1

GSM + UMTS

Wireless Communication

2

Contents

Introduction Network architecture Fundamental functionality Physical layer / radio interface UMTS

GSM – The idea of a common European mobile communications system

1982: A Nordic group is considering the next generation of mobile telephone. – NMT (Nordisk Mobil Telefon), the analogue first generation system has only just been started

These ideas are presented to CEPT (European Conference of Postal and Telecommunications Administrations) in June 1982

September 1982: The first meeting in CEPT GSM – Groupe Spécial Mobile

In 1988 ETSI (European Telecommunications Standards Institute) is established and the work is continued under a new name: SMG – Special Mobile Group

GSM - Specifications

Original specifications for the GSM system: Good subjective voice quality Low terminal and service cost Support for international roaming Support for handheld terminals Support for new services Spectrum efficient Compatible with ISDN

GSM - Growth 1991: First operational GSM network in Finland: Radiolinja 1993: Tele-mobil (later: Telenor Mobil) and NetCom GSM open their

networks in Norway 1998: GSM 1800 is deployed to increase capacity in cities and other

densely populated areas

0200400600800

1 0001 2001 4001 6001 8002 0002 2002 4002 6002 8003 0003 200

19

82

19

83

19

84

19

85

19

86

19

87

19

88

19

89

19

90

19

91

19

92

19

93

19

94

19

95

19

96

19

97

19

98

19

99

20

00 0 %

10 %

20 %

30 %

40 %

50 %

60 %

70 %

80 %

TM NMT TM GSM NetCom

9M

’01

GSM improvements – 2.5 G and 3 G The need for data services increase:

In 1998-99 the HSCSD – High Speed Circuit Switched Data - is standardised. Introduced in Norway 1. July 2001 (Telenor)

I 1999 packet switching using GPRS (General Packet Radio Service) is standardised. Introduced in Norway 1. February 2001 (Telenor) Theoretical data rates up to 171 kbit/s

"2.5 G" – EDGE – Enhanced Data rates for GSM Evolution Standardised in 2001-2002 Introduced in September 2004 Theoretical data rates up to 373 kbit/s

“3 G" – EDGE – Enhanced Data rates for GSM Evolution/UMTS

Standardised in 2001-2002 Introduced in September 2004 – deployment ongoing Theoretical data rates up to 2 Mbps

Some GSM terminals

Development.. HTC P4350Pocket computer running Windows

iPhone – Apple’sMobile phone initiative

High level network architecture (1/2)

SIM

ME:Mobile equipment

Services / Applications

Core Network(CN)

Ext.network

UE: User equipment

Access Network(AN)

High level network architecture (2/2)

The network contains functionally of: User Equipment (UE), Access Network (AN), and Core Network (CN) User equipment: Interfaces the user, handles radio

functionality Access network: Communication to and from the user

equipment, handles all radio related functionality in the network

Core network: Communication between access network and external networks, handles all switching and routing

Services and applications lie above the network

10

GSMThe European TDMA Digital Cellular Standard

General Architecture Of GSM

ME

SIMSIM

BTSBTS

BTSBTS

BSCBSC

BSCBSC

MSC

VLR

EIR

HLR

AuC

AUm

Abis

PSTN,ISDN

Mobile station

Base Station Subsystem

NetworkSubsystem

MS BSS NS

11

Network Overview

12

Network Overview A GSM system is basically designed as a combination of three

major subsystems: Network Sub-System (NSS), Radio subsystem called the Base station Sub-System (BSS), Operation Sub-System (OSS).

The Network Sub-System (NSS)

includes the equipment and functions related to end-to-end-calls, management of subscribers, mobility, and interfaces with the fixed network (PSTN). It is built on the switch of the system called Mobile-services Switching Center (MSC).

The Base station Sub-System (BSS)

includes the equipment and functions related to the management of the connection on the radio path. It mainly consists of Base Transceiver Stations (BTS) communicating with the Mobile Station (MS) and one Base Station Controller (BSC) managing the flow of information between the BTSs and the MSC.

