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1/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
R O U P EG
Microwave radio
Microwave radio
A very brief history of microwavesIntroductionPropagation
Digital codingSystems
2/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
R O U P EG
Microwave radio
1. A very brief history of microwaves
3/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Theoretical foundation
� Maxwell 1831-1879– light consists of transverse
undulations of the same medium which is the cause of electric and magnetic phenomena: "On aDynamical Theory of the Electromagnetic Field" (1865).
– formulation of electricity and magnetism: « A Treatise onElectricity and Magnetism » (1873),which included the formulas today known as the Maxwell equations that implicitly required the existence of electromagnetic waves traveling at the speed of light.
4/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
First experimental proof
� Hertz 1857 – 1894– He proved experimentally the
existence of electromagnetic waves (1888)
– a wire connected to an induction coil produces the waves and induced current produced a spark across a small loop of wire
– he showed his electromagnetic waves to have analogous propertiesas light.
5/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
First commercial exploitation
� Marconi 1874 – 1937– In 1895 he began laboratory
experiments and succeeded insending wireless signals over a distance of one and a half miles
– In 1899 he established wirelesscommunication between Franceand England across the EnglishChannel
– He obtained the first patent inthe history of radio (1900)
– On December 12, 1901, he sent a radio signal across the Atlantic (2100 miles)
– Nobel Prize in physics (1909)
6/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
2. Introduction
7/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Wavelength
� Wavelength is the distance between identical points in the adjacent cycles of a waveform. In wireless systems, this length is usually specified in meters, centimeters, or millimeters
� The size of the wavelength varies depending on the frequency of the signal. Generally speaking, the higher the frequency the smaller the wavelength
� Wavelength is of great interest for antenna dimensioning and positionning
300m
MHZ
cf f
λ = =
At 10 GHz, λ = 3 cmAt 1 GHz, λ = 30 cmAt 100 MHz, λ = 3 mAt 10 MHz, λ = 30 m
…
8/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Frequency
� Frequency is the number of complete cycles per second in alternating current direction. The standard unit of frequency is the hertz, abbreviated Hz. If a current completes one cycle per second, then the frequency is 1 Hz.
� 103 = Kilohertz (kHz)� 106 = Megahertz (MHz)� 109 = Gigahertz (GHz)� 1012 = Terahertz (THz)
9/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Power units
10/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Path loss in dB
11/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
dBm
12/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
What is Spectrum ? (1/8)
� The Electromagnetic Spectrum– A continuum of all electromagnetic waves arranged according
to frequency and wavelength– Electromagnetic waves:
• Vibrations of electric and magnetic fields that travel through space.
• The electrical fields and magnetic fields are coupled together but are perpendicular to each other and to the direction of the wave.
– Same frequency and phase• Mostly invisible except for the visible spectrum • Speed of light (c = 3 x 108m/s (vacuum)) (light is EM)• Sinusoidal waves• Do not need molecules to transmit energy. Can travel through air,
solid materials and empty space.
13/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
What is Spectrum ? (2/8)
� Electromagnetic Wave
14/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
What is Spectrum ? (3/8)
� The Electromagnetic Spectrum– Can be described in terms of wavelength, frequency
and energy– These terms are all related mathematically– Use most convenient units– For example:
• Radio waves - frequency• Light - wavelength• X-rays - energy
15/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
What is Spectrum ? (4/8)
� Electromagnetic Spectrum – Radio spectrum (a.k.a. RF) (frequency)– Microwave (frequency)– Infrared– Visible Spectrum– Ultraviolet– X-rays – Gamma-Rays
16/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
What is Spectrum ? (5/8)
17/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
What is Spectrum ? (6/8)Ultra-low frequency (ULF)
Extremely Low Frequency (ELF)Voice Frequencies
Very Low Frequency (VLF)Low Frequency (LF)
Medium Frequency (MF)
High Frequency (HF)
Very High Frequency (VHF)
Ultra High Frequency (UHF)
Super High Frequency (SHF)
Extremely High Frequency (EHF)
3-30 Hz30 – 300 Hz
300 Hz – 3 kHz3 – 30 kHz
30 – 300 kHz300 kHz – 3 MHz
3 – 30 MHz
30 – 300 MHz
300 MHz – 3 GHz
3 – 30 GHz
30 – 300 GHz
AM Broadcast
Microwave RelayEarth-Satellite
RadarMobile Radio
AeronauticalNavigation
NavigationSatellite
UHF TelevisionMobile Radio
VHF Television FM BroadcastMobile Radio Aeronautical
