mobile cellular networks

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Mobile Cellular Networks • Evolution 1st generation, 1980s • analogue • voice 2nd generation 1990s • digital • Voice, fax data • 95% coverage of UK by 1991 3rd generation - within 10 years • digital • anywhere, anytime, anything Most significant development in telecommunications in recent years

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Mobile Cellular Networks. Evolution 1st generation, 1980s analogue voice 2nd generation 1990s digital Voice, fax data 95% coverage of UK by 1991 3rd generation - within 10 years digital anywhere, anytime, anything Most significant development in telecommunications in recent years. - PowerPoint PPT Presentation

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Page 1: Mobile Cellular Networks

Mobile Cellular Networks

• Evolution– 1st generation, 1980s

• analogue

• voice

– 2nd generation 1990s

• digital

• Voice, fax data

• 95% coverage of UK by 1991

– 3rd generation - within 10 years

• digital

• anywhere, anytime, anything

• Most significant development in telecommunications in recent years

Page 2: Mobile Cellular Networks

Mobile Cellular Networks

• Cellular principle– Proposed as a solution to the bandwidth

problem

– Restrict the radio range of Base Station (transmitter)

– Can now reuse BS frequency in other parts of the network

– Taking this one step further

• tessellate network coverage area with cell reuse pattern (cluster)

• Each cell in cluster operates on a different frequency

• Cluster sizes of 4,7,9 etc are common

• Result - increase in capacity of network in terms of max number of simultaneous calls the network can support

Page 3: Mobile Cellular Networks

Mobile Cellular Networks

• Cellular principle– Cells are hexagonal shape

– Base station located in middle

– Radius of cell is governed by power of Base Station

– Increasing the power increases geographical size of cell

– Smaller sizes automatically increase the network capacity

• but can also increase interference

Page 4: Mobile Cellular Networks

Mobile Cellular Networks

A

B

C

D

E

F

GF

A

B

C

D

E

G

A

B

C

D

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F

G

Figure 1

Cellular structure and frequency spectrum allocation plan

Page 5: Mobile Cellular Networks

Mobile Cellular Networks

• Cellular principle– Trend is to have sophisticated cell structures

• essentially overlay large cells on smaller cells

– Common cell sizes

• Pico cells

– floor of a building

– a few metres

• Micro cells

– Street

– 10 -400 metres

– Base station mounted below roof level

– Street canyons

• Macro cells

– 5 kms

– special masts erected for Base station

– Pico cells give large capacity for a small area

– Macro cells give small capacity for a large area

Page 6: Mobile Cellular Networks

Mobile Cellular Networks

• Global System for Mobility (GSM)– Small amount of radio spectrum allocated for

cellular networks

– For GSM

• 890-915MHz uplink (Mobile station to Base station)

• 935-960Mhz downlink

– Each call requires a dedicated full duplex channel (circuit switched)

– Typically a network provider is allocated a subset of these for operation

– Note Mobile station must operate across all frequencies

Page 7: Mobile Cellular Networks

Mobile Cellular Networks

Uplink 890-915 MHz

Downlink 935-960 MHz

1 2 3 123 124

100kHz

200kHz

100kHz

124 X 200 kHz carriers + 2 X 100kHz guard bands at each end

Figure 3Structure of the Frequency Sprectrum for GSM

Page 8: Mobile Cellular Networks

Mobile Cellular Networks

• Network Components– Mobile Station

• Mobile Equipment (e.g. phone)

– antenna

• Subscriber Identity Module (SIM)

– Smart card

– SIM must be inserted into ME before ME will work

– Essentially personalises ME

– Contains subscription information

– Other information - subscriber’s short dialing codes

– Can make emergency codes

• Future is multi-media mobile stations

Page 9: Mobile Cellular Networks

Mobile Cellular Networks

• Network Components– Base Station System

• Base Transceiver Station– Antenna– Interfaces to MS– Able to transmit /receive signals on many

channels simultaneously• Base Station Controller

– Controls a number of Base Transceiver Stations

– Essentially a concentrator (multiplexer)• Multiplexes Base Transceiver Stations

onto high speed link– Undertakes some radio management tasks

• passes Location Area Code to Base Transceiver Station for broadcasting to MSs

– Also translates 13kbps speech from radio channels to 64Kbps PCM for transmission on fixed network

Page 10: Mobile Cellular Networks

Mobile Cellular Networks

• Network Components– Mobile Switching Centre (MSC)

• ISDN switch enhanced to operate in mobile network

• In addition to switching

– manages calls for all MSs within its domain

• Billing

• Handover

• Authentication

Page 11: Mobile Cellular Networks

Mobile Cellular Networks

• Network Components– ‘Intelligence’ (databases) in Network

• Equipment Identity Register (EIR)

– Stores information on lost or stolen MSs

– Each MS has a unique International Mobile Equipment Identifier (IMEI)

– Network can refuse access id IMEI is stored on EIR.

