WDN Lec1 Overview.key

8/18/2019 WDN Lec1 Overview.key

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WIRELESS DATA NETWORKSA/Prof Iain Murray314:312 Ext [email protected]

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WHAT TO EXPECT?

!

To provide an in-depth coverage of existing and emergingwireless data communication networks technologies.! To study the technology components which form the

infrastructure of the wireless data communicationnetworks.

! Concept of the underlying protocols and technologicalprinciples will be discussed.

! Added: The Internet of Things (IoT)

2

Tentative Topics

WEEK TOPIC ASSESSED IN

1-4 MAC/PHY/Networks Final Exam

5-8 WLAN/PAN/Mobile IP Lab Book and skills testFinal Exam

9-14 IoT/Sensor networksLab book and design

assignmentFinal exam

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ASSESSMENT BREAKDOWNTask Value % Date Due

1 Lab Book 1(Lab 1 to 5) 10 percent

Labs are dueFriday of eachweek

2 Ski ll Test 15 percentWeek: 8Book a day andtime

Lab1,2,3,4,5

3 Lab Book 1(Lab 6 to 9) 10 percentLabs are dueFriday of eachweek

4 Lab Assignment 25 percentWeek: 11Day: FridayTime: 16:00

Lab6,7,8,9

5 Exam 40 percent Week 12 inlecture

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Other Course-related Information

! No Textbook !

Most resources will be available on Blackboard! Reference books:

" Mobile Communications, 2nd Edition, Jochen Schiller, AddisonWesley

" Principles of wireless networks , Kaveh Pahlavan and PrashantKrishnamurthy, Prentice Hall, 2002

" Fundamentals of WiMaX: understanding broadband wireless networking, J .G. Andrews, A. Ghosh, R. Muhamed, Prentice Hall, 2007

" Mobile Ad Hoc Networks: from wireless LANs to 4G networks, Protocolsand Architectures for Wireless Sensor Networks, George Aggelou,McGraw Hill, 2005

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Areas of interest in WDN

! Wireless Communication" transmission quality (bandwidth, error rate, delay)" modulation, coding, interference" media access, regulations" ...

! Mobility" location dependent services" location transparency" quality of service support (delay, jitter, security)" ...

! Portability" power consumption" limited computing power, sizes of display, ..." usability" ...

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PROBLEM?

• Two different groups in this unit• B.Tech - Completing CCNA and have covered programming

• M.Eng.Sc - Varied experience• Extra “discussion” each week for those interested

• C programming• Introduction to Networking• IPv6• IP Routing

7

Simple reference model used here (TCP/IP)

Application

Transport

Network

Data Link

Physical

Medium

Data Link

Physical

Application

Transport

Network

Data Link

Physical

Data Link

Physical

Network Network

Radio

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LAYER INFLUENCE OF MOBILE COMMUNICATIONTO THE LAYER MODEL

APPLICATIONservice location

multimediaadaptive applications

TRANSPORTcongestion and ow control

quality of service

NETWORKaddressing, routing,

device locationhand-over

DATA LINKauthentication, media access

Multiplexingmedia access control

PHYSICAL encryption, modulation, interference, attenuation,frequency

9

Overlay Networks - the global goal

regional

metropolitan area

campus-based

in-house

verticalhandover

horizontalhandover

integration of heterogeneous fixed andmobile networks with varyingtransmission characteristics

10

Frequencies for communication

1 Mm300 Hz

10 km30 kHz

100 m3 MHz

1 m300 MHz

10 mm30 GHz

100 µ m3 THz

1 µ m300 THz

visible lightVLF LF MF HF VHF UHF SHF EHF infrared UV

optical transmissioncoax cabletwisted pair

VLF = Very Low Frequency UHF = Ultra High FrequencyLF = Low Frequency SHF = Super High FrequencyMF = Medium Frequency EHF = Extra High FrequencyHF = High Frequency UV = Ultraviolet LightVHF = Very High Frequency

Frequency and wave length:! = c/f

wave length ! , speed of light c " 3x10 8m/s, frequency f

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Frequencies for mobile communication

! VHF-/UHF-ranges for mobile radio" simple, small antenna for cars" deterministic propagation characteristics, reliable connections

!

