MATLAB Code for QPSK Modulation and Demodulation

• 📘 Overview
• 🧮 MATLAB Codes
• 🧮 Theory
• 🧮 BER performance of QPSK with BPSK, 4-QAM, 16-QAM, 64-QAM, 256-QAM, etc
• 📚 Further Reading

 

Quadrature Phase Shift Keying (QPSK) is a digital modulation scheme that conveys two bits per symbol by changing the phase of the carrier signal. Each pair of bits is mapped to one of four possible phase shifts: 0°, 90°, 180°, or 270°

00  ===> 0 degree phase shift of carrier signal

01  ===> 90 degree

11  ===> 180 degree

10  ===> 270 degree

 

MATLAB Script

clc; clear all; close all; clc; M = 4; data = randi([0 (M-1)], 1000, 1); Phase = 0; modData=pskmod(data,M,Phase); figure(1); scatterplot(modData); channelAWGN = 15; rxData2 = awgn(modData, channelAWGN); figure(2); scatterplot(rxData2); demodData = pskdemod(rxData2,M,Phase);  

Result

data

1

0

2

2

0

2

1

.

.

.

modData

-1.00000000000000 + 1.22464679914735e-16i

-1.83697019872103e-16 - 1.00000000000000i

1.00000000000000 + 0.00000000000000i

6.12323399573677e-17 + 1.00000000000000i

6.12323399573677e-17 + 1.00000000000000i

-1.83697019872103e-16 - 1.00000000000000i

1.00000000000000 + 0.00000000000000i

-1.00000000000000 + 1.22464679914735e-16i

6.12323399573677e-17 + 1.00000000000000i

-1.83697019872103e-16 - 1.00000000000000i

.

.

.

Fig 1: Constellation Diagram of Transmitted QPSK (or 4 PSK) Signal

Fig 2: Constellation Diagram of Received QPSK (or 4 PSK) Signal through Noisy Channel

Further Reading

1. MATLAB Code for Constellation Diagram of QPSK
2. Constellation Diagram of BPSK