Qam.pptx

QAM

1. QAM By/ HAMDY ELASYED 1 1

2. Objectives 1-Modulation 2-types of Modulation 3-QAM 4-uses of QAM 5-Advantage of QAM 6-Disadvatage of QAM 2 2

3. 1-Modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains information to be transmitted . 3 3

4. 2-Types of Modulation 1-Analog Modulation 2-Digital Modulation 3-pulse Modulation 4 4

5. Analog Modulation . Amplitude Modulation : In this type of modulation the amplitude of the carrier signal is varied with the modulating signal. Frequency Modulation : In this type of modulation the frequency of the carrier signal is varied with the modulating signal. Phase Modulation : In this type of modulation the phase of the carrier signal is varied with the modulating signal. - 5 5

6. Digital Modulation . The most fundamental digital modulation techniques are based on keying: PSK (phase-shift keying ): a finite number of phases are used. FSK (frequency-shift keying ): a finite number of frequencies are used. ASK (amplitude-shift keying ): a finite number of amplitudes are used. QAM (quadrature amplitude modulation ): a finite number of at least two phases and at least two amplitudes are used . 6 6

7. Pulse Modulation The Pulse wave modulation are of four types namely: Pulse amplitude Modulation Pulse position Modulation Pulse width Modulation Pulse code Modulation . 7 7

8. Pulse Modulation 8 8

9. 3-QAM 1-QAM mean :Quadrature amplitude modulation 2- is both an analog and a digital modulation scheme. It conveys two analog message signals, or two digital bit streams, by changing (modulating) the amplitudes of two carrier waves, using the amplitude-shift keying (ASK) digital modulation scheme or amplitude modulation (AM) analog modulation scheme 9 9

10. QAM 3-The two carrier waves of the same frequency, usually sinusoids, are out of phase with each other by 90° and are thus called quadrature carriers or quadrature components — hence the name of the scheme . 10 10

11. Carriers 11 11

12. QAM 4- The modulated waves are summed, and the final waveform is a combination of both phase-shift keying (PSK) and amplitude-shift keying (ASK), or, in the analog case, of phase modulation (PM) and amplitude modulation 12 12

13. QAM 5-At the receiver the signal is split and sent to the sine and cosine demodulators . After demodulation a low pass filter is . used to remove noise 13 13

14. QAM receiver 14 14

15. 4-QAM application 1- QAM is in many radio communications and data delivery applications. 2- . For broadcast applications for example, 64 QAM and 256 QAM are often used in digital cable television and cable modem applications 15 15

16. QAM application 3- In 16 QAM and 64 QAM are currently used for digital terrestrial television using DVB - Digital Video Broadcasting 4-In addition to this, variants of QAM are also used for many wireless and cellular technology applications . 5- QAM is being used in optical fiber systems as bit rates increase. 16 16

17. 5-Advantage of QAM the Basic advantage of QAM is that: Quadrature modulation is an efficient method of transmitting two message signals with the same bandwidth . 17 17

18. 6-Disadvantage of QAM 1- Basic disadvantage of QAM is that While it is possible to transmit more bits per symbol, if the energy of the constellation is to remain the same, the points on the constellation must be closer together and the transmission becomes more susceptible to noise. This results in a higher bit error rate than for the lower order QAM variants. In this way there is a balance between obtaining the higher data rates and maintaining an acceptable bit error rate for any radio communications system . 18 18

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