Amateur radioInternational radio
Citizen band
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Microwave radio
What is Spectrum ? (7/8)
19/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
What is Spectrum ? (8/8)
20/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Relationship between Data Rate and Bandwidth
� The greater the bandwidth, the higher the information-carrying capacity
� Hints– Any digital waveform will have infinite bandwidth– BUT the transmission system will limit the bandwidth
that can be transmitted– AND, for any given medium, the greater the
bandwidth transmitted, the greater the cost– HOWEVER, limiting the bandwidth creates
distortions
21/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Reasons for Choosing Data and Signal Combinations
� Digital data, digital signal– Equipment for encoding is less expensive than digital-to-
analog equipment� Analog data, digital signal
– Conversion permits use of modern digital transmission and switching equipment
� Digital data, analog signal– Some transmission media will only propagate analog
signals– Examples include optical fiber and satellite
� Analog data, analog signal– Analog data easily converted to analog signal
22/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Analog Transmission
� Transmit analog signals without regard to content
� Attenuation limits length of transmission link � Cascaded amplifiers boost signal’s energy for
longer distances but cause distortion– Analog data can tolerate distortion– Introduces errors in digital data
23/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Digital Transmission
� Concerned with the content of the signal� Attenuation endangers integrity of data� Digital Signal
– Repeaters achieve greater distance– Repeaters recover the signal and retransmit
� Analog signal carrying digital data– Retransmission device recovers the digital data from
analog signal– Generates new, clean analog signal
24/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
About 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
25/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Concepts Related to Channel Capacity
� Data rate - rate at which data can be communicated (bps)
� Bandwidth - the bandwidth of the transmitted signal as constrained by the transmitter and the nature of the transmission medium (Hertz)
� Noise - average level of noise over the communications path
� Error rate - rate at which errors occur– Error = transmit 1 and receive 0; transmit 0 and
receive 1
26/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Nyquist Bandwidth
� For binary signals (two voltage levels)– C = 2B
� With multilevel signaling– C = 2B log2 M
• M = number of discrete signal or voltage levels
27/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Signal-to-Noise Ratio
� Ratio of the power in a signal to the power contained in the noise that’s present at a particular point in the transmission
� Typically measured at a receiver� Signal-to-noise ratio (SNR, or S/N)
� A high SNR means a high-quality signal, low number of required intermediate repeaters
� SNR sets upper bound on achievable data rate
power noisepower signal
log10)( 10dB =SNR
28/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Shannon Capacity Formula
� Equation:
� Represents theoretical maximum that can be achieved
� In practice, only much lower rates achieved– Formula assumes white noise (thermal noise)– Impulse noise is not accounted for– Attenuation distortion or delay distortion not
accounted for
( )SNR1log2 += BC
29/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Example of Nyquist and Shannon Formulations
� Spectrum of a channel between 3 MHz and 4 MHz ; SNRdB = 24 dB
� Using Shannon’s formula
( )251SNR
SNRlog10dB 24SNRMHz 1MHz 3MHz 4
10dB
===
=−=B
( ) Mbps88102511log10 62
6 =×≈+×=C
30/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Example of Nyquist and Shannon Formulations
� How many signaling levels are required?
( )
16
log4
log102108
log2
2
266
2
==
××=×
=
M
M
M
MBC
31/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
3. Propagation
32/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
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
33/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Twisted Pair Wire
� Two or more pairs of single conductor wires that have been twisted around each other.
� Twisted pair wire is classified by category. Twisted pair wire is currently Category 1 through Category 5e.
� Twisting the wires helps to eliminate electromagnetic interference between the two wires.
� Shielding can further help to eliminate interference.
34/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Coaxial Cable
� A single wire wrapped in a foam insulation surrounded by a braided metal shield, then covered in a plastic jacket. Cable can be thick or thin.
– Baseband coaxial technology uses digital signaling (DC) in which the cable carries only one channel of digital data.
– Broadband coaxial technology transmits analog signals (RF) and is capable of supporting multiple channels of data.
