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)
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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
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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
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Overlay Networks - the global goal
regional
metropolitan area
campus-based
in-house
verticalhandover
horizontalhandover
integration of heterogeneous fixed andmobile networks with varyingtransmission characteristics
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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
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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!
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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
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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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