Transcript Chapter 3 Data Transmission

Konsep Dasar
Komunikasi Data
Ir. Hary Nugroho MT.
Simplified Communications
Model - Diagram
Protocols in Simplified
Architecture
Data Transmission

The Successful transmission of data
depends principally on two factor :
The quality of the signal being
transmitted
 The characteristics of transmission
medium

Terminology (1)
Transmitter
 Receiver
 Medium


Guided medium
• e.g. twisted pair, optical fiber

Unguided medium
• e.g. air, water, vacuum
Terminology (2)

Direct link


No intermediate devices
Point-to-point
Direct link
 Only 2 devices share link


Multi-point

More than two devices share the link
Terminology (3)

Simplex

One direction
• e.g. Television

Half duplex

Either direction, but only one way at a time
• e.g. police radio

Full duplex

Both directions at the same time
• e.g. telephone
Frequency, Spectrum and
Bandwidth

Time domain concepts

Analog signal
• Various in a smooth way over time

Digital signal
• Maintains a constant level then changes to
another constant level

Periodic signal
• Pattern repeated over time

Aperiodic signal
• Pattern not repeated over time
Analogue & Digital Signals
Periodic
Signals
s(t + T) = s(t)
-~ <t<+~
Sine Wave

Peak Amplitude (A)



Frequency (f)





maximum strength of signal
volts
Rate of change of signal
Hertz (Hz) or cycles per second
Period = time for one repetition (T)
T = 1/f
Phase ()

Relative position in time
Varying Sine Waves
s(t) = A sin(2ft +)
Wavelength




Distance occupied by one cycle
Distance between two points of
corresponding phase in two consecutive
cycles

Assuming signal velocity v
  = vT
 f = v

c = 3*108 ms-1 (speed of light in free space)
Frequency Domain
Concepts
Signal usually made up of many
frequencies
 Components are sine waves
 Can be shown (Fourier analysis) that
any signal is made up of component
sine waves
 Can plot frequency domain functions

Addition of
Frequency
Components
(T=1/f)
Contoh
Jika gelombang memiliki perioda 1 s maka frekuensinya adalah 1 Hz
Jika periodanya 1 ms maka frekuensinya adalah 1 Khz

Jika sebuah gelombang memiliki
perioda 100 ms, berapa frekuensi
gelombang tersebut dalam kilohertz
100 ms = 100 x 10e-3 s = 10e-1 s
F = 1/T = 1/10e-1 = 10 Hertz = 10e-2 Khz
Frequency
Domain
Representations
Spectrum & Bandwidth

Spectrum


Absolute bandwidth



range of frequencies contained in signal
width of spectrum
Effective bandwidth

Often just bandwidth

Narrow band of frequencies containing most
of the energy
DC Component

Component of zero frequency
Signal with DC Component
Data Rate and Bandwidth
Any transmission system has a limited
band of frequencies
 This limits the data rate that can be
carried

Analog and Digital Data
Transmission
Definition :
 Data


Signals


Entities that convey meaning
Electric or electromagnetic representations
of data
Transmission

Communication of data by propagation and
processing of signals
Analog and Digital Data

Analog
Continuous values within some
interval
 e.g. sound, video


Digital
Discrete values
 e.g. text, integers

Acoustic Spectrum (Analog)
Analog and Digital Signals


Means by which data are propagated
Analog


Continuously variable
Various media
• wire, fiber optic, space




Speech bandwidth 100Hz to 7kHz
Telephone bandwidth 300Hz to 3400Hz
Video bandwidth 4MHz
Digital

Use two DC components
Advantages & Disadvantages
of Digital
Cheaper
 Less susceptible to noise
 Greater attenuation

Pulses become rounded and smaller
 Leads to loss of information

Attenuation of Digital Signals
Example #1
Components of Speech

Frequency range (of hearing) 20Hz-20kHz




Speech 100Hz-7kHz
Easily converted into electromagnetic signal
for transmission
Sound frequencies with varying volume
converted into electromagnetic frequencies
with varying voltage
Limit frequency range for voice channel

300-3400Hz
Conversion of Voice Input
into Analog Signal
Example #1
Video Components