35/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Fiber Optic Cable
� A thin glass cable approximately a little thicker than a human hair surrounded by a plastic coating and packaged into an insulated cable.
� A photo diode or laser generates pulses of light which travel down the fiber optic cable and are received by a photo receptor.
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Microwave radio
Mixing Media
37/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Unguided Media
� Transmission and reception are achieved by means of an antenna
� Configurations for wireless transmission– Directional – Omnidirectional
38/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
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
39/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Terrestrial Microwave
� Description of common microwave antenna– 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
40/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
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
41/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
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
42/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Broadcast
� Guided propagation– Immunity to
interferences and noise– Quality of reception– Wide frequency band– No antenna
� Free space propagation– Free space propagation is
naturally omni-directional– Infinite number of receivers– Large area coverage
Attenuation(dB)
Guided propagation
Radio propagation
Distance (m)
43/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Point to point
� Guided propagation– Well known medium– Easy frequency reuse
with a new medium– Length and density are
not limited by interferences
– Confidential communications
– Long life
� Free space propagation– Communications possible
with difficult access area– Temporary communications
are possible– Quasi ready-to-use– Cost in quasi independant
of bandwith
44/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
R O U P EG
Microwave radio
Multiplexing
� Capacity of transmission medium usually exceeds capacity required for transmission of a single signal
� Multiplexing - carrying multiple signals on a single medium– More efficient use of transmission medium
45/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Multiplexing
46/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Reasons for Widespread Use of Multiplexing
� Cost per kbps of transmission facility declines with an increase in the data rate
� Cost of transmission and receiving equipment declines with increased data rate
� Most individual data communicating devices require relatively modest data rate support
47/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Multiplexing Techniques
� Frequency-division multiplexing (FDM)– Takes advantage of the fact that the useful
bandwidth of the medium exceeds the required bandwidth of a given signal
� Time-division multiplexing (TDM)– Takes advantage of the fact that the achievable bit
rate of the medium exceeds the required data rate of a digital signal
� Code-division multiplexing (CDM)– Takes advantage of the fact that each individual
communication is below the noise floor
48/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
FDMA-TDMA-CDMA
49/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Free space vs transmission line propagation
Guided propagation
Free space propagation
Increase with d
Increase with f1/2
Distance (d)
Frequency (f)
Increase with d2
Increase with f2
50/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Wired technology
� Advantages– High-quality 2-way Hybrid Fiber Coaxial (HFC) Networks– Data Networking Infrastructure: Routers, Routing
Switches, Switches, Servers, Network Management Systems, Cable Modem Internet Connectivity
– Serve Thousands of Broadband Internet Subscribers
� Disadvantages– High Cost
Broadband Internet Connection over a Cable Network
51/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Wireless technology (1/2)
Broadband Fixed Wireless Systems Operate at Different Frequencies
Multichannel Multipoint Distribution System (MMDS)
� 1-way Video Broadcast Service� Operates at 2 GHz
Microwave Video Distribution System (MVDS)
Local Multipoint Distribution System (LMDS)
� Undergo Technical Trials� Operate at 12GHz and 42 GHz
� Operates at 26 - 31 GHz
52/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Wireless technology (2/2)
� Advantages– Lower Cost of Deployment– Lower Cost of Network Maintenance, Management
and Operating Costs– Easier to Adapt to Changing Market Conditions
53/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Media Selection Criteria
� Speed:– What level of data transfer do we need (10Mbps-
100Mbps+)?� Cost:
– What can we afford (cat5e relatively inexpensive)?� Distance and expandability� Environment:
– What is the noise level?� Security/encryption:
– Possibility of wiretapping/“hot spots”?
54/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Radio Propagation modes
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Microwave radio
Fading
� Fade duration TD
� Fade occurrence interval TI
� Defined at the signal level Rp that is exceeded P(%) ofthe time.
56/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Radio path planning design (1/2)
1. Select the most direct route using survey maps. If possible inspect the terrain (by air!) for possible obstacles
2. Break route into sections approximately 40-50km long. A zigzag path may be required to avoid interference.Locate repeaters so as to use vantage points such ashills or tall buildings.