• Authentication Centre (AuC)

– provides access security for network

Page 12: Mobile Cellular Networks

Mobile Cellular Networks

• Network Components– ‘Intelligence’ (databases) in Network

• Home Location Register (HLR)

– One logical HLR in network

– Contains an entry for every subscriber

– Stores fairly static information about subscriber

• services subscribed to

– But also location information to allow mobility

• Location Area Code where MS is currently operating

Page 13: Mobile Cellular Networks

Mobile Cellular Networks

• Network Components– ‘Intelligence’ (databases) in Network

• Visitor Location Register (VLR)

– One VLR for every Location Area in network

– Typically an Mobile Switching Centre ‘covers’ a location area

• In this instance VLR is integrated with MSC

– VLR contains information on every subscriber (visitor) currently operating in the domain of VLR

– Entries are added when visitors enter VLR domain

– Entries are deleted when visitors leave VLR domain

• HLR and VLR jointly facilitate mobility

Page 14: Mobile Cellular Networks

Mobile Cellular Networks

MSC

EIR VLR HLR

AUC

NMC/OMC GMSC

BSC

MS

BTS BTS

BTS

MS

BSC

MS

BTS BTS

MS

MS

D

C

E

To

PSTN/ISDN

A

FB

Figure 2

GSM network architecture

Um

Abis

N.B. The letters shown on the links arethe network interfaces defined in GSM

Page 15: Mobile Cellular Networks

Mobile Cellular Networks

• Radio Interface– Traffic channels

• Full duplex, circuit switched

– Control channels for signalling

• Broadcast

– e.g. Broadcast Control Channel (BCCH)

• Gives Location Area Code

• Private

– e.g. Fast Associated Control Channel (FACCH)

• Used during call establishment, for handover etc.

• Other Interfaces - very like N-ISDN

Page 16: Mobile Cellular Networks

Mobile Cellular Networks

• Mobility

• Terminal Mobility (1st generation systems)– Keeps track of MS

– MS / subscriber more or less the same entity

– One-to-one relationship between subscriber and MS

– Give your MS to someone else, they will receive your calls

– Not unlike the fixed network

Page 17: Mobile Cellular Networks

Mobile Cellular Networks

• Mobility

• Personal mobility in GSM (2nd generation systems)– More flexible than terminal mobility

– Subscriber can receive calls on any MS

• provided their SIM card is inserted

– One-to-many relationship

– Separated MS from subscriber

Page 18: Mobile Cellular Networks

Mobile Cellular Networks

• Mobility

• Full personal mobility (3rd generation systems)– MS can be used by many subscribers

– Subscriber can be registered to receive calls on any MS

– Many-to-many relationship

Page 19: Mobile Cellular Networks

Mobile Cellular Networks

• Mobility Management (Network Mobility)

– Needed to deliver Incoming calls

• Various Approaches

– Network doesn’t keep track of subscribers’ moves

– To deliver an incoming call need to broadcast to every cell in the network

– Implications of extending this to an international level

Page 20: Mobile Cellular Networks

Mobile Cellular Networks

• Mobility Management

• Another approach (used by 2nd generation systems)– Network keeps track of subscribers’ moves

• HLR and VLR used for this purpose

• Two operations involved

– Update (location update)

– Find (finding subscriber to deliver an incoming call)

Page 21: Mobile Cellular Networks

Mobile Cellular Networks

if subscriber highly mobile (frequent updates)

if subscriber receives many calls (frequent finds)

location update approach is best

else subscriber receives few calls

..............

else (subscriber is stationary)

if subscriber receives many calls

..............

else subscriber receives few calls

..............

Page 22: Mobile Cellular Networks

Mobile Cellular Networks

• Mobility management

• Update - when a subscriber moves to a new location area – i.e. comes under the domain of a new VLR

– MS detects it has roamed into a new location area

– MS requests a location update from new MSC

– New MSC enters subscribers details in associated (new) VLR

– New VLR forwards location update to HLR

– HLR is updated with new VLR address

– HLR requests old VLR to delete subscribers entry

Page 23: Mobile Cellular Networks

Mobile Cellular Networks

MS NewMSC

NewVLR HLR Old

VLR

Location Update

Request Update Location

Area Update Location

Cancel Location

Cancel Location

AckInsert Sunscriber

Data

Insert Sunscriber

Data Ack

Update Location

AckUpdate Location

Area Ack

Location Update

Accept

Location Update OperationFigure 5

Page 24: Mobile Cellular Networks

Mobile Cellular Networks

• Mobility management

• Find (mobile subscriber)– HLR is used to find the subscriber’s current

location (VLR)

– HLR requests a temporary roaming number from VLR

– VLR returns roaming number to HLR

– HLR returns roaming number to call source

– Call may now be routed (to VLR)

– VLR meanwhile will be alerting MS that a call is expected

Page 25: Mobile Cellular Networks

Mobile Cellular Networks

PSTN/ISDN

GMSC

HLR

MSC

VLR

BS

1

2

3

4

6 7

8

9

10

5

MSC/VLR whereGMSC/HLR on MS'shome network MS is currently located

Figure 6Sequence of Operations for an Incoming CAll

MS

Page 26: Mobile Cellular Networks

Mobile Cellular Networks

GMSC

HLR

MSC

VLR

BS

1

2

3

4

6 7

8

9

10

5

MSC/VLR where calledGMSC/HLR on calledMS's home network MS is currently located

MS

GMSC MSC

HLR/VLR

BS

MSC where callingGMSC in network wherecalling MS is currently located MS is currently located

MS

PSTN/ISDN

12

3

4

5* * HLR if calling MS is a subscriber

VLR if calling MS is a visitor

Page 27: Mobile Cellular Networks

Mobile Cellular Networks

• Mobility Management

• Roaming Agreements

Page 28: Mobile Cellular Networks

Mobile Cellular Networks

UKNET SwissNET

UKNET Subscriber UKNET Subscriber

Incoming call from UKNET subscriber to remote UKNET subscriber

HLR

VLR

Page 29: Mobile Cellular Networks

Mobile Cellular Networks

UKNET SwissNET

UKNET Subscriber

Incoming call from SwissNET subscriber to UKNET subscriber resident in Switzerland

HLR

VLR

SwissNET Subscriber