personal communication systems: basic principles (part i) ian f. akyildiz broadband & wireless...

PERSONAL COMMUNICATION PERSONAL COMMUNICATION SYSTEMS: BASIC PRINCIPLESSYSTEMS: BASIC PRINCIPLES

(PART I) (PART I)

Ian F. AkyildizIan F. Akyildiz

Broadband & Wireless Networking LaboratoryBroadband & Wireless Networking Laboratory

School of Electrical and Computer EngineeringSchool of Electrical and Computer Engineering

Georgia Institute of TechnologyGeorgia Institute of Technology

Tel: 404-894-5141; Fax: 404-894-7883 Tel: 404-894-5141; Fax: 404-894-7883

Email: [email protected]: [email protected]

Web: http://www.ece.gatech.edu/research/labs/bwnWeb: http://www.ece.gatech.edu/research/labs/bwn

2IFA’2004

Overview of Wireless Networks:Overview of Wireless Networks:IntroductionIntroduction

3IFA’2004

Overview of Wireless Networks:Overview of Wireless Networks:Existing Network InfrastructureExisting Network Infrastructure

Public Switched Public Switched Telephone Network Telephone Network (PSTN): Voice(PSTN): Voice

Internet: DataInternet: Data Hybrid Fiber Coax Hybrid Fiber Coax

(HFC): Cable TV(HFC): Cable TV

4IFA’2004

Overview of Wireless Networks:Overview of Wireless Networks:Market Sectors for ApplicationsMarket Sectors for Applications

Four segments divided into two classes: voice-Four segments divided into two classes: voice-oriented and data-oriented, further divided into local oriented and data-oriented, further divided into local and wide-area marketsand wide-area markets

Voice:Voice:– Local: low-power, low-mobility devices with Local: low-power, low-mobility devices with

higher QoS – cordless phones, Personal higher QoS – cordless phones, Personal Communication Services (PCS)Communication Services (PCS)

– Wide area: high-power, comprehensive coverage, Wide area: high-power, comprehensive coverage, low QoS - cellular mobile telephone servicelow QoS - cellular mobile telephone service

Data:Data:– Broadband Local and ad hoc: WLANs and WPANs Broadband Local and ad hoc: WLANs and WPANs

(WPAN-Wireless Personal Area Network)(WPAN-Wireless Personal Area Network)– Wide area: Internet access for mobile usersWide area: Internet access for mobile users

5IFA’2004

Overview of Wireless Networks:Overview of Wireless Networks:Evolution of Voice-Oriented Evolution of Voice-Oriented ServicesServices

YearYear EventEvent

Early 1970sEarly 1970s First generation of mobile radio at Bell LabsFirst generation of mobile radio at Bell Labs

Late 1970sLate 1970s First generation of cordless phonesFirst generation of cordless phones

19821982 First generation Nordic analog NMTFirst generation Nordic analog NMT

19831983 Deployment of US AMPSDeployment of US AMPS

19881988 Initiation of GSM development (new digital TDMA)Initiation of GSM development (new digital TDMA)

19911991 Deployment of GSMDeployment of GSM

19931993 Initiation of IS-95 standard for CDMAInitiation of IS-95 standard for CDMA

19951995 PCS band auction by FCCPCS band auction by FCC

19981998 3G standardization started3G standardization started

FDMA – Frequency Division Multiple AccessNMT – Nordic Mobile TelephonyAMPS – Advanced Mobile Phone SystemGSM – Global System for Mobile CommunicationTDMA – Time Division Multiple Access

IS-95 – Interim Standard 95CDMA – Code Division Multiple AccessPCS – Personal Communication SystemFCC – Federal Communication Commission

6IFA’2004

Overview of Wireless Networks:Overview of Wireless Networks:Evolution of Data-Oriented Evolution of Data-Oriented ServicesServices

YearYear EventEvent

19791979 Diffused infrared (IBM Rueschlikon Lab - SwitzerlandDiffused infrared (IBM Rueschlikon Lab - Switzerland

Early 1980sEarly 1980s Wireless modem (Data Radio)Wireless modem (Data Radio)

19901990 IEEE 802.11 for Wireless LANs standardsIEEE 802.11 for Wireless LANs standards

19901990 Announcement of Wireless LAN productsAnnouncement of Wireless LAN products

19921992 HIPERLAN in EuropeHIPERLAN in Europe

19931993 CDPD (IBM and 9 operating companies)CDPD (IBM and 9 operating companies)

19961996 Wireless ATM Forum startedWireless ATM Forum started

19971997 U-NII bands released, IEEE 802.11 completed, GPRS U-NII bands released, IEEE 802.11 completed, GPRS startedstarted

19981998 IEEE 802.11b and Bluetooth announcementIEEE 802.11b and Bluetooth announcement

19991999 IEEE 802.11a/HIPERLAN-2 startedIEEE 802.11a/HIPERLAN-2 startedHIPERLAN – High Performance Radio LANCDPD – Cellular Digital Packet DataU-NII – Unlicensed National Information InfrastructureGPRS – General Packet Radio Service

7IFA’2004

Overview of Wireless Networks: Overview of Wireless Networks: Different GenerationsDifferent Generations

1G Wireless Systems: Analog systems1G Wireless Systems: Analog systems– Use two separate frequency bands for forward Use two separate frequency bands for forward

(base station to mobile) and reverse (mobile (base station to mobile) and reverse (mobile to base station) links: Frequency Division to base station) links: Frequency Division Duplex (FDD)Duplex (FDD)

– AMPS: United States (also Australia, southeast AMPS: United States (also Australia, southeast Asia, Africa)Asia, Africa)

– TACS: EU (later, bands were allocated to GSM) TACS: EU (later, bands were allocated to GSM) – NMT-900: EU (also in Africa and southeast NMT-900: EU (also in Africa and southeast

Asia)Asia)

– Typical allocated overall band was 25 MHz in Typical allocated overall band was 25 MHz in each direction; dominant spectra of operation each direction; dominant spectra of operation was 800 and 900 MHz bands.was 800 and 900 MHz bands.

