Session 2

Objectives:By the end of this session, the student will be able to:

•Distinguish between data and signals. Cite the advantages of digital data and signals over analog data and signals•Identify the 3 basic components of a signal•Discuss the bandwidth of a signal & how it relates to data transfer speed•Identify signal strength and attenuation, and how they are related•Outline the basic characteristics of transmitting analog data with analog signals, digital data with digital signals, digital data with analog signals and analog data with digital signals•List and draw diagrams of the basic digital encoding techniques, and explain the advantages and disadvantages of each•Identify the different shift keying (modulation) techniques and describe their advantages, disadvantages, and uses•Identify the two most common digitization techniques and describe their advantages and disadvantages•Discuss the characteristics and importance of spread spectrum encoding techniques•Identify the different data codes and how they are used in communication systems

Analog Waveform

3

Analog Waveform – with Noise

4

Digital Waveform

5

Digital Waveform - Noise

6

Digital Waveform – More Noise

7

Analog Signals

8

Amplitude

Frequency

Spectrum?Bandwidth?Effective bandwidth?

Analog Signals

9

Spectrum

Bandwidth = Y – XEffective Bandwidth = B - A

YX A B

noise noise

Human VoiceSpectrum: 300Hz – 3400HzBandwidth: 3100Hz

Waveforms - Phase

10

Attenuation / Amplification

11

dB = 10log10

(P2 / P

1)

P1 – power level at transmitter

P2 – power level at receiver

A loss of 50% power is -3dB. Whether the loss is from 1000W to 500W or from 10W to 5W.

Analog Data / Analog Signals

12

Digital Encoding Schemes

13

Digital Encoding Schemes

14

NRZ-L (Non-Return to Zero Level)Binary 0 – represented by presence of voltageBinary 1 – represented by absence (or low) voltage

Digital Encoding Schemes

15

NRZ-I (Non-Return to Zero Inverted)Binary 0 – represented by no voltage change at the time markBinary 1 – represented by a change in voltage at the time mark

What happens to NRZ-I and NRZ-L encoding when transmitting a long series of binary zeros?

Digital Encoding Schemes

16

ManchesterBinary 0 – represented by change from high to low in the middle of the time markBinary 1 – represented by a change from low to high in the middle of the time mark

Digital Encoding Schemes

17

Differential ManchesterBinary 0 – represented by change at the beginning of the time markBinary 1 – represented by no change at the beginning of the time mark

What happens to Manchester and Differential Manchester encoding when transmitting a long series of binary zeros?

Self-clocking

Bipolar-AMI

Bipolar-AMI Digital Encoding3 voltage levels:

binary 0 = zero voltagebinary 1 = positive or negative voltage sent depending on last binary 1 sent

(negative voltage last sent -> positive voltage sent this time)

18

4B/5B Digital Encoding Scheme

19

Amplitude Key Shifting

20

Amplitude Key Shifting

21

Frequency Key Shifting

22

Phase Key Shifting

23

Quadrature Phase Key Shifting

24

Quadrature Amplitude Key Shifting

25

Pulse Code Modulation

26

Pulse Code Modulation

27

Pulse Code Modulation

Twice the sample rate

28

Delta Modulation

29

Frequency Hopping Spread Spectrum

30

Direct Sequence Spread Spectrum

31

EBCDIC

32

ASCII

33

Review

NRZ-L

NRZ-I

Manchester

DiffManchester

Bipolar-AMI

4B/5B Encoding34

0V

0V

0V

0V

0V

0V