Infocommunication

Digital carrier

modulation

- Bálint TÓTH, BME TMIT -

Overview

PPT is for demonstration, not for learning!

Review

– Analog modulations (AM, PM, FM)

– Digital baseband modulations (PAM, PPM, PDM)

Digital carrier modulations: – Basic types:

ASK, OOK

PSK, BPSK, MSK, QPSK, 8PSK, 16PSK, …

FSK, AFSK, MFSK, DTMF, ...

– Quadrature Amplitude Modulation:

2-QAM, 4-QAM, 8-QAM, 16-QAM, 32-QAM, 64-QAM … 4096-QAM

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Basic types of digital carrier modulation

ASK

FSK

PSK

???

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a)

b)

c)

d)

t

t

t

t

0 T 2T 3T 4T 5T

1 0 1 1 0

ASK: Amplitude Shift Keying

Example:

- Morze

- Optical cables

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PSK:Phase Shift Keying

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BPSK

QPSK (or 4PSK) 8PSK

FSK: Frequency Shift Keying

More noise-

roboust than

ASK.

Example:

High-frequency

radio.

Bálint TÓTH – BME TMIT 6

Spectral Power Density Function of the Binary FSK Signal

Bálint TÓTH – BME TMIT 7

f

fc

fc

fc

fc

fc

fc

fc

- - - + + +1/T 1/T0.5/T 0.5/T1.5/T 1.5/T

G (f)s

f = 0.25/T

f = 0.75/T

f = 0.35/T

d

d

d

f =d

d

f = cc

QAM: Quadrature Amplitude Modulation

Modulating the amplitude of two signals with

different phases.

Block diagramm.

Constellation diagram.

Variants:

– 4-QAM

– 8-QAM

– 16-QAM

– …

– 4096-QAM

Bálint TÓTH – BME TMIT 8

8-QAM

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www.wikipedia.org

Circular Rectangular

16-QAM

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www.wikipedia.org

64-QAM

Example: digital TV (64-QAM, 256-QAM)

Bálint TÓTH – BME TMIT 11

Real world 4096-QAM

Bálint TÓTH – BME TMIT 12

www.dectek.com

Available symbol and bitrates

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