AMPS – Advanced Mobile Phone SystemTACS – Total Access Communication SystemNMT – Nordic Mobile Telephony

8IFA’2004


2G Wireless Systems: Four sectors 2G Wireless Systems: Four sectors

– Digital cellularDigital cellularGSM (EU/Asia): TDMAGSM (EU/Asia): TDMAIS-54 (US): TDMAIS-54 (US): TDMAIS-95 (US/Asia): CDMAIS-95 (US/Asia): CDMA

– PCS – residential applicationsPCS – residential applicationsCT-2 (EU,CA): TDMA/TDDCT-2 (EU,CA): TDMA/TDDDECT(EU):TDMA/TDDDECT(EU):TDMA/TDDPACS (US): TDMA/FDDPACS (US): TDMA/FDD

CT-2 – Cordless Telephone 2DECT – Digital Enhanced Cordless TelephonePACS – Personal Access Communication System

9IFA’2004


2G Wireless Systems: Four sectors 2G Wireless Systems: Four sectors (cont’d)(cont’d)

– Mobile data Mobile data CDPD shares AMPS bands and site infrastructure; CDPD shares AMPS bands and site infrastructure; GPRS shares GSM’s radio system - data rates GPRS shares GSM’s radio system - data rates

suitable for Internetsuitable for Internet– WLAN – Unlicensed bands, free of charge and WLAN – Unlicensed bands, free of charge and

rigorous regulations: very attractive! rigorous regulations: very attractive! IEEE 802.11 and IEEE 802.11b use DSSS physical IEEE 802.11 and IEEE 802.11b use DSSS physical

layer;layer;HIPERLAN/1 uses GMSK; HIPERLAN/1 uses GMSK; IEEE 802.11a and HIPERLAN/2 use OFDM: next IEEE 802.11a and HIPERLAN/2 use OFDM: next

generationgeneration

CDPD – Cellular Digital Packet DataGPRS – General Packet Radio Service DSSS – Direct Sequence Spread SpectrumGMSK – Gaussian Minimum Shift KeyingOFDM – Orthogonal Frequency Division Multiplexing

10IFA’2004


3G3G and Beyond and Beyond

– Purpose: develop an international standard Purpose: develop an international standard that combines and gradually replaces 2G that combines and gradually replaces 2G digital cellular, PCS, and mobile data digital cellular, PCS, and mobile data services, at the same time increasing the services, at the same time increasing the quality of voice, capacity of the network, and quality of voice, capacity of the network, and data rate of the mobile data services.data rate of the mobile data services.

– Radio transmission technology of choice: W-Radio transmission technology of choice: W-CDMACDMA

– 3G was envisioned to provide multimedia 3G was envisioned to provide multimedia services to users everywhereservices to users everywhere

11IFA’2004


3G and 3G and BeyondBeyond

– WLANs provide broadband services in hot WLANs provide broadband services in hot spotsspots

– WPANs connect personal devices together: WPANs connect personal devices together: laptop, cellular phone, headset,speakers, laptop, cellular phone, headset,speakers, printersprinters

– WLAN and WPAN are the future of WLAN and WPAN are the future of broadband and ad hoc wireless networksbroadband and ad hoc wireless networksWPAN’s first standard: bluetooth – lower rates than WPAN’s first standard: bluetooth – lower rates than

WLAN but uses a voice-oriented wireless access WLAN but uses a voice-oriented wireless access method for integration of voice and data servicesmethod for integration of voice and data services

12IFA’2004


Relative coverage, mobility, and data rates of generations of cellular systemsand local broadband and ad hoc networks.

13IFA’2004

Operation of Wireless Operation of Wireless NetworksNetworks

Getting familiar with terms:Getting familiar with terms:– MS/MT: Mobile Station/Mobile TerminalMS/MT: Mobile Station/Mobile Terminal– BS: Base StationBS: Base Station– MSC: Mobile Switching CenterMSC: Mobile Switching Center– HLR: Home Location Register (database)HLR: Home Location Register (database)– VLR: Visitor Location Register (database)VLR: Visitor Location Register (database)

Cellular Network ArchitectureCellular Network Architecture Mobility ManagementMobility Management

14IFA’2004

Cellular Network Cellular Network ArchitectureArchitecture

LocationRegister (Database)

Mobile Switching Center

MSC

Backbone Wireline Network

Base Station Controller

Base Station

MobileTerminal

RadioNetwork

Cell

15IFA’2004

BASIC BASIC ARCHITECTUREARCHITECTURE

BACKBONE TELEPHONE NETWORK

(HLR)

Mobile Switching Center

Visitor Location Register

Mobile Terminal(MT)

MSC

VLR

Local Signaling Long Distance Signaling

(MSC)

(VLR)

Home Location Register

16IFA’2004

Cellular ConceptCellular Concept

A CELL is the radio coverage area by a A CELL is the radio coverage area by a Base Station (BS).Base Station (BS). The most important factor is the SIZE and the SHAPE of a The most important factor is the SIZE and the SHAPE of a

CELL.CELL. Ideally, the area covered a by a cell could be represented Ideally, the area covered a by a cell could be represented

by a circular cell with a radius R from the center of a BS.by a circular cell with a radius R from the center of a BS. Many factors may cause reflections and refractions of the Many factors may cause reflections and refractions of the

signals, e.g., elevation of the terrain, presence of a hill signals, e.g., elevation of the terrain, presence of a hill or a valley or a tall building and presence in the or a valley or a tall building and presence in the surrounding area. surrounding area.

The actual shape of the cell is determined by the The actual shape of the cell is determined by the received signal strength.received signal strength.

Thus, the coverage area may be a little distorted.Thus, the coverage area may be a little distorted. We need an appropriate model of a cell for the analysis We need an appropriate model of a cell for the analysis

and evaluation. and evaluation. Many posible models: Many posible models: HEXAGON,HEXAGON, SQUARE, EQUILATERAL SQUARE, EQUILATERAL

TRIANGLE.TRIANGLE.

17IFA’2004

Cell

R

(a) Ideal Cell (b) Actual Cell

R

R R

R

(c) Different Cell Models

Cell ShapeCell Shape

18IFA’2004

Size and Capacity of a Cell per Unit of Area and Size and Capacity of a Cell per Unit of Area and Impact of the Cell Shape on System Impact of the Cell Shape on System CharacteristicsCharacteristics

19IFA’2004

Cellular Concept - Cellular Concept - ExampleExample

Consider a high-power Consider a high-power transmitter that can transmitter that can support 35 voice channels support 35 voice channels over an area of 100 kmover an area of 100 km22 with the available with the available spectrumspectrum

If 7 lower power If 7 lower power transmitters are used so transmitters are used so that they support 30% of that they support 30% of the channels over an area the channels over an area of 14.3 kmof 14.3 km2 2 each.each.

Then a total 7*30% * 35 = Then a total 7*30% * 35 = 80 channels are available 80 channels are available instead of 35. instead of 35.