13

Network Overview

The Operation Sub-System (OSS) mainly contains Operation and Maintenance Center for NSS (OMC-S)

and Operation and Maintenance Center devoted to the BSS (OMC-R). It is connected to all equipment in the switching system and to the BSC (BTSs are not connected to the OSS).

14

Mobile Station The Mobile Station (MS) is composed of three parts:

The handset includes the radio equipment (receiver-transmitter) and the Man-

Machine Interface (MMI), The SIM card (Subscriber Identity Module-card):

allows the identification of any subscriber The battery.

15

Subscriber Identification The International Mobile Subscriber Identity (IMSI) is the primary

identification of the subscriber within the GSM network and is permanently assigned to him.

The Mobile Subscriber ISDN Number (MSISDN) is the number that the calling party dials in order to reach the GSM subscriber. It is used by the land networks to route calls toward an appropriate GSM network. MSISDN is stored in HLR.

16

BSS Architecture The Base Station Sub-System (BSS)

is a set of equipment (aerials, transceivers and a controller) that is viewed by the Mobile Switching Center through a single A interface as being the entity responsible for communicating with mobile telephones or Mobile Stations (MSs) in a certain area.

The radio equipment of a BSS may be composed of one or more cells, such a BSS may contain one or more Base Transceiver Stations (BTSs).

The interface between the BSC and the BTSs is called an Abis interface

17

BSS BSC: Base station Controller

It manages radio resources for one or more BTS. Allocation and De-allocation of channels. Transmitter power control. Handoff control

BTS : Base Transceiver station It defines the cell .

It handles the radio link protocol with the mobile station

A BSS contains only one Base Station Controller (BSC). The function split is basically between a transmission equipment,

the BTS, and the BSC.

18

NSS Architecture

Network Subsystem MSC: Mobile Switching Center HLR: Home Location Register VLR: Visitor Location register AuC: Authentication Center EIR: Equipment Identity Register

BSCBSC MSC

VLR

EIR

HLR

AuC

PSTN,ISDN

19

NSS Architecture BSCs of a same area are connected to a switch. In a GSM system this

switch is called MSC (Mobile Switching Center). MSCs are connected to each others.

Mobile Switching center:(MSC) call set up/supervision/release/routing billing information collection mobility management paging, alerting connection to BSC, other MSC and other local exchange networks Access to HLR and VLR

Usually, each MSC is associated to four databases.

The Visitor Location Register (VLR) memorizes information about the subscribers physically

present in a geographic area. Temporary visitors database One VLR per MSC

20

NSS Architecture Home Location Register (HLR)

One HLR per GSM operator Contains permanent database of all the subscribers in the

network contains MSRN(mobile station routing no.) It is referred for every incoming call

Authentication Center (AuC): Provides security Authentication and encryption

The Equipment Identity Register (EIR) contains list of all the Mobile Equipment: it contains valid and invalid mobile equipment. Contains IMEI

Fundamental functionality The following functions are described:

Circuit switched connectivity Packet switched connectivity Mobile messaging Security Roaming Choice of network Location update Handover

Circuit Switched connectivity

ISDNMobile network

Fixed connection and reserved resources while the communication lasts. (Mobile) telephony Circuit switched data, e.g. WAP, mobile office solutions using data cards etc.

Transparent channel with defined performance Billing typically per time unit and dependant on transport data rate Standard GSM: up to 14.4 kbit/s (more using HSCSD - High Speed Circuit

Switched Data)

Packet Switched connectivity

Resources allocated only when data is transferred Same ”path” through network can be maintained (but not necessarily) Billing typically dependant on amount of data transferred (or fixed tarrifs) GPRS: Theoretically up to 171 kbit/s, typically 40 – 50 kbit/s- 4 different quality classes for packet ”bearer services”:

Internet ordifferent IP networkMobile network

Background Typically automatic download of email, MMS

Interactive Typically web/WAP-browsing, MMS, games

Streaming ”Network radio”, video streaming, web TV

Conversational Voice, video conferencing

Mobile messaging formats

SMS: Short Message Service Text based service to transfer up to 160 characters per message

(solutions exist to connect messages into longer messages, and also to carry other types of content – ring tones, logos…)

