quadrature amplitude modulation

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

1. MOBILE COMMUNICATION ENGINEERING Quadrature Amplitude Modulation(QAM) TUSHAR SINGHAL 1830069 E.CSc - 2

2. contents What is QAM Block Diagram of QAM modulation General FORM OF M-ARY QAM Coordinates of i th 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 E min = Energy of the signal with lowest amplitude a i & b i are independent intergers chosen acc. to location of the particular signal point. T s = duration of each symbol

6. Coordinates of i th point The coordinates of the ith message point are a i √ Emin and b i √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.

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