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8/8/2019 Lec 1 Intro Wireless Communication
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Wireless Communications
By
Dr. Mustafa Shakir
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Course Material
Text: Wireless Communications: Principles andPractice by T. Rappaport
References
Wireless Communications and Networks by W.Stallings
Wireless Communications by Andrea Goldsmith
Wireless Communications by Roy Blake.
Wireless & Mobile Networks Architecture by Yi Bing
and Imrich Chlamtac
Other Books & Internet.
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What is wireless
communication?
Any f ormof communication that does not require the transmitter
and receiver tobe in physical contact
Electr omagnetic wave propagated through free-space
Radar, RF, Microwave, Optical (infrared, Laser).
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Early History of Wireless
Communicati
on
. Many people in history used light for communication.
1. 150 BC smoke signals ( Greece)
2. 1794, optical telegraph,
Disadvantages of these forms of communication Limited alphabets
Noisy
Br oadcast (no privacy or security)
Limited distance (or require relay which is unreliable)
Require line-of-sight between transmitter and receiver
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Lateron Electromagnetic waves
becam
e im
po
rtant1. 1831 Faraday demonstrates
electromagnetic induction.
2. J. Maxwell (1831- 79): Theory ofelectromagnetic fields, wave equations
(1864)
3. H. Hertz (1857-94): demonstrated thewave characterof electrical transmission
through space.
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Evolution of Voice Oriented
Wireless Networks The origin of wireless communication dates back to
the era of Marconi ---- 1897, when he demonstratedthe radios communication ability to provide continuous
contact with the ships sailing the English channel. Mobile telephone service was first offered by AT&T in
1946. This service was mobile, but not cellular. Thebase station had a coverage of about 100 km.
Early systems, based on FM, required 120 KHz ofspectrum for an information bandwidth of 3 kHz. Largeequipment (mounted in cars). Low capacity: 50 usersormore cause overloading, 65% blocking probability.Multiple Access method used was FDMA.
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Evolution of Voice Oriented
Wireless Networks Next step was the introduction of trunking - relaxing theconstraint of using a channel for each user.
Cellular concept emerges in early 1970s. Cellular is not a newtechnology but rather a new organization.
Replication of the wide-area network concept. Cellularconcept leads to frequency-reuse concept. By late 60's therewere 70,000 users throughout US.
Invention of the microprocessor facilitated the implementationof the complex control algorithms required mainly for switching
between base stations.
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Todays Wireless Communication
System
sFollowing are some famous wireless
communication systems.
Cellular Teleph
one Syste
ms/P
CS
Cordless Telephone Systems
Paging Systems
WLAN/PAN/Ad-Hoc NetworkingBlue Tooth
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Personal Communication
Systems
PCS
Cell l r obile
Com ti
Cor less Pagi g
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CELLULAR CONCEPTS
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Single Cell Network
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History ofCellular Networks
Why cellular networks?
greater capacity
efficient use of frequency
To increase coverage of non cellular system
replaces a large transmitter with smallerones
smaller transmitting power
each cell is assigned a portion of the total frequency
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Replacement of huge single cell by a
number of small cells
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Types of Mobile Communication
CellsThe size of a cell is dictated by capacity demand
Macro-cell
Micr o-cell
Pico-cell
Mega-cell
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Capacity Computations
Assume there are N cells, each allocated k
different frequency channels. These N cells
are said to form a cluster. Total number of
channels per cluster is given by S = k N
Total capacity associated with Mclusters:
C=
M k N=
MS
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Means of Increasing System Capacity
There are several approaches for increasing cellular
system capacity including:
Cell clustering
Sectoring of cells
Cell splitting
Frequency reuse
Reduction of adjacent cell interference and co-channel
interference
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Cell Clusters
ServiceService areasareas areare normallynormally divideddivided intointo clustersclusters ofof
cellscells toto facilitatefacilitate systemsystem designdesign andand increasedincreased
capacitycapacity
DefinitionDefinition::
AA gr oupgroup ofof cellscells inin whichwhich eacheach cellcell isis assignedassigned aa
differentdifferent frequencyfrequency
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Cell Clusters
A clusterof 7 cells
1
2
5
6
7
4
3
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Cell Clusters (1)
A network of cell clusters in a densely populated Town
1
2
5
6
7
4
3
1
2
5
6
7
4
3
1
2
5
6
7
4
3
1
2
5
6
7
4
3
1
2
5
6
7
4
31
2
5
6
7
4
3
1
2
5
6
7
4
3
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Frequency Plan
Intelligent allocation of frequencies used
Each base station is allocated a group of channels
Adjacent cell base stations are assigned
completely different channel groups
Adjacent channels are not assigned to same
or even adjacent cells.
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Frequency Reuse Factor
Definition:
When each cell in a clusterof N cells uses one
of N frequencies, the frequency reuse factor
is 1/N
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Excitation of Cells
centre-excited, base station is at the centre of the cell
or
edge-excited, base station at 3 of the 6 cell vertices
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Finding the Nearest Co-Channel
After selecting smallest possible value of N we should see
that N should follow the f ollowing eg. N= i2+j2+ij
(1) Move i cells along any chain of hexagons
(2) Turn 600 counter-clockwise and move j cells, to reach the
next cell using same frequency sets
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Freq Reuse ( N=7 , i=2 j=1)
A
B
EDF
CG
A
B
E
DF
CGA
B
E
DF
CGi
j
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MULTIPLE ACCESS TECHNIQUES
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Multiple Access Techniques
FDMA
TDMA
CDMA
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FDMA-Frequency Division Multiple
Access
Time
Fr
e
q
u
en
c
y
-Requires no synchronization or central timing,
channels independent.
