CONTENTS

IntroductionBasic Concepts of Digital to analog

modulationPSKQAM

IntroductionWhat is Signal Constellation diagram ?

. Representation of signal modulated by a digital modulation.

. They also help you visually understand how a particular modulation mechanism works.

. Bit rate

. Baud rate

Digital to Analog ModulationIs the process of changing one of the

characteristics of an analog signal based on information in a digital signal(0s and 1s).

Example data from computer to another across a public access phone line.

Amplitude , frequency and phase.

Types of digital/analog modulation

Phase Shift keying(PSK)Phase of the carrier is varied to represent

binary 1 or 0.

Phase of 0 degrees to represent binary 0.

Phase to 180 degrees to send binary 1.

Conceptual view of PSK

PSK Constellation

4PSK- Conceptual view

4-PSK Constellation diagram

8 PSKWhen we have eight possible phases ,we can

send three bits at a time. 8-PSK is three times faster than 2-PSK

Three bit represents by each phase is called a tribit.

8-PSK Constellation diagram

Quadrature Amplitude ModulationPSK is limited by the ability of the

equipment .

This factors limits its potential bit rate.

Combine ASK and PSK.

Then we have maximum contrast between each bit

QAM Constellations4- QAM 8-QAM

Time domain for an 8- QAM

16- QAM Constellation

Bit and Baud comparison

Why are constellation maps or diagrams useful?They help you design a transmission system

that is less prone to errors and can possibly recover from transmission problems without relying on higher level protocols.

The analysis of a transmission system's constellation map allows the development of error detection and error correction schemes that can detect transmission problems.

Thanks

Indian Elango