SHF and higher for directed radio links, satellite communication" small antenna, beam forming" large bandwidth available

! Wireless LANs use frequencies in UHF to SHF range" some systems planned up to EHF" limitations due to absorption by water and oxygen molecules

(resonance frequencies)• weather dependent fading, signal loss caused by heavy

rainfall etc.

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Frequencies and regulations

Europe USA Japan

CellularPhones

GSM 450-457, 479-486/460-467,489-496, 890-915/935-

960,1710-1785/1805-1880UMTS (FDD) 1920-1980, 2110-2190UMTS (TDD) 1900-1920, 2020-2025

AMPS , TDMA , CDMA 824-849,869-894

TDMA , CDMA , GSM 1850-1910,1930-1990

PDC 810-826,940-956,

1429-1465,1477-1513

CordlessPhones

CT1+ 885-887, 930-932CT2864-868DECT1880-1900

PACS 1850-1910, 1930-1990PACS-UB 1910-1930

PHS 1895-1918JCT 254-380

WirelessLANs

IEEE 802.112400-2483HIPERLAN 25150-5350, 5470-5725

902-928IEEE 802.112400-24835150-5350, 5725-5825

IEEE 802.11 2471-24975150-5250

Others

RF-Control27, 128, 418, 433,868

RF-Control315, 915

RF-Control 426, 868

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802.11 LANs

! There are four major factors to consider before

implementing a wireless network:• High availability

• Scalability

• Manageability

• Open architecture

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Momentum is Building in Wireless LANs

• Wireless LANs are an “addictive”technology

• Strong commitment to Wireless LANs bytechnology heavy-weights – Cisco, IBM, Intel, Microsoft

• Embedded market is growing – IoT – Sensor networks

• The WLAN market is expanding

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Wireless LANs Are Taking Off

Future Growth Due To:" Standards" High Bandwidth Needs" Low Cost

" Embedded in Laptops" Variety of Devices" Voice + Data" Multiple Applications" Security Issues Solved" Ease of Deployment" Network Mgmt. Tools" Enterprise Adoption

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“Business-Class”vs Consumer WLAN

• Industry has segmented: consumer vs. business

“business-class” products:• Security• Upgradeability• Network management• Advanced features• Choice of antennas• Highest throughput• Scalability

“consumer-class” products•Ease of use•Reliability

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Benefits of WLANs

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Unlicensed Frequency Bands

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Wireless Data Networks

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Wireless Technologies (ignore speeds)

PAN

(Personal Area Network)

LAN

(Local Area Network)

WAN

(Wide Area Network)

MAN

(Metropolitan Area Network)

PAN LAN MAN WAN

Bluetooth

Peer-to-PeerDevice-to-Device

Short

1-25Mbps

802.11a, 11b, 11gHiperLAN2

Enterprise Networks

Medium

2–54+ Mbps

802.11MMDS, LMDS

Fixed, LastMile Access

Medium–Long

22+ Mbps

GSM, GPRS,CDMA, 2.5–3G

PDAs, MobilePhones, Cellular

Access

Long

10–384 Kbps

Standards

Speed

Range

Applications

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Wireless LAN Security: Lessons

“ War Driving ”

Hacking into WEP

Lessons:

• Security must be turned on (part of the installation process)

• Employees will install WLAN equipment on their own (compromisessecurity of your entire network)

• It takes just 3 seconds to extract a 104-bit WEP key from intercepteddata using a 1.7GHz Pentium M processor.

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Reliability and Connectivity

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IEEE 802. Standards

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802 Committee Architecture

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Basic Service Set (BSS)

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Independent Basic Service Set (IBSS)

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Extended Service Set (ESS) and Distributed System (DS)

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MAC Architecture

Before sending a frame, STAsmust get access to the medium.

