level ii introduction to gsm essentials day 1.pptx

7/27/2019 Level II Introduction to GSM Essentials Day 1.pptx

1/44

Level II

Introduction toGSM Essentialsand Basic

AnalysisQoS Department


2/44

Overview

Introduction to GSM Architecture

Introduction to GSM Channels


3/44

What is GSM ?

Global System for Mobile (GSM) is a

second generation cellular standarddeveloped to cater voice services and data

delivery using digital modulation .


4/44

GSM in WorldFigures: March, 2005

37%

1%4%43%

4%

3%

3%

3% (INDIA)

3%

Arab World

Asia Pacific

AfricaEast Central Asia

Europe

Russia

India

North America

South America


5/44

GSM Services

Tele-services Bearer or Data

Services

Supplementary

services


6/44

Tele Services

Telecommunication services that enable voice communication via

mobile phones

Offered services

- Mobile telephony

- Emergency calling


7/44

Bearer Services

Include various data services for informationtransfer between GSM and other networks like

PSTN, ISDN etc at rates from 300 to 9600 bps Short Message Service (SMS)

- up to 160 character alphanumeric datatransmission to/from the mobile terminal

Voice mailbox


8/44

Supplementary Services

Call related services :

Call Waiting- Notification of an incoming call while on thehandset

Call Hold- Put a caller on hold to take another call

Call Barring- All calls, outgoing calls, or incoming calls Call Forwarding- Calls can be sent to various numbers definedby the user

Multi Party Call Conferencing - Link multiple calls together


9/44

GSM System Architecture


10/44

GSM System Architecture-I

Mobile Station (MS)

Mobile Equipment (ME)

Subscriber Identity Module (SIM)

Base Station Subsystem (BSS)

Base Transceiver Station (BTS)

Base Station Controller (BSC)

Network Switching Subsystem(NSS)

Mobile Switching Center (MSC)

Home Location Register (HLR)Visitor Location Register (VLR)

Authentication Center (AUC)

Equipment Identity Register (EIR)


11/44

System Architecture

Mobile Station (MS)

The Mobile Station is made up of two entities:

1. Mobile Equipment (ME)

2. Subscriber Identity Module (SIM)


12/44

Mobile Equipment

Portable, vehicle mounted, hand held device

Uniquely identified by an IMEI (International MobileEquipment Identity)

Voice and data transmission Monitoring power and signal quality of surrounding cells

for optimum handover

Power level : 0.8W20 W

160 character long SMS.


13/44

Subscriber Identity Module(SIM)

Smart card contains the International Mobile SubscriberIdentity (IMSI)

Allows user to send and receive calls and receive othersubscribed services

Protected by a password or PIN

Can be moved from phone to phonecontains keyinformation to activate the phone


14/44

System Architecture

Base Station Subsystem (BSS)

Base Station Subsystem is composed of two parts that

communicate across the standardized Abis interface

allowing operation between components made by different

suppliers

1. Base Transceiver Station (BTS)

2. Base Station Controller (BSC)


15/44

Base Transceiver Station (BTS):

Encodes, encrypts, multiplexes, modulates and

feeds the RF signals to the antenna.

Communicates with Mobile station and BSC

Consists of Transceivers (TRX) units


16/44

Base Station Controller (BSC)

Manages Radio resources for BTS

Assigns Frequency and time slots for all MSs in its area

Handles call set up Handover for each MS

It communicates with MSC and BTS


17/44

Mobile Switching Center (MSC)

Heart of the network

Manages communication between GSM and other networks

Billing information and collection

Mobility management- Registration

- Location Updating

- Inter BSS and inter MSC call handoff


18/44

Home Location Registers (HLR)

Stores information about each subscriber that belongs to

it MSC in permanent and temporary fashion. As soon as mobile subscriber leaves its current local area,

the information in the HLR is updated.

database contains IMSI, MSISDN, prepaid/ postpaid,

roaming restrictions, supplementary services.


19/44

Visitor Location Registers (VLR)

Temporary database which updates whenever new MSenters its area, by HLR database

Assigns a TMSI to each MS entering the VLR area whichkeeps on changing.

Controls those mobiles roaming in its area

Database contains IMSI, MSISDN, Location Area,authentication key


20/44

Authentication Center (AUC)

Contains the algorithms for authentication as well asthe keys for encryption.

