Post on 05-Apr-2018
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Wireless Communications
Dr. Sameer Qazi
Dr. Khawaja Bilal Mahmood
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Syllabus Introduction to cellular communications Cellular System Design principles Radio Transmission Multi-path fading channel
Channel coding Multiple Access Technologies Modulation Techniques for Mobile Radio Equalization and Diversity CDMA Spread Spectrum Multi-user detection WCDMA (UMTS) Wireless computer networks
Prescribed Books (Primary Book): Wireless Communications,Theodore Rappaport(Names of other books or photocopied excerpts will be provided when
covering topics outside of primary book.)
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Radio Spectrum
VLF LF MF HF VHF UHF SHF EHF
RADIO
RADIO IR VISIBLE UV X-RAYS GAMMA RAYS
3kHz30kHz 300kHz 3MHz 30MHz 300MHz 3GHz 30GHz 300GHz
VLF: Very Low Frequency LF: Low Frequency MF: Medium Frequency HF: High Frequency
VHF: Very High Frequency UHF: Ultra High Frequency SHF: Super High Frequency EHF: Extremely High Frequency
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Radio WaveCharacterized by:
oscillating in time at its frequency.
traveling through the air at the speed of light :
c = 300,000,000 meters per sec
characterized by wavelength,
wavelength = the distance the wave travels as it goes through one
period (or cycle) of oscillation:
c f
meters se c
cycles se cmeterscycle
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Frequency bands and wavelengths
Different frequency for the carrier exhibit different physical
properties
propagation beyond the horizonenergy absorption by the air
propagation through rain, walls, etc.attenuation with distancesources of noise
The amount by which frequencies are affected by above properties varies. These properties can be better understood in terms of the wavelengths of the radiation .
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Wavelengths of Freq bands VLF, LF long wavesMF medium wavesHF, VHF short wavesUHF, SHF microwaves
EHF millimeter waves
Above microwave region, only certain windows of frequencies propagate freely through air, rain, etc.Infrared and visible light will not penetrate wallsX-rays and gamma rays interact with matter
Propagate well beyond line of sight
The distance the signal travels decreases
as the frequency increases in a single cycleor for a given power.
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Current Wireless SystemsMobile Radio Systems-->Cellular Systems
Cordless phonesPaging Systems
Satellite SystemsWireless LANs
Broadband Wireless AccessLow-cost Low Power Radios
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Broadcast (analog)
2-way communication(digital)
2-way communication(analog & digital)
Wireless Systems: Examples
AM, FM Radio
TV Broadcast
Satellite Broadcast
2-way Radios
Cordless Phones
Satellite Links
Mobile Telephony SystemsWireless Local Loop (WLL)
Microwave Links
Wireless LANsInfrared LANs
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Cellular System Introduction andDesign Fundamentals
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Cellular Communication Systems Cellular telephones are personally
portable devices that may be used inmotor vehicles or by pedestrians
Communicating by radio waves in the 800-900 MHz band they provide a significantdegree of mobility within a defined serving
region that may be hundreds of sq km inarea
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Cellular System
MSC PSTN
- Contains Mobile stations, Base
Stations and
- MSC -- Mobile Switching Center
also sometimes called
- MTSO - Mobile Telephone
Switching Office
- Base Stations consist of several
Transceivers to support full duplex
transmission
Basic Cellular System Diagram
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Bas ic Ce l lu la r Sys t em
- Contains Mobile stations, Base Stations and
- MSC -- Mobile Switching Center
also sometimes called -->> MTSO - Mobile Telephone Switching Office
- Base Stations (BS) consist of several Transceivers to support full duplex transmission- BS serves as Bridge b/w all mobile users in a Cell and connects mobile calls via
telephone lines or microwave links to the MSC
- MSC coordinate activities from all the BS and connect the entire cellular system to
PSTN
- MSC handles 100,000 cellular subscribers and 5,000 simultaneous conversations at a
time
- MSC also perform the billing and system maintenance functions
- Many MSCs are used by a service provider in a large city
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Why cells are Hexagons? Largest Area/R ratio over other shapes
RRR
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Cellular Coverage The geographic area served by a cellular radio
system is broken up into smaller geographicareas or cells
Uniform hexagons most frequently are employedto represent these cells on maps and diagrams
In practice though radio waves do not confinethemselves to hexagonal areas, so that theactual cells have irregular shapes
All communication with a mobile or portableinstrument within a given cell is made to thebase station that serves the cell
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Comments on hexagonal cells Hexagonal geometry approximates omni-
directional base station with free spacepropagation.