1

23

45

6

7

20IFA’2004

Cellular ConceptCellular Concept

If two cells are far away from enough If two cells are far away from enough that the same that the same set of frequenciesset of frequencies can be can be used in both cells, it is called used in both cells, it is called frequency frequency reusereuse..

With frequency reuse, a large area can With frequency reuse, a large area can be divided into small areas, each uses a be divided into small areas, each uses a subset of frequencies and covers a small subset of frequencies and covers a small area.area.

With frequency reuse, the system With frequency reuse, the system capacity can be expanded without capacity can be expanded without employing high power transmitters.employing high power transmitters.

21IFA’2004

Capacity Expansion by Capacity Expansion by Frequency ReuseFrequency Reuse

Same frequency band or channel Same frequency band or channel used in a cell can be “REUSED’ in used in a cell can be “REUSED’ in another cell as long as the cells are another cell as long as the cells are far apart and the signal strength do far apart and the signal strength do not interfere with each other.not interfere with each other.

This enhances the available This enhances the available bandwidth of each cell. bandwidth of each cell.

A group of cells that use a different set of A group of cells that use a different set of frequencies in each cell is called a frequencies in each cell is called a cell cell clustercluster..

22IFA’2004

NUMBER OF CELLS IN A NUMBER OF CELLS IN A CLUSTERCLUSTER

23IFA’2004

CELL CLUSTER

24IFA’2004

FREQUENCY REUSEFREQUENCY REUSEExample:Example: A typical cluster of 7 such cells and 4 A typical cluster of 7 such cells and 4 such clusters with no overlapping area such clusters with no overlapping area

F1

F2

F3F4

F5

F6

F7

F1

F2

F3F4

F5

F6

F7

F1

F2

F3F4

F5

F6

F7

F1

F2

F3F4

F5

F6

F7

|------||D|| ----------

FREQUENCY REUSE DISTANCE D

25IFA’2004

RULE to Determine the Nearest Co-RULE to Determine the Nearest Co-Channel NeighborsChannel NeighborsDetermining the Cluster SizeDetermining the Cluster Size

To find nearest co-channel To find nearest co-channel neighbors of a particular cellneighbors of a particular cell

Step 1: Move i cells along Step 1: Move i cells along any chain of hexagons;any chain of hexagons;

Step 2: Turn 60 degrees Step 2: Turn 60 degrees counterclockwise and counterclockwise and move j cells.move j cells.

i and j measure the i and j measure the number of nearest number of nearest neighbors between co-neighbors between co-channel cellschannel cells

The cluster size, N,The cluster size, N,

N = iN = i22+ij+j+ij+j22

i

j

If i =2 and j = 0, then N = 4If i = 2 and j = 1, then N =7

1

2

3

3

42

1

1 2

26IFA’2004

RULE to Determine the Nearest RULE to Determine the Nearest Co-Channel Neighbors Determining the Co-Channel Neighbors Determining the Cluster SizeCluster Size

27IFA’2004

Frequency ReuseFrequency Reuse

The distance between 2 cells using the The distance between 2 cells using the same channel is known as the REUSE same channel is known as the REUSE DISTANCE D.DISTANCE D.

There is a close relationship between D, There is a close relationship between D, R (radius of each cell) and N (the number R (radius of each cell) and N (the number of cells in a cluster)of cells in a cluster)

D = (sqrt 3N) . RD = (sqrt 3N) . R The REUSE FACTOR is thenThe REUSE FACTOR is then

D/R = sqrt (3N)D/R = sqrt (3N)

28IFA’2004

Frequency ReuseFrequency Reuse

Let N be the cluster size in terms of Let N be the cluster size in terms of number of cells within it and K be the number of cells within it and K be the total number of available channels total number of available channels without frequency reuse.without frequency reuse.

N cells in the cluster would then N cells in the cluster would then utilize all K available channels.utilize all K available channels.

Each cell in the cluster then uses 1/N-Each cell in the cluster then uses 1/N-th of the total available channels.th of the total available channels.

N is also referred as the N is also referred as the frequency frequency reuse factorreuse factor of the cellular system. of the cellular system.

29IFA’2004

Capacity Expansion by Capacity Expansion by Frequency ReuseFrequency Reuse

Assume each cell is allocated Assume each cell is allocated JJ channels channels ((J<=KJ<=K). If the ). If the KK channels are divided among channels are divided among the the NN cells into unique and disjoint channel cells into unique and disjoint channel groups, each with groups, each with JJ channels, then channels, then K = J NK = J N

TheThe N N cells in a cluster use the complete set of cells in a cluster use the complete set of available frequenciesavailable frequencies..

The cluster can be replicated many times. The cluster can be replicated many times. LetLet M M be the number of replicated clusters andbe the number of replicated clusters and

C C be the total number of channels in the entire be the total number of channels in the entire system with frequency reuse, then C is the system with frequency reuse, then C is the system capacity and computed bysystem capacity and computed by

C = M J NC = M J N

30IFA’2004

Cellular System Cellular System Capacity - ExampleCapacity - Example

Suppose there are 1001 radio channels, and each cell is Acell = 6 km2 and the entire system covers an area of Asys = 2100km2.

1. Calculate the system capacity if the cluster size is 7. 2. How many times would the cluster of size 4 have to be

replicated in order to approximately cover the entire cellular area?

3. Calculate the system capacity if the cluster size is 4.4. Does decreasing the cluster size increase the system capacity?

Solution:1. J=K/N=143, Acluster=N*6=42km2, M=2100/42=50, C=MJN=50,050 chs.

2. N=4, Ac=4*6=24km2, M=2100/24=87.

3. N=4, J = 1001/4 = 250 chs/cell. C = 87 * 250 * 4 = 87,000 chs.

4. Decrease in N from 7 to 4 increase in C from 50,050 to 87,000. Decreasing the cluster size increases system capacity. So the answer is YES!

31IFA’2004

Geometry of Hexagonal Cells Geometry of Hexagonal Cells (1)(1)How to determine the DISTANCEHow to determine the DISTANCEbetween the nearest co-channel cells ?between the nearest co-channel cells ?