Protects network operators from fraud.

Situated in special protected part of the HLR.


21/44

Equipment Identity Register (EIR)

Stores all devices identifications registered for this network.

Database that is used to track handsets using the IMEI(International Mobile Equipment Identity)

Prevents calls from stolen, unauthorised or defective mobile

devices


22/44

Operation and maintenance centre

(OMC) The centralized operation of the various units in the system

and functions needed to maintain the subsystems.

Dynamic monitoring and controlling of the network.

Functions :

- configuration management

- fault report and alarm handling

- performance supervision/management- storage of system software and data


23/44

Characteristics of GSM Standard

Fully digital system using 900,1800 MHz frequency band.

User/terminal authentication for fraud control.

Full international roaming capability.

Low speed data services (upto 9.6 Kb/s).

Compatibility with ISDN.

Support of Short Message Service (SMS).


24/44

Future Of GSM 2nd Generation

GSM -9.6 Kbps (data rate)

2.5 Generation ( Future of GSM)

HSCSD (High Speed ckt Switched data) Data rate : 76.8 Kbps (9.6 x 8 kbps)

GPRS (General Packet Radio service)

Data rate: 14.4 - 115.2 Kbps

EDGE (Enhanced data rate for GSM Evolution)

Data rate: 547.2 Kbps (max)

3 Generation

WCDMA(Wide band CDMA)

Data rate : 0.3482.0 Mbps


25/44

High level network architecture

(1/2)

SIM

ME:Mobile equipment

Services / Applications

Core Network(CN)

Ext.network

UE: User equipment

Access Network(AN)


26/44

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 andexternal networks, handles all switching and routing

Services and applications lie above the network


27/44

GSM radio interfaceMain

characteristics Frequency bands: GSM 900:

890915 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 Gross bit rate pr carrier: 270,833 kbit/s Modulation: GMSK Spectrum efficiency: 1.35 bps/Hz


28/44

Radio parameters:

MS:

Sensitivity: -104 (-102) dBm

Typical106 dBm

Max. output power: 33(30) dBm

Numbers in parenthesis for GSM-1800

BTS:

Sensitivity: -104 (-104) dBm

Typical:107 dBm

Max. output power: 43dBm


29/44

Channels in GSM900

890 MHz

45 MHz

960 MHz935 MHz

200 kHz

MS transmit MS receive

41 2 3 4 1241231

8

234567

1

8

234567

1231241 2 3 4

915 MHz


30/44

TDMA - principle

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

8 slots per frame


31/44

GSM Channel structure

Logical channels builtup of physical channels Control channels

Traffic channels

Logical channelsdivided between: Dedicated channels

Common channels

25 MHz

124 carriers

577 sBurst period Time slot 1

Time slot 2

..

Time slot 8

= 4.615 ms

=Physical

channel

TDMA frame


32/44

GSM traffic channels

Traffic channels (TCH) are used to carry voice or data

Typically uses one time slot per frame

Gross data rate per TCH: 22 kbps

Effective data rate lower because of forward error correction

Training

sequence

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

BP0 BP1 BP2 BP3 BP4 BP5 BP6 BP7

3 57 1 26 1 57 3 8.25

26 frame length: 120 ms

TDMA frame length: 4.6 ms

Data bitData bit

Normal burst


33/44

Some GSM control channels

BCCH Broadcast Control CHannel Continuously transmitted from the BTS. Containsinformation 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 thenetwork for access. This is a slotted Aloha channel, no pre-allocation possible

AGCH Access Grant CHannel Used by the network to inform the mobile that accesshas been granted and information about which channel to use

PCH Paging CHannel Used by the network to notify users about incoming calls.


34/44

GSM Channels

Traffic Channels (TCH)

Control Channels (CCH)

Common Control Channels (CCCH)

Paging Channel (PCH): Used by the BTS to inform the MS

about an incoming call. Broadcast channel. Random Access Channel (RACH): Used by the MS for call

establishment. Shared by all MS in cell. Slotted-ALOHArandom access.

Access Grant Channel (AGCH): Used to indicate the slot

assignment.


35/44

GSM Channels


Dedicated Control Channels (DCCH): Used to controlindividual MS

Standalone Dedicated Control Channel (SDCCH) :Two-way channel assigned to each MS for keeping

track of movement and call establishment. Certainslots periodically. About 2Kbps per MS.

