gsm total presentation latest1

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Copyright © UTL Technologies Ltd 2009. All rights reserved

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INTRODUCTION

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Communication:It is the process of transferring information

from one place to another place.

Any Communication System requires the following:

Transmitter

Channel

Receiver

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Types of communication Systems :

Type Description Example

Simplex One way only FM radio, Television etc..

Half Duplex Two way, only one at a time Walkie Talkie

Full Duplex Two way, both at the same time Mobile Systems


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Frequency Spectrum and its Applications


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Range Frequency Band Application

VLF 3 KHz – 30 KHz Submarine Application

LF 30KHz to 300 KHz Navigational Application

MF 300KHz to 3MHz Cordless Phones, AM radio

HF 3 MHz to 30 MHz Aeronautical, Amateur radio

VHF 30 MHz to 300 MHz FM Broadcast, TV Applications

UHF 300 MHz to 3GHz TV, Mobile Communication

SHF 3 GHz to 30 GHz Point to Point, Satellite Comm.

EHF 30 GHz to 300 GHz Point to Point microwave

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Multiple Access Method : It determines how several users can share a

medium with minimum or no interference.

Access MethodsFDMA (Frequency Division Multiple

Access)TDMA (Time Division Multiple Access)CDMA (Code Division Multiple Access)

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Frequency Division Multiple Access (FDMA) :

– An approach to sharing a channel by separating the simultaneous users in frequency

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f

c

t

FDMA

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Time division multiple access (TDMA)

– Approach for allotting single-channel usage amongst many users, by dividing the channel into slots of time during which each user has access to the medium.

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f

t

c

2.17.1

TDMA

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f

c

2.18.1

t

TDMA / FDD

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Code Division Multiple Access (CDMA) :

–Approach for allotting the channel usage amongst many users, by converting the speech signals of all users in to different codes.

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f

t

c

CDMA

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User Data : 1011 (to be transmitted)

PN Code : 110101

Transmitting Data : 001010 110101 001010 001010

Receiving Data : 001010 110101 001010 001010

PN Code : 110101

Final Data : 111111 000000 111111 111111

Received Data : 1011

How CDMA uses codes to the actual data?

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How CDMA uses codes to the actual data?

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What we do, we can undo

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EVOLUTION MOBILE COMMUNICATION

AMPS

TACS

NMT

D-AMPS

IS-95

GSM

ANALOG

1G

DIGITAL

2G

CDMA 2000

UMTS/

W-CDMA

IMT-2000

3G

GPRS

2.5G

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ANALOG MOBILE COMMUNICATION

AMPS

TACS

NMT

ANALOG SYSTEM

1G

Advanced Mobile Phone Service

US based, 800 MHz band

Total Access Communication System UK based, AMPS in 900 MHz band

Nordic Mobile Telephone System Scandinavian, Both in 450 MHz and 900 MHz band

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DIGITAL MOBILE COMMUNICATION

Dual mode AMPS US, Analog signaling and Digital voice coding

IS-95 US, CDMA based

GLOBAL SYSTEMS FOR MOBILE COMMUNICATIONS

European standard, Both in 900 MHz & 1800 MHz band

D-AMPS

IS-95

GSM

DIGITAL SYSTEM

2G

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Cellular Standards

Generation European Std US Std

1G ETACS AMPS

2G GSM CDMA (IS-95)

2.5G GPRS CDMA 2000 1X

3G UMTS/WCDMA CDMA 2000 1x EVDO, EVDV etc..


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First Generation Wireless Technologies

ETACS : European Total Access Cellular System.

AMPS : Advanced Mobile Phone System2G Wireless Technologies

GSM : Global System for Mobile Communication

IS 95 : Interim Standard 95 (CDMA-One)2.5G Wireless Technologies

GPRS : General Packet Radio Service

CDMA 2000 1x RTTUTL Technologies Ltd

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3G Wireless Technologies

CDMA 2000 1x EVDO, EVDV etc.WCDMA, IMT 2000 (UMTS)

3.5G Wireless TechnologieseHSPA : Evolved High-Speed Packet Access LTE : Long Term Evolution

4G Wireless Technologies


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Technology 1G2G

2.5G 3G 4G

Design began 19701980

1985 1990 2000

Implemen-tation

19841991

1999 2002 2010?