Planning for Co-channel cellsPlanning for Co-channel cells D is the distance to the center of the nearest co-channel cellD is the distance to the center of the nearest co-channel cell R is the radius of a cellR is the radius of a cell

R

30o

R3

R3i

j

D

0

32IFA’2004

Geometry of Hexagonal Cells Geometry of Hexagonal Cells (2)(2)

Let D be the actual distance between two centers of Let D be the actual distance between two centers of adjacent co-adjacent co-channel cellschannel cells where D= where D=

Let DLet Dnormnorm be the distance from the center of a candidate cell to the be the distance from the center of a candidate cell to the center of a nearest co-channel cell, normalized with respect to the center of a nearest co-channel cell, normalized with respect to the distance between the centers of two adjacent cells, .distance between the centers of two adjacent cells, .

Note that Note that the normalized distance between two adjacent cells either with (i=1,j=0) or (i=0,j=1) is unity.

R3

R3

33IFA’2004


Let D be the actual distance between the centers of two adjacent co-channel cells. D is a function of Dnorm and R.

From the geometry we have

ijji

jijD oonorm

22

2222 ))30sin(()30(cos

NDnorm

From N and Dnorm equations

34IFA’2004


RNRDD norm 33

With the actual distance between the centers of twoadjacent hexagonal cells, the actual distance between

the center of the candidate cell and the center of a nearest co-

channel is then

For hexagonal cells there are 6 nearest co-channel neighbors to each cell. Co-channel cells are located in tiers.In general, a candidate cell is surrounded by 6k cells in tier k.For cells with the same size the co-channel cells in each tier lie on the boundary of the hexagon that chains all the co-channel cells in that tier.

35IFA’2004


As D is the radius between two nearest co-channel cells, the radius of the hexagon chaining the co-channel cells in the k-th tier is given by k.D.

For the frequency reuse pattern with i=2 and j=1 so that N=7, the first two tiers of co-channel cells are given in Figure.

It can be readily observed from Figure that the radius of the first tier is D and the radius of the second tier is 2.D.

36IFA’2004

37IFA’2004

Number of Cells in A Number of Cells in A ClusterCluster

A candidate cell has 6 nearest co-A candidate cell has 6 nearest co-channel cells. Each of them in turn channel cells. Each of them in turn has 6 neighboring co-channel cells. has 6 neighboring co-channel cells. So we can have a large hexagon.So we can have a large hexagon.

This large hexagon has radius This large hexagon has radius equal to D which is also the co-equal to D which is also the co-channel cell separation.channel cell separation.

The area of a hexagon is The area of a hexagon is proportional to the square of its proportional to the square of its radius, (let radius, (let =2.598), =2.598),

D

R

])(3[ 2222arg

2

RjijiDA

RA

eL

Small

38IFA’2004

Number of Cells in A Number of Cells in A ClusterCluster

The number of cells in the large hexagon is thenThe number of cells in the large hexagon is then

222 )(3arg RjijiSmall

eL

A

A

In general the large hexagon encloses the center cluster of N cells plus 1/3 the number of the cells associated with 6 other peripheral large hexagons. Hence, the total number of cells enclosed by the large hexagon is

)(

3)(6

22

31

jijiN

Finally

NNN

39IFA’2004


We assume the size of all the cells is roughly the same, as long as the cell size is fixed We assume the size of all the cells is roughly the same, as long as the cell size is fixed co-channel interference will be independent of transmitted power of each cell.co-channel interference will be independent of transmitted power of each cell.

The co-channel interference will become a function of q where q = D/R = sqrt (3N).The co-channel interference will become a function of q where q = D/R = sqrt (3N).q is the CO-CHANNEL REUSE RATIO and is related to the cluster size.q is the CO-CHANNEL REUSE RATIO and is related to the cluster size.A small value of q provides larger capacity since N is small.A small value of q provides larger capacity since N is small.For large q, the transmission quality is better, smaller level of co-channel interference.For large q, the transmission quality is better, smaller level of co-channel interference.By increasing the ratio of D/R spatial separation between co-channel cells relative to the By increasing the ratio of D/R spatial separation between co-channel cells relative to the

coverage distance of a cell is increased.Thus, interference is reduced from improved coverage distance of a cell is increased.Thus, interference is reduced from improved isolation of RF energy from the nmber of cells per cluster N co-channel cells.isolation of RF energy from the nmber of cells per cluster N co-channel cells.

40IFA’2004


Furthermore, D (distance to the center of the nearest Furthermore, D (distance to the center of the nearest cochannel cell) is a function of Ncochannel cell) is a function of NII and S/I in which and S/I in which NNII is the number of co-channel interfering is the number of co-channel interfering

cells in the first tier and S/I = received signal to cells in the first tier and S/I = received signal to interference ratio at the desired mobile receiver.interference ratio at the desired mobile receiver.

41IFA’2004

Frequency Reuse Frequency Reuse RatioRatio

The The frequency reuse ratiofrequency reuse ratio, , qq, is defined as, is defined asq = D/Rq = D/R

which is also referred to as the co-channel which is also referred to as the co-channel reuse ratio.reuse ratio.

Also Also q = sqrt(3N) q = sqrt(3N) TradeoffTradeoff

– qq increases with increases with NN..– A smaller value of A smaller value of NN has the effect of has the effect of

increasing the capacity of the cellular system increasing the capacity of the cellular system and increasing co-channel interferenceand increasing co-channel interference

– Tradeoff between Tradeoff between qq and and NN

42IFA’2004

InterferenceInterference

MAJOR LIMITING FACTOR for Cellular System performance is the INTERFERENCEMAJOR LIMITING FACTOR for Cellular System performance is the INTERFERENCEImplications:Implications: CROSS TALKCROSS TALK Missed and Blocked Calls.Missed and Blocked Calls.SOURCES OF INTERFERENCE?SOURCES OF INTERFERENCE? Another mobile in the same cellAnother mobile in the same cell A call in progress in neighboring cell.A call in progress in neighboring cell. Other base stations operating in the same frequency bandOther base stations operating in the same frequency band Non-cellular systems leaking energy into cellular frequency bandNon-cellular systems leaking energy into cellular frequency band

43IFA’2004

InterferenceInterference

1. CO-CHANNEL INTERFERENCE2. ADJACENT CHANNEL INTERFERENCE

44IFA’2004

CO-CHANNEL INTERFERENCECO-CHANNEL INTERFERENCE

Frequency Reuse Frequency Reuse Given coverage area Given coverage area cells using the same set of frequencies cells using the same set of frequencies co-channel cell!!! co-channel cell!!! Interference between these cells is calledInterference between these cells is called CO-CHANNEL INTERFERENCE.CO-CHANNEL INTERFERENCE.(Thermal noise (Thermal noise increase SNR and combat it). increase SNR and combat it). However, co-channel interference However, co-channel interference cannot be overcome just by increasing the carrier power of a cannot be overcome just by increasing the carrier power of a

transmitter.transmitter. Because increase in carrier transmit power increases theBecause increase in carrier transmit power increases the interference.interference. Reduce co-channel interferenceReduce co-channel interference Co-channel cells must be physically separated by a minimum distance to provide sufficient isolation.Co-channel cells must be physically separated by a minimum distance to provide sufficient isolation.