USA - 483 lines scanned per frame at 30 frames per
second


So 525 lines x 30 scans = 15750 lines per second





525 lines but 42 lost during vertical retrace
63.5s per line
11s for retrace, so 52.5 s per video line
Max frequency if line alternates black and white
Horizontal resolution is about 450 lines giving 225
cycles of wave in 52.5 s
Max frequency of 4.2MHz
Example #1
Binary Digital Data
From computer terminals etc.
 Two dc components
 Bandwidth depends on data rate

Conversion of PC Input to
Digital Signal
Data and Signals
Usually use digital signals for digital
data and analog signals for analog
data
 Can use analog signal to carry digital
data



Modem
Can use digital signal to carry analog
data

Compact Disc audio
Analog Signals Carrying
Analog and Digital Data
Digital Signals Carrying
Analog and Digital Data
Analog Transmission
Analog signal transmitted without
regard to content
 May be analog or digital data
 Attenuated over distance
 Use amplifiers to boost signal
 Also amplifies noise

Digital Transmission








Concerned with content
Integrity endangered by noise, attenuation
etc.
Repeaters used
Repeater receives signal
Extracts bit pattern
Retransmits
Attenuation is overcome
Noise is not amplified
Advantages of Digital
Transmission

Digital technology


Data integrity



High bandwidth links economical
High degree of multiplexing easier with digital
techniques
Security & Privacy


Longer distances over lower quality lines
Capacity utilization


Low cost LSI/VLSI technology
Encryption
Integration

Can treat analog and digital data similarly
Transmission Impairments
Signal received may differ from signal
transmitted
 Analog - degradation of signal quality
 Digital - bit errors
 Caused by

Attenuation and attenuation distortion
 Delay distortion
 Noise

Attenuation
Signal strength falls off with distance
 Depends on medium
 Received signal strength:

must be enough to be detected
 must be sufficiently higher than noise to
be received without error


Attenuation is an increasing function of
frequency
Delay Distortion
Only in guided media
 Propagation velocity varies with
frequency

Noise (1)


Additional signals inserted between
transmitter and receiver
Thermal




Due to thermal agitation of electrons
Uniformly distributed
White noise
Intermodulation

Signals that are the sum and difference of
original frequencies sharing a medium
Noise (2)

Crosstalk


A signal from one line is picked up by
another
Impulse
Irregular pulses or spikes
 e.g. External electromagnetic
interference
 Short duration
 High amplitude

Channel Capacity

Data rate
In bits per second
 Rate at which data can be
communicated


Bandwidth
In cycles per second of Hertz
 Constrained by transmitter and
medium

Nyquist Bandwidth





If rate of signal transmission is 2B then
signal with frequencies no greater than B is
sufficient to carry signal rate
Given bandwidth B, highest signal rate is 2B
Given binary signal, data rate supported by
B Hz is 2B bps
Can be increased by using M signal levels
C= 2B log2M
Shannon Capacity Formula


Consider data rate,noise and error rate
Faster data rate shortens each bit so burst
of noise affects more bits





At given noise level, high data rate means
higher error rate
Signal to noise ration (in decibels)
SNRdb=10 log10 (signal/noise)
Capacity C=B log2(1+SNR)
This is error free capacity
Required Reading

Stallings chapter 3
Transmission Media
Overview






Guided - wire
Unguided - wireless
Characteristics and quality determined by
medium and signal
For guided, the medium is more important
For unguided, the bandwidth produced by
the antenna is more important
Key concerns are data rate and distance
Design Factors

Bandwidth


Transmission impairments



Higher bandwidth gives higher data rate
Attenuation
Interference
Number of receivers


In guided media
More receivers (multi-point) introduce more
attenuation
Electromagnetic Spectrum
Guided Transmission Media
Twisted Pair
 Coaxial cable
 Optical fiber

Transmission
Characteristics of Guided
Media
Frequency
Range
Typical
Attenuation
Typical
Delay
Repeater
Spacing
Twisted pair
(with
loading)
0 to 3.5 kHz
0.2 dB/km @
1 kHz
50 µs/km
2 km
Twisted pairs
(multi-pair
cables)
0 to 1 MHz
0.7 dB/km @
1 kHz
5 µs/km
2 km
Coaxial cable
0 to 500 MHz
7 dB/km @
10 MHz
4 µs/km
1 to 9 km
Optical fiber
186 to 370
THz
0.2 to 0.5
dB/km
5 µs/km
40 km
Twisted Pair
Twisted Pair - Applications
Most common medium
 Telephone network