Service Analog voice and

data Digital voice and data (SMS)

Higher-capacity data Transfer

(internet)

Higher-capacity data Transfer

with more data rates

Higher capacity

multimedia

Standards AMPS,TACS,

CDMA,GSM,

GPRS,EDGE,Cdma

20001XRTT

UMTS/WCDMA,CDMA2000 1xEVDO etc

Single standard

Data Rate 1.9kbps14.4kbps

384kbps 2Mbps 200Mbps

Multiplexing FDMATDMA,CDMA

TDMA,CDMA CDMA CDMA?

Comparison of 4G with Other Mobile Technologies

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GSM gives mobility without any loss in Audio quality

Encryption techniques used gives high security

Bit Interleaving for high efficiency in Transmission.

Why GSM?

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Variable Power (Power budgeting- extend battery life)

Minimum Interference (DTX)

Support International Roaming

SMS (Short Message Services)

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Frequency band Uplink : 890 MHz-915 MHz Downlink : 935 MHz-960MHzDuplex distance : 45MHzCarrier separation : 200KHzModulation : GMSKAccess method : FDMA/TDMASpeech Coder : RPE-LTP-LPC(Regular Pulse Excitation - Long Term Predictive - Linear Predictive Coder)

GSM System specifications

25 MHz

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GSM-900 (Channels 125, spacing 45Mhz)

GSM -1800 (Channels 374, spacing 95Mhz)

Due to frequency, a BTS transmitting information at 1800MHz with an output power of 10 Watts will cover only half the area of a similar BTS transmitting at 900MHz. To counteract this, BTSs using 1800MHz may use a higher output power.

What are the types in GSM Network?

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Frequency Resource

GSM900 :

Up link: 890~915MHz

Down link: 935~960MHz

Duplex interval: 45MHz

Total Available Bandwidth: 25MHz

Channel Bandwidth: 200KHz

Total Number of channels : 125

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GSM1800 :Up link: 1710-1785MHz Down link: 1805-1880MHzDuplex interval: 95MHz Total Available Bandwidth: 75MHzChannel Bandwidth : 200KHzTotal Number of channels : 375

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GSM1900MHz:

Up link :1850~1910MHz

Down link:1930~1990MHz

Duplex interval: 80MHz

Total Available Bandwidth: 60MHz

Channel Bandwidth : 200KHz

Total Number of Channels : 300

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1800MHz

1900MHz

900MHzWhich one?

Single Band Network General Priority

High

Low

Reason

For SubscriberFor Operator

Propagation Characteristic

New Operator

Frequency Resource

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1800MHz

1900MHz

900MHz

Single Band Network

Single Band

Dual Band

Triple Band

• The network determines the handsets to be selected.But nowadays, most handsets support dual band.

Frequency Resource

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Propagation characteristic

Cell coverage radius :

The higher the propagation frequency

The higher the propagation loss

The smaller the cell coverage radius.

900MHz

1800MHz

1900MHz

Single Band Network

Frequency Resource

We know

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System GSM 900 GSM 1800 GSM 1900

1.Frequencies 890 - 915 MHz 1710 – 1785 MHz 1850 – 1910 MHz

Uplink

Down Link 935 – 960 MHz 1805 – 1880 MHz 1930 – 1990 MHz

2.Wavelength 33cm 17cm 16cm

3.Band Width 25MHz 75MHz 60MHz

4.Duplex Distance 45MHz 95MHz 80MHz

5.CarrierSeparation

200kHz 200kHz 200kHz

6.Radio Channels 125 375 300

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Case Study 3:

Why different bands of frequencies are required for operators?

What is the difference between different bands of GSM frequencies?

Why uplink frequency is less compared to down link frequency?

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CELLULAR CONCEPT

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Wireless Communication

•A pair of RF channels require per active call

•Up link & down link frequency difference 45 MHz

890.

2 M

Hz

935.

2 M

Hz

UPLINK

DOW

NLINK

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Uplink 890 MHz to 915 MHz

Down Link 935 MHz to 960 MHz

25 MHz divided into 125 channels of 200 KHz bandwidth ( 25 / 0.2 = 125)

5 MHz BW allocated to each Cellular Service Provider( Maximum 5 operator )

890.0 890.2 890.4 914.8 915.0

935.0 935.2 935.4 959.8 960.0

UP

DOWN

Access Techniques

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ARFCN--> Absolute Radio Frequency Channel Number used to express one pair of RF channels

ARFCN = (fUP -890) / 0.2 or (fdown -935) / 0.2

What is ARFCN ?