1. IEEE 802.11 MAC, carriersense multiple access withcollision avoidance (CSMA/CA),is called the DistributedCoordination Function (DCF)

2. Point Coordination Function(PCF), creates contention-free(CF) access

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CSMA

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Interframe Spaces

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Interframe Space (IFS) Values

• Short IFS (SIFS)•Shortest IFS

•Used for immediate response actions• Point coordination function IFS (PIFS)•Midlength IFS•Used by centralised controller in PCF scheme when using polls

• Distributed coordination function IFS (DIFS)•Longest IFS•Used as minimum delay of asynchronous frames contending for

access

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IFS Usage

•SIFS•Acknowledgment (ACK)•Clear to send (CTS)•Poll response

•PIFS•Used by centralised controller in issuing polls•Takes precedence over normal contention traffic

•DIFS•Used for all ordinary asynchronous traffic

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Overview

! This module is an introduction to IoT fundamentalconcepts and its application.

! We will discuss the IoT components and theirfunctionalities.

! There are a set of lab experiments to give you some ideaabout the real world implementation of IoT

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Connecting the unconnected

!

There are currently 1.5 devices for every human being on theplanet.

! Sensors, smart objects, and other devices are some example ofdevices connecting through the reach and power of the Internet.

! They are dynamically generating, analysing, and communicatingintelligence to increase operational efciency, power newbusiness models, and improve quality of life.

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IoT Example

! https://www.youtube.com/watch?v=co2MLqkJVXs

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Lab Experiments

! Hardware" Sensor node (mote) gathers and process data in Wireless

sensor network " AS-XM1000 is a wireless sensor used in the lab" It includes Temperature, Humidity, and Light sensor" USB interface

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Lab Experiments

! Software" ContikiOS"

Open source operating System" Connects low-cost, low-power microcontrollers to

the Internet" Provides entire development environment" Applications are written in standard C" You will install it on a Virtual machine

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Overview

! Antennas! Modulation

! Coding

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Antennas: isotropic radiator

zy

x

z

y x idealisotropicradiator

• Radiation and reception of electromagnetic waves, coupling of wires tospace for radio transmission

•Isotropic radiator: equal radiation in all directions (three dimensional) -only a theoretical reference antenna

• Real antennas a lways have directive effects (vertically and/orhorizontally)

• Radiation pattern: measurement of radiation around an antenna

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Antennas: simple dipoles

side view (xy-plane)

x

y

side view (yz-plane)

z

y

top view (xz-plane)

x

z

simpledipole

! /4 ! /2

• Real antennas are not isotropic radiators but, e.g., dipoles with lengths # /4 on car roofs or #/2 as Hertzian dipole# shape of antenna proportional to wavelength

• Example: Radiation pattern of a simple Hertzian dipole

• Gain: maximum power in the direction of the main lobe compared to thepower of an isotropic radiator (with the same average power)

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Antennas: directed and sectorised

Often used for microwave connections or base stations for mobile phones (e.g., radiocoverage of a valley)

side view (xy-plane)

x

y

side view (yz-plane)

z

y

top view (xz-plane)

x

z

top view, 3 sector

x

z

top view, 6 sector

x

z

directedantenna

sectorisedantenna

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Antennas: diversity

+

! /4! /2! /4

ground plane

! /2

! /2

+

! /2

• Grouping of 2 or more antennas• multi-element antenna arrays

• Antenna diversity• switched diversity, selection diversity• receiver chooses antenna with

largest output• diversity combining

• combine output power toproduce gain

• cophasing needed to avoidcancellation

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Signal propagation ranges

distance

sender

transmission

detection

interference

• Transmission range•communication possible• low error rate• Detection range•detection of the signal

possible•no communication

possible• Interference range

•signal may not be detected•signal adds to the background

noise

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Signal propagation

reflection scattering diffractionshadowing refraction

• Propagation in free space always like light (straight line)• Receiving power proportional to 1 /d! in vacuum – much more in real

environments• (d = distance between sender and receiver)

• Receiving power additionally influenced by•fading (frequency dependent)•shadowing•reflection at large obstacles•refraction depending on the density of a medium•scattering at small obstacles•diffraction at edges

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Real world example

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Multipath propagation

signal at sender signal at receiver

LOS pulses multipathpulses

• Signal can take many different paths between sender and receiver due to reflection,scattering, diffraction

• Time dispersion: signal is dispersed over time# interference with “neighbour” symbols, Inter Symbol Interference (ISI)

• The signal reaches a receiver directly and phase shifted# distorted signal depending on the phases of the different parts

49

Effects of mobility

short term fading

long termfading

t

power

Channel characteristics change over time and location•signal paths change

•different delay variations of different signal parts•different phases of signal parts# quick changes in the power received (short term fading)

Additional changes in•distance to sender•obstacles further away

# slow changes in the average powerreceived (long term fading)

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s 2

s 3

s 1

Multiplexing

f

t

c

k2 k3 k4 k5 k6k1

f

t

c

f

t

c

channels k i

•Multiplexing in 4 dimensions•space (s i)•time (t)•frequency (f)•code (c)

•Goal: multiple useof a shared medium

•Important: guard spaces needed!

