IQ

IQ Signals¶

https://witestlab.poly.edu/blog/capture-and-decode-fm-radio/

Into¶

A: Amplitude
f: Frequency
phi: Phase

I: Amplitude of the cos wave
Q: Amplitude of the sin wave

\[ v(t) = A * \sin(2 \pi * f * t + \phi) v(t) = I * \cos(2 \pi * f * t + \phi) x(t) = Q * \sin(2 \pi * f * t + \phi) g(t) = v(t) + x(t) \]

By just varying I and Q you can make complex modulations to the phase and amplitude.
I and Q are used to remove the phase shift of a signal and use it as parts of the Amplitude of the signal. So by just using I and Q you can combine the two signals to generate a shifted signal

Plotting the values:
- The amplitude of the signal is the hypotenuse.
- The I value is the x value on the circle
- The Q value is the y value on the circle
- The phi is the angle the amplitude is at

Using the I and Q of an RF signal you can figure out the modulation of the signal

Types of Modulation¶

RF parameters that can be modulated:
- Amplitude (ASK)
- Example lower amplitude could be a 0 and a higher amplitude could be a 1
- Frequency (FSK)
- Example lower frequency could be a 0 and a higher frequency could be a 1
- Phase (PSK)
- In phase could be a 0 and reverse phase could be a 1

Symbol: discrete state representing some quantity of information

Fast Fourier Transform: Decomposes a signal in to its component frequencies. Any Periodic signal can be modeled as the sum of harmonic sine waves

ASK¶

Ook

Simple Amplitude modulation where the amplitude is either high or low.

FSK¶

2FSK: There are two frequencies one that represents a 1 and one that represents a 0

Binary Phase Shift Keying (BPSK)¶

I(t) is set to +1 or -1
Q(t) = 0

This gets one bit of information.

Quadrature Phase Shift Keying (QPSK)¶

I(t) is set to +1 or -1
Q(t) is set to +1 or -1

This gets two bit of information. Or 4 distinct states. 00, 01, 10, 11

Advanced¶

With this type of modulation you can have more states for each I and Q.
This increases the bandwidth but does not work well with noise

AM Modulation¶

The I and Q are both moving up and down in amplitude

FM Modulation¶

The I and Q are rotating around the circumference of the circle both clockwise and counterclockwise