When hexagons are used base stationscan either be: In the center (center excited)- omni directional
antennas or On 3 of the six cell vertices (edge excited)-
sectored directional antennas
In the center (center excited)- omni directional
antennas or On 3 of the six cell vertices (edge excited)-
sectore irectional antennas
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Frequency Reuse The transmitting power of battery operated
portable units is relatively low and theattenuation of the propagating radio waves isrelatively high.
That gives us the opportunity for the sending
and the receiving frequencies assigned to a cellto be reused in other (more distant) cells withinthe larger geographical area.
Thus, the spectral efficiency of a cellular systemis increased by a factor equal to the no. of timesa frequency may be reused within its servicearea.
Thus the s ectral efficienc of a cellular s stemis increased b a factor e ual to the no. of timesa requency may e reuse w t n ts serv cea ea.
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Handoff (Handover) Usually a mobile unit proceeds from one cell to
another during the course of the call A central controller (mobile telephone switchingoffice -MTSO) automatically reroutes the callfrom the old cell to the new cell without anoticeable interruption in the signal reception.
This process is known as handoff MTSO acts as an intelligent central office switch
that keeps track of the movement of the mobilesubscriber
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Handoff (Handover)
BS 1
BS 2BS 3
Connected to BS 2
Connected to BS 1
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Mobile Telephone Service (MTS)by AT&T
In MTS the user spoke with a mobileoperator who actually dialled the call overthe PSTN
The radio connection was simplex, i.e.Only one party could speak at a time
The call direction was controlled by a push
to talk switch in the mobile handset
In MT the user spoke with a mobileoperator who actually dialle the call overthe PSTN
simplexnly one party could speak at a time
call direction push
to talk switch in the mobile handset
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IMTS by AT&T In 1964, AT&T introduced a second generation
of mobile telephony known as improved mobiletelephone service (IMTS) IMTS provided:
11 channels in the 152-158 MHz band Full duplex operation Automatic dialling Automatic channel searching
1969 an additional 12 channels were added inthe 454-459 MHz band
improved mobiletelephone service (IMTS)
1964
1 channels in the 152-158 MHz band Full duplex operation Automatic dialling Automatic channel searching
454-459 z an12 c anne s
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Success of IMTS by AT&T Only 11 (or 12) channels were available for all
users of the system within a given geographicarea (such as the metropolitan area around thelarge city).
Each frequency was used only once in that area.
The IMTS system faced a high demand for avery limited channel resource. Example: in New York City during 1976, the
IMTS system served 545 customers 3700 customers were on a waiting list for the
service
Each frequency was used only once in that area.
The IMTS s stem faced a hi h demand for avery limited channel resource.
IMT system served 545 customers3700 customers were on a waiting list for theservice
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Drawbacks of IMTS In IMTS each base station antenna
located on a tall structure and Transmittedat high power in an attempt to providecoverage throughout the entire service
area Because of these high power
requirements, all subscriber mobile units inthe IMTS system were instruments thatcarried large batteriesarried large batteries
high powerrequirements
tall structure and Transmittedat hi h ower rovideoverage throughout the entire service
area
in an attem t to
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Start of AMPS During this time the American cellular radio
system, known as the advanced mobile phonesystem, or AMPS, was developed primarily byAT&T and Motorola, Inc.