51

Frequency multiplex

t

k2 k3 k4 k5 k6k1

f

c

Separation of the whole spectrum into smaller frequency bandsA channel gets a certain band of the spectrum for the whole timeAdvantages:• no dynamic coordination

necessary• works also for analog signals

Disadvantages:• waste of bandwidth if the traffic is

distributed unevenly• inflexible• guard spaces

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t

f

c

k2 k3 k4 k5 k6k1

Time multiplex

A channel gets the whole spectrum for a certainamount of time

Advantages:• only one carrier in the

medium at any time• throughput high even

for many users

Disadvantages:• precise

synchronisationnecessary

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Time and frequency multiplex

f

t

c

k2 k3 k4 k5 k6k1

Combination of both methodsA channel gets a certain frequency band for a certain amount of timeExample: GSM

Advantages:•better protection against tapping•protection against frequency

selective interference•higher data rates compared

to code multiplexbut: precise coordination

required

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Code multiplexk2 k3 k4 k5 k6k1

f

t

cEach channel has a unique code

All channels use the same spectrumat the same time

Advantages:

• bandwidth efficient• no coordination and synchronizationnecessary

• good protection against interference andtapping

Disadvantages:• lower user data rates• more complex signal regeneration

Implemented using spread spectrum technology

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Modulation

• Digital modulation•digital data is translated into an analog signal (baseband)•ASK, FSK, PSK - main focus•differences in spectral efficiency, power efficiency, robustness

• Analog modulation• shifts centre frequency of baseband signal up to the radio carrier

• Motivation• smaller antennas (e.g., #/4)•Frequency Division Multiplexing•medium characteristics

• Basic schemes•Amplitude Modulation (AM)•Frequency Modulation (FM)•Phase Modulation (PM)

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Modulation and demodulation

synchronizationdecision

digitaldata

analogdemodulation

radiocarrier

analogbasebandsignal

101101001 radio receiver

digital

modulation

digitaldata

analog

modulation

radiocarrier

analogbasebandsignal

101101001 radio transmitter

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Digital modulation

1 0 1

t

1 0 1

t

1 0 1

t

Modulation of digital signals known as Shift Keying• Amplitude Shift Keying (ASK):

•very simple• low bandwidth requirements•very susceptible to interference

• Frequency Shift Keying (FSK):•needs larger bandwidth

• Phase Shift Keying (PSK):•more complex•robust against interference

58

Advanced Phase Shift Keying

Q

I01

Q

I

11

01

10

00

BPSK (Binary Phase Shift Keying):• bit value 0: sine wave• bit value 1 : inverted sine wave• very simple PSK• low spectral efficiency

•robust, used e.g. in satellite systems

QPSK (Quadrature Phase Shift Keying):• 2 bits coded as one symbol• symbol determines shift of sine wave• needs less bandwidth compared to BPSK• more complex

Often also transmission of relative, not absolute phase shift: DQPSK –phase-shifts are 0°, 90°, 180°, " 90° corresponding to data '00', '01', '11',

'10'.

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DQPSK

phase-shifts are 0°, 90°, 180°, " 90°corresponding to data '00', '01', '11', '10'.

