ECE 5221 Personal Communication Systems

Florida Institute of technologies

ECE 5221 Personal Communication Systems Prepared by:

Dr. Ivica Kostanic

Lecture 2: Basics of cellular system architecture(Chapter 2.1 and 2.2)

Spring 2011


Outline of cellular system architectureElements of the cellular system architectureSupport for mobility – HandoffAutomatic roaming

Outline

Important note: Slides present summary of the results. Detailed derivations are given in notes.


Layout of the Cellular Comm. System

MSC - Mobile Switching CenterBSC - Base Station ControlerBTS - Base Transceiver SystemHLR - Home Location RegisterVLR - Visitor Location RegisterAC - Authentication CenterEIR - Equipment Identity RegisterPSTN - Public Switched Telephone NetworkISDN - Integrated Service Digital NetworkOA&M - Operation, Administration & Maintenance System

HLR

VLR EIR

AC

MSC

DATA-BASE SUBSYSTEM

SWITCHING SYSTEMS

OA&M

BTS

MSBSC

RADIO SYSTEMS

PSTN

ISDN

EXTERNAL NETWORKS

Other MSCs

Circuit switched part of cellular system


Mobile Subscriber Unit

Usually the only part of the system that users are aware of

Traditionally used for voice Becoming more data centric Performs any functions

o Voice processingo CS/PS Call managemento Packet data transfer

May be multi-band May be multi-technology

Keyboard

Control

Display

Transm itAudio SignalProcessing

Receive AudioSignal

Processing

Modulation

Demodulation RFAmplifier

RFAmplifier

Filter

Filter

Logic Unit

Duplexer

Antenna

ANTENNAASSEMBLY

TRANSMITTER

RECEIVER

TRANSCEIVER UNITCONTRO LSECTIO N

Block diagram of voice processing in mobile unit


Base Station Controller

MSC

BSC

PSTN

BSC

PSTN

MSCB SC

Two implementations Multiple BSCs BSC within MSC

Responsibility of BSC Radio resource management Handoff between cells


Base Transceiver Station

Base stationo Bank of radioso Responsible for radio link

between system and the mobile

Base station provides communication resources over given coverage area

The number of users that can be served = number of BTS resources

BTS connects to the core network (BSC) through T1/E1 lines

May be configured as omni-directional or sectored

unchannelized T1

from BSC

Receiver Multicoupler_A

Transmitter Combiner

Filter

to A receivers

...from

transmittersto B

receivers

Receiver Multicoupler_B

... ...

Scanning Receiver

Rx_

BRx

_A

Control Channel

Rx_

BTx

Rx_

A

. . .

Rx_B

TxR

x_A

Rx_B

TxR

x_A

Voice Channels

to BSC

......

Voice Links Signaling Links

Duplexer

Rx_B

... ...

Tx/Rx_A

Block diagram of a base station


Base Station Antenna Configuration

Omnidirectional (Omni) Antennas Coverage pattern is a

circle Usually located in low-

traffic

(rural) areasDirectional Antennas

Coverage directed to

a specific area Increase system capacity 60º, 90º and 120º are

the most common


Base Station Coverage ClassificationMacrocells

Microcells

Picocells

Coverage depends on; transmit power antenna gains antenna height

Cell Type Mega Cell Macro Cell Micro Cell Pico Cell Cell Radius 100 – 500 km <= 35 km <= 1 km <= 50 m Operating

Environment Global Suburban Urban In-building

Installation Mode

Satellites Top of the building or tower

Lamp-post or side of the

building

Inside the building

Subscriber’s Speed

<= 500 km/h <= 100 km/h < = 10 km/h


Towers

Monopole - 80’ - 150’

- small amount of

land required

- limited loading

Self Supporting - 100’ - 300’

- heavy loading

Guyed Tower - up to 1500’

- heavy loading

can be a problem


Circuit vs. packet switching

Legacy cellular technologies (1G and 2G) are circuit switched Dial-up type connections A single user occupies a channel for the

entire transmission Requires time-oriented billing GSM transmissions are bursty Bursty nature favors data services

Modern cellular networks (3G and 4G) is packet switched technology

More appropriate for data services Continuous flow is not required Access is based on demand only Several users can be multiplexed Billing based on negotiated QoS and

usage


Cellular architecture CS/PS (2G->3G)

GMSC

M S

ForeignPLMNBG

BSC

BSC

Other MSC

DATA-BASESUBSYSTEM

Other SGSN BG

VLR H LRG R

EXTERNALNETW ORKS

BTS

BTS

BTS

GSMRADIOSUBSYSTEM

GSMSW ITCHINGSUBSYSTEM

GPRSSUBSYSTEM

PDN

ISDN

MSCTRAU

GGSNSGSNPCU

AirInterface

AbisInterface

GbInterface

GnInterface

GnInterface

GpInterface

GiInterface

GcInterface

GrInterface

GsInterface

AInterface

BInterface

CInterface

EInterface

DInterface

AbisInterface

AirInterface

PSTNBTS

MS


Handoff

Fundamental requirement for mobility support Two types: hard handoff and soft handoff Hard Handoff … ‘Break before make!’

Analog Handoff - obsolete MAHO (Mobile Assisted Handoff)

Soft Handoff … ‘Make before break!’ currently just in CDMA systems Soft handoff is MAHO

Type of implemented handoff depends on air interface technology


MAHO

Neighboring Cell

Serving Cell

RSSI report + voice

(2) Decides about Handoff based on reported RSSIs

Sends Channel

Assignment Command to

new BSSends Retune Command to

MS through Serving Cell

Neighboring Cell

(1b)Measures

RSSI from the Neighboring

BSsReports RSSI to Swich through

Serving BS

RSSI report (1a)

RSSI report

Scanns Spectrum for users in need of

HandoffReports RSSI to Swich

Switch

PSTN

All modern technologies use

MAHO


Hard HO and Soft HO

Drop A2

Add B3

Drop B3

Add C2

A 1

A 2A 3

B 1

B 2B 3

C 1

C 2C 3

A 1

Add B1

Drop A2

A 2A 3

B 1

B 3 B 2

M S is he re in 2 -w a yH a nd o ff

(w ith A 2 & B 1 )!

Type of handoff – function of air interface Soft handoff more reliable Soft handoff – resource intense

Hard handoff

Soft handoff


Automatic Roaming

BS

ServingMSC/VLR

HLR

SS7 network

LocationUpdate

Registration Acknowledgment(Customer Profile)

Registraton Request

VLRUpdate

M SC - M obile S w itch ing CenterHLR - H om e Loca tion R egis te rVLR - V is itor Location Regis terM S - M obile S ta tionBS - B ase S tation

SS7 - Signaling N etwork

Current location of a mobile – kept in a VLR When mobile turns on – it registers As a part of registration – HLR is updated with

the current mobile’s VLR When the mobile is called, based on the HLR

entry, the call is located to the MSC of the mobile’s current VLR

The mobile is paged within the area or sub-area of current VLR

ECE 5221 Personal Communication Systems

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