Digital Modulation

Master the art of encoding digital data onto analog carrier waves. An interactive study guide for EEE 464-Digital Communication Systems

Fundamental Concepts

ASK

Amplitude Shift Keying

Varies the amplitude of the carrier wave to represent binary data. Simple but susceptible to noise.

Simulate
FSK

Frequency Shift Keying

Changes the frequency of the carrier. More robust against noise than ASK, commonly used in modems.

Simulate
PSK

Phase Shift Keying

Manipulates the phase of the carrier. Highly bandwidth efficient. Basis for complex schemes like QPSK and QAM.

Simulate

Signal Visualizer

Select a modulation scheme and input a binary sequence to see the waveforms.

Max 8 bits for clarity.

Carrier Frequency 2 Hz
Amplitude (Logic 1) 1.0

How it works

In ASK, a high amplitude represents '1' and zero amplitude represents '0'. It's like turning a light on and off to send Morse code.

Digital Data Input

NRZ-L

Modulated Carrier Signal

ASK

Constellation Diagrams

A graphical representation of the complex envelope of each symbol. The X-axis represents the In-Phase (I) component and the Y-axis represents the Quadrature (Q) component.

BPSK (Binary PSK)

0
1
I (In-Phase) Q (Quad)
  • 1 bit per symbol
  • Phase shifts: 0° and 180°
  • High noise immunity
  • Used in satellite communications

QPSK (Quadrature PSK)

00
01
10
11
I (In-Phase) Q (Quad)
  • 2 bits per symbol
  • Phase shifts: 45°, 135°, 225°, 315°
  • Double data rate of BPSK for same BW
  • Used in LTE, Wi-Fi, Satellite

Modulation Comparison

Feature ASK FSK PSK
Variable Parameter Amplitude Frequency Phase
Noise Immunity Low High Very High
Bandwidth Narrow Wide Narrow
Complexity Low Medium High
Bit Error Rate High Low Lowest