MMS: Multimedia Messaging Service A service for multimedia content, such as text, picture, sound, video

Both SMS and MMS are ”store and forward” services, i.e. messages are intermediately stored in the network

Security functions The purpose of security functions is to protect

users and network against improper and illegal use: Verify that the user has a valid subscription Protect the user’s identity against tracking Protection against wiretapping on the radio connection

The mechanisms in GSM are based on secure storage of information in the user’s SIM card

International network

Roaming (1/2)

Circuit switched call to a mobile in a visiting network

Home network

Visiting network

ISDN (country A)

ISDN (country B)

International network

Roaming (2/2)

Mobile to mobile call in a visiting network Effect referred to as ”tromboning”

Home network

Visiting network

ISDN (country A)

ISDN (country B)

Choice of network In GSM the following procedure is followed:

The latest used network is stored on the SIM As long as a cell that fulfils the criteria is

available from this network, the mobile will not search for alternatives (the exception is national roaming, in which case the mobile will periodically search for the home network and connect when this becomes available)

If the previously used network is not available, the mobile searches for alternative networks

The mobiles can perform manually or automatic choice of network

Location update A location update is performed when:

The mobile is connecting to a cell and discovers that the LAI read is different than the one stored in the mobile

The mobile has been turned on, but not used, for a pre-defined period of time since the last location update (periodic location update)

IMSI detach/attach: An additional function where the mobile informs that it is turned on

or off (in the same LA), saves resources on the radio interface and leads to faster response on incoming calls

Periodic detach A network functionality where the network assumes that the mobile

has been turned off if periodic location update has not been performed and no other activity has been observed for a pre-defined amount of time

Handover

To connect a call or communication session from one cell to another (or to a different channel in the same cell)

Is normally performed because the signal level from the current cell is becoming to low, but can also be done for different reasons, such as too much traffic in a cell

Types of handover

Intra cell (to another channel in the same cell) (1)

Inter cell, intra BSC (2) Inter BSC, intra MSC (3) Inter MSC (4)

In addition inter system handover can sometimes be performed, e.g. GSM to UMTS Complicated, special rules apply

Type of handover has network implications, but the algorithms to decide handover are the same

33

Physical layer/Radio interface GSM Radio Aspects :

GSM 900: 890 – 915 MHz: Uplink (MS transmit) 935 - 960 MHz: Downlink (MS receive)

GSM 1800: 1710 - 1885 MHz: Uplink 1805 - 1880 MHz: Downlink

Carrier bandwidth: 200 kHz Channels / carrier: 8 Multiple access: TDMA / FDMA Duplex: FDD Modulation: GMSK full rate calls 13 Kbps If half-rate used 16 calls at 6.5 kbps

45 MHz

960 MHz935 MHz

200 kHz

MS transmit MS receive

41 2 3 4 1241231

8

2345

67

1

8

2345

67

1231241 2 3 4

915 MHz

Total Frequency range(Uplink)=25Mhz

Spacing between two carriers= 200kHzNo. of Carriers=25MHz/200KHz = 124

Suggested use: only 122Use top & bottom as additional guard

35

GSM uses TDMA within each carrier Each user occupies the entire carrier one time slot/time frame

8 slots per frame

0 71 2 4 5

0 33 3 5 6 7

Time

Freq

Down Link carrier

Up Link carrier

200 KHz

Time slots

4.6 ms0.57ms

3 6

5421

TDMA Frame

36

0 1 2 653 7

1 2 2524

4

0 10

3 57 57261

Data Data Training

Tdma Frame

Frame Multiframe

Format of a single Burst

Duration=120ms

Duration=4.615ms

Duration=0.577ms

25

37

Classification of channels in GSM Channels are used to carry speech , data and control information. Two types

Traffic channels (TCH) Typically uses one time slot per frame Gross data rate per TCH: 22 kbps Effective data rate lower because of forward error correction

Control channels (CCH)

Traffic Channels are defined using 26 TDMA frame multi-frame. Length of 26 TDMA frames = 120 msec

Length of 1 TDMA frame =120/26 = 4.615 msec 1 TDMA frame consists of 8 burst frames Length of 1 burst frame = 0.577msec Out of 26 frames