1 2 124 125ARFCN

890.0 890.2 890.4 914.8 915.0

935.0 935.2 935.4 959.8 960.0

UP

DOWN

fup=890+0.2*n; fdown=935+0.2*n;

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ARFCN 1

ARFCN 2

ARFCN 3

ARFCN 4

……….ARFCN24

ARFCN25

5 MHz

TDMA FRAME PER ARFCN

TDMA FRAME AT AIR INTERFACE

890.2

935.2

T0 T5T4T3T2T1 T6 T7

T0 T5T4T3T2T1 T6 T7

FOR A PARTICULAR MS

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What is the problem with one cell?

• One BTS is covering whole city

• All 25 ARFCN are used

High Transmission Power Required

•Limited Capacity of the Network due to limited spectrum

•Problem with High power Transmission ----Talk time supported by battery will be less ----Human body Hazards

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ARFCN 1

ARFCN 2

ARFCN 3

ARFCN 4

……….ARFCN24

ARFCN25

5 MHz

TDMA FRAME PER ARFCN

Maximum Capacity with one cell

• 5 MHz / 0.2 MHz = 25 CHANNEL

• 8 MOBILES CAN SHARE ONE CHANNEL BY TDMA

• MAXIMUM ACTIVE CALL AT A TIME = 25 * 8=200

T0 T5T4T3T1T1 T6 T7

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Cellular Structure

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GSM Concepts - Cellular Structure

Cell: A cell is the basic geographic unit of a cellular system and is defined as the area of radio coverage given by one BS antenna system.

Classification of cells in GSM Network:

1. Large Cells:

large cells are employed in

1. Remote areas.

2. Coastal regions.

3. Areas with few subscribers.

4. Large areas which need to be covered with the minimum number of cell sites

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Small Cells or Micro Cells: Urban areas.

Low transmission power required.

High number of MSs.

However, micro cells are cells where the antenna height is under the average roof top level and they are typically used in urban areas.

Pico cells :The Pico cells are small cells whose diameter is a

few dozen meters and are mainly used indoors.

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Umbrella cells are used to cover shadow regions of smaller cells and fill in gaps of coverage between those cells. These cells are usually built on high ways to cover the uncovered region.

Umbrella Cells

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Case Study 4 :

How a cell site will be planned in the network?... Reg.Drive Test &Planning.

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What is a Cluster ?

A Cluster is a group of cells. No channels are reused within a cluster. If a cluster has 3 cells, it is called 3 cell cluster, if a cluster has 4 cells, it is called 4 cell cluster, and if it is 7 cells, it is called 7 cell cluster.

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Cellular

Networking technology that breaks geographic area into cells shaped like honey comb

Cell

Area of coverage provided by one or more Radio terminals(TRX)

TRX => TX + RX

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2

3

4

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7

2

1

5

Frequency reuse : The concept of using the same frequencies again and again is called frequency reuse.

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2

3

4

56

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7

2

1

5

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4 Cell Cluster

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7 cell Cluster

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12 Cell Cluster

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1

2

3

4

5

6

7

6

7

2

1

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GSM Concepts - Cellular Structure

To Overcome Network Congestion problem, We can add more channel in that particular cell

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To Overcome Coverage problem, We have to install new BTS in that nearby location

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Case Study 5:

How frequency planning will be done generally in cell sites?

How sectorization will be done in cell sites?

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GSM NETWORK ARCHITECTURE

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GSM Architecture

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MS

MS

BTS

BTS

BTS

BSC

BSC

MSC

MSC

VLR

VLR

GMSC

HLR

PSTN

EIR

AuC

Um

Abis

Abis

A

A

OMC Server

Um

GSM - Network Structure

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Mobile Station (MS)

•Hand portable unit

•Frequency and Time Synchronization

•Voice encoding and transmission

•Voice encryption/decryption functions

•Power measurements of adjacent cells

•Display of short messages

Mobile Handset + SIM =>

Mobile Station

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GSM IdentifiersSubscriber Identities - MSISDN

Human Identity to call a MS

MSISDN uniquely identifies a mobile subscriber in PSTN

Calls will be routed from the PSTN and other networks based on MSISDN number.

