RADIO SYSTEMS – ETI 051Lecture no: 11

IntroductionPresented by Peter Almers

Ove Edfors, Department of Electrical and Information TechnologyOve Edfors@eit lth seOve.Edfors@eit.lth.se

2007-10-22 Ove Edfors - ETI 051 1

Contents

• Course information

• What is a radio system?

• Some concepts

2007-10-22 Ove Edfors - ETI 051 2

COURSE INFORMATIONCOURSE INFORMATION

2007-10-22 Ove Edfors - ETI 051 3

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

2007-10-22 Ove Edfors - ETI 051 4

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.

2007-10-22 Ove Edfors - ETI 051 5

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

2007-10-22 Ove Edfors - ETI 051 6

Lectures

• Overview of the contents in the textbook

• Additional material

• Application examples

2007-10-22 Ove Edfors - ETI 051 7

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

2007-10-22 Ove Edfors - ETI 051 8

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.

2007-10-22 Ove Edfors - ETI 051 9

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

2007-10-22 Ove Edfors - ETI 051 10

WHAT IS ARADIO SYSTEM?

2007-10-22 Ove Edfors - ETI 051 11

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 )

2007-10-22 Ove Edfors - ETI 051 12

– 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.)

2007-10-22 Ove Edfors - ETI 051 13

Example: Microwave oven

Why is 2.45 GHz used?Dielectric permittivity and dielectric loss of water between 0°C and 100°C

2007-10-22 Ove Edfors - ETI 051 14

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.)

2007-10-22 Ove Edfors - ETI 051 15

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.

2007-10-22 Ove Edfors - ETI 051 16

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

2007-10-22 Ove Edfors - ETI 051 17

SOME CONCEPTS

2007-10-22 Ove Edfors - ETI 051 18

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

2007-10-22 Ove Edfors - ETI 051 19

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

2007-10-22 Ove Edfors - ETI 051 20

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.

2007-10-22 Ove Edfors - ETI 051 21

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

2007-10-22 Ove Edfors - ETI 051 22

(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.

2007-10-22 Ove Edfors - ETI 051 23

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

2007-10-22 Ove Edfors - ETI 051 24

THE RADIO CHANNELPath lossPath loss

TX RX

Received power [log scale]2/1 d∝

4/1 d∝

Distance, d [log scale]

2007-10-22 Ove Edfors - ETI 051 25

THE RADIO CHANNELLarge-scale fadingLarge-scale fading

Received power

D

C

D

d

Position A

B

PositionA B C C

2007-10-22 Ove Edfors - ETI 051 26

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

+ = + =

2007-10-22 Ove Edfors - ETI 051 27

THE RADIO CHANNELSmall-scale fading (cont )Small-scale fading (cont.)

RXTX

With a large number ofreflection points thereflection points theinterference patternbecomes extremly

complicated.

2007-10-22 Ove Edfors - ETI 051 28

THE RADIO CHANNELSmall-scale fading (cont )Small-scale fading (cont.)

Illustration of interference pattern from aboveReceived power [log scale]

MovementA B

TransmitterPosition

ReflectorA B

2007-10-22 Ove Edfors - ETI 051 29

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

2007-10-22 Ove Edfors - ETI 051 30

DUPLEX AND MULTIPLE ACCESSOverviewOverview

Garage openers, car alarm, ...

Audio and video broadcasting, paging, ...

Microwave links, ...

2007-10-22 Ove Edfors - ETI 051 31

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),

2007-10-22 Ove Edfors - ETI 051 32

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),

2007-10-22 Ove Edfors - ETI 051 33

Wideband CDMA (WCDMA)

MULTIPLE ACCESSFreq -division multiple access (FDMA)Freq.-division multiple access (FDMA)

Users are separatedin frequency bands.

deC

od

2007-10-22 Ove Edfors - ETI 051 34

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

2007-10-22 Ove Edfors - ETI 051 35

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

2007-10-22 Ove Edfors - ETI 051 36

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.

2007-10-22 Ove Edfors - ETI 051 37

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

2007-10-22 Ove Edfors - ETI 051 38

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

2007-10-22 Ove Edfors - ETI 051 39