated. bit = x>.5 will set bit to be of type logical, and once it is type logical all assignments to part of the vector will saturate to 0 or 1.

This would fix the problem, though:

bit = 0 + (x>.5);

Then bit would be of type double and assigning -3 or +3 to it would not be a problem.

[Sven]

True, Walter. Updated accordingly.

Answer 2

[Will]

Is there a way to calculate bit error rate with this system?

[Sven]

I'm not quite sure what you mean here, Will.

Your best bet will be to accept an answer to this question and write a new question about bit error rates. I'm afraid the short sentence above is a little unclear to me. Your original question here was well written: clearly written, well described, and you showed the code you were running. If you can do that again with this next question I'm sure you'll get an answer quickly.

[Walter Roberson]

The bit error rate with this system is 0.