24 are TCH used for traffic,1 is SACCH used for control,1 is unused

38

Traffic/Signaling

39

Logical channels Logical channels built up of physical channels

Traffic channels Control channels

Logical channels divided between: Dedicated channels Common channels

Traffic (TCH) Speech

Full rate 22.8 kb/s Half rate 11.4 kb/s

Data 9.6kb/s,4.8kb/s,2.4kb/s

40

Control channels Control (CCH)

Broadcast (BCCH) Freq correction (FCCH) Synchronization (SCH)

Common (CCH) Paging (PCH) Access grant (AGCH) Random Access (RACH)

Dedicated (DCCH) Fast Associative (FACCH) Slow Associative (SACCH) Stand alone (SDCCH)

41

Control Channel BCCH (Broadcast Control Channel )

Continuously transmitted from the BTS. Contains information about cell identity, frequency etc.

FCCH/SCH (Frequency Correction Channel / Synchronisation Channel ) Used to correct/synchronise the frequency (FCCH) + time synchronise to the

frame structure. Each cell has a FCCH and a SCH RACH (Random Access Channel )

Used by the mobile to send a request to the network for access. AGCH (Access Grant Channel )

Used by the network to inform the mobile that access has been granted and information about which channel to use

PCH (Paging Channel) Used by the network to notify users about incoming calls.

42

Modulation Assuming that everyone is familiar with digital

modulation :-)

Considerations upon choosing modulations scheme: Spectrum efficiency Out of band emission (rapid drop off desired to limit

adjacent channel interference) Constant envelope desired for low cost amplifiers, e.g. in

handheld equipment

In GSM: GMSK – Gaussian Minimum Shift Keying is used

43

GMSK Gaussian Minimum Shift Keying Bandwidth-time product

Describes the amount the symbols overlap BT = 0.3 for GSM networks Characterized by the value

of BT T = bit duration B = 3dB Bandwidth of the shaping filter BT = 0.3 for GSM BT = 0.5 for DECT Good spectral efficiency At the expense of some inter-symbol interference (ISI)

44

GMSK GMSK further reduces side lobes by using a Gaussian filter

Cost: introduces inter-symbol-interference (ISI) Figures show time and frequency response

GSM uses BT = 0.3

45

UMTS

UMTS Universal Mobile Telecommunication

systems

46

SYSTEM ARCHITECTURE Functional network elements

User Equipment (UE) interfaces with user and radio interface

Radio Access Network (RAN, UMTS Terrestrial RAN = UTRAN) handles all radio-related functionality

Core Network switches and routes calls and data connections to external

networks

47

SYSTEM ARCHITECTURE PLMN (Public Land Mobile Network)

operated by a single operator distinguished from each other with unique identities connected to other PLMNs as well as to other types of network,

such as ISDN, PSTN, Internet, etc

48

UE consists of two parts Mobile Equipment (ME)

the radio terminal used for radio communication over Uu interface

UMTS Subscriber Identity Module (USIM) a smartcard that holds the subscriber identity performs authentication algorithms stores authentication and encryption keys some subscription information that is needed at the terminal

User Equipment (UE)

49

UTRAN consists of two elements Node B

converts data flow between Iub and Uu interfaces participates in radio resource management

channel coding and interleaving rate adaptation Spreading

Radio Network Controller (RNC) owns and controls radio resources in its domain the service access point (SAP) for all services that

UTRAN provides to the CN e.g., management of connections to UE

UTRAN

50

Core Network Main elements of CN

a) HLR (Home Location Register)

b) MSC/VLR (Mobile Services Switching Centre/Visitor Location Register)

c) GMSC (Gateway MSC)

d) SGSN (Serving GPRS (General Packet Radio Service) Support Node)

e) GGSN (Gateway GPRS Support Node)

51

Core Network- HLR (Home Location Register)

a database located in user’s home system that stores the master copy of user’s service profile

service profile consists of, e.g., information on allowed services, forbidden roaming areas supplementary service information such as status of call

forwarding and the call forwarding number it is created when a new user subscribes to the system, and

remains stored as long as the subscription is active for the purpose of routing incoming transactions to UE (e.g. calls

or short messages) HLR also stores the UE location on the level of MSC/VLR

and/or SGSN

52

Core Network - MSC/VLR and GMSC(Mobile Services Switching)Centre/Visitor Location Register)