3. For each hop, plot the profile of the terrain taking elevations from a contour map. Remember to take into account unmarked obstructions such as buildings and forests.
http://ludo.ece.jcu.edu.au/subjects/ee3710/notes/Propagation.PDF
57/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Radio path planning design (2/2)
4. Select antenna heights and superimpose the beam profileand the 1st Fresnel zone on the terrain profile.
5. Inspect the path profile for obstructions and repeat step 4until the first Fresnel zone or at least 0.6 of it is clear. Ifthe path remains obstructed calculate additional losses expected.Ensure the selected antenna heights do notleads to severe fading under varying conditions. Forexample, could there be reflections from the earth, will trees grow so as to obstruct the path?
6. Determine total path losses and assign a fading margin.From the specified system signal-to-noise ratio Determine the antenna gains and the transmitter power.
http://ludo.ece.jcu.edu.au/subjects/ee3710/notes/Propagation.PDF
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Free space propagation (1/4)
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Microwave radio
Free space propagation (2/4)
� Assumptions: isotropic antennas (homogeneouspropagation in all directions)
� PT = power radiated� Power density
� Field strength
Tx
Rx
( )22 W/m
4TP
PDdπ
= d
( )120 V/mFS PDπ=
60/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Free space propagation (3/4)
� Received power depends on effective aperture of receiving antenna
� For the hypothetical isotropic receiving antenna
� Free space loss equation
� Free space losses
( )WR effP PD A= ⋅
2
4effAλπ
=
( )2 2
2 24W
4R T TP P P f dd c
λ ππ
� � � �= =� � � �� � � �
10 1032.44 20log ( ) 20 log ( )(dB)MHz kmFSL f d= + +
61/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Free space propagation (4/4)
� Free space losses increase with the distance– Radiated power is
spread on the surface of a sphere with increasing radius
� Free space losses increase with thefrequency– Receiving antenna
effective aperture decreases with frequency
� But, antenna directivity gain increases…
Loss (dB)
Distance (m)
62/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Free Space Losses Calculations
� Hertzian Link– 40 km @ 3.5 GHz
� Spatial Link– 36000 km @ 12 GHz
� GSM Link– 5 km @ 900 MHz
� UMTS Link– 500 m @ 2 GHz
135.4 dB
205.1 dB
105.5 dB
92.44 dB
63/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Propagation Mechanisms
� Reflection– Propagating wave impinges on an object which is large
compared to wavelength– E.g., the surface of the Earth, buildings, walls, etc.
� Diffraction– Radio path between transmitter and receiver obstructed by
surface with sharp irregular edges– Waves bend around the obstacle, even when LOS does not
exist� Scattering
– Objects smaller than the wavelength of the propagating– wave– E.g., foliage, street signs, lamp posts
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2nd*2nd* 1st*1st*3rd*3rd*
* * FresnelFresnelZonesZones
Fresnel Zones
65/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
• Fresnel Zone diameter depends upon Wavelength, and Distances from the sites along axis
• For minimum Diffraction Loss, clearance of at least 0.6F1 is required
Radius of n th
Fresnel Zone given by:
21
21
dd
ddnrn+
= λ
The First Fresnel Zone
Site A
Site Bd2
d1
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The Path Profile (1/3)
Path Profile characteristics may change over time, due to vegetation, building construction, etc.
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The Path Profile (2/3)
See calculations on next slide…
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The Path Profile (3/3)
� d1 = 4 km� d2 = 33.6 km� f = 6 GHz� λ = 5 cm
1 21
1 2
13.4 md d
rd dλ= =
+
d1 d2
60% clearance of F1 = 8 m
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Path loss
Received power = K d-n
n = 2 for free space propagation2 < n < 4 for practical cases
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Long term propagation modes
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Short term propagation modes
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Line of sight : radio horizon
� Radio horizon: The locus of points at which direct raysfrom a point source of radiowaves are tangential to thesurface of the Earth.
