Transcript ppt - people

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
Frequency
Amplitude
Spectrum?
Bandwidth?
Effective bandwidth?
8
Analog Signals
n
o
i
s
e
X
n
o
i
s
e
B
A
Spectrum
Y
Human Voice
Spectrum: 300Hz – 3400Hz
Bandwidth: 3100Hz
Bandwidth = Y – X
Effective Bandwidth = B - A
9
Waveforms - Phase
10
Attenuation / Amplification
dB = 10log10(P2 / P1)
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.
11
Analog Data / Analog Signals
12
Digital Encoding Schemes
13
Digital Encoding Schemes
NRZ-L (Non-Return to Zero Level)
Binary 0 – represented by presence of voltage
Binary 1 – represented by absence (or low) voltage
14
Digital Encoding Schemes
NRZ-I (Non-Return to Zero Inverted)
Binary 0 – represented by no voltage change at the time mark
Binary 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?
15
Digital Encoding Schemes
Manchester
Binary 0 – represented by change from high to low in the middle of the time
mark
Binary 1 – represented by a change from low to high in the middle of the time
mark
16
Digital Encoding Schemes
Differential Manchester
Binary 0 – represented by change at the beginning of the time mark
Binary 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
17
Bipolar-AMI
Bipolar-AMI Digital Encoding
3 voltage levels:
binary 0 = zero voltage
binary 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
0V
NRZ-I
0V
Manchester
0V
DiffManchester
0V
Bipolar-AMI
0V
4B/5B Encoding
34
0V