Mobile Communications 2012

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MobileCommunications 2 12

[1] Wireless Digital Communications Dr. Kamilo Feher/ Prentice Hall 1995

[2] Text: Wireless Communications, Theodore S. Rappaport/ Prentice Hall 1996

[3] RF microelectronics, Razavi/Prentice Hall 1998

Course Contents

A. Introduction

Introduction to Wireless, Cellular, Digital, PCS-Mobile Radio [1- Chap.1,2- Chap.1] Wireless/Cellular/PCS Mobile Environment Regulation

Transceiver Element

B M bil E i t


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Course Schedule:

2 23Introduction

3 1Overview of Wireless Communications and Cellular

System

3 8

Large Scale PropagationsSmall Scale Propagations

3 15

3 22

3 29Case Study: Bluetooth

4 5RF Transceivers (I)

4 12RF Transceivers (II)

4 194 26Digital Modulation and Detection

Spread Spectrum Modulations5 3

5 10

5 17Case Study: UWB

5 24Equalization

5 31Diversity6 7Channel Coding (I)


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Institute of Electronics2012/1/19

National Chiao Tung University

Wireless Communications


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N a t i o n a l C h i a o T u n g U n i v e r s i t yI n s t i t u t e o f E l e c t r o n i c sStella Kuei Ann Wen 2012/1/19

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Changing Lifestyles


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Wireless Link Between All Devices

www.bluetooth.com


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Applications :System ConsiderationsWhere :Environment (Channel)

How :Regulation

Implementation:Transceiver

KEY Factors on Wireless Design


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A. System Considerations


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Services:Voice-Oriented Services

Low-Power, Local Area Systems ( Cordless

Telephone)High-power, Wide-Area Systems (Cellular)

Data-Oriented Services

High-Speed, Local Area Systems ( WLANs)

Low-Speed, Wide-Area Systems ( Mobile Data)


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Page 13

PCMCIA

RADIO

BOARD

Modem

PSTN

Cable

.. etc.

Access

Point

Internet

ATM.. etc.

High-Speed, Local Area Systems

( WLANs)


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Page 15

Large Scale Path Loss

Reflection

DiffractionScattering

Small Scale Fading

Mul tipath time delay spread

Doppler spread

Cochannel I nterf erenceAdjacent Channel I nterference

Environments


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CapacityWith fixed number of channels to support an

arbitrarily large number of subscribers


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Cellular Concept (Cell Split)


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Handoff :When a mobile moves into a different

cell while a conversation is in progress, the MSC

automatic transfers the call to a new channel of a

new basestation.

Need to be successful and unfrequented


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2nd Generation Cellular


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Page 25

Tranceiver :Propagation Environment :

Path Loss Fading Interference

External Noise

Power Constrain

Bandwidth Constrain

Modulation Equilization

Transceiver Design:

Coding Diversity Multiple Access

Overcome impairments

Encrease bandwidth

Encrease bit r ate


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Page 27

Cases

HFA3524

DUAL

SYNTHESIZER

PRISM Antenna to Bits

HFA3624

RF/IF

HSP3824

BASEBAND

PROCESSOR

A Complete DS Spread Spectrum Radio Chipset

HFA3424

LNA

HFA3724

QMODEM

HFA3925

RF POWERAMPLIFIER

AND Tx/Rx

SWITCH

I ADC

Q ADC

DE-

SPREAD

DE-

MODULATE

SPREADMODULATE/

ENCODE

Tx/Rx

DATA I/O

CONTROL -

TEST I/O

ADC CCA

AP96358 4-4

LO


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B. Mobile Environment

Model Analysis


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Page 31

( 1.) CalculateEIRP(effective isotropically

radiated power) at the transmit antenna.

( 2.) Calculatefree-space lossbetweenTX & RX, f (distance, freq.)

( 3.) Calculate on estimateRSL

(Receive Signal Level) at the first

active stage of receiver.

Path Analysis Approaches


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Page 33


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Page 35

EIRP = PtGt

Free-space path loss :Pr

(d)=P

d L

tGt Gr( )

( )

2

2 24

PL = 10log (Pt/Pr)= -10log (Pr/Pt)

= -10logGtGr2/ (4d)2. (=c/f )

(Unit Gain Antenna, Gt=Gr=1)

= -10log2

/ (4d)2

.(=c/f )


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Page 37

Conceptual layout of a cellular system

MTSO: Mobil telephone switching office

CGSA: Cellular geographic survey areaCell site apart: 6.4~12.8Km

Outdoor Propagation Model


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Page 39

Indoor Model

.

Figure 6.2 Tx and Rx at different floors. B3 is in the building. B4

outside the building, at street level. B5 outside the

building , above street level.

M1

B3

M2

M5

M4

M3

B4

B5


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Page 41

Construction materials.Types of interiors.Locations within a building.Location of Tx and Rx antennas

Parameters Being Considered


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Transceiver Overview

Theoretic Brief

Building Blocks Brief

C. Transceiver Elements


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Page 45

Continous Variable Slope Delta-Modulation

(CVSD)

1 1 0 0 0 0 0 0 1 0 1 1 1 1 1 0 1 0 0 0 0 1 1 1 0 0 0 1 0 1 0 1 0 . . . . . . .

Bluetooth Audio


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Times Frames, Time Slots and Bursts

0 1 204720462 20453 2044

1 hyperframe = 2048 superframes = 2715648 TDMA frames ( 3h 28min 53s 760ms )

0 1 2 3 47 48 49 50

1 superframes = 1326 TDMA frames ( 6.12s )

= 51 (26-frame) multiframes or 26 (51-frame)multiframes

0 1 24 25

GSM Packets


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Page 49

Forward-Error Correction (FEC) 1/3 rate: bit-repeat code

2/3 rate: (15,10) shortened Hamming code

Automatic Retransmission Query (ARQ) 1-bit fast ACK/NAK

1-bit sequence number

header piggy-backing

BTEr ror Control Coding


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Page 51

Modulation Brief


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Page 53

1 0 0

Baseband RX


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(2): Passband TX/RX :

Modulation ( Transform baseband signal to radio signal )


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Wave being transmitted in wireless environment:

Impairments: Carrier wave and Timing


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Page 59


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Page 61

Received:V(t) = Acos(ct + ) : phase delay caused by transmission.

Carrier recovery :V2(t) = A2cos2(ct + ) = (1/2)[A2+ A2cos2(ct + )]

Freq. divided by 2 carry recovered: cos(ct + )

Demodulation by multiply:Acos(ct + ) 2cos(ct + ) = (A)[1 + cos2(ct + )]

Lowpass filtering for cos2(ct + ) and I(t) =+A extracted !

