Wireless Communication – Seven: QPSK

This is the seventh in a series of computer science lessons about wireless communication and digital signal processing. In these lessons you’ll learn about the nature of electromagnetic radiation, digital modulation and multiplexing techniques, and how to get the best out of mobile communication systems such as LTE, 5G and WiFi. In this particular lesson, you will learn about quadrature phase shift keying or QPSK for short, and variations of it including Offset QPSK, Differential QPSK and 8PSK. You will learn how a sine wave and a cosine wave can be modulated then combined to generate a QPSK radio signal that encodes 2 bits per symbol. You will also see how higher order phase shift keying, such as 8PSK can encode even more bits per symbol. This lesson includes descriptions of QPSK, OQPSK and 8PSK by means of constellation diagrams and explains how DQPSK can overcome the need for a coherent receiver. Chapters: 00:00 Introduction 00:36 Linear superposition and quadrature 01:54 QPSK line coding 03:09 I and Q 04:04 QPSK waveforms 04:40 QPSK modulator and demodulator 06:03 Constellation diagram 07:44 Offset QPSK 09:52 Differential QPSK 14:02 8PSK 17:04 QPSK and 8PSK applications