� Radio waves go behind the geometrical horizon due to refraction in the air
Approximate distance 17 17km Tx Rxd h h= +
73/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Radio Horizon Calculation
� hTx = 60 m� hRx = 60 m
� Radio Horizon is about 64 km
� Geometrical Horizon is about 55 km– r = 6368 km (earth radius)– h = tower height
2 2( )GH r h r= + −
74/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Diffraction
� Caused by obstacles in or near path� Examples: buildings, hills� Can cause destructive interference which
weakens received signal
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Multipath
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Atmospheric Attenuation (1/2)
� attenuation caused by atmospheric gases� note molecular resonance peaks
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Atmospheric Attenuation (2/2)
� attenuation caused by rain� can increase path loss by an order of magnitude (
10 x)
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ITU North American rain zones
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ITU European rain zones
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Rainfall effects
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Parameters affecting propagation
� Free space parameters– Frequency (GHz)– Path Length (km)– Excess attenuation due to water vapor– Excess attenuation due to mist and fog– Excess attenuation due to Oxygen– Gaseous loss– Excess attenuation due to rainfall
� Others– Trees, Buildings, Terrain and other blockage
82/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Example of total excess attenuation (LMDS)
� a = excess attenuation in dB due to water vapor
– 0.08 dB/km at sea level and 15degrees C (7.5 g/m3)
� b = excess attenuation in dB due to mist/fog
– 0.1 dB/km
� c = excess attenuation in dB due to Oxygen
– 0.02 dB/km at sea level and 15degrees C
� d = absorption losses due toother gases
– 0.08 dB/km
� e = excess attenuation due torain
– 3.67 dB/km for Dallas-Houston, Vertical Polarization, 99.9Avail.
– = 2.0 dB/km for Chicago, Vertical Polarization, 99.9Avail.
Total = 3.95 dB/km (Dallas-Houston)
Total = 2.28 dB/km (Chicago)
83/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Basic link budget (1/5)
Coverage radius = 2.3 kmRain zone = KHorizontal polarization41 GHz band with a 99,985 % availability.
AP antenna gain: 18 dBi ± 1 dB(90° sector antenna)
AT antenna gain: 37 dBi ± 1 dB(30 cm diameter antenna)
84/144 D. Courivaud, Groupe ESIEE, Paris, May 2004
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Microwave radio
Basic link budget (2/5)
� Rain attenuation = 23 dB– ITU-R Recommendation P.530-6– ITU-R Recommendation P.838– ITU-R Recommendation P.837-1
� Free space loss = 133.1 dB� Antenna gain = 55 dB
Required system gain (@ 99,985 %)= Rain attenuation + Free space loss - Antenna gain
= 101.1 dB.
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Basic link budget (3/5)
� BER = 10-6 for link availability� BER = 10-11 for link quality.� Receiver sensitivity
– ∆loss includes all implementation losses– Rxloss is the receiver branching loss
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Basic link budget (4/5)
PHY C/N dB(BER=10-6) 10-6 10-11
Prx @ 28 GHzdBm
10-6 10-11
Prx @ 32 GHzdBm
10-6 10-11
Prx @ 42 GHzdBm
QAM4 5 -88 -87 -87 -86 -86 -85
QAM16 18 -75 -74 -74 -73 -73 -72
QAM64 25 -66 -65 -65 -64 -64 -63
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Basic link budget (5/5)
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Sources of Interference
� Intra-System Interference– Multipath– Cross Polarization Component– Adjacent Channel Interference– Co-channel Interference
� Inter-System Interference– Satellite Systems– Other Systems– Out-of-Band Interference
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Interference Mitigation (Intra-System) (1/2)
� Multi-Path– Use Highly Directional Antennas– Give Careful Consideration to Placement of Antennas– Use antennas with low side lobes for CPE– Use robust modulation and error correction techniques
� Cross Polarization– Major factor for systems which exploit polarization at same
base– station for frequency reuse--need antennas with good cross-pol– Minor problem for systems which use polarization for separating– base stations– Use robust modulation and error correction techniques
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Interference Mitigation (Intra-System) (2/2)
� Adjacent Channel– Use constant envelope modulation– Use linear power amplifiers– Use robust modulation and error correction techniques
� Co-Channel Interference– Use highly directional antennas with low side lobes for CPE– Deploy base stations with maximum separation distance for
same– frequency, same polarization– Use minimum transmit power; control TX power on return path– Use robust modulation and error correction techniques– Use adaptive interference suppression techniques
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Interference Mitigation (Inter-System)
� Use highly directional antennas with low side lobes� Use high-dynamic range LNA’s and first mixers� Develop standards for coexistence� Employ low LO leakage designs in TX and RX circuits� Develop adequate image rejection receivers� Employ filtering at MMW frequencies� Use linear Power Amplifiers� Use constant envelope modulation
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Frequency Diversity (1/2)
� Use two transmitters and two receivers operating at different frequencies, preferably separated by at least 5%.