Actual case : with noise : domodulation with matching

Acos(ct + ) + n(t) x -------> Integral --> Sample at T+(A2T + N) --> Decision

2 Acos(ct + )

Decoding by integrator + symbol timing recovery circuitoutput = integrator output at the end of bit interval

T

dt0


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Multiple Access Scheme


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m(t)cosct x

2cosLOt

m(t)cosIFt ( IF= c+LO)

2m(t)cosctcosLOt=m(t) cos(c-LO)t+cosLO (c+LO)t

e.g. : IF=281MHz c=2.4GHz .. LO=(2400-281) MHz

Image Signal : c+ 2 IF IF= (c+ 2 IF ) + LO= (c+ 2 IF ) + (IF + c)= IF

Frequency Shift Basics


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Page 69

Constant Envelope Modulation

GFSK v.s FSK


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Page 81

Transceiver Overview (Cont.)
http://c/doc/Present/GSM.ppthttp://c/doc/Present/GSM.ppthttp://c/doc/Present/GSM.ppt


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Page 83

HFA3524DUAL

SYNTHESIZER

HFA3624

RF/IF

HSP3824

BASEBAND

PROCESSOR

A Complete DS Spread Spectrum Radio Chipset

HFA3424

LNA

HFA3724

QMODEM

HFA3925

RF POWER

AMPLIFIER

AND Tx/Rx

SWITCH

I ADC

Q ADC

DE-

SPREAD

DE-

MODULATE

SPREADMODULATE/

ENCODE

Tx/Rx

DATA I/O

CONTROL -

TEST I/O

ADC CCA

LO

2012/1/19


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Mobile Communications 1

Mobile CommunicationsOverview of Wireless Communications

Trans Wireless Technology LaboratoryNational Chiao Tung University

Overview of Wireless Communications

Outline 2012/1/19


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3Mobile Communications

Early Wireless Communications

Visual Communication

Line of Sight (LOS)communication

LOS distance further extended by telescopes

e.g. Smoke signals, Heliographs and Semaphore

Heliograph signaling Semaphore signaling Semaphore wheel

History of Wireless Communications

[Source: Wikipedia] [Source: Portsdown Tunnels] [Source: ThinkQuest]


Origin of Wireless CommunicationsHistory of Wireless Communications

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History of Wireless CommunicationsHistory of Wireless Communications

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Wireless vs. Mobile Communications

Wireless Vision and Future Trends


Wired/Wireless Network Today


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Future of the Wired/Wireless World

Mobile Data

DevicesPC / Server

Broadband

Digital Data

(Fiber/FWA)

BT

WPAN

3G

WWN802.11

WLAN

OC3

WAN

GPS

Digital

Camera

DVD /

HDTV

Printer

Real-Time

Video

Auto

Consumer

POS

SODA

3G Mobile

Devices

Red: Multi-Mode

Green: Single Mode

Wireless Legend

UWB



Wireless Industry At A Crossroad


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Trend Convergence of 4C

Wireless PAN

Wireless LAN

Wireless MAN

NotebookPCs

PDAs

Personal Computer(Internet)

Scanners

StorageDevices

Printers

Mobile

Communication

3GHandsets

CordlessPhones GSM

ConsumerElectronics(Broadcast)

GamePlatforms

DVDs

STBs

Contents

overEverywhere

PortableGame Cube

MP3Players

DigitalCameras

DVCamcorders

PortableProjectors



Trend Ubiquitous Wireless Connectivity


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Wireless Home Network

Digital Home/e-HomeBroadband

Wireless

AccessHome

Security

Senor

Network Wireless

Home

Network

Wireless

PAN

Broadband

InternetxDSL



Convergence of Consumer Electronic Devices


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Wireless Industry Trends

2002 2006 2010

DataRates

WLAN

>100Mbps

WWAN-Cellular

WPAN-UWB

WPAN BT

300 - 500Mbps

>1 Gbps

WMAN (WiMax)

Technology Issues and Challenges


Heterogeneous Wireless Network Access


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Challenges in Wireless Communications

Spectrum is scarceLicense fee

High data ratesMultimediaapplications

ReliabilityQuality of service

MobilityChannelcharacteristics

PortabilityLow powerconsumption

Connectivityin various wireless networksMultimode

Interferencefrom other usersLimited user capacity

SecurityMobile commerce



Requirements for Multimedia Applications


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Issues of Portable Devices

Power consumption limited computing power, low quality displays, small disks due

to limited battery capacity

CPU: power consumption ~ CV2f C: internal capacitance, reduced by integration

V: supply voltage, can be reduced to a certain limit

f: clock frequency, can be reduced temporally

Loss of data higher probability, has to be included in advance into the

design (e.g., defects, theft)

Limited user interfaces compromise between size of fingers and portability

integration of character/voice recognition, abstract symbols

Limited memory limited value of mass memories with moving parts

flash-memory or ? as alternative



Wireless v s Wired Networks


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Cross-Layer Design for Quality of Service

service location

data rates, delay constraints

adaptive applications

congestion and flow control

quality of service

addressing, routing,device location

hand-over

authentication

media access

multiplexing

media access control

encryption

modulation

interference

attenuation

frequency

Application layer

Transport layer

Network layer

Access layer

Physical layer



Cross-Layer Design


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Wireless System On a Chip


Memory

ControllerCPU

RFModules

ADC/DACModule

Bridge

Peripheral Bus

UART Timer

USB

1.1/2.0

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MAC

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PHY

Wireless MAC

Wireless PHY

Wireless SOC

Wireless Transceiver

Connectivity interface in SOC

Peripheral Bus


Wireless SOC


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Wireless Communications in Physical Layer

Transmitter Channel Receiver

Coder Modulator RF FrontEnd

DeCoderDemodulatorRF FrontEnd

101100111..



Wireless Transceiver Elements


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Typical RF Transceiver System

0

90

LNA Mixer

VCOAntenna

0

90

Power

Amplifier

Mixer

T/R Switch

Power

Driver

A/D

A/D

D/A

D/A

Power

ControlLogic

PA & PM

RF Front-End

Analog Mixed Signal

Switch & Filter

1/N

Fref

ReferenceI, V, Freq

ClockTree

Regulators



Propagation Channel Effects


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Interference

890.4

890.4 890.4

890.4890.4

890.4 890.4

DesiredChannel

MHz890.4

Co-channelInterference

DesiredChannel

AdjacentChannel AdjacentChannel

MHz890.2 890.4 890.6

891.0

890.4

890.8

891.2

890.6

890.0

890.2

Co-Channel Interference Adjacent-Channel Interference



Noise


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Modern Wireless Communication Systems

