RADIO SYSTEMS – ETI 051Lecture no: 11
IntroductionPresented by Peter Almers
Ove Edfors, Department of Electrical and Information TechnologyOve Edfors@eit lth [email protected]
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Contents
• Course information
• What is a radio system?
• Some concepts
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COURSE INFORMATIONCOURSE INFORMATION
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Course web-site
• All course information is available at:
http://www.eit.lth.se/course/ETI051
• Most important:ost po ta t– Continuously updated schedule– Lecture handouts (available before each lecture)– Exercises– Any additional material
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Textbook
WirelessCommunications
• Published by Wiley/IEEE Press in September 2005.Communications p
• Available through most on-line b b k tweb book stores
• Same book as in the ChannelSame book as in the Channel Modelling course (ETI085)
Andreas F. Molisch
• Authored by Andreas F. Molisch, professor of Radio Systems at Lund University/LTH.
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y
Schedule
• Three recurring components– Lectures: [Ove Edfors]
MONDAYS (13-15) and THURSDAYS (13-15)Except first week: MONDAY (13-15, NOW) and FRIDAY (08-10)p ( , ) ( )
– Exercise classes: [Johan Kåredal]FRIDAYS (08-10)Except first week: FRIDAY (13 15)Except first week: FRIDAY (13-15)
• Two special componentsTwo special components– Student presentations:
At the end of the course– Written exam:
Friday, December 19, 08.00-13.00
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Lectures
• Overview of the contents in the textbook
• Additional material
• Application examples
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Exercise classes
• Exercises from the textbook
• During exercise classes, some of the exercises will be analysed in detail
• By working through the exercises beforehand, you can give l bl i t hi h i t f d ivaluable input on which exercises to focus on during
classes
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Reading and presenting a journal paper
• During the course you will read and give a short t ti f t ( i tifi ) j l i thpresentation of a recent (scientific) journal paper in the
area.Performed in groups of TWO or THREE students• Performed in groups of TWO or THREE students.
• Propose your own topic/paper or select from a list of suitable paperssuitable papers.
• Presentations (about 10 minutes each) will be done at the end of the courseend of the course.
• THIS IS A COMPULSORY PART OF THE COURSE!• THIS IS A COMPULSORY PART OF THE COURSE!Participate in a group that reads and presents a paper.Attend the presentations given by other students.
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p g y
Written exam
• How?– Total of 5 hours– Part A: 1.5 hours – closed book questions (15 points)
Part B: 3 5 hours open book problems (15 points)– Part B: 3.5 hours – open book problems (15 points)
• When?• When?Friday, December 19, 08.00-13.00
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WHAT IS ARADIO SYSTEM?
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Radio system?
• From Merriam-Webster Dictionary– Radio:
1 : of, relating to, or operated by radiant energy2 : of or relating to electric currents or phenomena (as electromagnetic2 : of or relating to electric currents or phenomena (as electromagnetic
radiation ) of frequencies between about 15 kHz and 100 GHz– System:
1 l l i t ti i t d d t f it f i1 : a regularly interacting or interdependent group of items forming a unified whole
• ”Radio systems” can be used for many purposes, e.g.y y p p , g– Detection and ranging (Radar)– Astronomical observation (Radio telescope)– Heating food (Microwave oven)– Navigation (GPS, etc.)
Communication (Cellular telephony etc )
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– Communication (Cellular telephony, etc.)
Some questions to ask
• What do we want to achieve with our system?– This gives us design constraints (system requirements)
• What frequency band should we use?– Properties of the radio channel changes with frequency– Radio spectrum is firmly regulated
• Which technology should we use?Not all technologies can perform the task– Not all technologies can perform the task
– Cost is important (design, production, deployment, etc.)
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Example: Microwave oven
Why is 2.45 GHz used?Dielectric permittivity and dielectric loss of water between 0°C and 100°C
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Graph from www.sbu.ac.uk/water/ microwave.htmlMost absorbtion here Microwave oven here
Example: Human eye
Why is the human eye sensitive atthe electromagnetic wavelengths(frequency band) we call visible light?
