gsm seminar on technology. md. omar ali shamim ahmed nasrin akter khandakar menhaz morshed speakers

GSMSEMINAR

ON

TECHNOLOGY

Md. Omar AliShamim Ahmed Nasrin Akter

Khandakar Menhaz Morshed

Speakers

# What’s a cellular phone?

Now all of these mobile devices are shining in your hands.

# Why it calls cellular?

> Uses hexagonal Cells

# Why use cells?

• # If there was no cell• Limited frequency spectrum for available Mobile

Communication• Frequency utilization is inefficient • Single high power antenna => limited number of

users

# Why use cells?

# Benefits of cellular technology• Smaller cells => frequency reuse possible =>

more number of users• As demand increases (more channels needed)

– Number of base stations is increased (by reducing cell size)

– Transmitter power is decreased correspondingly to avoid interference (to eliminate adjacent-channel interference)

# Frequency reuse:

• Adjacent cells assigned different frequencies to avoid interference or crosstalk.

• The same frequency is reused in different areas for different transmissions

• In GSM networks a frequency reuse patternwith k = 3, 4, 7, 12 or 21.

Here, k= Frequency reuse factor• Each ‘k’ number of cells make a cluster.

# Frequency reuse:

>Reuse factor = 33 cell Cluster


# Frequency reuse:


# Frequency Reuse Problems:

• Adjacent-channel interference

• Co-channel Interference

# Adjacent-channel interference

• Comes from imperfect filters that allow frequency leakage into the band

• Serious problem if interferer is nearby, near-far effect– Nearby mobile transmits on a frequency near to that

of a weak mobile

• Base station receivers need high-Q filters to reject adjacent channel interference.

# Adjacent-channel interference

# Co-channel Interference

• One of the primary forms of man-made signal degradation associated with digital radio, co-channel interference occurs when the same carrier frequency reaches the same receiver from two separate transmitters


F1 F1

F1

F1

F1MS

# Sectored Cells

• To reduce the adjacent channel interference & co-channel interference a cell can divide into 3 or 6 sectors according to the demand.

• 3 sectors per cell• 3 cells per cluster

1

2

3

2

3

1

2

3

2

3

2

3

• 3 sectors per cell• 4 cells per cluster

3

12

43

2

41

3

12

4

3

12

4

41

21

• 6 sectors per cell

• 2 cells per cluster

12

121

11

2

22

# Original view of sectors

# Multiplexing & Access Methods

SDMASDM

CDMACDM

TDMATDM

FDMAFDM

Access MethodMultiplexing

# FDM & FDMA

Time

Fre

qu

enc

y

F3

F2

F1

# TDM & TDMA

Time

Am

pli

tud

e

T3T2T1

Frequen

cy

# CDM & CDMA

Time

Co

de

Code3

Code2

Code1

Frequen

cy

# SDM & SDMA

# Frequency Spectrum

Down link 935~960MHz

Up link 890~915MHz

MS

BTS

# Channels

• GSM 900 uses 25 MHz frequency spectrum with 124 channels for uplink & downlink.

• Each channels have 200 KHz bandwidth.

• Each two channels are separated by 1.6 KHz guard band.

• Each channel have 8 time slots which allows 8 subscribers to use same frequency by TDMA.

# Channels

1 2 4 5 6 123 1243

1 42 3 5 86 7

Channels with 200 KHz bandwidth

Time slots

4.615 ms

# Cell Types

Cells can be classified into three types

according to cell size

• Macro cell

• Micro cell

• Pico cell

# Cell Types

# Antenna

Two types of antenna used

• Unidirectional antenna

• Omni directional antenna

# Unidirectional antenna

# Omni directional antenna

Semi omni directional antenna

# Modulation Technique

BPSK Two phases represent two binary digits


QPSK & OQPSK Each signal element representing more than one bit


MSK Just like OQPSK, but the rectangular pulses are replaced by half-sinusoids


GMSK Using FSK modulation

On the next session

Shamim Ahmedwill with you

BSS — Base Station System

BTS — Base Transceiver Station

BSC — Base Station Controller

MS — Mobile Station

NSS — Network Sub-System

MSC — Mobile-service Switching Controller

VLR — Visitor Location Register

HLR — Home Location Register

AuC — Authentication Server

GMSC — Gateway MSC

GSM 2G Architecture

SS7BTS

BSCMSC

VLR

HLRAuC

GMSC

BSS

PSTN

NSS

AE

CD

PSTNAbis

B

H

MS

GSM — Global System for Mobile communication

GSMSub-Systems

• Radio Sub System (RSS)

• RSS = MS + BSS

• BSS = BTS+ BSC

• Network Sub System (NSS)