Paging System

Cordless Phone System

Cellular Phone System

Satellite Network

Wireless Local Area NetworkWireless Personal Area Network

Wireless Metropolitan Network



Paging System


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Cordless Phone System

Full duplex system

1stgeneration primarily for in-home use

Now as extended telephone in-home/in-building use or

outdoor locations within urban centers

Limited range and mobility

PSTN

Public

Switched

Telephone

Network

Fixed Port

Base

Station

Wireless Link

Cordless

Handset



Cellular Phone System


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Fundamental of Cellular Phone System

Frequency Reuse Signal power falls off with distance

Reuse the same frequency spectrum at spatially-separatedlocations

Inter-cell Interference Interference caused by users in different cells operating on the

same channel set

Must remain below a given threshold for acceptable systemperformance

Reuse Distance Should be as small as possible so that frequencies are reused

as often as possible, thereby maximizing spectral efficiency more user capacity

Difficult to determine the minimum reuse distance since bothtransmitting and interfering signals experience random powervariations due to the characteristics of wireless signal

propagation



Cell Types of Cellular Phone System


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Common Terms in Cellular Phone System

CAI: Common air interface

FVC: Forward voice channel

Voice transmission channel for BSMS

RVC: Reverse voice channel

Voice transmission channel for MS

BSFCC: Forward control channel

Control channel for setting up a call for BS MS

RCC: Reverse control channel

Control channel for setting up a call for MS BS



Call Process: Landline User Mobile User


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Call Process: Mobile User 1Mobile User 2


FCC

RCC

FVC

FCC

FCC

RCC

FVC

FCC

Receives call initiation

request from BS and

verifies that mobile has

a valid MIN, ESN pair

Paging for called mobile,

instructing the mobile to

move to voice channel

Instruct FCC of

originating BS to

move mobile to a

pair voice channels

Receives page and matches

the MIN with its own MIN.

Receives instruction to move

to voice channel.

Connects the

mobile with the

called party on

the PSTN

Begin Voice

transmission

Begin voice

reception

Begin Voice

transmission

Begin voice

reception

Sends a call

initiation request

along with subscribe

MIN and number of

called party

Receives call

initiation request and

MIN, ESN, Station

Class Mark

MSC

BS

MS


Evolution From 2G to 3G Cellular Systems


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Migration of Digital Cellular Systems

UMTS

GSM Circuit-Switched Voice

GPRS

GPRS: General Packet Radio Service

(17.6 kbps x 8)

EDGE: Enhanced Data for GSM Evolution(59.2 kbps x 8)

UMTS: Universal Mobile Telecomm Systems

EDGE

IS-136 Circuit-Switched Voice

IS-136+

EDGE

Packet Voice & Dataover EDGE

Packet Voice & Data

over UMTS (WCDMA)

Circuit-SwitchedCircuit-Switched Voice

Packet-Switched DataPacket-Switched

CDMA2000

Packet

Data



Circuit Switched vs Packet Switched


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Multiple Access

FDMA

Frequency Division Multiple Access

TDMA

Time Division Multiple Access

CDMA Code Division Multiple Access

TDMA

CDMAtimeFDMA

freq

time

freq

TDMA

time

freq

code


Satellite Network


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Wireless Local Area Network


Hub

Server

Switch

Internet

Wireless LAN (WLAN) as an

extension to wired LAN

Access PointHub

Workgroup Bridge


Infrastructure vs Ad-hoc Networks


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Wireless Personal Area Network


Personal Ad-hot Network Cable Replacement


Wireless Personal Area Network


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Wireless Metropolitan Area Network


BWA Operator Network

Backbone

INTERNET

BACKBONE

Mobile

Backhaul

3

RESIDENTIAL & SoHo DSL

LEVEL SERVICE

1

802.16d

FRACTIONAL E1 for

SMALL BUSINESS

T1+ LEVEL SERVICE

ENTERPRISE

BACKHAUL for

HOTSPOTS

2

802.16d

Mobility

5802.16e

H

H

HH

H

H

H

H

WMAN Nomadic Coverage -->

handoff from HOT SPOTS

4

= wide area coverage

outside of Hot Spots

H


Wireless Regional Area Network


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Wireless Regional Area Network

WRANRepeater

TV Transmitter

WRANBase Station

Wireless

MIC

WirelessMIC

WRANBase Station

: CPE: Customer Premise Equipment

: WRAN Base Station

Typical ~33km

Max. 100km

Deployment Scenario



Electromagnetic Spectrum

Wireless Spectrum, Regulations and Standards

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Spectrum Regulation Agencies

Since frequency spectrum is scarce, the

application of spectrum is regulated by

governments.

Taiwan: National Communications Commission

(NCC)

Japan: Ministry of Internal Affairs andCommunication (MIC)

United States: Federal Communications

Commission (FCC)

Europe: European Telecommunications Standards

Institute (ESTI)

Global: Internal Telecommunications Union (ITU)



Applications of Frequency Spectrums


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O i f Wi l C i ti

Wi l S t R l ti d St d d


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Applications of Frequency Spectrums

US License-Exempt Band



Standard Organizations


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Wireless Spectrum Regulations and Standards


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Current and Evolving Wireless Standards

IEEE 802.15.3

UWB, Bluetooth

Wi-Media, BTSIG,

MBOA

WWAN

WMAN

WLAN

WPAN ETSIHiperPAN

IEEE 802.11

Wi-Fi Alliance

ETSI-BRAN

HiperLAN2

IEEE 802.16d

WiMAX

ETSI HiperMAN &

HIPERACCESS

IEEE 802.20

IEEE 802.16e

3GPP (GPRS/UMTS)

3GPP2 (1X--/CDMA2000)

GSMA, OMA

SensorsIEEE 802.15.4(Zigbee Alliance)

RFID

(AutoID Center)

IEEE

802.2

1,

IEEE

802.1

8802.1

9

WRANIEEE 802.22


Cellular Systems


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Mobile CommunicationsCellular Systems

Wen-Shen Wuen

Trans. Wireless Technology Laboratory


Vincent W.-S. Wuen Mobile Communications 1

Outline Cellular Systems

Outline
http://find/


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1 Cellular System Fundamentals

2 Frequency Reuse

3 Interference and System Capacity

4 Trunking and Grade of Services

5 Improving Coverage and Capacity in Cellular Systems

6 Channel Assignment Strategies

7 Handoff Strategies


Cellular System Fundamentals Cellular Systems

Outline
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2 Frequency Reuse








Introdcution

Early mobile radio systems:
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y y

Cover a large area by using a single, high powered transmitter

with an antenna mounted on a tall tower.