Within buildings


Between house and local exchange
(subscriber loop)
To private branch exchange (PBX)
For local area networks (LAN)

10Mbps or 100Mbps
Twisted Pair - Pros and
Cons
Cheap
 Easy to work with
 Low data rate
 Short range

Twisted Pair - Transmission
Characteristics

Analog


Digital






Amplifiers every 5km to 6km
Use either analog or digital signals
repeater every 2km or 3km
Limited distance
Limited bandwidth (1MHz)
Limited data rate (100MHz)
Susceptible to interference and noise
Near End Crosstalk
Coupling of signal from one pair to
another
 Coupling takes place when transmit
signal entering the link couples back
to receiving pair
 i.e. near transmitted signal is picked
up by near receiving pair

Unshielded and Shielded TP

Unshielded Twisted Pair (UTP)





Ordinary telephone wire
Cheapest
Easiest to install
Suffers from external EM interference
Shielded Twisted Pair (STP)



Metal braid or sheathing that reduces
interference
More expensive
Harder to handle (thick, heavy)
UTP Categories

Cat 3




Cat 4






up to 20 MHz
Cat 5


up to 16MHz
Voice grade found in most offices
Twist length of 7.5 cm to 10 cm
up to 100MHz
Commonly pre-installed in new office buildings
Twist length 0.6 cm to 0.85 cm
Cat 5E (Enhanced) –see tables
Cat 6
Cat 7
Comparison of Shielded and
Unshielded Twisted Pair
Attenuation (dB per 100 m)
Frequenc
y (MHz)
Category
3 UTP
Category
5 UTP
150-ohm
STP
Near-end Crosstalk (dB)
Category
3 UTP
Category
5 UTP
150-ohm
STP
1
2.6
2.0
1.1
41
62
58
4
5.6
4.1
2.2
32
53
58
16
13.1
8.2
4.4
23
44
50.4
25
—
10.4
6.2
—
41
47.5
100
—
22.0
12.3
—
32
38.5
300
—
21.4
—
—
—
31.3
Twisted Pair Categories and Classes
Category 3
Class C
Category 5
Class D
Bandwidth
16 MHz
100 MHz
Cable
Type
UTP
Link Cost
(Cat 5 =1)
0.7
Category
5E
Category 6
Class E
Category 7
Class F
100 MHz
200 MHz
600 MHz
UTP/FTP
UTP/FTP
UTP/FTP
SSTP
1
1.2
1.5
2.2
Coaxial Cable
Coaxial Cable Applications


Most versatile medium
Television distribution



Long distance telephone transmission




Ariel to TV
Cable TV
Can carry 10,000 voice calls simultaneously
Being replaced by fiber optic
Short distance computer systems links
Local area networks
Coaxial Cable - Transmission
Characteristics

Analog
Amplifiers every few km
 Closer if higher frequency
 Up to 500MHz


Digital
Repeater every 1km
 Closer for higher data rates

Optical Fiber
Optical Fiber - Benefits

Greater capacity

Data rates of hundreds of Gbps
Smaller size & weight
 Lower attenuation
 Electromagnetic isolation
 Greater repeater spacing


10s of km at least
Optical Fiber - Applications
Long-haul trunks
 Metropolitan trunks
 Rural exchange trunks
 Subscriber loops
 LANs

Optical Fiber - Transmission
Characteristics

Act as wave guide for 1014 to 1015 Hz


Light Emitting Diode (LED)




Cheaper
Wider operating temp range
Last longer
Injection Laser Diode (ILD)



Portions of infrared and visible spectrum
More efficient
Greater data rate
Wavelength Division Multiplexing
Optical Fiber Transmission
Modes
Frequency Utilization for
Fiber Applications
Wavelength (in
vacuum) range
(nm)
Frequency
range (THz)
820 to 900
366 to 333
1280 to 1350
234 to 222
1528 to 1561
1561 to 1620
Band
label
Fiber type
Application
Multimode
LAN
S
Single mode
Various
196 to 192
C
Single mode
WDM
185 to 192
L
Single mode
WDM
Attenuation in Guided Media
Wireless Transmission
Frequencies