MSISDN= CC + NDC + SN

CC= Country Code (91)

NDC= National Destination Code(9848)

SN= Subscriber Number (012345)

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International Mobile Subscriber Identity [IMSI]

A subscriber is always identified within the GSM network by the IMSI

- Used for all signaling in the PLMN. - Stored in the SIM, HLR & VLR. - The IMSI consists of three different parts.

IMSI= MCC + MNC + MSIN

(Maximum of 15 digits) = (3 digits)+(1-2digits)+ (maximum 11 digits)

MCC = Mobile Country Code

MNC = Mobile Network Code

MSIN = Mobile Station Identification Number

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International Mobile Equipment Identity [IMEI]

The IMEI is used for equipment identification. An IMEI uniquely identifies a mobile station as a piece or assembly of equipment.

IMEI = TAC + FAC + SNR + sp

TAC= Type Approval Code (6 digits),determined by GSM body

FAC= Final Assembly Code (2 digits), identifies the manufacturer

SNR= Serial Number (6 digits), uniquely identifying all equipment within each TAC & FAC

sp = Spare for future use (1 digit)

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Subscriber Identity Module (SIM)

•Dynamic Information–Temporary Mobile Subscriber identity (TMSI)–Cell Identity (CID)–Location Area Identity (LAI)–Phone memories, billing information–Ability to store Short Messages received

•Portable Smart Card with memory (ROM- 6 to 16KB, RAM- 128 to 256KB, EEPROM- 3 to8KB

A3/A8 algorithm)

SIM

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Static Information on the SIM card:International Mobile Subscriber Identity

(IMSI) = (MCC + MNC+MSIN)Personal Identification Number (PIN)Authentication Key (Ki)MSISDN (Mobile Number)

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Base Transceiver Station (BTS)

•Consists of one or more radio terminals (TRX) for transmission and reception•Each TRX represents an RF Channel(ARFCN)•TRX and MS communicates over Um interface•BTS Hardware : TRX, Combiner, Splitter, OMU etc..•BTS Type: Omnidirectional, Bi-directional(2 Sector) & Sctorised (3 Sector)

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BTS Hardware : TRX, Combiner, Splitter, OMU, Filters, Multi couplers, Power Supply Modules etc..

BTS Type: Omni-directional, Bi-directional(2 Sector) & Sctorised (3 Sector)


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3 sectored1 sector

2 sectored

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Sectorised BTS Configuration

TRX 1

ARFCN 1

TRX 4

ARFCN 10

TRX 2

ARFCN 4

TRX 3

ARFCN 7

TRX 5

ARFCN 13

TRX 6

ARFCN 16

BTS CONFIGURATION

1+1+1

BTS CONFIGURATION

2+2+2

Maximum 12 TRX (4+4+4)

SECTOR 1

SECTOR 2

SECTOR 3

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Base Station Controller (BSC)

•External Interfaces

–‘Abis’ interface towards the BTS

–‘A’ interface towards the MSC

•Monitors and controls several BTSs

•Management of channels on the radio interface

•Performs inter-cell Handover

•Interface to OMC for BSS Management

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The connectivity between BTS and BSC may be through Optical Fiber or Micro Wave Link.

BSS Configurations

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Case Study 6: BTS and BSC configurations

How BTS will be configured?

How BSC will be configured?

How many BTS will be connected to a BSC?

How BTS will be connected to a BSC?

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Gateway Mobile Switching Center (GMSC)

•Interface of the cellular network to PSTN

•Routes calls between PLMN and PSTN

•Inter-BSC Handover

•Performs call switching

•Billing

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Home Location Register (HLR)

Stores user data of all Subscribers related to the GMSC•International Mobile Subscriber Identity(IMSI)•Users telephone number (MS ISDN)•Current Subscriber VLR (current Location).•Subscription information and services.•Authentication Key and Authentication functionality•Subscriber Status (Registered / deregistered).

