Transcript Lecture-03: Antenna Fundamentals

TLEN 5830 Wireless Systems
Lecture Slides
30-August-2016
Primary Overview Topics:
•
•
•
•
•
•
Software Defined Radio architecture (for context)
Finish overview topics
Decibels Review
Complete Signals Overview
SNR: Signal-to-Noise Ratio
Antenna Fundamentals
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Additional reference materials
Required Textbook:
Antennas and Propagation for Wireless Communication Systems, by Simon R.
Saunders and Alejandro Aragon-Zavala, ISBN 978-0-470-84879-1; March 2007
(2nd edition).
Optional References:
Wireless Communications and Networks, by William Stallings, ISBN 0-13040864-6, 2002 (1st edition);
Wireless Communication Networks and Systems, by Corey Beard & William
Stallings (1st edition); all material copyright 2016
Wireless Communications Principles and Practice, by Theodore S. Rappaport,
ISBN 0-13-042232-0 (2nd edition)
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Week
1
Date
08/23/2016
2
08/25/2016
08/30/2016
3
4
5
6
7
8
9
10
11
12
13
14
15
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09/01/2016
09/06/2016
09/08/2016
09/13/2016
09/15/2016
09/20/2016
09/22/2016
09/27/2016
09/29/2016
10/04/2016
10/06/2016
10/11/2016
10/13/2016
10/18/2016
10/20/2016
10/25/2016
10/27/2016
11/01/2016
11/03/2016
11/08/2016
11/10/2016
11/15/2016
11/17/2016
11/29/2016
12/01/2016
12/06/2016
12/08/2016
Topic
Introduction to Communications Systems and Radio
Basics I – Signals fundamentals
Radio Basics II – Physics of Propagation mechanisms &
Antenna fundamentals
Radio Basics III – Antennas fundamentals &
Propagation models
Radio Basics IV – Path Loss Models
SNR / SINR I
SNR / SINR II
Radio Basics V – Signal Encoding
Radio Basics V – Signal Encoding
TEST-01
Sampling Theory and Considerations
IQ signal data
FFT: Fast Fourier Transform I
FFT: Fast Fourier Transform II
Filters: Analog & Digital
Antennas, Cables & Connectors
Microwave & Satellite Components
Digital Modulation I (CDMA, OFDM)
Digital Modulation II (CDMA, OFDM)
Channel Models I
Channel Models II
TEST-02
Channel Statistics I
Channel Statistics II
MIMO and Beamforming I
MIMO and Beamforming II
Link Budgets I
No classes – Fall Break
Link Budgets II
Shannon and Small Cells I
Shannon and Small Cells II
Review
FINAL EXAM
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Software Defined Radio architecture
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Data Communication Terms
• Data - entities that convey meaning, or
information
• Signals - electric or electromagnetic
representations of data
• Transmission - communication of data by the
propagation and processing of signals
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Analog Signals
• A continuously varying electromagnetic wave that
may be propagated over a variety of media,
depending on frequency
• Examples of media:
– Copper wire media (twisted pair and coaxial cable)
– Fiber optic cable
– Atmosphere or space propagation (wireless!)
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Digital Signals
• A sequence of voltage pulses that may be
transmitted over a copper wire medium
• Generally cheaper than analog signaling
• Less susceptible to noise interference
• Suffer more from attenuation
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Wireless Systems focus: Maximize channel capacity
• Impairments, such as noise, limit data rate
that can be achieved
• For digital data, to what extent do
impairments limit data rate?