Is it a coincidence or a ”cleverdesign”?
(This is not radio waves, but it illustratesthe importance of the used frequency band.)
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Graph from http://earth.usc.edu/geol150/weather/
Example: Radar
Distance d
Transmitted pulse Calculation of distance
2103
2
8 ttcd Δ××=
Δ×=
p
Received pulse
Time 22tΔ
The accuracy of our ”measured” time delay determines the accuracyof the ”measured” distance.
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Does this have any influence on the bandwidth requirement?
Example: Mobile telephony
Amplifiers with low dynamic range can beAmplifiers with low dynamic range can bemade more power efficient than highlylinear amplifiers.
Does this affect the choice of modulationtechnique?
Radio signal Radio signal
Ampl
itude
Ampl
itude
A A
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SOME CONCEPTS
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A rough breakdown into areas
Fundamental problemsin wireless communications
Propagationand antennas
Digital transmissionover wireless channels
Mobile communicationssystems
Deterministic Probabilistic
Channel models
Modulation
Speech and
Multiple access
Cellular telephonyChannel models
Narrow-bandchannels
Wide-bandchannels
Speech andchannel coding
Equalization
Cellular telephony
Speech codingchannels channels
Antennas
Equalization
DiversityWireless data networks
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SINGLE LINKThe link budget – a central conceptThe link budget – a central concept
”POWER” [dB]P
This is a simple ersion of theTXP
TXfL , TXaG ,
ain
version of the link budget.
pL
RXG RXfL
Ga
oss Required
C/N at
CRITERIONTO MEET:
N
RXaG , RXfL ,
C
Lo C/N atreceiver
input
Noise
NNoise reference level
Antenna Noise
Transmitter Receiver
Transmit Feeder
Antennagain
Propagationloss
Antennagain
Feeder Recei ed
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Transmitpower
Feederloss
Feederloss
Receivedpower
SINGLE LINKThe link budget – depends on what?The link budget – depends on what?• Some examples:
– Regulations (transmit power, etc.)– Antenna placement (feeder loss)
Antenna type and quality (antenna gain)– Antenna type and quality (antenna gain)– Frequency band and environment (propagation loss)– Receiver design (noise power)g ( p )– Modulation, coding and signal processing (required C/N)
This is a rather complex issue thatcomplex issue that we will spend quite
some effort on.
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SINGLE LINKRequired C/N – another central conceptRequired C/N another central concept
Quality INQ lit OUT
DETECTOR
y(C/N) Quality OUT
Q lit OUTDETECTOR CHARACTERISTIC The detector characteristic
is different for differentQuality OUT is different for differentsystem design choices.
REQUIRED QUALITY OUT:
Audio SNR
Quality IN(C/N)
Audio SNRPerceptive audio qualityBit-error ratePacket-error rate
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(C/N) etc.
SINGLE LINKRequired C/N – depends on what?Required C/N – depends on what? • The most important: This one is usually
– Required output quality determined by the application
• ... then, through the detector characteristic:
Signal constellation– Signal constellation– Modulation type– Error-correcting codes All these will have to g– Equalization– Antenna processing
be chosen in a system design
process
– Synchronization– etc.
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THE RADIO CHANNELSome propertiesSome properties
• Path loss• Path loss– Roughly, received power decays with some exponent of
distance
L l f di
exponentn PropagatioDistance power dTransmitte power Received −×∝
• Large-scale fading– Large objects, compared to a wavelength, in the signal path
obstruct the signalobstruct the signal
• Small-scale fadingg– Objects reflecting the signal causes multipath propagation
from transmitter to receiver
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THE RADIO CHANNELPath lossPath loss
TX RX
Received power [log scale]2/1 d∝
4/1 d∝
Distance, d [log scale]
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THE RADIO CHANNELLarge-scale fadingLarge-scale fading
Received power
D
C
D
d
Position A
B
PositionA B C C
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THE RADIO CHANNELSmall-scale fadingSmall-scale fading
Signal on reflectedSignal on reflectedpath arrives later
Signal on direct RXTXpath arrives first
Constructive (self-)interference Destructive (self-)interference
+ = + =
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THE RADIO CHANNELSmall-scale fading (cont )Small-scale fading (cont.)