◦ the switch (MSC) and database (VLR) that serve the UE in its current location for Circuit Switched (CS) services

◦ the part of the network that is accessed via MSC/VLR is often referred to as CS domain

MSC- used to switch CS transactions

VLR- holds a copy of the visiting user’s service profile, as well as

more precise information on the UE’s location within the serving system

GMSC (Gateway MSC) the switch at the point where UMTS PLMN is connected to

external CS networks all incoming and outgoing CS connections go through GMSC

53

Core Network - SGSN and GGSN

SGSN (Serving GPRS (General Packet Radio Service) Support Node) functionality is similar to that of MSC/VLR but is typically used for

Packet Switched (PS) services the part of the network that is accessed via SGSN is often

referred to as PS domain

GGSN (Gateway GPRS Support Node) functionality is close to that of GMSC but is in relation to PS

services

54

External Networks External networks can be divided into two

groups CS networks

provide circuit-switched connections, like the existing telephony service

ISDN and PSTN are examples of CS networks

PS networks provide connections for packet data services Internet is one example of a PS network

55

Main open interfaces Cu interface

the electrical interface between USIM smartcard and ME Uu interface

the WCDMA radio interface the interface through which UE accesses the fixed part of the

system Iu interface

connects UTRAN to CN Iur interface

allows soft handover between RNCs Iub interface

connects a Node B and an RNC

56

• UMTS Band : 1900-2025 MHz and 2110-2200 MHz for 3G transmission.

• Terrestrial UMTS (UTRAN) : 1900-1980 MHz, 2010-2025 MHz, and 2110-2170 MHz bands

UMTS Frequency Spectrum

57

Radio Interface

UMTS uses Wideband-Code Division Multiple Access (W-CDMA) Also known as “IMT-2000 Direct Spread” Extremely complex algorithms Uses 10x the 2G processing power! Modulation is done with Quadrature phase shift keying (QPSK)

This encodes 2 bits with each change Supports two modes of operation

Frequency Division Duplex (FDD) Time Division Duplex (TDD)

58

UMTS - Air Interface UMTS FDD (Frequency Division Duplex)

Uplink: 1920 - 1980 MHz Downlink: 2110 - 2170 MHz 190 MHz duplex distance ca. 5MHz (variable) carrier spacing (DS CDMA – Direct

Sequence CDMA) 12 bands in uplink & downlink

59

UMTS - Air Interface UMTS TDD (Time Division Duplex) Uplink & Downlink: 1900 - 1920 MHz and 2020 - 2025 MHz

5 carriers in total, 15 timeslots per frame a user may use one or several timeslots a timeslot can be assigned to either uplink or downlink

60

UMTS – history and planned standards February 1995 UMTS Task Force established; "The Road to

UMTS" report December 1996 The UMTS Forum established. "European"

WCDMA standard known as Universal Mobile Telecommunications System (UMTS)

June 1997 UMTS Forum produces first report: "A regulatory Framework for UMTS"

October 1997 ERC decided on UMTS core band. January 1998 ETSI meeting: W-CDMA and TD-CDMA proposals

combined to UMTS air interface specification June 1998 Terrestrial air interface proposals (UTRAN,

WCDMA(s), CDMA2000(s), EDGE, EP-DECT, TD-SCDMA) were handed into ITU-R

3GPP Release ‘99

61

UMTS – history and planned standards

March 2001 in Palm Springs 3GPP approves UMTS Release 4 specification

Release 4 and 5 specifies an “All IP standard” Streaming services (fast handover) Seamless UMTS/WLAN integration, interworking Push-to-Talk over cellular Presence for chat, instant messaging, ...

Release 6 Extended location based services (LBS) Packet switches streaming services, with adaptation to available

network resources (GERAN/GPRS, UTMS, WLAN) Charging Management Framework (for extended payment

systems) For more see www.3gpp.org