• Channel Capacity – the maximum rate at
which data can be transmitted over a given
communication path, or channel, under given
conditions
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Signal-to-Noise Ratio: Most important wireless communications metric
• Ratio of the power in a signal to the power contained in
the noise that is present at a particular point in the
transmission
• Typically measured at a receiver
• Signal-to-noise ratio (SNR, or S/N)
signal power
( SNR) dB  10 log 10
noise power
• A high SNR means a high-quality signal, low number of
required intermediate repeaters
• SNR sets upper bound on achievable data rate
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Classifications of Transmission Media
• Transmission Medium
– Physical path between transmitter and receiver
• Guided Media
– Waves are guided along a solid medium
– E.g., copper twisted pair, copper coaxial cable, optical fiber
• Unguided Media
– Provides means of transmission but does not guide
electromagnetic signals
– Usually referred to as wireless transmission
– E.g., atmosphere, outer space
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Unguided Media
• Transmission and reception are achieved by
means of an antenna
• Configurations for wireless transmission
– Directional
– Omnidirectional
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Electromagnetic spectrum of telecommunications
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General Frequency Ranges
• Microwave frequency range
–
–
–
–
1 GHz to 40 GHz
Directional beams possible
Suitable for point-to-point transmission
Used for satellite communications
• Radio frequency range
– 30 MHz to 1 GHz
– Suitable for omnidirectional applications
• Infrared frequency range
– Roughly, 3x1011 to 2x1014 Hz
– Useful in local point-to-point multipoint applications
within confined areas
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Terrestrial Microwave
• Description of common microwave antenna
–
–
–
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Parabolic "dish", 3 m in diameter
Fixed rigidly and focuses a narrow beam
Achieves line-of-sight transmission to receiving antenna
Located at substantial heights above ground level
• Applications
– Long haul telecommunications service
– Short point-to-point links between buildings
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Satellite Microwave
• Description of communication satellite
– Microwave relay station
– Used to link two or more ground-based microwave
transmitter/receivers
– Receives transmissions on one frequency band (uplink),
amplifies or repeats the signal, and transmits it on another
frequency (downlink)
• Applications
– Television distribution
– Long-distance telephone transmission
– Private business networks
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Broadcast Radio
• Description of broadcast radio antennas
– Omnidirectional
– Antennas not required to be dish-shaped
– Antennas need not be rigidly mounted to a precise
alignment
• Applications
– Broadcast radio
• VHF and part of the UHF band; 30 MHZ to 1GHz
• Covers FM radio and UHF and VHF television
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Decibels Review: Why Important
As a signal propagates along a transmission medium, there will be
a loss, or attenuation, of signal strength. It is customary to express
gains, losses, and relative levels in decibels because:
• Signal strength often falls off logarithmically, so loss is easily
expressed in terms of the decibel, which is a logarithmic
unit of measure
• The net gain or loss in the transmission path can be
calculated by simple addition and subtraction
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Decibels Review
Decibels are defined as:
GaindB = GdB = 10 Log10 (Pout/Pin)
NOTE – Decibels in the above formula always represents a Power
Ratio
You can add and subtract dBs to represent just about any power
ratio without resorting to a calculator by remembering the rules:
• Positive dBs mean multiply (or gain).
• Negative dBs mean divide (or attenuate).
• Memorize one dB value!
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Decibels Review
There are only two dB conversions you ever really need:
+3 dB means 2 times bigger (multiply by 2)
+10 dB means 10 times bigger (multiply by 10)
And by corollary:
-3 dB means 2 times smaller (divide by 2)
-10 dB means 10 times smaller (divide by 10)
Now consider the obvious you already know, like 2 x 2 = 4. Since dB’s add for
multiplication, then a gain of 4x means +3 dB +3 dB = +6 dB, a gain of 8x means
+3 dB +3 dB +3 dB = 9 dB. Likewise a gain of 10x is +10 dB and of 100x is +20 dB.
Remember that attenuation (loss) is negative dB’s. So, 1/100th the power would
be -20 dB and 1/1000th the power is -30 dB.
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Decibels Review
You can always make a table like this whenever you need to convert to dBs
Some Examples:
The ratio of 16 times = 2 x 2 x 2 x 2 which is
+3 dB + 3 dB + 3 dB + 3 dB = + 12 dB.
A gain of 500 is simply 1000 divided by 2 or
+30 dB - 3 dB = 27 dB.
1/2000 is - 30 dB – 3 dB = - 33 dB.