•Referred when call comes from public land network

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Visitor Location Register (VLR)

•Copy of subscriber data from HLR

•Generates and allocates TMSI for Subscriber confidentiality

•Location Area Identity (LAI)

•Mobile Status

•Mobile Station Roaming Number (MSRN)

•Provides necessary data when mobile originates call

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LAI 01 LAI 02

VLR 1

VLR 2

LAI 03 LAI 04

HLR

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Authentication Center (AuC)

•Stores Subscriber authentication data called Ki, a copy of which is also stored in in the SIM card

•Generates security related parameters to authorize a subscriber (SRES)

•Generates unique data pattern called Cipher key (Kc) for user data encryption

•Provides triplets - RAND, SRES & Kc, to the HLR on request.

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EIR is a database of all valid Subscriber’s Handset Identity (IMEI).

EIR has different databases as follows.,

White list - For all known,good IMEI’s

Black list - For all bad or stolen handsets

Implementation depends on Service Provider

EIR (Equipment Identity Register)

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Operations & Maintenance Center

The OMC provides a central point from which to control and monitor the other network entities (i.e. base stations, switches, database, etc)


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There are two types of OMCs. These are:

OMC (R)

OMC controls specifically the Base Station System.

OMC (S)

OMC controls specifically the Network Switching System.


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The OMC should support the following

functions

Event/Alarm Management.

Fault Management.

Performance Management.

Configuration Management.

Security Management.

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Case Study 7:

How many elements will be there in network with a network operator (for a state)

Elements wise description of a network.

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An operator’s Network Elements

Element 2004-2005 2007-2008

OMC 1 1

HLR 2 4

MSC 4 7

BSC 7 42

BTS 400 4000

IN 2 6

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Network Elements

MSC – Nokia DX 200 (sub rack and i-series)

HLR – Nokia DX 200 (sub rack and i-series)

BSC – Nokia DX 200 (2E, 2i, 3i)

OMC – Nokia DX 200

BTS – Nokia (Talk Family, Ultra family, metro etc)

IN – Telcordia

SMSC - Nokia

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MSC – 120 K subscribers, 150 K subscribers, 300 K subscribers, 100 K subscribers.

BSC – 512 TRx, 256 TRx,

660 TRx

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Transmission Elements Nokia DMR – 15/18 GHz

DMC Radio – 15 GHz

Nokia Flexi Hopper – 7/15/18 GHz

ERICSON mini link – 15 GHz

AT&T COMBIMUX – Optical Equipment

NOKIA SYNFONET – Optical Equipment

Micro wave Back bone Network :

SIEMEN’S SRT – 1C – 7 GHz

SIEMEN’S SRT – 1S – 7 GHz

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Interfaces between different blocks of GSM Architecture.

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GSM Network Parts

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.

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AKS 268

MSMS BTSBTS BSCBSC MSCMSC

GSM Network

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Performance characteristics of GSM

Communication

Total mobility

Worldwide connectivity

High capacity

High transmission quality

Security functions

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HAND OVERS IN GSM

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HAND OVER IN GSM

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Internal Handover (Intra-BSS) 1. Within same base station - intra cell Hand over 2. Between different base stations - inter cell or intra BSC Hand over

External Handover (Inter-BSS) 1. Within same MSC -intra MSC or Inter BSC Hand over 2. Between different MSCs - inter-MSC Hand over.

TYPES OF HAND OVERS

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BTS BTS BTS BTS

BSC BSC BSC

MSC MSC

Cell Site

Cell Site

Cell Site

Cell Site

1 2 34

1.Intra Cell Hand over

2.Inter cell/Intra BSC Hand over

3.Inter BSC/Intra MSC Hand over

4.Inter MSC Hand over

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Case study 8:

Why call drops will happen in a network even when handovers are present in a network?

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ROAMING CONCEPT

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Roaming:

Roaming is defined as the ability for a cellular customer to automatically make & receive voice calls, send & receive data, or access other services when traveling outside the geographical coverage area of the home network, by means of using a visited network.

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1.National Roaming:If the visited network is in the

same country as the home network, this is known as National Roaming. 2. International Roaming:

If the visited network is outside the home country, this is known as International Roaming (the term Global Roaming has also been used).

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3.Inter-Standard Roaming:If the visited network operates

on a different technical standard than the home network, this is known as Inter-standard roaming.

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AUTHENTICATION

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Authentication ProcessTo discuss the authentication

process, assume that the VLR has all the information required to perform that authentication process (Kc, SRES and RAND). If this information is unavailable, then the VLR would request it from the HLR/AUC.