2GHz to 40GHz





30MHz to 1GHz



Microwave
Highly directional
Point to point
Satellite
Omnidirectional
Broadcast radio
3 x 1011 to 2 x 1014


Infrared
Local
Antennas


Electrical conductor (or system of..) used to radiate
electromagnetic energy or collect electromagnetic
energy
Transmission





Reception




Radio frequency energy from transmitter
Converted to electromagnetic energy
By antenna
Radiated into surrounding environment
Electromagnetic energy impinging on antenna
Converted to radio frequency electrical energy
Fed to receiver
Same antenna often used for both
Radiation Pattern
Power radiated in all directions
 Not same performance in all
directions
 Isotropic antenna is (theoretical) point
in space

Radiates in all directions equally
 Gives spherical radiation pattern

Parabolic Reflective Antenna


Used for terrestrial and satellite microwave
Parabola is locus of point equidistant from a line and
a point not on that line



Revolve parabola about axis to get paraboloid



Cross section parallel to axis gives parabola
Cross section perpendicular to axis gives circle
Source placed at focus will produce waves reflected
from parabola in parallel to axis


Fixed point is focus
Line is directrix
Creates (theoretical) parallel beam of
light/sound/radio
On reception, signal is concentrated at focus, where
detector is placed
Parabolic Reflective Antenna
Antenna Gain





Measure of directionality of antenna
Power output in particular direction
compared with that produced by isotropic
antenna
Measured in decibels (dB)
Results in loss in power in another direction
Effective area relates to size and shape

Related to gain
Terrestrial Microwave
Parabolic dish
 Focused beam
 Line of sight
 Long haul telecommunications
 Higher frequencies give higher data
rates

Satellite Microwave



Satellite is relay station
Satellite receives on one frequency,
amplifies or repeats signal and transmits on
another frequency
Requires geo-stationary orbit




Height of 35,784km
Television
Long distance telephone
Private business networks
Satellite Point to Point Link
Satellite Broadcast Link
Broadcast Radio
Omnidirectional
 FM radio
 UHF and VHF television
 Line of sight
 Suffers from multipath interference


Reflections
Infrared
Modulate noncoherent infrared light
 Line of sight (or reflection)
 Blocked by walls
 e.g. TV remote control, IRD port

Wireless Propagation

Signal travels along three routes

Ground wave
• Follows contour of earth
• Up to 2MHz
• AM radio

Sky wave
• Amateur radio, BBC world service, Voice of America
• Signal reflected from ionosphere layer of upper
atmosphere
• (Actually refracted)

Line of sight
• Above 30Mhz
• May be further than optical line of sight due to refraction
• More later…
Ground Wave Propagation
Sky Wave Propagation
Line of Sight Propagation
Refraction

Velocity of electromagnetic wave is a function of density
of material


As wave moves from one medium to another, its speed
changes





Causes bending of direction of wave at boundary
Towards more dense medium
Index of refraction (refractive index) is


~3 x 108 m/s in vacuum, less in anything else
Sin(angle of incidence)/sin(angle of refraction)
Varies with wavelength
May cause sudden change of direction at transition
between media
May cause gradual bending if medium density is varying


Density of atmosphere decreases with height
Results in bending towards earth of radio waves
Optical and Radio Horizons
Line of Sight Transmission

Free space loss



Atmospheric Absorption





Water vapour and oxygen absorb radio signals
Water greatest at 22GHz, less below 15GHz
Oxygen greater at 60GHz, less below 30GHz
Rain and fog scatter radio waves
Multipath





Signal disperses with distance
Greater for lower frequencies (longer wavelengths)
Better to get line of sight if possible
Signal can be reflected causing multiple copies to be
received
May be no direct signal at all
May reinforce or cancel direct signal
Refraction

May result in partial or total loss of signal at receiver
Free
Space
Loss
Multipath Interference
Required Reading

Stallings Chapter 4