Nofrequency reuse, nointerference

Limited user capacity

Cellular concept:

Based on power fall off with distance of signal propagation andreuse the same channel frequency at spatially separated

locations

Sovling problem of spectral congestion and user capacity

Replacing a single, high power transmitter (large cell) with

many low power transmitters (small cells)

Available channels can be reused as many times as necessary

so long as theco-channel interferenceis kept below acceptable

levels



Cellular System
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Each cell is assigned to a uniquechannel set,Cn

Adjacent cells: cells assigned to a different channel sets

Co-channel cells: cells using the same channel sets



Tesselating Cell Shapes

To approximate thecontours of constant received power
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pp p

around the base station

Hexagonalcells:Having largest area for a given distance between the center of a

polygon and its farthest perimeter points

Approximating a circular radiation pattern for an omnidirectional

base station antenna and free space propagation

Diamondcells: better approximating contours of constantpower in modern urban microcells


Frequency Reuse Cellular Systems

Outline
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2 Frequency Reuse







Frequency Reuse Cellular Systems

Frequency Reuse

S: total number of duplex channels available for use
http://goforward/http://find/http://goback/


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p

k: number of channels assigned to a cell (k

15dB, thereforeN= 12should be used.

Vincent W -S Wuen Mobile Communications 19 Interference and System Capacity Cellular Systems

Channel Planning of Wireless Systems

Typically 5% of the entire mobile spectrum is devoted to control

h l d 9 % f h i d di d i
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channels and 95% of the spectrum is dedicated to voice

channels.

Air interface standards ensure a distinction between voice and

control channels and control channels are not allowed to be

used as voice channels and vice versa.

Different frequency reuse strategy is applied to control

channels to ensure greater S/I protection in control channels.

For propagation consideration, most practical CDMA systems

limits frequency reuse with f1/f2cell planning.

CDMA system has a dynamic, time-varying coverage region

depending on the instantaneous number of users on the radiochannel. breathing celldynamic control of power levelsand thresholds assigned to control channels, voice channels for

changing traffic intensity

Vincent W -S Wuen Mobile Communications 20 Interference and System Capacity Cellular Systems

Adjacent Channel Interference

results from imperfect receiver filters which allows nearby

frequency to leak into the passband.
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q y p

causes near-far effect, a nearby TX captures the receiver of thesubscriber.

ACI can be minimized through careful filtering and channel

assignments.

Keeping frequency separation between each channel as large as

possible

Avoiding the use of adjacent channels in neighboring cell sites

For a close-in mobile (MS1) isXtimes as close to the BS as

another mobile (MS2) and has energy leaks to the passband,

theS/Iat the BS for the weak mobile (MS2) before receiver

filtering is approximately

S

I=Xn

forn= 4 SI 40dB

Vincent W -S Wuen Mobile Communications 21 Trunking and Grade of Services Cellular Systems

Outline

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2 Frequency Reuse






Vincent W -S Wuen Mobile Communications 22 Trunking and Grade of Services Cellular Systems

Definition of Common Terms in Trunking Theory

Set-up Time: The time required to allocated a trunked radio

channel to a requesting user.
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q g

Blocked Call (Lost Call): Call which cannot be completed at timeof request, due to congestion.

Holding Time: Average duration of a typical call. Denoted byH

(in seconds).

Traffic Intensity: Measure of channel time utilization, which is

the average channel occupancy measured in Erlangs.

Load: Traffic intensity across the entire trunked radio system,

measured in Erlangs.

Grade of Service (GOS): A measure of congestion specified as

the probability of a call being blocked (for Erlang B), or the

probability of a call being delayed beyond a certain amount of

time (for Erlang C).

Request Rate: The average number of call requests per unit

time. Denoted by second1.

Vincent W S Wuen Mobile Communications 23 Trunking and Grade of Services Cellular Systems

Trunking Theory

Each user generates a traffic intensity ofAuErlangs:
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Au=H

The total offered traffic intensityAfor a system containingU

users:

A= UAuIn aCchannel trunked system, if the traffic is equally

distributed, the traffic i ntensity per channel, Ac:

Ac= UAu/C

Erlang: the amount of traffic intensity carried by a channel thatis completely occupied (1 Erlang = 1 call-hour / hour).

Busy hour traffic,Ab= call/busy hourmean call holding time.

Vincent W S Wuen Mobile Communications 24 Trunking and Grade of Services Cellular Systems

Example 2

Call established at 2 am between a central computer and a data
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Call established at 2 am between a central computer and a data

terminal. Assuming a continuous connection and data transferred at34 kbit/s what is the traffic if the call is terminated at 2:45am?

Solution:

Traffic=(1 call)(45 min)(1 hour / 60 min) =0.75 Erlangs

Example 3

A group of 20 subscribers generate 50 calls with an average holding

time of 3 minutes, what is the average traffic per subscriber?

Solution:

Traffic=(50 calls)

(3min)

(1 hour/60 min)=2.5 Erlangs

2.5/20=0.125 Erlangs per subscriber.

Vincent W.-S. Wuen Mobile Communications25

Trunking and Grade of Services Cellular Systems

Erlang B: Blocked Calls Cleared
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p[blocked]= AC

C!Ck=0

Ak

k!

= GOS

whereC: the number of trunked channels offered by a trunked radio

system;A: the total offered traffic.

Assumptions of Erlang B:There are memoryless arrivals of requests.

The probability of a user occupying a channel is exponentially

distributed.

There are a finite number of channels available in the trunking

pool.

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Erlang B Chart


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Erlang C: Blocked Calls Delayed

Probability of a call not having immediate access to a channel

and being queued:
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g q

p[delay > 0]=AC

C!

AC+C!1 A

C

C1k=0

Ak

k!

= GOS

The probability that the delayed call is forced to wait more than

tsecond:

p[delay > t] = p[delay > 0]p[delay > t|delay > 0]

= p[delay > 0]exp (CA)t

H

(12)

Average delayDfor all calls in a queued system

D= p[delay > 0] HCA



Erlang C Chart
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Example 4

How many users can be supported for 0.5% blocking probability for

the following number of trunked channels in a blocked calls clear
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g

system? (a) 1, (b) 5, (c) 10, (d) 20, (e) 100. Assume each usergenerate 0.1 Erlangs of traffic.

Solution:

(a)C= 1,Au= 0.1,GOS= 0.005, from the chart,A= 0.005 U=A/Au= 0.005/0.1= 0.05users(b)C= 5,Au= 0.1,GOS= 0.005, from the chart,A= 1.13 U=A/Au= 1.13/0.1 11users(c)C= 10,Au= 0.1,GOS= 0.005, from the chart,A= 3.96 U=A/Au= 3.96/0.1 39users(d)C= 20,Au= 0.1,GOS= 0.005, from the chart,

A= 11.1 U=A/Au= 11.1/0.1 111users(e)C= 100,Au= 0.1,GOS= 0.005, from the chart,A= 80.9 U=A/Au= 80.9/0.1 809users



Example 5

Trunked mobile networks A, B, and C provide cellular services in an urban

area with 2 million residents. The (no. of cells, no. channels/cell) for the

three providers are (394,19), (98,57) and (49,100). Find the number of
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ee p o de s a e (39 , 9), (98,5 ) a d ( 9, 00) d e u be o

users that can be supported at 2% blocking if each user averages twocalls/hour at an average call duration of 3 min. Find the percentage market

penetration for each provider.

