Understanding unexpected i/q calculation on a downsampled signal

1. Does downsampling cause aliasing?
2. How do you downsample a signal?
3. What are I and Q signals?
4. What is IQ sampling?

Does downsampling cause aliasing?

If a discrete-time signal's baseband spectral support is not limited to an interval of width 2 π / M radians, downsampling by M results in aliasing. Aliasing is the distortion that occurs when overlapping copies of the signal's spectrum are added together.

How do you downsample a signal?

y = downsample( x , n ) decreases the sample rate of x by keeping the first sample and then every n th sample after the first. If x is a matrix, the function treats each column as a separate sequence. y = downsample( x , n , phase ) specifies the number of samples by which to offset the downsampled sequence.

What are I and Q signals?

I/Q signaling refers to the use of two sinusoids that have the same frequency and a relative phase shift of 90°. Amplitude, phase, and frequency modulation can be performed by summing amplitude-modulated I/Q signals. Quadrature modulation refers to modulation that involves I/Q signals.

What is IQ sampling?

IQ sampling is the form of sampling that an SDR performs, as well as many digital receivers (and transmitters). It's a slightly more complex version of regular digital sampling (pun intended), so we will take it slow and with some practice the concept is sure to click!