AMPS was based on 666 paired voice channelsspaced every 30KHz in the 800 MHz region
AMPS system employed an analog frequency
modulation and was designed to support bothmobile and portable suscbriber units.
a vance mo e p onesystem, or AMPS
was ase on 666 pa re vo ce c anne sspaced every 30KHz in the 800 MHz region
ana og requency
mo u at on
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Success of AMPS AMPS was formally introduced in Chicago in
1983 and was a success from the beginning At the end of the first year of service there was a
total of 200,000 AMPS subscribers throughoutthe US.
In 1988, there were more than 2,000,000. Inresponse to this growth, an additional 166 voicechannels were allocated to the cellular carriersin each market
Still, the cellular system soon experiencedcapacity shortages
additional 166 voicehannels were allocate to the cellular carriers
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AMPS improvements The American cellular industry responded with
several proposals for increasing capacity withoutrequiring additional spectrum allocations. One analog FM approach, proposed by Motorola
in 1991, was known as narrowband AMPS, orNAMPS.
In NAMPS systems each existing 30KHz voice
channel is split into three 10 KHz channels
n systems eac ex st ng 30 z vo ce
hannel is split into three 10 KHz channels
narrow an , orNAMPS.
AMPS:
- Frequency band --> 824-894MHz
- Modulation --> FM- Channel Bandwidth --> 30KHz (For NAMPS: Channel BW is reduced to 10KHz)
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NAMPS and IS-54 In place of the 832 channels available to AMPS
the NAMPS system offered 2,496 channels. A second approach named IS-54 (IS-136),developed by the Telecommunications IndustryAssociation (TIA) in 1988, employed Digital modulation Digital voice compression Time division multiple access (TDMA) method
IS-54 permitted also three new voice channels inplace of one AMPS channel
In lace of the 832 channels available to AMPS
the NAMPS system offered 2,496 channels.
Digital modulation Digital voice compression Time division multiple access (TDMA) method
t ree new vo ce c anne s nlace of one AMPS channel
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IS-95 In 1994 appeared a third approach, developed
originally by Qualcomm Inc, but also adopted asa standard IS-95 by the TIA. This third approach used a form of spread
spectrum multiple access (CDMA) a techniquethat combined digital voice compression withdigital modulation
The CDMA system offered 10 to 20 times thecapacity of existing AMPS cellular techniques.
a tec n quethat combined digital voice compression withdigital modulation
The CDMA system offered 10 to 20 times theapacity o existing AMP cellular techniques.
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Developments outside US All of these improved capacity cellular systems
are deployed in the US In Oct 2000 Telstra, Australia replaced its analog
AMPS network with CDMA IS-95 network. AMPS was the first cellular system developed,
yet the first cellular system actually to bedeployed was a Japanese system deployed in1979.
Japanese system was followed by the Nordicmobile telephone (NMT) system, deployed in1981 in Denmark, Finland, Norway and Sweden.
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Need for GSM Total Access Communication System (TACS) was
deployed in the UK in 1983. A number of other cellular systems were developed and
deployed in many more countries in the 80s and the90s. All of them were incompatible with one another.
In 1988 a group of government owned public telephonebodies within the European Community announced thedigital global system for mobile (GSM) communications.
GSM was the first system that would permit a cellular
user in one European country to operate in anotherEuropean country with the same equipment
of other cellular s stems were develo ed andde lo ed in man more countries in the 80s and the
0s. All of them were incompatible with one anothe .