45IFA’2004

Co-Channel Co-Channel InterferenceInterference

Intracell Interference: interferences from other mobile terminals in the same cell.– Duplex systems – Background white noise

Intercell interference: interferences from other cells.– More evident in the downlink than uplink for

reception– Can be reduced by using different set of frequencies

Design issue– Frequency reuse– Interference– System capacity

Bottomline: It determines link performance which in turn dictates the frequency reuse plan and overall capacity of the system.

46IFA’2004

Co-Channel InterferenceCo-Channel Interference

Cell Site-to-Mobile Interference (Downlink)

Mobile-to Cell-Site Interferences (Uplink)

47IFA’2004


Base Mobile DOWNLINKMobile Base UPLINKUPLINK All mobiles in 6 cells + central cell assigned to the same frequency channelDOWNLINK All base stations in 6 cells and central cell have the same frequency channel.DOTTED LINES show the interference of all 6 mobiles (all co-channel) received at central base station (interference)Actual signal is from the mobile in the center cell to its own base station.(Uplink Signal Interference ratio)

48IFA’2004


Base Mobile DOWNLINK CASEFrom the base stations (from co-channel cells) interference received by the mobile in the center cell.Desired signal is from the base to mobile in the center cell.Alarge is the area of the hexagonal cells of the large one.Asmall is the area of each cell.

Alarge/Asmall A number of cells in this each repetitous pattern (3N).

49IFA’2004


For simplicity, we consider only the average channel quality as a function of the distance dependent path loss.

Signal-to-Co-channel interference ratio, (S/I), at the desired mobile receiver which monitors the forward channel is defined by

S is the desired signal power from desired base S is the desired signal power from desired base stationstation

IIii interference power caused by the i-th interfering interference power caused by the i-th interfering co-channel cell base station.co-channel cell base station.

NI is the number of co-channel interfering cells

IN

iiI

S

I

S

1

50IFA’2004


The desired signal power S from desired base The desired signal power S from desired base stationstation

is proportional to is proportional to rr--, where , where rr is the distance is the distance between the mobile and the serving base station. between the mobile and the serving base station. is the path loss component. is the path loss component.

The received interference, The received interference, IIii, between the , between the iith th interferer and the mobile is proportional to interferer and the mobile is proportional to (D(Dii))--..

The white background noise is neglected in the The white background noise is neglected in the interference-dominant environment.interference-dominant environment.

Assume the transmisson powers from all base Assume the transmisson powers from all base stations are equal, then we havestations are equal, then we have

IN

iiD

r

I

S

1

51IFA’2004


Consider only the first tier of interfering Consider only the first tier of interfering cells, if all interfering base stations are cells, if all interfering base stations are equidistant from the desired base station equidistant from the desired base station and if this distance is equal to the distance and if this distance is equal to the distance D between cell centers, then the above D between cell centers, then the above equation can be simplified to:equation can be simplified to:

(i.e., r=R(i.e., r=R and assume and assume DDii=D and use q=D/R)=D and use q=D/R)::

IIIN

ii

N

q

N

RD

DN

R

D

r

I

SI

)/(

1

52IFA’2004


Frequency reuse ratio,Frequency reuse ratio,

e.g., Ne.g., NII = 6 = 6

/1)]([ IS

INq

/1)](6[ ISq

53IFA’2004

Co-Channel InterferenceCo-Channel Interference Example: In AMPS systems; Example: In AMPS systems; for for =4, S/I = 18dB (i.e., 63.1), =4, S/I = 18dB (i.e., 63.1), [20 log (S/I) [20 log (S/I) dB] dB] are acceptable; then (assume N=6)are acceptable; then (assume N=6)

q = (6q = (6 63.1) 63.1)1/4 1/4 4.41. 4.41.

Thus, the cluster sizeThus, the cluster size N N should beshould be (from eq. q=sqrt(3N)(from eq. q=sqrt(3N) N = q N = q22/3 = 6.79 /3 = 6.79 7. 7.

i.e.,A 7-cell reuse pattern is needed for an S/I ratio of 18dB. Based i.e.,A 7-cell reuse pattern is needed for an S/I ratio of 18dB. Based on q=D/R, we can select D by choosing the cell radius R.on q=D/R, we can select D by choosing the cell radius R.

54IFA’2004


An S/I of 18 dB is the measured An S/I of 18 dB is the measured value for the accepted voice value for the accepted voice quality from the present day quality from the present day cellular mobile receivers.cellular mobile receivers.

Sufficient voice quality is provided Sufficient voice quality is provided when S/I is greater than or equal to when S/I is greater than or equal to 18dB.18dB.

55IFA’2004

Example: Example: Co-Channel InterferenceCo-Channel Interference

If S/I = 15 dB required for satisfactory performance for If S/I = 15 dB required for satisfactory performance for forward channel performance of a cellular system.forward channel performance of a cellular system.

a)a) What is the Frequency Reuse Factor?What is the Frequency Reuse Factor?b)b) What Cluster Size should be used for maximum What Cluster Size should be used for maximum

capacity? capacity? (Use path loss component of =3 and =4) .

Assume 6 co-channels all of them (same distance from the mobile)

56IFA’2004


a)a) N= 7 and N= 7 and =4The co-channel reuse ratio is

q=D/R=sqrt(3N)=4.5833.75)583.4( 4

61

IN

q

I

S

Or 18.66 dB greater than the minimum required level ACCEPT IT!!!

b) N= 7 and N= 7 and =3

04.16)583.4( 361

IN

q

I

S

Or 12.05 dB less than the minimum required level REJECT IT!!!

57IFA’2004


36)6( 361

IN

q

I

S

Or 15.56 dB N=12 can be used for minimum requirement, but it decreases the capacity since 12 cell reuse offers a spectrum utilization of 1/12 within each cell.