-14 dB = -20 dB + 3 dB + 3 dB or -20 dB + 6 dB
which is 1/100 x 4 = 1/25th.
Make up some of your own and test it with a
calculator.
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Decibels Review
When dB’s are absolute values and not ratios:
The use of dBm, dBμ, dBw, etc. is really an abbreviation
An exception to using dB notation for pure ratios is a "shorthand" scheme for
indicating a ratio of power compared to a given defined level.
One example is the common artifice of using a subscript such as dBm to indicate
Power compared to one milliwatt. Therefore, -3dBm means 1/2 of one milliwatt or 3 dB
below 1 milliwatt. Similar notation is used with the Greek letter mu (μ) for dBs
compared to a microwatt, as in 10 dBμ to mean 10 microwatts or 1/100th of a
milliwatt.
Therefore, -20 dBm = +10 dBμ. Get it?
Get used to the above--get really comfortable with dBs--as you will encounter all this
again in Optical Communications, Satellite, and Wireless courses and FOR THE REST OF
YOUR CAREER.
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Decibels Review
Recall that Decibels are defined as:
GdB = 10 Log10 (Pout/Pin)
• If the value of GdB is positive, this represents an actual gain in
power, i.e., a gain of 3 dB means the power has doubled
• If the value of GdB is negative, this represents an actual loss in
power, i.e., a gain of -3 dB means that the power has halved
• Normally this is expressed be saying there is a loss of 3 dB
• We can define a decibel loss, then, as
LdB = -10 Log10 (Pout/Pin)
• We use the above decibel loss form when we discuss path loss
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Antenna Fundamentals
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Antenna Fundamentals
• An antenna is an electrical conductor or
system of conductors
– Transmission - radiates electromagnetic energy
into space
– Reception - collects electromagnetic energy from
space
• In two-way communication, the same antenna
can be used for transmission and reception
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Antenna Radiation Patterns
• Radiation pattern
– Graphical representation of radiation properties of an
antenna
– Depicted as two-dimensional cross section
• Beam width (or half-power beam width)
– Measure of directivity of antenna
• Reception pattern
– Receiving antenna’s equivalent to radiation pattern
• Sidelobes
– Extra energy in directions outside the mainlobe
• Nulls
– Very low energy in between mainlobe and sidelobes
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Antenna Radiation Patterns
Also termed
isotropic
radiation
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Types of Antennas
• Isotropic antenna (idealized)
– Radiates power equally in all directions
• Dipole antennas
– Half-wave dipole antenna (or Hertz antenna)
– Quarter-wave vertical antenna (or Marconi antenna)
• Parabolic Reflective Antenna
• Directional Antennas
– Arrays of antennas
• In a linear array or other configuration
– Signal amplitudes and phases to each antenna are adjusted to
create a directional pattern
– Very useful in modern systems
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Simple Antennas
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Radiation Pattern in Three Dimensions
y
y
x
Side view (xy-plane)
z
z
Side view (zy-plane)
x
Top view (xz-plane)
(a) Simple dipole
y
y
x
Side view (xy-plane)
z
Side view (zy-plane)
(b) Directed antenna
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z
x
Top view (xz-plane)
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Parabolic Reflective Antennas
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Antenna Gain
• Antenna gain
– Power output, in a particular direction, compared
to that produced in any direction by a perfect
omnidirectional antenna (isotropic antenna)
• Effective area
– Related to physical size and shape of antenna
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Antenna Gain
• Relationship between antenna gain and effective
area
G=
•
•
•
•
•
4p Ae
l
2
4p f Ae
2
=
c
2
G = antenna gain
Ae = effective area
f = carrier frequency
c = speed of light 3  108 m/s)
λ = carrier wavelength
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Spectrum Considerations for Signal Transmission
• Controlled by regulatory bodies
– Carrier frequency
– Signal Power
– Multiple Access Scheme
• Divide into time slots –Time Division Multiple Access
(TDMA)
• Divide into frequency bands – Frequency Division
Multiple Access (FDMA)
• Different signal encodings – Code Division Multiple
Access (CDMA)
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Spectrum Considerations for Signal Transmission
• Federal Communications Commission (FCC) in the
United States regulates spectrum
–
–
–
–
–
–
Military
Broadcasting
Public Safety
Mobile
Amateur
Government exclusive, non-government exclusive, or
both
– Many other categories
