Cellular Systems

Market GSM

Overview Services Sub-systems Components

GPRS EDGE

Worldwide cellular subscriber growth

Mobile Wireless Generations

1G - AnalogAMPS, TACS, NMT

2G - DigitalGSM, TDMA,

CDMA,PDC, DECT

Data Rate, Quality, Capacity, Services

1980 20001990

2.5GGPRS, 1xRTT

2010

3G – About dataEVDO, WCDMA,

HSPA, EDGE

3.9G – About BroadbandSAE/LTE, UMB

WiMAX

Growth in peak and average spectral efficiency

Peak efficiency lies around upper line

Average efficiency of deployed systems lags well behind

Capacity growth and will level off due to interference

Cells need to get smaller!!

Source: Agilent

Migration To 3G

CDMA

GSM

TDMA

PHS (IP-Based)

64 Kbps

GPRS

115 Kbps

CDMA 1xRTT

144 Kbps

EDGE

384 Kbps

cdma20001X-EV-DV

Over 2.4 Mbps

W-CDMA (UMTS)

Up to 2 Mbps

2G2.5G

2.75G 3G

1992 - 2000+ 2001+ 2003+

1G

1984 - 1996+

2003 - 2004+

TACS

NMT

AMPS

GSM/GPRS

(Overlay) 115 Kbps

9.6 Kbps

9.6 Kbps

14.4 Kbps/ 64 Kbps

9.6 Kbps

PDC

Analog Voice

Digital VoicePacket Data

IntermediateMultimedia

Multimedia

PHS

TD-SCDMA

2 Mbps?

9.6 Kbps

iDEN(Overlay)

iDEN

Source: U.S. Bancorp Piper Jaffray

cdma2000

1X EV-DO revA

Global Technology Roadmap: 3G to 4G

3GPP

3GPP2

WiMAX

WCDMA HSDPA HSUPA

CDMA1xEV-DORev 0

EV-DORev A

EV-DORev B

LTE

EV-DORev C

Fixed WiMAX

Mobile WiMAX

3G rel99 Architecture (UMTS)

SS7

IP

BTSBSC MSC

VLR

HLR AuC

GMSC

BSS

SGSN GGSN

PSTN

PSDN

CN

CD

GcGr

Gn Gi

Abis

Gs

B

H

BSS Base Station System

BTS Base Transceiver Station

BSC Base Station Controller

RNS Radio Network System

RNC Radio Network Controller

CN Core Network

MSC Mobile-service Switching Controller

VLR Visitor Location Register

HLR Home Location Register

AuC Authentication Server

GMSC Gateway MSC

SGSN Serving GPRS Support Node

GGSN Gateway GPRS Support Node

AE PSTN

2G MS (voice only)

2G+ MS (voice & data)

UMTS Universal Mobile Telecommunication System

Gb

3G UE (voice & data)

Node BRNC

RNS

Iub

IuCS

ATMIuPS

AMPS

Design Goals of AMPS

The very first cellular phone technology Conceived by Bell Labs High voice quality (near wire line)Small coverage area (cell radius: 1-16 miles)Large cells thermal noise limited and small cells interference limited666 channels (later increased to 832 channels)Low power mobile (handheld) transmitters (4 watts or less)Medium power base stations (100’s of watts)Low blocking (2%) during busy hourImmediate service (1-5 business days; now 1-5 hours)System capacity for 100,000 or more customers per city

Characteristics of AMPS

Frequency range (45 MHz separation): 824 MHz ~ 849 MHz for mobile stations to transmit 869 MHz ~ 894 MHz for base station to transmit

3 KHz analog voice channels modulated on to 30 KHz channelsFM (frequency modulation) for voiceMFM (Manchester frequency modulation) at 10 kbps for dataControl channelsVoice channels

AMPS Frequency Allocation

Band A Transmit: 824 MHz ~ 835 MHz and 845 MHz ~846.48 MHz Receive: 869 MHz ~ 880 MHz and 890 MHz ~ 891.5 MHz

Band B Transmit: 835 MHz ~ 845 MHz and 846.5 MHz ~ 849 MHz Receive: 880 MHz ~ 890 MHz and 891.5 MHz ~ 894 MHz

312 usable RF pairs divided by 7 (the reuse factor) = roughly 45 channel pairs per cell