We need a larger N. Use eq. N =i N =i22+ij+j+ij+j22

for i=j=2 next possible value is N=12.N=12.

q=D/R=sqrt(3.N) = 6 and q=D/R=sqrt(3.N) = 6 and =3

58IFA’2004

Worst Case Co-Channel InterferenceWorst Case Co-Channel Interferencei.e., mobile terminal is located at the cell boundary i.e., mobile terminal is located at the cell boundary where it receives the weakest signal from its own cell where it receives the weakest signal from its own cell but is subjected to strong interference from all all the but is subjected to strong interference from all all the interfering cells.interfering cells.

We need to modify our assumption, i.e., We need to modify our assumption, i.e., assume assume DDii=D=D..

The S/I ratio can be expressed asThe S/I ratio can be expressed as

R

D-RD-R

D+R

D+R

D

D44

1

)1(22)1(2

1

)(22)(2

qqqI

S

RDDRD

R

D

r

I

SIN

ii

Used D/R=q and =4. Where q=4.6 for normal seven cell reuse pattern.

59IFA’2004

Example: Worst Case Example: Worst Case Cochannel Interference Cochannel Interference (2)(2)

A cellular system that requires an S/I ratio of 18dB. A cellular system that requires an S/I ratio of 18dB.

(a) (a) If cluster size is 7, what is the worst-case S/I?If cluster size is 7, what is the worst-case S/I? (b) Is a frequency reuse factor of 7 acceptable (b) Is a frequency reuse factor of 7 acceptable in terms of co-channel interference? in terms of co-channel interference? c) If not, what would be a better choice of c) If not, what would be a better choice of frequency reuse ratio?frequency reuse ratio?

60IFA’2004

Example: Worst Case Example: Worst Case Cochannel Interference Cochannel Interference (2)(2)

Solution (a) N=7 q = . If a path loss component of =4, the

worst-case signal- to-interference ratio is S/I = 54.3 or 17.3 dB.

(b) The value of S/I is below the acceptable level of 18dB. To ncrease S/I we need to decrease I,

I.e., Increase the frequency reuse factor, q=5.20 by using N =9.

The S/I becomes then 95.66 or 19.8dB. Acceptable…

6.43 N

61IFA’2004

ADJACENT CHANNEL INTERFERENCEADJACENT CHANNEL INTERFERENCE

Interference resulting from signals which are adjacent Interference resulting from signals which are adjacent in frequency to the desired signal is called in frequency to the desired signal is called ADJACENT CHANNEL INTERFERENCE.ADJACENT CHANNEL INTERFERENCE.WHY?WHY?From imperfect receiver filters (which allow nearby frequencies) to leak into the pass-band.From imperfect receiver filters (which allow nearby frequencies) to leak into the pass-band.NEAR FAR EFFECT:NEAR FAR EFFECT: Adjacent channel user is transmitting in very close range to a subscriber’s receiver, while the receiver Adjacent channel user is transmitting in very close range to a subscriber’s receiver, while the receiver

attempts to receive a base station on the desired channel.attempts to receive a base station on the desired channel. NEAR FAR EFFECT also occurs, when a mobile close to a base station transmits on a channel close to NEAR FAR EFFECT also occurs, when a mobile close to a base station transmits on a channel close to

one being used by a weak mobile.one being used by a weak mobile. Base station may have difficulty in discriminating the desired mobile user from the “bleedover” caused Base station may have difficulty in discriminating the desired mobile user from the “bleedover” caused

by the close adjacent channel mobile.by the close adjacent channel mobile.

62IFA’2004

ADJACENT CHANNEL INTERFERENCEADJACENT CHANNEL INTERFERENCE

How to reduce?How to reduce?• Careful filteringCareful filtering• Channel assignmentChannel assignment no channel assignment which are all adjacent in frequency. no channel assignment which are all adjacent in frequency.• Keeping frequency separation between each channel in a given cell as large as possible.Keeping frequency separation between each channel in a given cell as large as possible.e.g., in AMPS System there are 395 voice channels whiche.g., in AMPS System there are 395 voice channels which are divided into 21 subsets each with 19 channels.are divided into 21 subsets each with 19 channels.• In each subset, the closest adjacent channel is 21 channels away.In each subset, the closest adjacent channel is 21 channels away.• 7-cell reuse -> each cell uses 3 subsets of channels.7-cell reuse -> each cell uses 3 subsets of channels.• 3 subsets are assigned such that every channel in the cell is assured of being separated 3 subsets are assigned such that every channel in the cell is assured of being separated

from every other channel by at least 7 channel spacings.from every other channel by at least 7 channel spacings.

63IFA’2004

Cell SplittingCell Splitting A method to increase the capacity of a cellular A method to increase the capacity of a cellular

system by dividing one cell into more smaller system by dividing one cell into more smaller cells.cells.

Each smaller cell has its own base station and Each smaller cell has its own base station and accordingly antenna height and transmission accordingly antenna height and transmission power can be reduced.power can be reduced.

Cell splitting reduces the call blocking probability Cell splitting reduces the call blocking probability because the number of channels is increased. because the number of channels is increased.

But it increases the handoff rate, i.e., more But it increases the handoff rate, i.e., more frequent crossing of borders between the cells.frequent crossing of borders between the cells.

We have the formula in calculating path loss: We have the formula in calculating path loss: PPrr(dBW) = P(dBW) = P00(dBW) - 10 (dBW) - 10 loglog1010(d/d(d/d00))

where dwhere d00 is the distance from the reference point is the distance from the reference point to the transmitter, andto the transmitter, and P P00 is the power received is the power received at the reference point.at the reference point.

64IFA’2004

Cell Splitting (2)Cell Splitting (2) Let PLet Pt1t1 and P and Pt2t2 be the transmit be the transmit

power of the large cell BS and power of the large cell BS and medium cell BS, respectively.medium cell BS, respectively.

The received power at the The received power at the edge of large cell is edge of large cell is

PPr1r1 = P = P0 0 - 10 - 10 log log1010(R/d(R/d00)) The received power at the The received power at the

edge of large cell, Pedge of large cell, Pr1r1 is is proportional to proportional to

PPt1t1 (R (R))- - .. The received power at the The received power at the

edge of R/2 cell, Pedge of R/2 cell, Pr2r2 is is proportional to proportional to

PPt2t2 (R/2 (R/2))- - .. With the equal received With the equal received

power, we have power, we have PPt1t1 (R (R))-- = = PPt2t2 (R/2(R/2))- - ,, i.e., i.e., PPt1t1/P/Pt2t2= 2 = 2

R

R/2

65IFA’2004

Example – Cell Example – Cell SplittingSplitting

Suppose each BS is allocated 60 channels regardless Suppose each BS is allocated 60 channels regardless of the cell size. Find the number of channels of the cell size. Find the number of channels contained in a 3x3 kmcontained in a 3x3 km22 area without cell splitting, area without cell splitting, i.e., R= 1km and with cell splitting, R/2 = 0.5km. i.e., R= 1km and with cell splitting, R/2 = 0.5km.

