Full description of QAM modulation along with general form and constellation diagrams

1. MOBILE COMMUNICATION
ENGINEERING
TUSHAR SINGHAL
1830069
E.CSc - 2

2. CONTENTS
• What is QAM
• Block Diagram of QAM modulation
• General FORM OF M-ARY QAM
• Coordinates of ith point
• CONSTELLATION DIAGRAM OF M-ARY QAM
• QAM APPLICATIONS
• ADVANTAGES AND DISADVANTAGES

3. WHAT IS QAM??
• Quadrature Amplitude Modulation or QAM is a form of modulation which is widely used for
modulating data signals onto a carrier used for radio communications.
• It is widely used because it offers advantages over other forms of data modulation such as PSK,
although many forms of data modulation operate along side each other.
• Quadrature Amplitude Modulation, QAM is a signal in which two carriers shifted in phase by 90
degrees are modulated and the resultant output consists of both amplitude and phase variations.
In view of the fact that both amplitude and phase variations are present it may also be
considered as a mixture of amplitude and phase.

4. BLOCK DIAGRAM OF QAM MODULATION

5. GENERAL FORM OF M-ARY QAM
• The general form of an M-ary QAM signal can be defined as
• Emin = Energy of the signal with lowest amplitude
• ai & bi are independent intergers chosen acc. to location of the particular signal point.
• Ts = duration of each symbol

6. COORDINATES OF ITH POINT
• The coordinates of the ith message point are ai √ Emin and bi√Emin where (a, b) iz
element of the L by L matrix given by:
• Where L = √M,

7. CONSTELLATION DIAGRAM OF M-ARY QAM
 This is a constellation
diagram for M=16.
 The constellation
consists of square lattice
of signal points.
 For M=16, L=4.

8. QAM APPLICATIONS
 QAM is in many radio communications and data delivery
applications. However some specific variants of QAM are
used in some specific applications and standards.
 In addition to this, variants of QAM are also used for
many wireless and cellular technology applications.

9. ADVANTAGES
• QAM appears to increase the
efficiency of transmission for
radio communications systems
by utilizing both amplitude and
phase variations,
DISADVANTAGES
• more susceptible to noise because
the states are closer together so that
a lower level of noise is needed to
move the signal to a different
decision point.

10. THANKYOU