number
digital global system for mobile (GSM) communications.GSM was the first s stem that would ermit a cellu ar
ser in one Euro ean countr to o erate in anotherEuropean country with the same equipment
Need or M
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Path to 3G Mobile CommunicationSystems
First Major Migration Path
1st
Gen 80s, ETACS (C-450, NMT-450..), (FDMA),Analog 2 nd Gen 90s, GSM, GPRS, EDGE, (TDMA) Digital
3rd
Gen, 00s, W-CDMA, (CDMA), All digital Second Major Migration Path
1 st Gen 80s, AMPS, (FDMA), Analog
2nd
Gen 90s, IS-54 (TDMA), IS-95 (CDMA), Digital 3 rd Gen 00s, CDMA 2000 (CDMA), All Digital
In Europ e
In U SA
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Key Specifications of leading 2Gtechnologies
869-894MHz (US Cellular),1930-1990 MHz (US PCS)800 MHz, 500 MHz (Japan)
935-960 MHz (Europe)1930-1990 MHz (US PCS)
869-894 MHz (US Cellular)1930-1990 MHz (US PCS)
Downlink frequencies
3864Voice channels percarrier
48.6 kbps (IS-136)(42 kbps for PDC)
270.833 kbps1.2288 Mchips/secChannel Data Rate
30 kHz (IS-136)25kHz for PDC
200 KHz1.25 MHzCarrier Separation
/4 DQPSKGMSK with BT=0.3BPSK with Quadraturespreading
Modulation
TDMATDMACDMAMultiple AccessTechnology
FDDFDDFDDDuplexing
800MHz, 1500 MHz(Japan)1850-1910 MHz (US PCS)
890-915 MHz (Europe)1850-1910 MHz (US PCS)
824-849 MHz (US Cellular)1850-1910 MHz (US PCS)
Uplink frequencies
NADC, IS-54/IS-136, ANSIJ-STD-011, PDC
GSM, DCS-1900, ANSI J-STD-007
cdmaOne, IS-94, ANSI J-STD-008
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Cellular Telephone SystemStructure
A cellular telephone system consists of:
Mobile stations (MS) Handheld or vehicular
Base stations (BS) Towers supporting several transceivers
Mobile switching center (MSC) or mobiletelephone switching office (MTSO)
Activity control of all BS, connects to PSTN
Mobile stations (MS)
Base stations (BS)
o e sw tc ng center or mo etelephone switching office (MTSO)
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Cellular system Radio Interface The common air interface (CAI) defines
communication between BS and MS Types of channels used in a mobile
system Forward voice channel (FVC) Forward control channel (FCC)
Reverse voice channel (RVC) Reverse control channel (RCC)
common air interface (CAI)
ommunication between B and MTypes of channels
Forward voice channel (FVC) Forward control channel (FCC)
Reverse voice channel (RVC) Reverse control channel (RCC)
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Cellular Telephone System Forward voice channel (FVC)
BS to MS voice transmission Reverse voice channel (RVC)
MS to BS voice transmission
Forward control channel (FCC) andReverse control channel (RCC) Setting up mobile call and moving it to voice
channel
BS to MS voice transmission
(FVC)
(RVC) M to B voice transmission
(FCC)(RCC)
Setting up mobile call and moving it to voicehannel
- Control Channels are also called Setup Channels
- They Set-up a call and move it to an Unused Voice channel
- They transmit and receive data messages that carry call initiation and service requests which is monitored bymobiles when they are idle
- FCC serves as a beacon which broadcasts all traffic requests for all mobiles in the system.
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Cellular Telephone System
Forward ControlChannelTransmit
informationfrom BS to mobile
Forward Voice
ChannelTransmit voicefrom BS to mobile
Control Channel-Call setting
-Call request-Call initiation-Other control
settings
Reverse ControlChannelTransmit
informationfrom mobile to BS
Reverse Voice
ChannelTransmit voicefrom mobile to BS
Base TransceiverStation
Mobile SwitchingCenter(MSC) PSTN
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Cellular Telephone Call Mobile station (phone) turned on
It scans for the group of forward controlchannels (FCC) to find the one with thestrongest signal
Monitors that control channel until the signaldrops below usable level
Again scans for the strongest control channel
The control channels are defined andstandardized over the entire area
But no t Engaged ina c a l lMobile station (phone) turned on
Monitors that control channel until the signaldrops below usable level
strongest signal(FCC)
Again scans for the strongest control channel
- Ou t o f t o t a l c hanne ls 5% o f t he c hanne l a r e c on t ro l c hanne l s- Ot he r 95% o f t he c hanne ls a r e ded ica t ed fo r vo ice and da t a t r a ff i c .