1. Triples (Kc, SRES and RAND) are stored at the VLR.

2. The VLR sends RAND via the MSC and BSS, to the MS (unencrypted).

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3. The MS sends SRES unencrypted to the VLR.

4. Within the VLR the value of SRES is compared with the SRES received from the mobile. If the two values match, then the authentication is successful.

5. If ciphering is to be used, Kc from the assigned triple is passed to the BTS.

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6. The mobile calculates Kc from the RAND and A8 and Ki on the SIM.

7. Using Kc, A5 and the GSM hyper frame number, encryption between the MS and the BSS can now occur over the air interface .

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GSM Channels on Air Interface

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Physical channel:One timeslot of a TDMA-frame on one ARFCNis referred to as a physical channel.There are 8 physical channels per carrier in GSM,channel 0-7(timeslot 0-7)Logical channel:Depending on the kind of information transmitted, we refer to different logical channels.These logical channels are mapped on physical channel.

Channel concept

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Logical channels

Control channels Traffic channels

BCH CCCH DCCHHalf

rateFullrate

FCCH SCH BCCH PCH AGCH RACH SDCCH SACCH FACCH

Logical channels

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1)Broadcast Control Channel-BCCHThe last information the MS must receive in order to receive calls or make calls is someinformation concerning the cell. This is BCCH.

This is transmitted Downlink point to multipoint.

Control channelsI. Broadcast channels BCH

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Broadcast Control Channel (BCCH)

– Carries the following information (this is only a partial list):

Location Area Identity (LAI).

List of neighboring cells, which should be monitored by the MS.

List of frequencies used in the cell.

Cell identity.

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Control channels

2)Frequency correction channel-FCCHThis is transmitted frequently on

the BCCH timeslot and allows the mobile to synchronize its own frequency to that of the transmitting base site.

I. Broadcast channels BCH

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3) Synchronization Channel-SCH

This is used by the MS to synchronize to the TDMA frame structure within the particular cell.

Listening to the SCH the MS receives

1. TDMA frame number

2. BSIC (Base Station Identity code).

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1) Paging Channel-PCHThe information on this channel is a

paging message including the MS’s identity(IMSI).This is transmitted on Downlink.

Control channels II. Common Control Channels,CCCH

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2) Random access channel-RACH:

When the mobile realizes it is paged, it answers by requesting a signaling channel on RACH. RACH is also used by the MS if it wants to originate a call. It is transmitted in Uplink point to point.

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3) Access Grant Channel-AGCHOn request for a signaling channel by MS the network assigns a signaling channel(SDCCH) on AGCH. AGCH is transmitted on the downlink point to point.

Control channels Common Control Channels,CCCH

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1) Stand alone dedicated control channel (SDCCH)•AGCH assigns SDCCH on request by MS.•Used during Call setup•Steppingstone between BCH & TCH•MS is informed about frequency & timeslot to use •Up and Downlink, point-point.

Control channelsIII. Dedicated Control Channels-DCCH

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2) Slow associated control channel-SACCH

Timing Advance

Control channelsDedicated Control Channels-DCCH

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3) Fast associated control channel-FACCH§ Used for handover.

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Traffic Channels-TCH

Full rate traffic channel occupies one physicalChannel (one TS on a carrier)

Two half rate TCHs can share one physical channel.

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TDMA FRAME

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BURSTS

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BurstThe information format transmitted

during one timeslot in the TDMA frame is called a burst.A Burst consists of several different elements.

Information : This is the area in which the speech, data or control information is held.• Tail Bits : These are used to indicate the beginning and end of the burst.

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Stealing Flags : These two bits are set when a traffic channel burst has been ‘‘stolen” by a FACCH (the Fast Associated Control Channel). One bit set indicates that half of the block has been stolen.

Training Sequence : This is used by the receiver’s equalizer as it estimates the transfer characteristic of the physical path between the BTS and the MS. The training sequence is 26 bits long.

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Guard Period :

The BTS and MS can only receive the burst and decode it, if it is received within the timeslot designated for it.

To be precise, the timeslot is 0.577 ms long, whereas the burst is only 0.546 ms long; therefore there is a time difference of 0.031 ms to enable the burst to hit the timeslot.