Slow Associated Control Channel (SACCH): Two-waychannel assigned to a TCH or SDCCH. Used to reportparameters, such as signal power, to maintain the link.

Fast Associated Control Channel (FACCH) : Two-waychannel used to support fast transitions when SACCHis not adequate. FACCH steals the TCH.


36/44

GSM Channels


Broadcast Channels (BCH). Used to broadcastinformation to the MSs in the cell

Frequency Correction Channel (FCCH) and

Synchronization Channel (SCH): Keep the MSsynchronized

Broadcast Control Channel (BCCH): providesinformation such as cell ID, available services, Can also be used to keep track of signal

strength for handoff


37/44


38/44

GSM Call Flow (Simplified) When the MS wishes to make a phone call

1. User enters the phone number and presses the send button.

2. To set up the phone call, the MS needs to send information to the MSC. TheMS sends Radio Resource Channel Request to the associated BSS on theRandom Access Channel (RACH) according to ALOHA The phone then waitsto hear from the BSS at the Access Grant Channel (AGCH).

3. The BSS allocates a Traffic Channel (TCH), including the frequency and time

slot, and broadcast it in the AGCH. It also contains information about timeand frequency corrections.

4. The MS applies the corrections and tune to the assigned TCH.

5. MSC checks whether the MS is authenticated.

6. The BSS enables ciphering with the phone. At this step the connection hasbeen set up between the MS and MSC. The BSS just forwards the message.

7. The MS sends a connection set up request to the MSC with the called phone

number. The MSC connects to the PSTN and allocates the voicecommunication channel between the BSS.

8. Make the conversation.

9. User presses the end button. The MSC releases the voice channel with theBSS. The MSC informs the PTSN about the call release and the PTSN will informthe call has been released on its end. MSC informs the MS then releases theTCH.


39/44

39

Public switched

telephone

network

mobile

user

home

Mobile

Switching

Center

HLR homenetwork

visited

network

correspondent

Mobile

Switching

Center

VLR

GSM: indirect routing to mobile

1 call routed

to home network

2

home MSC consults HLR,

gets roaming number of

mobile in visited network

3

home MSC sets up 2nd leg of call

to MSC in visited network

4

MSC in visited network completes

call through base station to mobile


40/44

40

Handoff goal: route call vianew base station (withoutinterruption)

reasons for handoff:

stronger signal to/from newBSS (continuing connectivity,less battery drain)

load balance: free upchannel in current BSS

GSM doesnt mandate why to

perform handoff (policy), onlyhow (mechanism)

handoff initiated by old BSS

Mobile

Switching

Center

VLR

old BSSnew BSS

old

routing

new

routing

GSM: handoff with common MSC


41/44

41

Mobile

Switching

Center

VLR

old BSS

1

3

24

5 6

78

GSM: handoff with common MSC

new BSS

1. old BSS informs MSC of impending handoff,provides list of 1+ new BSSs

2. MSC sets up path (allocates resources) to

new BSS

3. new BSS allocates radio channel for use by

mobile4. new BSS signals MSC, old BSS: ready

5. old BSS tells mobile: perform handoff to

new BSS

6. mobile, new BSS signal to activate new

channel

7. mobile signals via new BSS to MSC: handoff

complete. MSC reroutes call

8 MSC-old-BSS resources released


42/44

General Packet Radio Service

(GPRS) General Packet Radio Service

Supports data service.

Use the same physical link between the network and the MS

An MS maybe assigned with 1 or multiple time slots in achannel

The number of time slot in uplink and downlink may bedifferent

Special network infrastructure added to support data traffic

Serving GRPS Supporting Node (SGSN): a router serves agroup of BSCs. Send and receive packets from the MS.

Gateway GRPS Supporting Node (GGSN): interface tothe Internet. Maintains routing information related to theMS, such that given an IP packet, it knows which SGSN toforward to.


43/44

GRPSMultiple Access

Users are assigned frequency channels and

time slots. Packets are constant length, determined

by the GSM slot.

Downlink: first come first served

Uplink: Slotted ALOHA for reserving,dynamic TDMA for data transmission


44/44

Thank You

level ii introduction to gsm essentials day 1.pptx

Documents