lecture-1_wireless + mobile communications - cellular system design principles

7/31/2019 Lecture-1_Wireless + Mobile Communications - Cellular System Design Principles

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EE851-Wireless Communications-Summer 2010

1

Wireless Communications

Dr. Sameer Qazi

Dr. Khawaja Bilal Mahmood


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2

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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3

Cellular System Introduction andDesign Fundamentals


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4

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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5

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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6

Why cells are Hexagons? Largest Area/R ratio over other shapes

RRR


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7

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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8

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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9

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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12

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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13

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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15

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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16

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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20

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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23

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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27

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


RVC


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






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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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EE851-Wireless Communications-Summer 2010 38

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

lecture-1_wireless + mobile communications - cellular system design principles

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