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Different Types of Bursts

Normal Burst

Random Access Burst

Frequency Correction Burst

Synchronization Burst

Dummy Burst

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Normal Burst

T3

Coded Data57

S1

T. Seq.26

S1

Coded Data57

T3

GP8.25

Tail Bit(T) :Used as Guard TimeCoded Data :It is the Data part associated with the burstStealing Flag :This indicates whether the burst is carrying

Signaling data.Training Seq. :This is a fixed bit sequence known both to

the BTS & the MS.This takes care of the signal deterioration.

156.25 bits OR 576.92 us

Normal Burst : The normal burst carries traffic channels and all types of control channels apart from those mentioned specifically below. (Bi-directional).

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Frequency Correction Burst

This burst carries FCCH downlink to correct the frequency of the MS’s local oscillator, effectively locking it to that of the BTS.

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Synchronization Burst

It is so called because its function is to carry SCH downlink, synchronizing the timing of the MS to that of the BTS

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Dummy Burst

Used when there is no information to be carried on the unused timeslots of the BCCH Carrier (downlink only).

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Access Burst

This burst is of much shorter duration than the other types. Whenever the MS tries to access the BTS, the information that is sent is called Access Burst. (The Access Burst is uplink only.)

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What does a Mobile do in idle mode?

Reads BCCH (System Information Messages)

Listen To Paging

Monitors Neighbor for cell selection

Mobile Station in IDLE mode

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GSM TRANSMISSION PROCESS

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Speaker

Micro phone Keypad

LCD

Display

SIM card/ Controller

Inside A GSM Cellphone

Signal Processing Chipset

ARM Processor

Transeiver Battery

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A/D CONVERSION

TX MODULATOR

BURST FORMATING

CIPHERING

INTERLEAVING

CHANNEL CODING

SPPECH CODING

SEGMENTATION

Microphone

D/A CONVERSION

RX DEMODULATOR

VITERBI EQULISER

DE-CIPHERING

DE-INTERLEAVING

DECODING

SPPECH DECODING

Receiver

MOBILE STATION

TX PART RX PART

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ANALAG TO DIGITAL (A/D) CONVERSION

One of the primary functions of an MS is to convert the analog speech information into digital form for transmission using a digital signal.

The analog to digital conversion (A/D) conversion process outputs a collection of bits; binary ones and zeroes which represent the speech input

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The A/D Conversion is performed by using a process called Pulse Code Modulation (PCM). PCM involves three main steps.

Sampling

Quantization

Coding.

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Sampling:

Sampling involves measuring the analog signal at specific time intervals.

The accuracy of describing the analog signal in digital terms depends on how often the analog signal is sampled. This is expressed as the sampling frequency

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The sampling theory states that :

To reproduce an analog signal without distortion, the signal, must be sampled with at least twice the frequency of the highest frequency component in the analog signal.

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Normal speech mainly contains frequency components lower than 3400 Hz.

Applying the sampling theory to analog speech signals, the sampling frequency should be at least 2X3.4 kHz=6.8 kHz.

Telecommunication systems use a sampling frequency of 8 kHz, which is acceptable based on the sampling theory.

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The amplitude of the signal at the time of sampling is measured and approximated to one of a finite set of values

The degree of accuracy depends on the number of quantization levels used. Within common telephony, 256 levels are used while in GSM 8,192 levels are used.

Quantization:

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Coding

Coding involves converting the quantized values into binary. Every value is represented by a binary code of 13 bits (213=8192).

For example, a quantized value of 2,157 would have a bit pattern of 0100001101101:

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Bit 12 11 10 9 8 7 6 5 4 3 2 1 0 Total

Set to 0 1 0 0 0 0 1 1 0 1 1 0 1 2157

Value 0 2048 0 0 0 0 64 32 0 8 4 0 1

Coding of Quantized value 2157.

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Summary of A/D Conversion

The result from the process of A/D Conversion is 8,000 samples per second of 13 bits each. This is a bit rate of 104 kbits/s.

When it is considered that 8 subscribers use one radio channel, the overall bit rate would not fit into the 200 kHz available for all 8 subscribers. The bit rate must be reduced somehow. This is achieved using segmentation and speech coding

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STAGE 2: SEGMENTATION AND STAGE 3: SPEECH CODING

The speech coding process analyzes speech samples and outputs parameters of what the speech consists of.