Solution:

System A:GOS= 0.02,C= 19,Au=H= 2(3/60)= 0.1Erlangs. ForGOS= 0.02andC

=19

A

=12ErlangsU

=A/Au

=12/0.1

=120

total number of subscribers is120394= 47289System B:GOS= 0.02,C= 57,Au=H= 2(3/60)= 0.1Erlangs. ForGOS= 0.02andC= 57A= 45ErlangsU=A/Au= 45/0.1= 450total number of subscribers is45098= 44100System C:GOS= 0.02,C= 100,Au=H= 2(3/60) = 0.1Erlangs. ForGOS= 0.02andC= 100A= 88ErlangsU=A/Au= 88/0.1 = 880total number of subscribers is88049= 43120Market penetration: A: 47280/2,000,000=2.36%; B:

44100/2,000,000=2.205%;C: 43120/2,000,000=2.156%



Example 6

Given a city area: 1300 mile2, with 7-cell reuse pattern, cell radius=4 miles

and frequency spectrum: 40MHz with 60KHz channel bandwidth. Assume

GOS=2% for an Erlang B system, if the offered traffic per user is 0.03

E l t ( ) th f ll i th i (b) th f
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Erlangs, compute (a) the no. of cells in the service area (b) the no. of

channels per cell (c) traffic intensity of each cell (d) the maximum carried

traffic (e) the total no. of users can be served for the GOS (f) the no. of

mobiles per unique channel (g) the theoretical maximum no. of users that

could be served at one time by the system.

Solution:

(a)Acell= 1.53R2 = 2.598142 = 41.57square mile. Total no. of cellsNc= 1300/41.57= 31cells.(b) Total no. of channels per cell C= 40MHz/(60kHz7)= 95channels/cell.(c)C= 95,GOS= 0.02traffic intensity per cellA= 84Erlangs/cell.(d) Maximum carried traffic=no. of cellstraffic intensity per cell =31

84

=2604 Erlangs.

(e) Traffic/user=0.03 Erlangs Total no. of users = 2604/0.03=86800 users(f) no. of mobiles per channel= no. of users/no. of channels =86800/(40

MHz/60 kHz)=130 mobiles/channel.

(e) The theoretical maximum no. of served mobiles (all channels are

occupied)=CNc= 9531= 2945usersVincent W.-S. Wuen Mobile Communications 33


Example 7

A hexagonal cell within a four-cell system has a radius of 1.387 km. A total

of 60 channels are used within the entire system. If the load per user is

0.029 Erlangs and = 1call/hour, compute the following for an Erlang C
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system which has a 5% probability of delayed call: (a) how many user persquare kilometer will the system support? (b) the probability that a delayed

call will have to wait for more than 10 seconds? (c) the probability that a

call will be delayed for more than 10 seconds?

Solution:

Cell area=2.598

(1.387)2

=5km2. no. of channel per cellC

=60/4

=15

channels.

(a) For Erlang C of 5% probability of delay with C= 15, the trafficintensity=9.0 Erlangs.

no. of users=total traffic intensity/traffic per user = 9/0.029=310 users for

5km2 or 62 users/km2

(b)H=Au/ = 0.029hour= 104.4second.p[delay > 10|delay]= exp((CA)t/H)= exp((159)10/104.4) = 56.29%(c)p[delay > 0]= 5%= 0.05p[delay > 10]= p[delay > 0]p[delay > 10|delay]= 0.050.5629= 2.81%


Improving Coverage and Capacity Cellular Systems

Outline

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2 Frequency Reuse








Cell Splitting
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LetRand keepsD/Runchanged

Pr[at old cell boundary] Pt1Rn

Pr[at new cell boundary] Pt2(R/2)n

forn= 4Pt2 =

Pt1

16



Cell Splitting

Example 8
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Assume each BS uses 60channels and large cell radius of 1

km and microcell radius of 0.5

km. Find the number of channels

in a 3 km by 3 km square around

A when (a) without the use ofmicrocells (b) the labeled

microcells are used (c) all original

BS are replaced by microcells.

Solution:

(a) 560= 300(b)(5+6)60= 660(2.2x) (c)(5+12)60= 1020(3.4x)



Sectoring

IncreasingS/Iratio, keeping cell radiusRthe same and


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g , p g

decreasingD/RD Nfrequency reuse cluster sizeNcan be reduced because ofS/I is improved.



Sectoring, contd
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Microcell Zone
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Microcell Zone
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Channel Assignment Strategies Cellular Systems

Outline

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2 Frequency Reuse







Channel Assignment Strategies Cellular Systems

Channel Assignment Strategies

Fixed channel assignment

each cell is allocated to a predetermined set of voice channelsthe call is blockedis all the channels are occupied.
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borrowing strategy: a cell is allowed to borrow channels from a

neighboring cell if all of its own channels are occupied.

MSC supervises the borrowing procedure to ensure no disrupting

calls or interference with any of the calls in progress in the donor

cell.

Dynamic channel assignmentthe serving BS request a channel from MSC whenever a call

request is made.

following an algorithm considering the likelihood of future

blocking in the cell, the frequency of use of the candidate cell, the

reuse distance of the channel and other cost functions.

MSC needs to collect real-time data on channel occupancy, traffic

distribution, and radio signal strength indicator (RSSI) of all

channels on a continuous basis. increasing storage andcomputational load on the system.

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Handoff Strategies Cellular Systems

Handoff

When a mobile moves into a different cell when a conversation


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is in progress, the MSC automatically transfer the call to a newchannel belonging to a new BS.

Many handoff strategy prioritize handoff requests over call

initiation requests when allocating an unused channel.

Handoff threshold: a signal level slightly stronger than the

minimum usable signal for acceptable voice quality.

= Pr,handoffPr,min.usable

too largeunnecessary handoffs burden MSCtoo smallmay be insufficient time to complete a handoffbefore a call is lost



Handoff Scenario at Cell Boundary
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Handoff Decision

Monitor the signal level of MS for a period of time

to ensures MS is actually moving away from the serving BS.

Dwell time
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The time over which a call may be maintained within a cell,without handoff, depending on propagation, interference,

distance between the MS and BS, and other time varying

effects

Monitor RSSI

BS monitors the signal strengths of all its reverse voice

channels to determined the relative location of each MS.

Locator receivers monitor the signal strength of users in

neighboring cells need of handoff and report RSSI to MSC.