� Phase relationship between direct and reflected path will be different at the two frequencies
� Also provides a redundant system in case of equipment failure (“hot standby”)
� Disadvantage: uses twice the bandwidth
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Frequency Diversity (2/2)
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Space Diversity (1/2)
� Use two receiving antennas separated in space (preferably by 200 wavelengths or more, though less separation is often used)
� Path length will be different to the two antennas, so cancellation is unlikely over both paths
� Needs larger towers, but does not require increased bandwidth
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Space Diversity (2/2)
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4. Digital coding
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Digital Coding
� Character: A symbol that has a common, constant meaning.
� Characters in data communications, as in computer systems, are represented by groups of bits [1’s and 0’s].
� The group of bits representing the set of characters in the “alphabet” of any given system are called a coding scheme, or simply a code.
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Digital Coding
� A byte consists of 8 bits that is treated as a unit or character. (Some Asian languages use 2 bytes for each of their characters, such as Chinese.)
� (The length of a computer word could be 1, 2, 4 bytes.)� There are two predominant coding schemes in use
today:� United States of America Standard Code for Information
Interchange (USASCII or ASCII) � Extended Binary Coded Decimal Interchange Code
(EBCDIC)
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Advantages of Digital Transmission
� The signal is exact� Signals can be checked for errors� Noise/interference are easily filtered out� A variety of services can be offered over one
line� Higher bandwidth is possible with data
compression
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Why Use Analog Transmission?
� Already in place� Significantly less expensive� Lower attenuation rates� Fully sufficient for transmission of voice signals
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Analog Encoding of Digital Data
� Data encoding and decoding technique to represent data using the properties of analog waves
� Modulation: the conversion of digital signals to analog form
� Demodulation: the conversion of analog data signals back to digital form
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Methods of Modulation
� Amplitude modulation (AM) or amplitude shift keying (ASK)
� Frequency modulation (FM) or frequency shift keying (FSK)
� Phase modulation or phase shift keying (PSK) � Differential Phase Shift Keying (DPSK)
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Amplitude Shift Keying (ASK)
� In radio transmission, known as amplitude modulation (AM)
� The amplitude (or height) of the sine wave varies to transmit the ones and zeros
� Major disadvantage is that telephone lines are very susceptible to variations in transmission quality that can affect amplitude
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Amplitude Modulation and ASK
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Frequency Shift Keying (FSK)
� In radio transmission, known as frequency modulation (FM)
� Frequency of the carrier wave varies in accordance with the signal to be sent
� Signal transmitted at constant amplitude� More resistant to noise than ASK� Less attractive because it requires more
analog bandwidth than ASK
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Frequency Modulation and FSK
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Phase Modulation
� Frequency and amplitude of the carrier signal are kept constant
� The carrier signal is shifted in phase according to the input data stream
� Each phase can have a constant value, or value can be based on whether or not phase changes (differential keying)
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Phase Modulation and PSK
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Microwave radio
Differential Phase Shift Keying (DPSK)
0 1 1 0
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PSK constellation
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Analog Channel Capacity: BPS vs. Baud
� Baud=# of signal changes per second. ITU-T now recommends the term baud rate be replaced by the term symbol rate.
� BPS=bits per second� In early modems only, baud=BPS. The bit rate and the
symbol rate (or baud rate) are the same only when one bit is sent on each symbol.
� Each signal change can represent more than one bit, through complex modulation of amplitude, frequency, and/or phase
� Increases information-carrying capacity of a channel without increasing bandwidth
� Increased combinations also leads to increased likelihood of errors
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Sending Multiple Bits Simultaneously
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Sending Multiple Bits Simultaneously
� In practice, the maximum number of bits that can be sent with any one of these techniques is about five bits. The solution is to combine modulation techniques.
� One popular technique is quadrature amplitude modulation (QAM) involves splitting the signal into eight different phases, and two different amplitude for a total of 16 different possible values.