Digital Cellular - D-AMPS

During 1990’s, analog cellular service increased in popularity…carriers wanted to add capacity (besides just breaking up cells into smaller sizes) and wanted to add new services…led to development of digital cellular

Designed with backward compatibility in mind

Digital Cellular

Advantages more efficient use of bandwidth (more capacity) new services (caller ID, call waiting, data service) improved security (harder to listen in because digital bits are

scrambled when they are multiplexed using TDMA or CDMA

D-AMPS (IS-54)

800-900 MHz and 1900 MHzTDMA/FDMA

6 slots per channel/2 slots per conversation 30 KHz channel Quadrature Phase Shift Keying (QPSK) modulation

Emphasis on vehicular trafficAT&T called their 800-900 D-AMPS system PCS

FDMA/TDMA in D-AMPS

Frq1

Frq2

Frq3

Frq4

TS 1 TS 2 TS 3 TS 4 TS 5 TS 6

TS 1 TS 2 TS 3 TS 4 TS 5 TS 6

TS 1 TS 2 TS 3 TS 4 TS 5 TS 6

TS 1 TS 2 TS 3 TS 4 TS 5 TS 6

FDMA: divide assigned bandwidth into several channelsTDMA: 3 calls (2 time slots each) per channel

CDMA (IS-95)

Most systems use direct sequence SS1.25 MHz channels (in narrowband)Same frequencies used in all cells

means no need for complex frequency coordination10 fold capacity gain over AMPSMain problem is controlling power

Other CDMA Benefits

No hard capacity limit too many users increases general level of system noise, but doesn't

block callerSoft handoffs

using same frequency in each cell means that handoffs can be gradual

Variable rate vocoding (voice coding) reduces bit rate when caller not speaking

Multipath signal processing techniques increase signal integrityMore secure transmissions

GSM

GSM: Overview

GSM formerly: Groupe Spéciale Mobile (founded 1982) now: Global System for Mobile Communication Pan-European standard (ETSI, European Telecommunications

Standardisation Institute) simultaneous introduction of essential services in three phases (1991,

1994, 1996) by the European telecommunication administrations (Germany: D1 and D2) seamless roaming within Europe possible

today many providers all over the world use GSM (more than 212 countries in Asia, Africa, Europe, Australia, America)

more than 4.3 billion subscribers more than 70% of all digital mobile phones use GSM over 10 billion SMS per month in Germany, > 360 billion/year worldwide

Performance characteristics of GSM (wrt. analog sys.)

Communication mobile, wireless communication; support for voice and data

servicesTotal mobility

international access, chip-card enables use of access points of different providers

Worldwide connectivity one number, the network handles localization

High capacity better frequency efficiency, smaller cells, more customers per cell

High transmission quality high audio quality and reliability for wireless, uninterrupted phone

calls at higher speeds (e.g., from cars, trains)Security functions

access control, authentication via chip-card and PIN

Architecture of the GSM system

several providers setup mobile networks following the GSM standard within each country

components MS (mobile station) BS (base station) MSC (mobile switching center) LR (location register)

subsystems RSS (radio subsystem): covers all radio aspects NSS (network and switching subsystem): call forwarding, handover, switching OSS (operation subsystem): management of the network

GSM: overview

fixed network

BSC

BSC

MSC MSC

GMSC

OMC, EIR, AUC

VLR

HLRNSSwith OSS

RSS

VLR

GSM: elements and interfaces

NSS

MS MS

BTS

BSC

GMSC

IWF

OMC

BTS

BSC

MSC MSC

Abis

Um

EIR

HLR

VLR VLR

A

BSS

PDN

ISDN, PSTN

RSS

radio cell

radio cell

MS

AUCOSS

signaling

O

Um

Abis

ABSS

radiosubsystem

MS MS

BTSBSC

BTS

BTSBSC

BTS

network and switching subsystem

MSC

MSC

fixedpartner networks

IWF

ISDNPSTN

PSPDNCSPDN

SS

7

EIR

HLR

VLR

ISDNPSTN

GSM: system architecture

System architecture: radio subsystem

Components MS (Mobile Station) BSS (Base Station Subsystem):

consisting of BTS (Base Transceiver Station):

sender and receiver BSC (Base Station Controller):

controlling several transceivers

Interfaces Um : radio interface Abis : standardized, open interface with

16 kbit/s user channels A: standardized, open interface with

64 kbit/s user channels

Um

Abis

A

BSS

radiosubsystem

network and switchingsubsystem

MS MS

BTSBSC MSC

BTS

BTSBSC

BTSMSC

System architecture: network and switching subsystem

Components MSC (Mobile Services Switching Center): IWF (Interworking Functions)

ISDN (Integrated Services Digital Network) PSTN (Public Switched Telephone Network) PSPDN (Packet Switched Public Data Net.) CSPDN (Circuit Switched Public Data Net.)