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Spectrum Considerations for Signal Transmission
• Industrial, Scientific, and Medical (ISM) bands
– Can be used without a license
– As long as power and spread spectrum regulations
are followed
• ISM bands are used for
– WLANs
– Wireless Personal Area networks
– Internet of Things
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Signal Propagation Modes
• Ground-wave propagation
• Sky-wave propagation
• Line-of-sight propagation
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Propagation Modes
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Ground Wave Propagation
• Follows contour of the earth
• Can propagate considerable distances
• Frequencies up to 2 MHz
• Example
– AM radio
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Sky Wave Propagation
• Signal reflected from ionized layer of atmosphere
back down to earth
• Signal can travel a number of hops, back and forth
between ionosphere and earth’s surface
• Reflection effect caused by refraction
• Examples
– Amateur radio
– CB radio
– AM radio at night
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Line-of-Sight Propagation
• Transmitting and receiving antennas must be within line
of sight
– Satellite communication – signal above 30 MHz not reflected by
ionosphere
– Ground communication – antennas within effective line of site
due to refraction
• Refraction – bending of microwaves by the atmosphere
– Velocity of electromagnetic wave is a function of the density of
the medium
– When wave changes medium, speed changes
– Wave bends at the boundary between mediums
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Line-of-Sight Equations
• Optical line of sight
d  3.57 h
• Effective, or radio, line of sight
d  3.57 h
• d = distance between antenna and horizon (km)
• h = antenna height (m)
• K = adjustment factor to account for refraction, rule
of thumb K = 4/3
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Optical and Radio Horizons
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Line-of-Sight Equations
• Maximum distance between two antennas for
LOS propagation:

3.57 h1  h2

• h1 = height of first antenna
• h2 = height of second antenna
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Basic Propagation Mechanisms
1. Free-space propagation
2. Transmission
– Through a medium
– Refraction occurs at boundaries
3. Reflections
– Waves impinge upon surfaces that are large compared to the
signal wavelength
4. Diffraction
– Secondary waves behind objects with sharp edges
5. Scattering
– Interactions between small objects or rough surfaces
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Antenna Fundamentals
• An antenna is an electrical conductor or
system of conductors
– Transmission - radiates electromagnetic energy
into space
– Reception - collects electromagnetic energy from
space
• In two-way communication, the same antenna
can be used for transmission and reception
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Antenna Radiation Patterns
• Radiation pattern
– Graphical representation of radiation properties of an
antenna
– Depicted as two-dimensional cross section
• Beam width (or half-power beam width)
– Measure of directivity of antenna
• Reception pattern
– Receiving antenna’s equivalent to radiation pattern
• Sidelobes
– Extra energy in directions outside the mainlobe
• Nulls
– Very low energy in between mainlobe and sidelobes
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Attenuation
• Strength of signal falls off with distance over
transmission medium
• Attenuation design factors for unguided media:
– Received signal must have sufficient strength so that
circuitry in the receiver can interpret the signal
– Signal must maintain a level sufficiently higher than noise
to be received without error
– Attenuation is greater at higher frequencies, causing
distortion
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Free Space Loss
• Free space loss, ideal isotropic antenna
Pt
Pr
4p d ) ( 4p fd )
(
=
=
2
l2
2
c2
• Pt = signal power at transmitting antenna
• Pr = signal power at receiving antenna
• λ = carrier wavelength
• d = propagation distance between antennas
• c = speed of light 3 ×108 m/s)
where d and λ are in the same units (e.g., meters)
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Free Space Loss
• Recall we defined a decibel loss via the equation
LdB = -10 Log10 (Pout/Pin) = 10 Log10 (Pin/Pout)
• We can recast the free space loss equation then as:
Pt
æ 4pd ö
LdB = 10log = 20log ç
Pr
è l ÷ø
 20 log    20 log d   21.98 dB
 4fd 
 20 log 
  20 log  f   20 log d   147.56 dB
 c 
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Free Space Loss
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Path Loss Exponent in practical
systems
• Practical systems – reflections, scattering, etc.