• NSS = MSC+ HLR + VLR + GMSC

• Operation Sub System

• OSS = EIR + AuC

GSM network layer

#Radio resource management (RR) sublayer– Establishment, maintenance, and termination

of radio channel connections

#Mobility management (MM) sublayer– Registration, authentication, and location

tracking

#Call control (CC) sublayer– Establishment, maintenance, and termination

of circuit-switched calls

SS7BTS

BSCMSC

VLR

HLRAuC

GMSC

BSS

PSTN

NSS

AE

CD

PSTNAbis

B

H

MS




NSS — Network Sub-System






2.5G Architectural Detail

SGSN — Serving GPRS Support Node

GGSN — Gateway GPRS Support Node

GPRS — General Packet Radio Service

IP

2G+ MS (voice & data)

PSDNGi

SGSN

Gr

Gb

Gs

GGSN

Gc

Gn

2G MS (voice only)

3G rel99 Architecture (UMTS) — 3G Radios

SS7

IP

BTS

BSCMSC

VLR

HLRAuC

GMSC

BSS

SGSN GGSN

PSTN

PSDN

CN

CD

GcGr

Gn Gi

Abis

Gs

B

H




RNS — Radio Network System

RNC — Radio Network Controller

CN — Core Network








AE PSTN

2G MS (voice only)


UMTS — Universal Mobile Telecommunication System

Gb

3G UE (voice & data)

Node B

RNC

RNS

Iub

IuCS

ATM

IuPS

3G rel4 Architecture (UMTS) — Soft Switching

SS7

IP/ATM

BTS

BSCMSC Server

VLR

HLRAuC

GMSC server

BSS

SGSN GGSN

PSTN

PSDN

CN

CD

GcGr

Gn Gi

Gb

Abis

Gs

B

H




RNS — Radio Network System

RNC — Radio Network Controller

CN — Core Network








ANc

2G MS (voice only)


Node B

RNC

RNS

Iub

IuCS

IuPS

3G UE (voice & data)

Mc

CS-MGW

CS-MGWNb

PSTNMc

ATM

GSM Speech Coding

Low-passfilter

Analogspeech

A/DRPE-LTPspeechencoder

Channelencoder

8000 samples/s,13 bits/sample

104 kbps 13 kbps

MS Hands off

GSM Call Routing For Incoming Call 1. MSISDN

2. MSISDN

VLRHLR

AUCEIR

GMSC/IWF

MSC

BSC

BSC

BTS

BTS

BTS

ISDN

3. MSRN

4. MSRN

5. MSRN

6. TMSI

7. TMSI

7. TMSI

7. TMSI

8. TMSI

LA2

LA1

MS

MS

PSTN-to-Mobile Call

(STP)

(SCP)

PSTNPLMN

(SSP)(SSP)BSSMS

PLMN(Home)(Visitor)

(STP)

HLR

GMSC

(SSP)

VMSC

VLR

IAM

6

2

Where is the subscriber?

5Routing Info

3Provide Roaming

4

SCP

1

IAM

514 581 ...

ISUP

MAP/ IS41 (over TCAP)

Signalingover SS7

Mobile-Terminated Short Message Example (MTSM)

Mobile-Originated Short Message Example (MOSM)

GSM Security

• Fetched triplets are stored in VLR– Every call uses up one triplet (discarded)– Another set must be fetched when exhausted

Visited system

Registration requestIMSI/TMSI identifies user, LAI points to old VLR,requests data toauthenticate user

IMSI/TMSI + LAI

Subscriber data

Old VLR

GSM Security

Visited system

Challenge

Requests tripletsfrom home system,chooses a tripletCalculates

responseby authen-

ticationalgorithm

Challenge response Compares to storedresponse in triplet, registration successfulif matches

New TMSI

Acknowledge

Assigns new TMSI

GSM Security

Visited system

Registrationcancel

Location update

AcknowledgeHLR

Old VLR

Next Speaker

Nasrin Akter

Enhancing GSM• Speech coder

– Trade off speech and error correction bits– Fewer dropped calls

• DTX — discontinuous transmission– Less interference (approach 0 bps during silences)– More calls per cell

Data transfer over GSM

• Four enhancements to GSM for data– HSCSD - High Speed Circuit Switched Data– GPRS - General Packet Radio Service– EGPRS: Enhanced GPRS– EDGE: Enhanced Data rates for the GSM

Evolution• Technically EGPRS and EDGE are same

GPRS — 2.5G for GSM

• General packet radio service– First introduction of packet technology

• Aggregate radio channels– Support higher data rates (115 kbps)– Subject to channel availability– From 1 to 8 time slot / TDMA frame can be allocated for particular

service – Physical Channel are taken from common pool of available

channel in the cell

• Share aggregate channels among multiple users• No changes to voice network, but only new GPRS logical

channels are defined

GPRS features

• Radio resources are allocated for only one or a few packets at a time, so GPRS enables– many users to share radio resources, and

allow efficient transport of packets– fast setup/access times– connectivity to external packet data networks

• GPRS also carries SMS in data channels rather than signaling channels as in GSM

EDGE

• Enhanced Data rates for Global Evolution

• Increased data rates with GSM compatibility– Still 200 KHz bands; still TDMA– 8-PSK modulation: 3 bits/symbol give 3X data rate– Shorter range (more sensitive to

noise/interference)– New GSM/ EDGE radios but evolved ANSI-41

core network

• The EDGE technology uses the same bandwidth allocated for GSM voice and GPRS data services,

• but It delivers a higher capacity and fast data services to the mobile network by using a new modulation scheme called 8 PSK (8-level Phase Shift Keying). With this 8 PSK modulation, there are eight distinct phase changes. Each phase represents a symbol and carries three bits of information.