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Quadrature Amplitude Modulation

0000

0001

0011

1000

Q

I

0010

!

a

Quadrature Amplitude Modulation (QAM): combines amplitude andphase modulation

• it is possible to code n bits using one symbol• 2n discrete levels, n=2 identical to QPSK• bit error rate increases with n, but less errors compared to

comparable PSK schemes

Example: 16-QAM (4 bits = 1 symbol)Symbols 0011 and 0001 have the same

phase $ , but different amplitude a.0000 and 1000 have different phase, but same

amplitude.* used in standard 9600 bit/s modems

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Problem of radio transmission: frequency dependent fading ca n wipe out narrowband signals for duration of the interference

Solution: spread the narrow band signal into a broad band signal using a special

code protection against narrow band interference

protection against narrowband interference

Side effects:• coexistence of several signals without dynamic coordination• tap-proof

Alternatives: Direct Sequence, Frequency Hopping

Spread spectrum technology

detection atreceiver

interference spread signal signal

spreadinterference

f f

power power

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DSSS (Direct Sequence Spread Spectrum) I

user data

chippingsequence

resultingsignal

0 1

0 1 1 0 1 0 1 01 0 0 1 11

XOR

0 1 1 0 0 1 0 11 0 1 0 01

=

tb

tc

tb: bit periodtc: chip period

XOR of the signal with pseudo-random number(chipping sequence)• many chips per bit (e.g., 128) result in higher

bandwidth of the signalAdvantages

• reduces frequency selective fading• in cellular networks• base stations can use the s ame frequency

range• several base stations can detect and recover

the signal• soft handover

Disadvantages• precise power control necessary

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DSSS (Direct Sequence Spread Spectrum) II

X

user data

chippingsequence

modulator

radiocarrier

spreadspectrumsignal

transmitsignal

transmitter

demodulator

receivedsignal

radiocarrier

X

chippingsequence

lowpassfilteredsignal

receiver

integrator

products

decisiondata

sampledsums

correlator

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FHSS (Frequency Hopping Spread Spectrum) I

Discrete changes of carrier frequency•sequence of frequency changes determined via pseudo random number

sequence

Two versions•Fast Hopping:

several frequencies per user bit•Slow Hopping:

several user bits per frequencyAdvantages

•frequency selective fading and interference limited to short period•simple implementation•uses only small portion of spectrum at any time

Disadvantages•not as robust as DSSS•simpler to detect

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FHSS (Frequency Hopping Spread Spectrum) II

user data

slowhopping(3 bits/hop)

fasthopping(3 hops/bit)

0 1

tb

0 1 1 t

f

f 1

f 2

f 3

t

td

f

f 1

f 2

f 3

t

td

tb: bit period t d: dwell time

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FHSS (Frequency Hopping Spread Spectrum) III

modulator

user data

hoppingsequence

modulator

narrowbandsignal

spreadtransmitsignal

transmitter

receivedsignal

receiver

demodulator data

frequencysynthesizer

hoppingsequence

demodulator

frequencysynthesizer

narrowbandsignal

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Cell structure

Implements space division multiplex: base station covers a certaintransmission area (cell)

Mobile stations communicate only via the base station

Advantages of cell structures:

• higher capacity, higher number of users• less transmission power needed• more robust, decentralised• base station deals with interference, transmission area etc. locally

Problems:• fixed network needed for the base stations• handover (changing from one cell to another) necessary• interference with other cells

Cell sizes from100 m in cities to 35 km on the country side (GSM) - even less forhigher frequencies

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Frequency planning I

f 4

f 5

f 1

f 3

f 2

f 6

f 7

f 3

f 2

f 4

f 5

f 1

Frequency reuse only with a certain distance between the basestations

Standard model using 7 frequencies:

Fixed frequency assignment:• certain frequencies are assigned to a certain cell• problem: different traffic load in different cells

Dynamic frequency assignment:• base station chooses frequencies depending on the frequencies

already used in neighbour cells• more capacity in cells with more traffic• assignment can also be based on interference measurements

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Frequency planning II

f 1

f 2

f 3f 2

f 1

f 1

f 2

f 3f 2

f 3

f 1

f 2f 1

f 3f 3

f 3f 3

f 3f 4

f 5

f 1

f 3

f 2

f 6

f 7

f 3

f 2

f 4

f 5

f 1

f 3

f 5f 6

f 7f 2

f 2

f 1f 1 f 1f 2

f 3

f 2

f 3

f 2f 3

h1h2

h3g1

g2

g3

h1h2

h3g1

g2

g3g1

g2

g3

3 cell cluster

7 cell cluster 3 cell clusterwith 3 sector antennas

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WDN Lec1 Overview.key