Modulação digital

Introduction to Digital Modulation

EE4367 Telecom. Switching & Transmission

Prof. Murat Torlak

Introduction
In a digital communication system, the source to be transmitted is discrete both in time and amplitude Digital information carrying signals must be first converted to an analog waveform prior to transmission At the receiving end, analog signals are converted back to a digital format before presentation to the end user The conversion process at the transmitting end is known as modulation The receiving end is known as demodulation or detection
EE4367 Telecom. Switching & Transmission
Prof. Murat Torlak

1

Functional Block Diagram of a Binary Digital Communication System
Binary Sequence

Source encoder

Channel encoder

Modulator

Analog Waveform

A/D Converter Physical Waveform Channel

Analog Waveform

D/A Converter Binary Sequence

Source Decoder

Channel Decoder

Demodulator

EE4367 Telecom. Switching & Transmission

Prof. Murat Torlak

Digital Modulation
Overview:
In digital wireless communication systems, the modulating signal may be represented as a time sequence of symbols or pulses, where each symbol has m finite states. Each symbol represents n bits of information where n = log2m bits/symbol.

Advantages of Digital over Analog:
Greater noise immunity (due to its finite process) Robustness to channel impairments Easier multiplexing of various forms of information like voice, data, video

EE4367 Telecom. Switching & Transmission

Prof. Murat Torlak

2

Digital Modulation
Security – by using coding techniques to avoid jamming Accommodation of digital error control codes which detect and/or correct transmission errors Equalization to improve the performance of over all communication link Supports complex signal conditioning and processing methods

EE4367 Telecom. Switching & Transmission

Prof. Murat Torlak

Digital Modulation
Factors that influence Digital Modulation:
Low BER at low