GPRS and EGPRS Modulation Principles

GSM Evolution for Data Access

1997 2000 2003 2003+

GSM

GPRS

EDGE

UMTS

9.6 kbps

115 kbps

384 kbps

2 Mbps

GSM evolution 3G

SS7BTS

BSCMSC

VLR

HLRAuC

GMSC

BSS

PSTN

NSS

AE

CD

PSTNAbis

B

H

MS

BSS Base Station System

BTS Base Transceiver Station

BSC Base Station Controller

NSS Network Sub-System

MSC Mobile-service Switching Controller

VLR Visitor Location Register

HLR Home Location Register

AuC Authentication Server

GMSC Gateway MSC

GPRS architectural detail

SGSN Serving GPRS Support Node

GGSN Gateway GPRS Support Node

GPRS General Packet Radio Service

IP


PSDNGi

SGSN

Gr

Gb

Gs

GGSN

Gc

Gn

2G MS (voice only)

GSM to GPRS

Element Software Hardware

MS Upgrade required Upgrade required

BTS Upgrade required No Change

BSC Upgrade required PCU Interface

TRAU No Change No Change

MSC/VLR Upgrade required No Change

HLR Upgrade required No Change

SGSN New New

GGSN New New

GPRS capacity

• Difficult to estimate actual bandwidth available to the GPRS user - will vary a lot– depending on time of day– total number of active users– current geographical location and others...

• Technical Limitations to capacity– Allocation of time slots - between GSM and GPRS

and which multislot classes available– Restrictions in terminals– Availability of coding schemes

GPRS charging• Can be based on

– data volume– duration of call– type of service– destination point

• Charging data output from SGSN and GGSN is encoded in ASN.1/BER and transferred via ftp to a Charging Gateway Function (CGF) node (Billing Gateway)

Modem Modem

Email Server

Auth. Server

InternetGSM PSTN

User

Email via GSM

Email via GPRSEmail Server

GPRS

User

Auth. Server

Internet

Authenticated path to Email server

Virtual GPRS Data Tunnel

GSM v/s GPRS

Next Speaker

Khandaker Menhaz Morshed

Types Of Billing System

• Post Paid:

Pay After Use

• Pre Paid:

Pay Before Use

Prepaid

Advantages:• operator has the money • operator saves• customer: no need for credit worthiness.• prepaid fits well with the expectation of

these customers• many customers will never use up all their

balance

Difference Between Mobile And Fixed Prepaid

• Mobile servers needs: more complex billing system due to more

complex tariffs

complex taxation

real-time usage metering

complexity of customer care

Four Alternatives For Mobile Prepaid

• Wireless Intelligent Network (WIN)

• Service Node

• Hot Billing

• Handset-Based

BTSMS BSC MSC

IntelligentPeripheral

SSP

P-SCP

Wireless Intelligent Network (WIN)

SignalingVoice Trunk

WIN Call termination when called party pays

BTSMS BSC MSC SSP

P-SCP

GMSC


Service Node

BTSMS BSC MSC

ServiceNode

SSP

PBP


Hot Billing

BTSMS BSC MSC SSP

PSCHLR/AuCDatabase


Handset-Based

BTSMSBSC MSC SSP


GSM Summary

Uplink frequencies 890-915 MHz

Downlink frequencies 935-960 MHz

Total GSM bandwidth 25 MHz up + 25 MHz down

Channel bandwidth 200 kHz

Number of RF carriers 124

Multiple access TDMA

Users/carrier 8

Number of simul. users 992

Speech coding rate 13 kb/s

FEC coded speech rate 22.8 kb/s

GSM service quality requirements

Speech intelligibility 90%

Max one-way delay 90 ms

Max handoff gap 150 ms if intercell

Time to alert mobile ofinbound cell

4 sec first attempt, 15 sec final attempt

Release time to callednetwork

2 sec

Connect time to callednetwork

4 sec

GSM 900 and GSM 1800

GSM 900 GSM 1800Frequency band 890-915 MHz

935-960 MHz1710-1785 MHz1805-1880 MHz

Border spacing 25 MHz 75 MHzDuplex spacing 45 MHz 95 MHzCarrier spacing 200 kHz 200 kHzCarriers 124 374Timeslots per carrier 8 8Multiple access TDMA/FDMA TDMA/FDMATypical cell range <300m – 35 km <100m – 15 kmHandset Power 0.8 & 8 W 0.25 & 1 W

THANKS TO ALL

gsm seminar on technology. md. omar ali shamim ahmed nasrin akter khandakar menhaz morshed speakers

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