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TDMA-Time Division Multiple
Access: Fixed Slots
Time
F
r
e
qu
e
n
c
y
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CDMA-Code Division Multiple
Access: Frequency Hopping
Time
F
r
e
qu
e
n
c
y
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Terminology
Base Station Fixed station used f or radio communication with
mobiles. Located at the centeror edge of coverageregion. Consists of radio channels, transmit/receiveantennas.
Control Channels Radio channels used for transmission of call setup,
request, initiation and other control purposes
Full Duplex
Communication system that allows simultaneoustwo-way communication, transmission receptionusually on two different frequencies (FDD)
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Forward Channel
Radio channel for transmission from base station to mobile
Reverse channel
Radio channel for transmission from mobile to base station
Handoff
Pr ocess of transferring a mobile fr om one channel orbase
station to another
Mobile Switching Center
Switching center that coordinates call r outing in a large
service area. MSC connects cellularbase stations and themobiles to the PSTN (also called Mobile Telephone switching
office (MTSO)
Terminology
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Wireless System Basics
Forward Link
Reverse Link
Mobile UnitBase Station
Control or
Setup Channels
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Major Division OfCellular Technologies
1 G ( AMPS ,NAMPS,TACS,NMT)
2G ( IS-54A, IS-136 ,GSM, IS95 CDMA )
2.5G ( IS-95B , HSCSD , GPRS , EDGE )
3G (CDMA2000, WCDMA)
4G (MIMO, WiMAX)
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1G Technologies
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1G Cellular System
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First Generation
Advanced Mobile Phone Service (AMPS)
US trials 1978; deployed in Japan (79) & US (83)
800 MHz band two 20 MHz bands
TIA-553
Still widely used in US and many parts of the worldNordic Mobile Telephony (NMT)
Sweden, Norway, Demark & Finland
Launched 1981; now largely retired
450 MHz; later at 900 MHz (NMT900)
Total
Access Communications System (
TACS)
British design; similar to AMPS; deployed 1985
Some TACS-900 systems still in use in Europe
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Characteristics Of 1G
Analog Systems
Digital Signaling
Low Capacity Limited Roaming
Less Secure
Only voice service
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2G Technologies
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Issues regarding 2G Deployment
Digital
Capacity
Spectrum Utilization Infrastructure changes
Subscriber unit upgrade
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GSM Network Architecture
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Evolution of wireless in Europe and the US can be
summarized in the following diagrams:
F M T e c h n o lo g y
T D M A C D M A
M a n y S ta n d a r d s
U n t il 1 9 8 8
G S M
1 9 8 9
D C S 1 8 0 0
1 9 9 1
A M P S
( A n a lo g )1 9 7 9
D ig i t a l T e c h n o lo g y
L a t e 1 9 8 0
U S E u ro p e
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Modern cellular standards
1979: NTT (Japan), FDMA, FM, 25 kHz channels, 870-940 MHz
1983: AMPS (US), FDMA, FM, 30 kHz channels, 824-894 MHz
1985: TACS (Europe), FDMA, FM, 25 kHz channels, 900 MHz
1990: GSM (Europe), TDMA, GMSK, 200 kHz channels, 890-960 MHz
1991: USDC/IS-54 (US), TDMA, T/4 DQPSK, 30 kHz channels, 824-894MHz
1993: IS-95 (US), CDMA, BPSK/QPSK, 1.25 MHz channels, 824-894 MHand 1.8-2.0 GHz
1993: CDPD (US), FHSS, GMSK, 30 kHz channels, 824-894 Mhz
2001: UMTS/IMT-2000 (3rd generation European cellular standard),supports data and voice (up to 2 Mbps), 1885-2025 MHz and 2110-2200Mhz
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Evolution OfCellular Mobile
Engineering Research To full fill the necessity : As the requirement of wireless connections and required data rate
increased engineers tried to full fill the requirement.
Simple Analog Mobile To Analog Cellular Mobile :
First simple mobile system was upgraded to cellular in the formofAMPS in 1983.
Analog Cellular Mobile to Digital Cellular Mobile : Then GSM was introduced with TDMA approach having more capacity
and data rate.
Digital Cellular Mobile ToCDMA:
After that to full fill the requirements ofmore data and more subscriberCDMA was introduced by Qualcomm.
CDMA supports a variable numberof users in 1.25MHz wide channelsusing direct sequence spread spectrum.
Interference Affordability:
CDMA system can operate at much larger interference levelsbecause of their inherent interference resistance properties.
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Evolution OfCellular Mobile
Just an overview Contd.
Large Capacity ofCDMA : The ability ofCDMA tooperate with a much smaller S/N ratio
than FM techniques allows CDMA systems to use the same
setof frequencies in every cell which pr
ovides a largeimprovement in capacity.