The number of cells for R=1km.1. Each large cell can cover 3.14km2, for 9

km2 approximately need 9/3.14 => 3 cells. However, 3 hexagon cannot cover a square of 3x3. A better approximation is 4 cells. So the number of channels is 4x60=240.

2. With small cells, the number of cells is approximately (1/0.5)2x4 = 16. Then the number of channels is 16x60=960.

66IFA’2004

Cell SectoringCell Sectoring(Directional (Directional Antennas)Antennas)

Omni-directional antennas allow transmission of radio signals with equal power Omni-directional antennas allow transmission of radio signals with equal power strength in all directions.strength in all directions.

Reality is an antenna covers an area of 60 degrees or 120 degrees Reality is an antenna covers an area of 60 degrees or 120 degrees DIRECTIONAL DIRECTIONAL ANTENNAS!!!!ANTENNAS!!!!

Cells served by these antennas are called SECTORED CELLS!!!Cells served by these antennas are called SECTORED CELLS!!! Many sectored antennas are mounted a BS tower located at the center of the cell and Many sectored antennas are mounted a BS tower located at the center of the cell and

an adequate number of antennas is placed to cover the entire 360 degrees of the cell.an adequate number of antennas is placed to cover the entire 360 degrees of the cell..

67IFA’2004

CELL SECTORINGCELL SECTORINGDirectional Antennas Directional Antennas (Sectoring)(Sectoring)

1

2

3

1

24

5 1

4

3

6

23

OMNIDIRECTIONAL 120 DEGREE SECTOR 90 DEGREE SECTOR

60 DEGREE SECTOR

68IFA’2004

Cell SectoringCell Sectoring(Directional (Directional Antennas)Antennas)

Advantages of Cell Sectoring:Advantages of Cell Sectoring: Borrowing of channelsBorrowing of channels Coverage of smaller area by each antenna and hence lower power is Coverage of smaller area by each antenna and hence lower power is

required in transmitting radio signals.required in transmitting radio signals. Helps to decrease interference between co-channels.Helps to decrease interference between co-channels. Also the spectrum efficiency of the overall system is enhanced.Also the spectrum efficiency of the overall system is enhanced..

69IFA’2004

Co-Channel Interference ReductionCo-Channel Interference Reduction with the Use of Directional with the Use of Directional Antennas (Cell Sectoring)Antennas (Cell Sectoring)

The basic form of antennas are The basic form of antennas are omnidirectional. Directional antennas can omnidirectional. Directional antennas can increase the system capacity.increase the system capacity.

If we sectorize the cell with If we sectorize the cell with 120120oo in each sector, the S/I in each sector, the S/I becomes:becomes: (The number of interferers is reduced from 6 (The number of interferers is reduced from 6

to 2.)to 2.)

The capacity increase in (S/I)The capacity increase in (S/I)120 120 vsvs (S/I)(S/I)omni omni

is 3.is 3.

6)(

1

q

D

R

I

SIN

ii

omni

1 23

3

12

2)( 120

q

I

S

70IFA’2004

Worst-Case Scenario in 120Worst-Case Scenario in 120oo SectoringSectoring

Let Let DD be the be the distance between distance between the adjacent co-the adjacent co-channel cells.channel cells.

With the distance With the distance approximation and approximation and use path loss use path loss component component , , the the signal-to-signal-to-interference ratio isinterference ratio is

3

12

D

D+0.7R

)7.0()( 120 RDD

R

I

S

71IFA’2004

Fixed Channel Assignment Fixed Channel Assignment (FCA)(FCA)

Each cell is allocated a Each cell is allocated a predetermined set of voice channels. predetermined set of voice channels.

The BS is the entity that allocates The BS is the entity that allocates channels to the requests. If all channels to the requests. If all channels are used in one cell, it may channels are used in one cell, it may borrow a channel from its neighbors borrow a channel from its neighbors through MSC.through MSC.

Fast allocation, but may result high Fast allocation, but may result high call blocking probabilities.call blocking probabilities.

72IFA’2004

Dynamic Channel Assignment Dynamic Channel Assignment (DCA)(DCA)

Voice channels are not allocated to each cell permanently.

When a request is received at the BS, this BS request a channel from MSC.

DCA can reduce the call blocking probability, but it needs real-time data collection and signaling transmission between BS and MSC.

73IFA’2004

Call Admission Call Admission ControlControl

CAC is used to avoid congestions over the CAC is used to avoid congestions over the radio links and to ensure the QoS radio links and to ensure the QoS requirements of ongoing services.requirements of ongoing services.

Quality of service (QoS)Quality of service (QoS)– Packet-level factorsPacket-level factors– Packet loss rate, packet delay, packet Packet loss rate, packet delay, packet

delay variation, and throughput rate.delay variation, and throughput rate. Grade of service (GoS)Grade of service (GoS)

– Call-level factorsCall-level factors– New call blocking probability, handoff call New call blocking probability, handoff call

dropping probability, connection forced dropping probability, connection forced termination probability. termination probability.

74IFA’2004

CAC ProcedureCAC Procedure Determine the amount of available channels, i.e., the Determine the amount of available channels, i.e., the

number of channels for accepting new and handoff number of channels for accepting new and handoff requests.requests.

When the N-th request arrives, i.e., there are (N-1) When the N-th request arrives, i.e., there are (N-1) ongoing services. ongoing services.

If there are enough resources to admit the N-th If there are enough resources to admit the N-th request, then the new request is admitted.request, then the new request is admitted.

Otherwise, it will be denied.Otherwise, it will be denied. In order to maintain the continuity of a handoff call, In order to maintain the continuity of a handoff call,

handoff calls are given higher priority than the new handoff calls are given higher priority than the new call requests.call requests.

The prioritized call admission is implemented by The prioritized call admission is implemented by reserving channels for handoff calls. This method is reserving channels for handoff calls. This method is referred to as referred to as guard channelsguard channels..– Fixed reservation and dynamic reservation.Fixed reservation and dynamic reservation.