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Call from a Mobile Phone
all rom a Mobile Phone
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Call from a Mobile Phone
Begin voicetransmission
RVC
Begin voicereception
FVC
Sends a call initiationrequest along withsubscribe MIN and
number of called party
RCC
Receives page andmatches the MINwith its own MIN.Receivesinstruction to moveto voice channel
FCC
Begin voicereception
RVC
Begin voicetransmission
FVC
Receives call initiationrequest and MIN, ESNand station Class Mark
RCC
Page for calledmobile, instructingthe mobile to moveto voice channel
FCC
Connects themobile with thecalled party onthe PSTN
Instructs FCC oforiginating base station tomove mobile to a pair ofvoice channels
Receives callinformation requestfrom base station andverifies that the mobilehas a valid MIN, ESNpairMSC
BaseStation
Mobile
time
all rom a Mobile Phone
Sends a call initiationrequest along withsubscribe MIN and
number of called party
Receives call initiationrequest and MIN, ESNand station Class Mark
Receives callinformation requestfrom base station andverifies that the mobilehas a MIN, ESNalidpair
Instructs FCC oforiginating base station tomove mobile to a pair ofvoice channels
Page for calledmobile, instructingthe mobile to moveto voice channel
matches the MINwith its own MIN.Receivesinstruction to moveto voice channel
Receives page and
Connects themobile with the
alled party onthe PSTN
Begin voicetransmission
Begin voicereception
Begin voicereception
Begin voicetransmission
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Roaming (1) Roaming allows subscribers to operate in mobile
phone service areas other than the service areawhere the service is subscribed When a mobile enters area outside the home
service area it is registered as roamer in the newservice area Since FCC are everywhere the same, roamer is
receiving information form the FCC
operate n mo e
hone service areas other than the service areawhere the service is su scri e
roamer
roamer s
receiving information form the FCC
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Roaming (2) Every several minutes MSC issues command over each FCC to all
mobiles previously unregistered to report their MIN and ECN overthe RCC
Unregistered mobiles periodically report back subscriber informationupon receiving the registration request
The MSC uses MSN/ESN data to request billing status from theHome Location Register (HLR)
If the mobile has roaming authorization at home, MSC registers asubscriber in a visiting location register (VLR) as a valid roamer Once registered roaming mobiles are allowed to receive and place
calls from the new service area Billing is routed automatically to the subscribers home service
provider (HLR)
Ever several minutes MSC issues command over each FCC to allmobiles reviously unregistered to report their MIN and ECN overthe RCC
nreg stere per o ca y report ac su scriber informationmo es
MSC uses MSN/ESN data to request billing status from theome Location Register (HLR)
mobile has roamin authorization at home MSC re isters asubscriber in a visiting location register (VLR) as a valid roamer
ome serv ce
HLR)provider
n s route
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Cellular Concept Simple solution
Single high powered Tx on a tall tower Good coverage but very low capacity No frequency reuse
High capacity solution Cellular concept solves problem of low capacity Replaces a single high power Tx (large cell) with
many low power Txs (small cells) Much smaller and more efficient mobile units
Simple solution
g capac ty so ut on
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Operation The cellular concept is a system level idea:
Each base station is allocated a portion of the totalnumber of channels available to the entire system Nearby base stations are assigned different groups of
channels All channels are assigned to a relatively small number
of neighboring base stations
The level of interference between base stations(and the mobile users) is controlled.
base station is allocated a portion of the totalnumber of channels available to the entire systemearby base stations are assigned different groups of
channels
Each
bec ause Ne ighbor ing BS a re a ss igned d i ffe ren t g roups o f
channe l s
controlledlevel of between base stationsinterference
(and the mobile users) is
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Scalability Frequency can be reused as many times
as necessary as long as interferencebetween co-channel stations can be keptwithin acceptable limits.