Databases HLR (Home Location Register) VLR (Visitor Location Register) EIR (Equipment Identity Register)

networksubsystem

MSC

MSC

fixed partnernetworks

IWF

ISDNPSTN

PSPDNCSPDN

SS

7

EIR

HLR

VLR

ISDNPSTN

Radio subsystem

The Radio Subsystem (RSS) comprises the cellular mobile network up to the switching centers

Components Base Station Subsystem (BSS):

Base Transceiver Station (BTS): radio components including sender, receiver, antenna - if directed antennas are used one BTS can cover several cells

Base Station Controller (BSC): switching between BTSs, controlling BTSs, managing of network resources, mapping of radio channels (Um) onto terrestrial channels (A interface)

BSS = BSC + sum(BTS) + interconnection

Mobile Stations (MS)

possible radio coverage of the cell

idealized shape of the cellcell

segmentation of the area into cells

GSM: cellular network

use of several carrier frequencies not the same frequency in adjoining cells cell sizes vary from some 100 m up to 35 km depending on user

density, geography, transceiver power etc. hexagonal shape of cells is idealized (cells overlap, shapes depend on

geography) if a mobile user changes cells

handover of the connection to the neighbor cell

Example coverage of GSM networks (www.gsmworld.com)

e-plus (GSM-1800)

T-Mobile (GSM-900/1800) Berlin

O2 (GSM-1800)

Vodafone (GSM-900/1800)

Network and switching subsystem

NSS is the main component of the public mobile network GSM switching, mobility management, interconnection to other networks, system

control Components

Mobile Services Switching Center (MSC)controls all connections via a separated network to/from a mobile terminal within the domain of the MSC - several BSC can belong to a MSC

Databases (important: scalability, high capacity, low delay) Home Location Register (HLR)

central master database containing user data, permanent and semi-permanent data of all subscribers assigned to the HLR (one provider can have several HLRs)

Visitor Location Register (VLR)local database for a subset of user data, including data about all user currently in the domain of the VLR

Mobile Services Switching Center

The MSC (mobile switching center) plays a central role in GSM switching functions additional functions for mobility support management of network resources interworking functions via Gateway MSC (GMSC) integration of several databases

Functions of a MSC specific functions for paging and call forwarding termination of SS7 (signaling system no. 7) mobility specific signaling location registration and forwarding of location information provision of new services (fax, data calls) support of short message service (SMS) generation and forwarding of accounting and billing information

Operation subsystem

The OSS (Operation Subsystem) enables centralized operation, management, and maintenance of all GSM subsystems

Components Authentication Center (AUC)

generates user specific authentication parameters on request of a VLR authentication parameters used for authentication of mobile terminals and

encryption of user data on the air interface within the GSM system Equipment Identity Register (EIR)

registers GSM mobile stations and user rights stolen or malfunctioning mobile stations can be locked and sometimes even

localized Operation and Maintenance Center (OMC)

different control capabilities for the radio subsystem and the network subsystem

Mobile Terminated Call

PSTNcallingstation GMSC

HLR VLR

BSSBSSBSS

MSC

MS

1 2

3

45

6

7

8 9

10

11 12

1316

10 10

11 11 11

14 15

17

1: calling a GSM subscriber2: forwarding call to GMSC3: signal call setup to HLR4, 5: request MSRN from VLR6: forward responsible MSC to GMSC7: forward call to current MSC8, 9: get current status of MS10, 11: paging of MS12, 13: MS answers14, 15: security checks16, 17: set up connection

Mobile Originated Call

PSTN GMSC

VLR

BSS

MSC

MS1

2

6 53 4

9

10

7 8

1, 2: connection request3, 4: security check5-8: check resources (free circuit)9-10: set up call