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The 4-PSK method
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The 4-PSK characteristics
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Microwave radio
Time domain for an 8-QAM signal
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Microwave radio
The 4-QAM and 8-QAM constellations
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Sending Multiple Bits Simultaneously
� Trellis coded modulation (TCM) is an enhancement of QAM that combines phase modulation and amplitude modulation. It can transmits different numbers of bits on each symbol (6-10 bits per symbol).
� The problem with high speed modulation techniques such as TCM is that they are more sensitive to imperfections in the communications circuit.
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16-QAM constellations
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Modem
� An acronym for modulator-demodulator� Uses a constant-frequency signal known as a
carrier signal� Converts a series of binary voltage pulses into
an analog signal by modulating the carrier signal
� The receiving modem translates the analog signal back into digital data
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Digital Transmission of Analog Data
� Codec = Coder/Decoder� Converts analog signals into a digital form and
converts it back to analog signals� Where do we find codecs?
– Sound cards– Scanners– Voice mail– Video capture/conferencing
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Codec vs. Modem
� Codec is for coding analog data into digital form and decoding it back. The digital data coded by Codec are samples of analog waves.
� Modem is for modulating digital data into analog form and demodulating it back. The analog symbols carry digital data.
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Digital Encoding of Analog Data
� Primarily used in retransmission devices� The sampling theorem: If a signal is sampled at
regular intervals of time and at a rate higher than twice the significant signal frequency, the samples contain all the information of the original signal.
� Pulse-code modulation (PCM)– 8000 samples/sec sufficient for 4000hz
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5. Communication systems
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Fixed Wireless - Broadband
� MMDS: Multi-channel multi-point distribution service at 2.5 GHz
� Point-to-point wireless broadband at greater than 18 GHz
� LMDS: Local multi-point distribution service at 28 GHz
Note: Cell size for low frequency solutions are large,while cell size for high frequency solutions are small
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Frequency spectrum
1 GHz 2.5 3.5 5.8 10 24 26 28 38 40 60
LOSLOS
5000200013501000400 30020020 30
Voice, Data, Fax,
ISDN
256 Kbps256 Kbps
1 to 501 to 50MbpsMbps
+ TDMLeased Lines
Ban
dwid
th(M
Hz)
1400200
100
+ High SpeedInternet and Multimedia
+ UltraHigh-SpeedLAN/WAN
No LOSNo LOS
10 to 10010 to 100MbpsMbps
>100 Mbps>100 Mbps
LMDSMMDS UNII
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Cost per suscriber
CPE Cost
���
�� �
# of Subscribers
Cos
t Per
Sub
scr i
ber
This is the point at which PMP becomes more economically viable than
a PTP network, generally ~8 links.
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Reach Distance From Hub
Point-to-Point Links Point-to-Multipoint
28 GHz
38 GHz
5.34 6.92
Reach Distance, Km
3.577.5 5.0
2.5 GHz
20.050.0
23 GHz
6 GHz
28 GHz
2.5 GHz
40
24 GHz
2.5 GHz
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MMDS, MVDS (1/3)
MMDS, MVDS2,5 GHz, 40 GHz
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MMDS, MVDS (2/3)
� Multichannel Multipoint Distribution Service (MMDS)� A cost-effective, wireless alternative to digital subscriber
lines (DSL) and cable modem service for delivering broadband wireless access (BWA) to the last mile (> T1 connexion)
� MMDS uses licensed microwave frequencies in the 2.1 GHz to 2.7 GHz band
� MMDS is less affected by weather and can deliver reliable service up to a 25 mile radius under line-of-sight (LOS) conditions
� MMDS offers physical layer technologies for next generation broadband wireless access.
