Baseband Transmistion with Noise

I have a project where I am to assume a baseband transmission scheme that sends a stream of binary rectangular pulses of height A = ±1 V (with the positive pulse representing a binary 1 and the negative pulse represents a binary 0).

The transmitted signal will then contain noise, additive noise, which would be introduced.

I am to use use the mean and variance estimators to determine an estimate of the mean and the variance using the generated noise with no signal transmitted.

After I would like to then subtract the estimated mean from the noise process rendering it zero-mean (approximately).

Sounds like a long process and expecially one from someone who never used MatLab before.

I have a few quesions, lets start with if I am on the rihgt track. I am not sure if this is how I should start but below is my initial code:

close all
clc

%%Generation of a signal
%This takes a set of random numbers and converts them to bits 0's & 1's
%The 2*X-1 will create -1's in place of the 0's from the bit conversion.
signal_i = 2*(rand(1,10^5)>0.5)-1;
signal_q = zeros(1,10^5);
%In communication systems we have two channels, Tx and Rx for serial as
%an example. This is why we have singal i and q
scatterplot(signal_i, signal_q);

If considering this code as a good start, I have encountered an error running scatterplot()

This error is as follows:

Operands to the || and && operators must be convertible to logical scalar values.

Error in scatterplot (line 60)
if ((fix(n) ~= n) || (n <= 0))

Error in signalGeneration (line 11)
scatterplot(signal_i, signal_q);

Any thoughts?

Answer 1

[Walter Roberson]

scatterplot() takes as its second argument an "n" which says to plot every n'th signal.

You might want

scatterplot(signal_i + 1i * signal_q)

[James Hayek]

That worked to alleviate the error, thanks. May I ask, why write:

signal_i + 1i*signal_q
what is the 1i?

Why not just

scatterplot(signal_i+signal_q) ?

[Walter Roberson]

1i is the imaginary unit, which can also be written as i alone. signal_i + 1i*signal_q makes each signal complex with the real part from signal_i and the imaginary part from signal_q . The documentation for scatterplot() says that when given complex data, it uses the two components for quadrature plot. Which sounded a lot like what you wanted for your *_q signal.

Another way of building the complex signal would have been

scatterplot(complex(signal_i, signal_q))