RXTX
With a large number ofreflection points thereflection points theinterference patternbecomes extremly
complicated.
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THE RADIO CHANNELSmall-scale fading (cont )Small-scale fading (cont.)
Illustration of interference pattern from aboveReceived power [log scale]
MovementA B
TransmitterPosition
ReflectorA B
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MULTIPLE LINKSConceptual changes (comp single link)Conceptual changes (comp. single link)
• The same ”radio spectrum” resource has to be shared– Multiple access schemes
A h h diff t ti– Access schemes have different properties
I t f b j d i i• Interference becomes a major design issue– Interference can become a much bigger issue than noise– Even these cases can cause significant interference:– Even these cases can cause significant interference:
• A close transmitter on a different channel• A distant transmitter on the same channel
– Network planning to minimize effects of interference
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DUPLEX AND MULTIPLE ACCESSOverviewOverview
Garage openers, car alarm, ...
Audio and video broadcasting, paging, ...
Microwave links, ...
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Mobile telephony, wireless LAN, ...
DUPLEXFrequency-division Duplex (FDD)Frequency-division Duplex (FDD)
DuplexfilterU
p lin
k
Dow
n lin
k
Receiver
Transmitter
D ReceiverFrequency
FDD gives a more complexsolution (the duplex filter).
Can be used for continuousCan be used for continuoustransmission.
Examples: Nodic Mobile Telephony (NMT), Global System for Mobile communications (GSM),
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Wideband CDMA (WCDMA)
DUPLEXTime-division duplex (TDD)Time-division duplex (TDD)
link
wn
link
link
wn
link
link
wn
link
Transmitter
Up
Dow U
p
Dow U
p
Dow Receiver
Time
Duplex switch
TDD gives a low complexitysolution (the duplex switch).
Cannot be used for continuoustransmission.
Examples: Global System for Mobile communications (GSM),
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Wideband CDMA (WCDMA)
MULTIPLE ACCESSFreq -division multiple access (FDMA)Freq.-division multiple access (FDMA)
Users are separatedin frequency bands.
deC
od
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Examples: Nordic Mobile Telephony (NMT), Advanced Mobile Phone System (AMPS)
MULTIPLE ACCESSTime-division multiple access (TDMA)Time-division multiple access (TDMA)
Users are separatedin time slots.
de USE
R 1
SER
2
3
Cod
U
US
USE
R
USE
R 1
SER
2U
S
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Example: Global System for Mobile communications (GSM)
MULTIPLE ACCESSCode-division multiple access (CDMA)Code division multiple access (CDMA)
Users are separatedby spreading codes.
deC
od
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Examples: CdmaOne, Wideband CDMA (WCDMA), Cdma2000
MULTIPLE ACCESSCarrier-sense multiple access (CSMA)Carrier-sense multiple access (CSMA)
Users are separatedin time but not in
an organized way.1
g yThe terminal listens to
the channel, andtransmits a
packet if it’s free
de
USE
R
SER
3packet if it’s free.
R 2
Cod US
USE
R
ER 2
Collissionscan
occur andU
SEoccu a d
data is lost.
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Example: IEEE 802.11 (WLAN)
LINK LIMITATIONSNoise and interference limited linksNoise and interference limited links
NOISE LIMITED INTERFERENCE LIMITED
TX TX TXRX RX
C
Power
C
Power
I
Min C/I
N
Min C/N
N
Min C/I
N
Distance
N
Distance
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Max distance Max distance
Summary
• Reading and presenting a journal paper – compulsory!– Start thinking about a subject you would like to study
• The link budget concept• The detector characteristic concept• Overview on propagation: Path loss, large- and small-scale
f difading• Duplex schemes: FDD and TDD
M lti l FDMA TDMA CDMA d CSMA• Multiple access: FDMA, TDMA, CDMA and CSMA• Link limitations: Noise-limited and interference-limited
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