As the demand increases, the number ofbase stations can be increased (with acorresponding decrease in Tx power)
This fundamental principle is thefoundation of all modern wireless systems.
re uenc can e reuse as man t mes
as as lon as interferencenecessarbetween co-channel stations can be keptwithin acceptable limits
This fundamental rinci le is thefoundation of all modern wireless systems.
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Frequency Reuse The process of selecting and allocating channel groups for all base stations
within a system is known as frequency re-use or frequency planning.
G
FAE
B
D
C
GF AE
B
DCG
FAE
B
D
C
selecting and allocating channel groups for all base stationswithin a system is known as frequency re-use or frequency planning.
- Ce l l s w i t h s ame l e t t e r u set he same g roup o f c hanne l s- Ac t ua l rad io c overage of ac e l l i s k n o w n a s fo o t p r i nt a n dde te rm ined f rom f i e ldm e a s u r e m e n t s
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Simple calculation Let S be the total number of duplex channels
Let k be the number of channels in each cell N cells collectively use the complete set of S
available channels
N is the cluster size (N=4,7 or 12) then S=kN If a cluster is replicated M times Total number of duplex channels = MS= MkN 1/N is called freq reuse factor
S be the total number of duplex channels
e t e num er o c anne s n eac ceN cells collectively use the complete set of Savailable channels
Express to t a l no .
o f ava i l ab le r ad io
channe l s
- 'N ' ce l l s w hich
c o l l e c t i v e ly u s e
t h e c o m p l e t e se t
o f ava i l ab le
f requenc ies i sc a l led CLUSTER
N is the cluster size (N=4,7 or 12) S=kNcluster is replicated M times
Total number of duplex channels = MS= MkN
- Capac i t y o f ce l lu l a r sys t em s i s d i r ec t ly p ropor t iona l t o t he number o ft imes a c lu s t e r i s r epl i ca t ed in a f i xed se rv i ce a r ea
1/N is called freq reuse factor
Sim ple Ca lc u la t ion
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- I f t he Clus t e r s i ze 'N ' i s r educed w h i l e ce l l s i ze i s k ep t c ons t an t , m orec lus t e r s a r e r equ i red t o c ove r a g iven a rea hence m ore Capac i t y 'C' c anbe ac h ieved- Larger Clus t e r s i ze c auses t he ra t io b /w c e l l r ad ius and d i s t anc e b /wc o-c hanne l c e l l s t o dec rease l ead ing t o w eake r c o -channe l
in t e r f e rence- On t he o t her hand:- Sm a l l c lu s t e r s i ze i nd ica t e s t ha t c o -c hanne l c e l l s a re l oca t ed muc h
c l o s e r t o g e t h e r- Va lue o f 'N ' i s a func t ion o f how m uch in t e r f e rence a MS o r BS c an
t o l e r a t e w h i le m a i n t a i n i n g a s uf f ic i e n t c o m m u n ic a t i o n q u al i t y- For Sys t em 's des ign v iew po in t Sm al les t va lue o f N i s des i rab le in
o rde r t o max im ize capac i t y ove r a g iven c ove rage a rea- Problem :I f a t o t a l o f 33MHz o f bandw id th i s a l l oca t ed to a pa r t i c u l a r ce l lu l a rt e l ephone sys t em w hich uses t w o 25KHz s imp lex c hanne ls t o p rovide fu l ldup lex vo ice and c on t ro l c hanne ls . Comput e t he number o f channe l sava i l ab l e pe r ce l l i f a sys t em uses(a) Four c e l l reuse , (b) Seven c e l l reuse an d (c ) Tw elve c e l l reuse