Mobile assisted handoff (MAHO)

MS measures the received power from the surrounding BSs

and continuously reports to the serving BS.

Faster handoff time than first generation analog system

Suited for microcellular environments



Handoff Considerations
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Prioritizing Handoffs

Guard channel concept: reserves a fractional of total available

channels exclusively for handoffreducing total carried trafficcombining with dynamic channel assignment to offerefficient spectrum utilization

Queuing of handoff requests: using the finite time interval

between the time the received signal levels drops below the

handoff threshold and the time the call is terminatednotguarantee a zero probability of forced termination



Handoff Considerations

Umbrella cells
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Cell dragging

Hard handoff

Soft handoff


Large-Scale Propagation Effects

bil i i
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Mobile CommunicationsLarge-Scale Propagation Effects

Wen-Shen Wuen

Trans. Wireless Technology Laboratory


WS Wuen Mobile Communications 1

Outline Large-Scale Propagation Effects

Outline

1 Radio Wave Propagation

2 Transmit and Receive Signal Models

3 F S P ti M d l
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3 Free Space Propagation Model4 Ray Tracing Path Loss Models

Reflection

Diffraction

Scattering

5 Empirical Path Loss Models

Outdoor Propagation Models

Indoor Propagation Models

6 Practical Link Budget Design Using Path Loss Model

Link Budget AnalysisSimplified Path Loss Model

Log-normal Shadow Fading

Percentage of Cell Coverage Area


Radio Wave Propagation Large-Scale Propagation Effects

Outline



3 F S P ti M d l
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3 Free Space Propagation Model4 Ray Tracing Path Loss Models

Reflection

Diffraction

Scattering





Link Budget AnalysisSimplified Path Loss Model





Radio Wave Propagation

Radio Wave Propagation

Reflection, diffraction and scattering

Line-of-sight (LOS) path: direct path between a transmitter

(TX) and a recei er (RX)
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(TX) and a receiver (RX)

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Radio Wave Propagation, contd

Propagation channel properties

N i i t f d th h l i di t


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Noise, interference, and other channel impediments

Channel impediments change over time

Random and unpredictable due to user movementLimits thereliability and performance of wireless communications and

requires channel models to characterize

Propagation ModelsLarge-scale modelspredict the mean signal strength for an

arbitrary TX-RX separation distance (100 to1000 m)Small-scale/fading modelscharacterize the rapid fluctuation of

the received signal strength over very short travel distances (

wave lengths) or short time duration (seconds)



Propagation Effects

Propagation Effects

Path Loss: caused by dissipation of power radiated by the TX

as well as effects of channels
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a

Measurement of local received signal power: Average signal powermeasurements over a measurement track of 5to 40. e.g. fc= 1 2GHz,= c/fc= 0.3 1.5mmeasuring the local average received power over movementsof 1m to 10m.



Propagation Effects

Propagation Effects


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Shadowing: caused by obstacles between the TX and RX that

attenuate signal power through absorption, reflection,

scattering and diffraction

a




Propagation Effects

Propagation Effects


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Shadowing: caused by obstacles between the TX and RX that

attenuate signal power through absorption, reflection,

scattering and diffraction

Multipath Fading

The received signal of a mobile moving over very small distancesis a sum of many contributions coming from different directions.

The received signal powera may vary by as much as three or four

orders of magnitude (30 or 40 dB) when the receiver is moving by

only a fraction of a wave length.

a




Relation of Path Loss, Shadowing and Multipath


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Transmit and Receive Sign al Models Large-Scale Propagation Effects

Outline



3

Free Space Propagation Model
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Free Space Propagation Model4 Ray Tracing Path Loss Models

Reflection

Diffraction

Scattering





Link Budget Analysis

Simplified Path Loss Model





Transmit and Receive Signal Model

Noise
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s(t) Channel,h(t) +

n(t)

r(t)

Transmitted

Signal

Received

Signal

Noise

Transmitted signal: s(t)=Res(t)ej2fct

Received signal: r(t)=Re

r(t)ej2fct

+n(t)For time-invariant channels: r(t)= s(t)h(t)

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Representation of Bandpass Signals

Complex lowpass representation ofs(t)

s(t)= sI(t)cos(2fct) sQ(t)sin(2fct) (5)


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( ) ( ) ( f ) ( ) ( f ) ( )

sI(t)andsQ(t)are real lowpass (baseband) signals with

bandwidthBfcand also called in-phaseandquadraturecomponents ofs(t).

s(t) = ResI(t)+jsQ(t)

cos(2fct)+jsin(2fct)

(6)

= Re{s(t)} cos(2fct) Im {s(t)} sin(2fct) (7)= Re

s(t)ej2fct

(8)

s(t) sI(t)+jsQ(t)is theequivalent lowpass signal fors(t)oritscomplex envelope.


Free Space Propagation Model Large-Scale Propagation Effects

Outline



3

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p p g4 Ray Tracing Path Loss Models

Reflection

Diffraction

Scattering












TX and RX have a clear, unobstructed LOS path in between

Examples: satellite communication systems and microwave

LOS radio links
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LOS radio links

Friis Free Space Equation

Pr(d)

=

PtGtGr2

(4)2

d2

L

(9)

Pt: transmitted power,

Pr(d): received power at T-R separation distance dmeters,

Gt: transmitter antenna gain,

Gr: receiver antenna gain,

: wave length in meters,L: system loss factor not related to propagation (L 1).



Free Space Propagation Model, contd

System Loss Factor: L(L 1), usually due to transmission lineattenuation, filter losses and antenna losses; L= 1no loss inthe system hardware

1
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yReceived Power: Pr 1d220 dB/decadeIsotropic Radiatoran ideal antenna which radiates powerwith unit gain uniformly in all directions.

Effective Isotropic Radiated Power,EIRP=PtGt

the

maximum radiated power available from a transmitter in the

direction of maximum antenna gain, as compared to an

isotropic radiator

Effective Radiated Power,ERPas compared to ahalf-wave dipole antenna.

dBi vs dBd: dipole antenna has a gain of 1.64 (2.15 dB above

an isotrope)EIRP[dB]= 2.15+ERP[dB]



Power Flux Density
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Power flux densityPd (W/m2) in free space

Pd=EIRP

4d2= PtGt

4d2= E

2

Rfs= E

2

= |E|

2

120= |E|

2

377W/m2 (10)

Rfs: the intrinsic impedance of free space;|E|: the magnitude of theradiating portion of the electric field in the far field



Received Power

Received Power

Pr(d)=PdAe=|E|2

120Ae=PtGtGr

2

(4)2d2 =|E|2Gr2

4802 W (11)
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whereAe= Gant2

4 is effective aperture of the antenna.

