CONTENTS Introduction Basic Concepts of Digital to analog modulation PSK QAM
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