A First Course in Digital Communications Ha H. Nguyen and E. Shwedyk - - PowerPoint PPT Presentation

Chapter 1: Introduction

A First Course in Digital Communications

Ha H. Nguyen and E. Shwedyk February 2009

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Chapter 1: Introduction

Analog and Digital Amplitude Modulations

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 −1 1 t Analog message 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 −1 1 t AM signal 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 −1 1 t Digital message 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 −1 1 t BASK signal

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Chapter 1: Introduction

What is Digital Communication?

• A First Course in Digital Communications

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Chapter 1: Introduction

Why Digital Communications?

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 −1 1 t Transmitted AM 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 −2 2 t Received AM 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 −1 1 t Transmitted BASK 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 −2 2 t Received BASK

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Chapter 1: Introduction

Why Digital Communications?

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 −1 1 t Transmitted AM 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 −5 5 t Received AM 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 −1 1 t Transmitted BASK 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 −5 5 t Received BASK

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Chapter 1: Introduction

Regenerative Repeater in Digital Communications

• Digital communications: Transmitted signals belong to a

finite set of waveforms → The distorted signal can be recovered to its ideal shape, hence removing all the noise. Analog communications: Transmitted signals are analog waveforms, which can take infinite variety of shapes → Once the analog signal is distorted, the distortion cannot be removed.

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Chapter 1: Introduction

Block Diagram of a Communication System

• Note: “Synchronization” block is only present in a digital system.

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Chapter 1: Introduction

Digital vs. Analog

Advantages: Digital signals are much easier to be regenerated. Digital circuits are less subject to distortion and interference. Digital circuits are more reliable and can be produced at a lower cost than analog circuits. It is more flexible to implement digital hardware than analog hardware. Digital signals are beneficial from digital signal processing (DSP) techniques. Disadvantages: Heavy signal processing. Synchronization is crucial. Larger transmission bandwidth. Non-graceful degradation.

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