Received Power

Pr(d) = Pr(d0)d0

d

2, d d0 df (12)

Pr(d)[dBm] = 10log Pr(d0)

0.001W

+20log

d0

d

(13)

d0 is the reference distance and typically chosen to be 1m (indoor)

or 100m1Km (outdoor).



Equivalent Received Voltage at Receiver Input
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Equivalent Received Voltage at Receiver Input

Pr(d) =V2rxRant

= (Vant/2)2

Rant= V

2ant

4Rant

Vrx =RantPr(d) (14)

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Path Loss

Path Loss in Free Space

PL[dB]= 10logPt

Pr = 10logGtGr2

(4)2d2

(15)


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valid fordin the far-field (d d0 df)a of the transmitter antenna.

aFar Field (Fraunhofer Region): df= 2D2

,dfD,df , whereDis the largest

physical linear dimension of the antenna.

Example 2

Find the far field distance for an antenna with maximum dimension

of 1m and operating frequency of 900MHz.

Solution:

far field distance df= 2D2 = 2D2

c/f= 2(1)2

3108900106

= 213

= 6m



Free-Space LOS Received Signal

Free-Space LOS Received Signal

r(t)=ReGtGre

j2 d4d

s(t)ej2fct (16)
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Example 3

If a transmitter produces 50W of power, express the transmit power

in (a) dBm (b) dBW. If 50W is applied to a unit gain antenna with a

900MHz carrier frequency, (c) find the received power in dBm at afree space distance of 100m from the antenna. (d) What is

Pr(10km)? AssumeGr= 1.Solution:

(a) Pt(dBm)= 10log(Pt(mW)/1mW)= 10log(50103)= 47dBm

(b) Pt(dBW)= 10log(Pt(W)/1W)= 10log(50)= 17dBW(c) Pr(d)= PtGtGr

2

(4)2d2L= 50(1)(1)(1/3)2

(4)2(100)2(1)=3.5106W= 3.5103mW

Pr(dBm)= 10logPr(mW)= 10log(3.5103mW)=24.5dBm(d) Pr(10km)=Pr(100m)+20log

10010000

=24.540=64.5dBmWS Wuen Mobile Communications 20

Ray Tracing Path Loss Models Large-Scale Propagation Effects

Outline



3 Free Space Propagation Model

4 Ray Tracing Path Loss Models
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Reflection

Diffraction

Scattering

5 Empirical Path Loss ModelsOutdoor Propagation Models









Ray Tracing Path Loss ModelsTracing radio ray propagation paths

Reflection

Diffraction

Scattering
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Reflection of Radio Waves

When a radio wave propagating in one medium impinges upon

another medium having different electrical propertiespartiallyreflected and partially transmitted.

Material of 2nd medium
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Material of2 medium

Perfect Dielectric: partially transmitted into the2nd medium

and partially reflected back to the 1st medium, andno loss of

energy.

Perfect Conductor: all energyis reflected backwithout loss of

energy.

Lossy Dielectric: absorbs powercomplex dielectric constant:

=0r

j

=0r

j

2f(17)

0 = 8.851012 F/m is the free space dielectric constant.



Material Parameters at Various Frequencies

Material Relative Conductivity Frequency

Permittivity r (s/m) (MHz)

Poor Ground 4 0.001 100

Typical Ground 15 0.005 100Good Ground 25 0 02 100
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Good Ground 25 0.02 100

Sea Water 81 5.0 100

Fresh Water 81 0.001 100

Brick 4.44 0.001 4000

Limestone 7.51 0.028 4000Glass, Corning 707 4 1.8107 1Glass, Corning 707 4 2.7105 100Glass, Corning 707 4 0.005 10000

Good conductor: rand are generally insensitive to operatingfrequency

Lossy dielectric: ris constant with frequency, but may be

sensitive to operating frequency

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Reflection Coefficients

Reflection Coefficients

= Er

Ei =2 sint

1 sini

2 sint+1 sini (E-field in POI) (19)E i i


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= Er

Ei= 2 sini1 sint2 sini+1 sint

(E-fieldPOI) (20)

=/is the intrinsic impedance of the medium= 1/is the velocity of an EM wavePOI: plane of incidence

Fresnel Reflection Coefficient,

The ratio of the E-field intensity of the reflected to the

transmitted waves.

Depends on the material properties, wave polarization, incident

angle and frequency of the propagating wave.



Snells Law and Brewster Angle

Snells Law

11 sin(90i)=

22 sin(90t) (21)

Brewster Angle

th i id t l t hi h fl ti i th di
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the incident angle at which no reflection occurs in the medium

Condition: the incident angleBis such that the reflection

coefficient is equal to zero.

sinB=

1

1+2(22)

Example: if the first medium is free space and the second medium

has a relative permittivityr

sinB=r12r1

(23)

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Example 4

Demonstrate that if medium 1 is free space and medium 2 is a

dielectric both||and||approach 1 asiapproach0 regardlessofr.Solution:


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=rsin0+

rcos2 0

rsin0+rcos2 0= 1, (28)

=sin0

rcos2 0

sin0+rcos2 0

=r1r1

=1 (29)

Ground may be modeled as a perfect reflector with|| = 1whenan incident wave grazes the earth, regardless of polarization or

ground dielectric properties.



Ground Reflection (Two-Ray) Model
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Reasonably accurate for predicting

the large-scale signal strength over long distances (km) formobile systems that use tall towers (heights>50m)line-of-sight microcell channels in urban environments

Free space propagation E-field:

E(d,t)= E0d0d

cos

c

t d

c

d> d0 (30)



Deriving Total Received E-fieldE-field due to line-of-sight component

EL(dL, t)=E0d0

dLcos

c

tdL

c

(31)

E-field for the ground reflected wave

ER(dR, t)= E0d0dR

cosc

tdR

c

(32)
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Total Received E-field

ETOT(d, t)=E0d0

dLcos

c

tdL

c

+E0d0

dRcos

c

tdR

c

(33)



Deriving Total Received E-field, contd

Consider grazing incidence

Small incident angle: i 0

Perfect horizontal E-field polarization

Ground reflection: =1and Et=0


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Total E-field envelope:|ETOT| = |EL+ER|

ETOT(d, t)=E0d0

dLcos

c

tdL

c

+ (1)E0d0

dRcos

c

tdR

c

(34)

Path difference: = dRdL=

(ht+hr)2+d2

(hthr)2+d2 2hthrd(dht+hr)Time Delay: d= c= 2c=

c=

2fc

Phase difference: =cd= 2 = cc

Large distance: dht+hrd dLdR E0d0

d

E0d0dL

E0d0dR



Deriving Total Received E-field, contdThe received E-field evaluated att= dRc

ETOT

d, t= dR

c

= E0d0

dLcos

c

dRdL

c

E0d0

dRcos0

= E0d0

dLcos

E0d0

dR =E0d0

dcos1 (35)

E-field normal to the POI, horizontal polarization, =1
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ETOT(d)(=1) =

E0d0

d

2 cos1

2+E0d0d

2sin2 (36)

= E0d0d 22cos = 2

E0d0

dsin

2(37)

E-field in the POI, vertical polarization, =1ETOT(d)(=1) = E0d0d

2+2cos = 2E0d0

dcos

2(38)



Deriving Total Received E-field, contd

For

2 < 0.3rad sin

2

2 = 2hthr

d < 0.3

Approximation of the received E-field at large distanced

d> 20hthr3

20hthr

(39)

2E d 2 h h 1
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ETOT(d)2E0d0

d

2hthr

d 1

d2 (40)

Received Power at T-R distance dhthr

Pr=PtGtGrh2th

2r

d4 1

d4 (41)

Received power is independent of frequency!