75IFA’2004

The average number of mobiles requesting service The average number of mobiles requesting service (average call arrival rate): (average call arrival rate):

The average length of time a mobile requires service The average length of time a mobile requires service (the average holding time): (the average holding time): TT

The offered traffic load: The offered traffic load: A = A = TT– e.g., in a cell with 100 mobiles, on an average, if e.g., in a cell with 100 mobiles, on an average, if

30 requests are generated during an hour, with 30 requests are generated during an hour, with average holding time average holding time T=360T=360 seconds, then the seconds, then the arrival rate arrival rate =30/3600=30/3600 requests/sec. requests/sec.

A servicing channel that is kept busy for an hour is A servicing channel that is kept busy for an hour is quantitatively defined as one Erlang. quantitatively defined as one Erlang.

Hence, the offered traffic load (A) by Erlang is thenHence, the offered traffic load (A) by Erlang is then

Erlangscall

Sec

Sec

CallsA 3

360

3600

30

Cell CapacityCell Capacity

76IFA’2004

Call BlockingCall Blocking How likely a new user can get a connection How likely a new user can get a connection

established successfully? Admission control of new established successfully? Admission control of new calls.calls.

It is measured by the probability of call blocking, It is measured by the probability of call blocking, which is a quality of service (QoS) factor, a.k.a., which is a quality of service (QoS) factor, a.k.a., (GoS) factor.(GoS) factor.

Assume we have a total number of Assume we have a total number of CC channels in a channels in a radio cell. radio cell.

If the number of active users during any period of If the number of active users during any period of time is time is CC, then the call blocking probability is , then the call blocking probability is 11. .

If and only if the number of ongoing calls is less If and only if the number of ongoing calls is less than than CC, the probability of call blocking will be less , the probability of call blocking will be less than than 11..

77IFA’2004

Probability of an arriving call being blocked Prob that Probability of an arriving call being blocked Prob that (Blocked Calls Cleared; Lost)) is (Blocked Calls Cleared; Lost)) is

where where C C is the number of channels in a cell.is the number of channels in a cell.Prob(A,C) is also called blocking probability, probability Prob(A,C) is also called blocking probability, probability

of loss, or probability of rejection.of loss, or probability of rejection.

,

!

1

!,Pr)_[Pr][Pr

0

C

k

k

C

kAC

ACAobLossesCellobBlockingob

Erlang BErlang B

78IFA’2004

Probability of an arriving call being delayed, i.e.,

probability that no trunk (server=channel) is available for an arriving call in a system with C channels and the call is delayed, is

1

0!)1(!

,Pr]0Pr[ C

kk

kACAC

C

CA

ACAobdelay

where Prob(A, C) is the probability of an arriving call being delayed with load A and C channels.

Erlang CErlang C

79IFA’2004

SEMANTICSSEMANTICSProb that calls are lost..Prob that calls are lost..

GOS for telephone calls (realstic values 10^{-2} – 10^{-3}GOS for telephone calls (realstic values 10^{-2} – 10^{-3}

Physical Interpretation-> Ratio of calls rejected to the total Physical Interpretation-> Ratio of calls rejected to the total number of calls.number of calls.

What can we do with these Erlang formulas?What can we do with these Erlang formulas?

a)a) Given a fixed offered traffic A in Erlangs and a fixed Given a fixed offered traffic A in Erlangs and a fixed device capacity C, then find the prob of blocking…device capacity C, then find the prob of blocking…

b)b) Determine the offered traffic in Erlangs that produces a Determine the offered traffic in Erlangs that produces a given blocking probability for a fixed device capacity C.given blocking probability for a fixed device capacity C.

c)c) Determine the required device capacity given the Determine the required device capacity given the blocking probability and the offered traffic in Erlangs.blocking probability and the offered traffic in Erlangs.

80IFA’2004

EXAMPLEEXAMPLE

An urban PC area has a population of 2 Million An urban PC area has a population of 2 Million residents. A cellular company serves this residents. A cellular company serves this area. System has 394 cells with 19 channels area. System has 394 cells with 19 channels each.each.

Find the number of users that can be Find the number of users that can be supported at 2% blocking if each user supported at 2% blocking if each user averages 2 calls/per hour at an average call averages 2 calls/per hour at an average call duration of 3 minutes!!duration of 3 minutes!!

81IFA’2004

EXAMPLEEXAMPLE

Prob of BlockingProb of Blocking 0.02 (GOS) 0.02 (GOS)

Number of Channels Number of Channels C=19 C=19

Traffic Intensity per User Traffic Intensity per User A/mu = 2* 3/60 = 0.1 Erlangs A/mu = 2* 3/60 = 0.1 Erlangs

From Erlang B chart, total carried traffic obtained as 12 From Erlang B chart, total carried traffic obtained as 12 ERLANGS.ERLANGS.

The number of users which can be supported per cell isThe number of users which can be supported per cell is

12/0.1 = 120.12/0.1 = 120.

There are 39 cells There are 39 cells total number of subscribers total number of subscribers supported is 120 * 394 = 47280.supported is 120 * 394 = 47280.

82IFA’2004

Example: for previous example, if CExample: for previous example, if C=2, A= 3=2, A= 3

then then

B(2, 3) = 0.6B(2, 3) = 0.6, ------ Blocking probability, , ------ Blocking probability,

i.e., 60% calls are blocked. i.e., 60% calls are blocked.

Total number of rerouted calls = 30 x 0.6 = Total number of rerouted calls = 30 x 0.6 = 1818

Efficiency = 3(1-0.6)/2 = 0.6Efficiency = 3(1-0.6)/2 = 0.6

)(channelstrunksofNumber

trafficnonblockedofportionsErlangs

Capacity

nonblockedTrafficEfficiency

Efficiency Efficiency (Utilization)(Utilization)

83IFA’2004

SummarySummary The advantage of cellular communicationsThe advantage of cellular communications

– Capacity extension by frequency reuseCapacity extension by frequency reuse– Cell cluster and cochannel cellsCell cluster and cochannel cells– Number of cells in a clusterNumber of cells in a cluster– Frequency reuse ratioFrequency reuse ratio

Co-Channel interferenceCo-Channel interference– Impact of cluster sizeImpact of cluster size– Worst-case cochannel interferenceWorst-case cochannel interference

Traffic load and call blocking probabilityTraffic load and call blocking probability– Average delayAverage delay– Probability of queuing delayProbability of queuing delay

Cell splitting and sectoringCell splitting and sectoring Fixed channel allocation and dynamic channel allocationFixed channel allocation and dynamic channel allocation

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