Part I
Elements of Digital Communications
System
Advanced RF and Wireless Techniques
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COMP 1160
Objectives:
Study the general architecture of digital communications system
Identify the functions of each element of communications system
Discuss different types of communication channels
Discuss the frequency spectrum allocation
Advanced RF and Wireless Techniques
slide 2
COMP 1160
Elements of Digital Communications System
Input
Signal
A/D
Source
Encoder
Channel
Encoder
Digital
Modulator
Channel
Output
Signal
D /A
Source
Decoder
Advanced RF and Wireless Techniques
Channel
Decoder
slide 3
Digital
Demodulator
COMP 1160
A/D
Convert analog signal to digital format
A / D conversion is achieved by using
the following three operations:
a) Sampling
b) Quantization
c) Encoding
a) Sampling
0 ------- 000
1 ------- 001
2 ------- 010
3 ------- 011
4 ------- 100
5 ------- 101
6 ------- 110
7 ------- 111
b) Quantization
c) Encoding
Advanced RF and Wireless Techniques
slide 4
COMP 1160
Source Encoding or Data Compression
The purpose of source encoder is to remove any redundancy in
digital bits to minimize bandwidth requirements.
It is also called Data Compression
Data compression algorithms can be classified into two categories:
Lossless compression
Lossy compression
Lossless compression algorithms usually exploit statistical redundancy
in such a way as to represent the sender's data more concisely
without error.
Lossy data compression or perceptual coding, is possible if some loss
of fidelity is acceptable.
Advanced RF and Wireless Techniques
slide 5
COMP 1160
Channel Encoding or Forward Error
Correction (FEC)
The operation of the channel encoder is the inverse of the source
encoder
The main operation is to add redundancy in such a way that the
system will be capable to detect and correct errors
It is also called Forward Error Correction (FEC)
The FEC can be classified into three categories:
a) Repetition Coding
b) Block Coding
c) Convolutional Coding
d) Turbo Coding
Advanced RF and Wireless Techniques
slide 6
COMP 1160
Modulator
Modulation is the process of converting the transmitted signal from
base band frequency to RF frequency.
The modulation techniques can be classified into two categories:
1. Analog Modulation
2. Digital Modulation
Analog modulation can be classified into three categories:
1. AM
2. FM
3. PM
Digital modulation can be classified into following categories:
1.
2.
3.
4.
ASK
FSK
PSK
QAM
Advanced RF and Wireless Techniques
slide 7
COMP 1160
Communication Channels
Wireline Channels
Twisted-pair of wire lines (telephone lines)
Coaxial cable
Fiber Optic Channels
Wireless Electromagnetic Channels
Underwater Acoustic Channels
Storage Channels
Advanced RF and Wireless Techniques
slide 8
COMP 1160
Frequency Spectrum
Generally there are three types of frequencies in communication systems:
1. Baseband Frequency
2. Intermediate Frequency (IF)
3. Radiation Frequency (RF)
Baseband Frequency: describes signals and systems whose range of
frequencies is measured from zero to a maximum bandwidth.
Intermediate Frequency: is a frequency to which a carrier frequency is
shifted as an intermediate step in transmission or reception.
Radiation Frequency: is the frequency that the transmitted signal will be
radiated at from the antenna.
Where c is the speed of the light (3x108 m/sec) and is the wave length
Advanced RF and Wireless Techniques
slide 9
COMP 1160
Frequency Spectrum
Advanced RF and Wireless Techniques
slide 10
COMP 1160
Part II
Spectrum Analyzer
Advanced RF and Wireless Techniques
slide 11
COMP 1160
Outline
Advanced RF and Wireless Techniques
Overview:
What is spectrum analysis?
What measurements do we make?
Theory of Operation:
Spectrum analyzer hardware
Specifications:
Which are important and why?
slide 12
COMP 1160
Overview
What is Spectrum Analysis?
8563A
Advanced RF and Wireless Techniques
SPECTRUM ANALYZER
9 kHz - 26.5 GHz
slide 13
COMP 1160
Overview
.
Types of Tests Made
Modulation
Noise
Distortion
Advanced RF and Wireless Techniques
slide 14
COMP 1160
Overview
Frequency versus Time Domain
Amplitude
(power)
Time domain
Measurements
Advanced RF and Wireless Techniques
Frequency Domain
Measurements
slide 15
COMP 1160
Overview
Different Types of Analyzers
Fourier Analyzer
A
Parallel filters measured
simultaneously
LCD shows full
spectral display
f1
Advanced RF and Wireless Techniques
f2
f
slide 16
COMP 1160
Overview
Different Types of Analyzers
Swept Analyzer
A
Filter 'sweeps' over range
of interest
LCD shows full
spectral display
f1
Advanced RF and Wireless Techniques
f2
f
slide 17
COMP 1160
Theory of Operation
Spectrum Analyzer Block Diagram
RF input
attenuator
IF gain
IF filter
detector
mixer
Input
signal
Log
Amp
Pre-Selector
Or Low Pass
Filter
video
filter
local
oscillator
sweep
generator
Crystal
Reference
Advanced RF and Wireless Techniques
CRT display
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COMP 1160
Theory of Operation
MIXER
Mixer
f sig
input
f LO+ f sig
f LO- f sig
RF IF
LO
f sig
f LO
f LO
Advanced RF and Wireless Techniques
slide 19
COMP 1160
Theory of Operation
IF FILTER
IF Filter
Input
Spectrum
IF Bandwidth
(RBW)
Display
Advanced RF and Wireless Techniques
slide 20
COMP 1160
Theory of Operation
DETECTOR
Detector
amplitude
"bins
"
Positive detection: largest value
in bin displayed
Negative detection: smallest value
in bin displayed
Sample detection: last value in bin
displayed
Advanced RF and Wireless Techniques
slide 21
COMP 1160
Theory of Operation
Video Filter
VIDEO
FILTER
Advanced RF and Wireless Techniques
slide 22
COMP 1160
Theory of Operation
Other Components
LO
SWEEP
GEN
RF INPUT
ATTENUATOR
frequency
LCD DISPLAY
IF GAIN
Advanced RF and Wireless Techniques
slide 23
COMP 1160
Theory of Operation
How it all works together
fs
0
Signal Range
f LO
f LO- f s
fs
3 (GHz)
mixer
LO Range
input
f LO+ f s
IF filter
fs 2
4
3.6
detector
6.5
3.6
f IF
sweep generator
LO
f LO
3
4
3.6
0
5
(GHz)
3 (GHz) f
LCD display
6.5
Advanced RF and Wireless Techniques
slide 24
COMP 1160
Theory of Operation
Front Panel Operation
Softkeys
Primary functions
(Frequency, Amplitude,
Span)
8563A
SPECTRUM ANALYZER
9 kHz - 26.5 GHz
Control functions
(RBW, sweep
time, VBW)
RF Input
Advanced RF and Wireless Techniques
Numeric
keypad
slide 25
COMP 1160
Specifications
8563A
SPECTRUM ANALYZER
Advanced RF and Wireless Techniques
9 kHz - 26.5 GHz
Frequency Range
Accuracy: Frequency & Amplitude
Resolution
Sensitivity
Distortion
Dynamic Range
slide 26
COMP 1160