Path Loss for Ground Reflection (Two-Ray) Model

PLdB= 40logd (10logGt+10logGr+20loght+20loghr) (42)Path loss is independent of frequency!



Received Signal for Two-Ray Model

Received Signal for Two-Ray Model

(G G ) d
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r2ray(t) = Re

4

(GtGr)L

dLs(t)ej2

dL

+

(GtGr)R

dRs(t

d)e

j2dR ej2fct (43)

where(GtGr)Lis the transmit and receive antenna gain in the LOS

direction and(GtGr)Ris the transmit and receive antenna gain

corresponding to the reflected ray.

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Diffraction


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Causes: the propagation of secondary wavelets into a

shadowed (obstructed) region; explained by HuygensPrinciple1.

Locations: curved surface of the earth, hilly or irregular terrain,

building edges or obstructions blocking the LOS path between

TX and RX.

Model: theFresnel knife-edge diffraction model.

1Huygens Principle: all points on a wavefront can be consider as point sources for

the production of secondary wavelets and these wavelets combine to produce a new

wavefront in the direction of propagation.

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Fresnel Zones


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The loss due to knife-edge diffraction is a function ofand can

be explained by Fresnel zones.2

nth Fresnel zone radius (rn)

rn=nd1d2

d1+d2valid ford1,d2 rn (49)

Fresnel zones will have maximum radii if the knife-edge

obstacle is midway between TX and RX

rn=nd

2(d1 = d2 = d2 ) (50)

2Fresnel zone: successive regions where secondary waves have an excess path

length equal to n2 ,nN.WS Wuen Mobile Communications 39


Knife-Edge Diffraction Loss ModelThe diffraction loss occurs from the blockage of secondary

wavesonly a portion of the energy is diffracted around anobstacle.

Ideally, for an 80%-free Fresnel zone, no significant signal loss

presents. Keep at least 60% of the zone free, or the link will be

unreliable, poor or may never work.
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p y

Diffraction loss isLd()= 20log|F()|, whereF()is the complexFresnel integral (F() EdE0 =

1+j2

e

jt22 dt) (relative to LOS

path)

Lees Approximation forLd()

Ld()[dB]=

0 120log(0.5

0.62)

1

2.4

(51)


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Received Signal for Knife-Edge Diffraction Model

Received Signal for Knife-Edge Diffraction Model Ld()

(GrGt )d j2 d / j2 f t
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r(t)=Re

4

Ld()

(GrGt)d

dDs(t)ej2dD/ej2fct

(52)

where(GrGt)dis the TX and RX antenna gain product in the

diffracted ray direction; = dc is the delay associated with thediffracted ray relative to LOS path and dD= d1+d2 is the traveledpath of the diffracted ray .



Example 6

If an obstacle is 10km away from a TX antenna and 2km away from

RX antenna, find (a) the1st Fresnel zone boundary, and (b) the

boundary for 80% clearance for transmitting 900MHz signal.

Solution:

(a)r1 =

d1d2d1+d2 =

3108900106(210

3)(10103)1210

3 = 23.57m (b)0.8r1 = 18.86m
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1 2

12 10

Example 7

Continue the above example. If the TX antenna height is 50m andRX antenna height is 25m, determine the loss due to knife-edge

diffraction. Assume the obstacle height is 100m.

Solution:

= tan1 1005010000 = 0.005,= tan

1

10025

2000 = 0.0375,=+= 0.0425 = 0.0425 2100002000(1/3)(10000+2000)=4.25Gd(4.25)= 20log(0.225/4.25) =25.52dB.



Scattering

When a radio wave impinges on arough surface, the reflected
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energy is spread out in all directions.

Rayleigh criterionhc: determines surface roughness by defining

a critical heighthc

=

8sini

Smooth surface: maximum to minimum protuberancehhcRough surface:h> hc

Scatter loss factors: rough= sflatAments:s= exp

8

hsini

2

Boithiass:s= exp8hsini 2 I0 8hsini 2whereh is the standard deviation of the surface height about

the mean surface height,I0 is the Bessel function of the first kind

and zero order.



Radar Cross Section Model

Radar cross sectionRCS: the ratio of the power density of the

signal scattered in the direction of RX to the power density of

the radio wave incident upon the scattering object, in unit ofdBm2.
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Received power:

Pr [dBm]

= Pt [dBm]

+Gt [dBi]

+20log()

+RCS[dB

m2]

30log(4)20logd20logd (53)

wheredandd are the distance from the scattering objects toTX and RX

Useful for predicting receiver power which scatters off large

objects such as buildings.



Received Signal Due to a Scattered Ray

Bistatic Radar Equation

(G G ) RCS
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r(t)=Re

(GtGr)sRCS

(4)3/2dd s(t)ej2(d+d)/ej2fct

(54)

where

=(d

+d

dL)/cis the delay associated with the scattered

ray;RCSis the radar cross-section of the scattering objects,

depending the roughness, size and shape of the scattering objects.



Ray Tracing Model

Totoal received signal for a LOS path,Nr reflected,Nddiffracted and

Nsscattered rays:

Ray Tracing Model

G G
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r(t) = Re

4

GtGr

dLs(t)ej2dL/

+Nri=1

i(GtGr)R,idR,i s(ti)e

j2dR,i/

+Ndj=1

Ld()

(GtGr)D,j

dD,js(tj)ej2dD,j/

+Nsk=1

(GtGr)S,kRCS,k4dkdk s(tk)ej2(dk

+dk

)/ej2fct

(55)


Empirical Path Loss Models Large-Scale Propagation Effects

Outline



3 Free Space Propagation Model


Reflection
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Diffraction

Scattering

5 Empirical Path Loss ModelsOutdoor Propagation Models




Simplified Path Loss ModelLog-normal Shadow Fading



Empirical Path Loss Models Large-Scale Propagation Effects

Empirical Path Loss

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