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MMDS, MVDS (3/3)
� Start with very large cells and expand capacity with cell splitting and antennas on CMRS towers
� Originally used for analog wireless cable– One way broadcast video of up to 28 channels– Up to 168 MHz of spectrum– Up to 25 miles coverage from one antenna
� In the USA, FCC modified rules to increase competition– Two way digital services allowed– Use for video, data, or voice telephony– Allow point-to-multipoint operation
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PMP
2 Mbit/s
broadband PMP3,5 GHz, 10,5 GHz, 26 GHz
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Point to multipoint
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LMDS
1 Mbit/s
LMDS28 GHz, 40 GHz
25-50 Mbit/s
n*2 Mbit/s
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LMDS
� Use Millimeter-wave Signals� Can be used for voice, data, and/or video� Intended for point-to-multipoint operation, but early
implementations have been PTP� Much smaller cells than MMDS (3-10 miles in diameter)� Unlikely for residential video / telephony because of high
cost & line-of-sight issues� Likely use is DS3 to business customer� Travel through Copper Wire, Co-axial Cable,
CAT5
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LMDS concept
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LMDS & MMDS COMPARISON
Wireless Systems LMDS MMDS
Frequency Range 10-43 GHz 2.5-2.7 GHz,3.4-3.7 GHz
Signal Radius Two-way Mostly One-way
Access Interface TDMA, TDMAFDMA, TDM
Bandwidth IP, ATM IP, ATMAllocation Method
Target Market Multi-dwelling Rural and Urbanhigh-rise units, Residential, SOHOSME, SOHO
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Modulations vs Data rate
0.4 MHz0.4 MHz6464--QAMQAM
0.6 MHz0.6 MHz1616--QAMQAM
1.4 MHz1.4 MHz44--QAMQAM
0.8 MHz0.8 MHz8PSK8PSK
1.4 MHz1.4 MHzQPSKQPSK
1.4 MHz1.4 MHzDQPSKDQPSK
2.8 MHz2.8 MHzBPSKBPSK
MHz for 2Mbps CBR MHz for 2Mbps CBR ConnectionConnection
NameName
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LMDS key applications
� Broadband Access for SOHOs and SMEs� Cellular Backbone� Consumer Multimedia� Copper or Fibre Backup� LAN Interconnect� Video Conferencing� Video Monitoring
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LMDS
� An LMDS system consists of a series of cells whose centers are defined by individual base stations, and of a central control point to which all of the base stations communicate
� LMDS network uses highly directional antennas -sectorized antennas at the base station and single-beam parabolic microwave reflectors at the subscriber site
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Advantages of LMDS
� Fast to deploy, no digging roads
� Solution to lack of fiber in some rural areas
� Build-out on demand, scalable
� Multi-Gigabit capacity� Can provide integrated
services: voice/data/video
� Challenges– Requires “line of sight”
between Tx and Rx– Signal attenuation by
rain and moisture in vegetation
– Shorter range requires more hub sites for coverage
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Experience with LMDS
� Quick to deploy (enables service provider to capture customers before a competitor does)
� Build-out, or relocate, as needed� Useful for sites not readily accessible to other
broadband services� Signal loss due to rain must be compensated for � Operation, Administration, Maintenance, and
Provisioning is similar to other telecomm. equip.
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Bibliography (1/2)
� www.terena.nl/conferences/nato-anw2000/ 03_bb_fixed_wirel.ppt� Broadband Radio Access Networks (BRAN); HIPERACCESS; System
Overview - ETSI TR 102 003 V1.1.1 (2002-03)� Broadband Wireless Access - IEEE 802 Executive Committee Meeting
Albuquerque, NM November 12, 1998� Fixed Radio Systems; Digital Multipoint Radio Systems; Part 1:
Common Characteristics and Non Essential Parameters of Multipoint Radio Systems – ETSI DEN/TM-04130-1 v0.0.2 (2003-03-25)
� Fundamentals of Communications 15: Radio Channels - Professor Ian Groves - King's College London
� Local Multipoint Distribution System - Berkin Özmen. Sercan Uslu -Computer Networks.
� Local Multipoint Distribution Service Tutorial - 1999 IEEE EmergingTechnologies Symposium on Wireless Communications and Systems -Langston, Marks, Reese
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Bibliography (2/2)
� Physical Layer Chapter 8: Data communication Fundamentals –Computer Science Department – University of Geneva
� Propagation Considerations important for today’s Radiocommunication Systems - Kevin A. Hughes - ITU Radiocommunication Bureau
� Radio Propagation – Katz - University of California, Berkeley� Radio-wave Propagation Basics - Struzak – Radio Regulations Board,
ITU� Terrestrial Microwave Systems – Niagara College – Canada� Transmission fundamentals, The Media Conducted and Wireless –
Georgia State University� The last mile: wireless technologies for broadband and home networks
– Cordeiro, Gossain, Ashok, Agrawal – University of Cincinnatti� ITU-T Recommendation G.821: "Error performance of an international
digital connection operating at a bit rate below the primary rate and forming part of an integrated services digital network".