Mobile Cellular Networks

• Cellular principle– 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

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

Mobile Cellular Networks

A

B

C

D

E

F

GF

A

B

C

D

E

G

A

B

C

D

E

F

G

Figure 1

Cellular structure and frequency spectrum allocation plan

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

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

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

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

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

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

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