• Beyond a certain distance, received power
decreases logarithmically with distance
– Based on many measurement studies
2
2
Pt æ 4p ö n æ 4pf ö n
=ç ÷ d =ç
d
÷
Pr è l ø
è c ø
LdB = 20log ( f ) +10nlog ( d ) -147.56 dB
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Path Loss Exponent in practical
systems
Table 5.1 Path Loss Exponents for Different Environments [RAPP02]
Environment
Free space
Path Loss Exponent, n
2
Urban area cellular radio
2.7 to 3.5
Shadowed cellular radio
3 to 5
In building line-of-sight
1.6 to 1.8
Obstructed in building
4 to 6
Obstructed in factories
2 to 3
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Models Derived from Empirical
Measurements
• Need to design systems based on empirical data applied to
a particular environment
– To determine power levels, tower heights, height of mobile
antennas
• Okumura developed a model, later refined by Hata
– Detailed measurement and analysis of the Tokyo area
– Among the best accuracy in a wide variety of situations
• Predicts path loss for typical environments
–
–
–
–
–
Urban
Small, medium sized city
Large city
Suburban
Rural
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Categories of Noise
•
•
•
•
Thermal Noise
Intermodulation noise
Crosstalk
Impulse Noise
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Thermal Noise
• Thermal noise due to agitation of electrons
• Present in all electronic devices and
transmission media
• Cannot be eliminated
• Function of temperature
• Particularly significant for satellite
communication
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Noise Terminology
• Intermodulation noise – occurs if signals with
different frequencies share the same medium
– Interference caused by a signal produced at a frequency
that is the sum or difference of original frequencies
• Crosstalk – unwanted coupling between signal paths
• Impulse noise – irregular pulses or noise spikes
– Short duration and of relatively high amplitude
– Caused by external electromagnetic disturbances, or faults
and flaws in the communications system
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EXPRESSION Eb/N0
• Ratio of signal energy per bit to noise power density
per Hertz
Eb S / R
S


N0
N0
kTR
• The bit error rate (i.e., bit error probability) for digital
data is a function of Eb/N0
– Given a value for Eb/N0 to achieve a desired error rate,
parameters of this formula can be selected
– As bit rate R increases, transmitted signal power must
increase to maintain required Eb/N0
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5.4 GENERAL SHAPE OF BER VERSUS Eb/N0 CURVES
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Other Impairments
• Atmospheric absorption – water vapor and
oxygen contribute to attenuation
• Multipath – obstacles reflect signals so that
multiple copies with varying delays are
received
• Refraction – bending of radio waves as they
propagate through the atmosphere
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Antennas
• Transmission Medium
– Physical path between transmitter and receiver
• Guided Media
– Waves are guided along a solid medium
– E.g., copper twisted pair, copper coaxial cable, optical fiber
• Unguided Media
– Provides means of transmission but does not guide
electromagnetic signals
– Usually referred to as wireless transmission
– E.g., atmosphere, outer space
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Additional reference materials
Required Textbook:
Antennas and Propagation for Wireless Communication Systems, by Simon R.
Saunders and Alejandro Aragon-Zavala, ISBN 978-0-470-84879-1; March 2007
(2nd edition).
Optional References:
Wireless Communications and Networks, by William Stallings, ISBN 0-13040864-6, 2002 (1st edition);
Wireless Communication Networks and Systems, by Corey Beard & William
Stallings (1st edition); all material copyright 2016
Wireless Communications Principles and Practice, by Theodore S. Rappaport,
ISBN 0-13-042232-0 (2nd edition)
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