Segmentation: Given that speech organs are relatively slow in adapting to changes, the filter parameters representing the speech organs are approximately constant during 20 ms..

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For this reason, when coding speech in GSM, a block of 20 ms is coded into one set of bits. In effect, it is similar to sampling speech at a rate of 50 times per second instead of the 8,000 used by A/D conversion

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Summary of segmentation and speech coding

The GSM speech coder produces a bit rate of 13 kbits/s per subscriber. When it is considered that 8 subscribers use one radio channel, the overall bit rate would be 8X13kbits/s =104kbits/s. This compares favorably with the 832 kbits/s from A/D conversion.

However, speech coding does not consider the problems which may be encountered on the radio transmission path. The next stages in the transmission process, channel coding and interleaving, help to overcome these problems.

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Speech & Channel Coding

A/D CONVERSION

260 bits / 20ms

Microphone

SPEECH CODER

BITS ORDERED

BLOCK CODER

CONVOLUTION CODER

456 bits => 8 Block of 57 bits

Other 78 bits

Important 132 bits

Very Important 50 bits

Sampling at 8 KHz & Coding using 13bits

=104 Kbps

= 2080 bits/20msSEGMENTATION

20 ms block2080 bits / 20ms

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STAGE 4: CHANNEL CODING

Channel coding in GSM uses the 260 bits from speech coding as input to channel coding and outputs 456 encoded bits.

The 260 bits are split according to their relative importance:

Block 1 : 50 very important Bits.

Block 2 : 132 important Bits and

Block 3 : 78 not so important bits.

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The first block of 50 bits is sent through a block coder, which adds three parity bits that will result in 53 bits. These three bits are used to detect errors in a received message.

The 53 bits from first block, the 132 bits from the second block and 4 tail bits (total: 189) are sent to a 1:2 convolutional coder which outputs 378 bits. Bits are added by the convolutional coder enable the correction of errors when the message is received.

The bits of block 3 are not protected.

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STAGE 5 : INTERLEAVINGFirst level of interleaving:

The channel coder provides 456 bits for every 20 ms of speech. These are interleaved, forming eight blocks of 57 bits each, as shown in the figure below.

In a normal burst, there is space for two of these speech blocks or 57 bits, as can be seen in figure. The remaining bits are like tail bits, stealing flags, training sequence and guard period. Thus, if one burst of transmission is lost, there is a 25% BER for the entire 20 ms of speech (2/8=25%).

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First Stage of Interleaving

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Second level of interleaving or Diagonal interleaving:

If only one level of interleaving is used, a loss of this burst results in a total loss of 25%. This is too much for the channel decoder to correct. A second level of interleaving can be introduced to further reduce the possible BER to 12.5%.

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Instead of sending two blocks of 57 bits from the same 20 ms of speech within one burst, a block from one 20 ms and a block from next sample of 20 ms are sent together.

A delay is introduced in the system when the MS must wait for the next 20 ms of speech. However, the system can now afford to loose a whole burst, out of eight, as the loss is only 12.5% of the total bits from each 20 ms speech frame. 12.5% is the maximum loss level that channel decoder can correct

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Diagonal interleaving

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STAGE 6: CIPHERING/ENCRYPTION

The purpose of ciphering is to encode the burst so that it cannot be interpreted by any other device than the intended receiver. The ciphering algorithm in GSM is called A5 algorithm.

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STAGE 7 : BURST FORMATTING

As previously explained, every transmission from an MS/BTS must include some extra information such as training sequence.

The process of burst formatting is to add these bits (along with some others such as tail bits) to the basic speech/data being sent.

This increases the overall bit-rate, but is necessary to counteract problems encountered on the radio path.

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In GSM, the input to burst formatting is the 456 bits received from ciphering, Burst formatting adds a total of 136 bits per block of 20 ms, bringing the overall total to 592.

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STAGE 8: MODULATION & TRANSMISSON

The bits must then be sent over the air using a carrier frequency.

GSM uses the GMSK modulation technique. The bits are modulated onto a carrier frequency and transmitted (e.g. 912.2MHz).

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Commissioning Flow of a BTS Open Nokia BTS Manager

Go to Tools

Launch BTS Hardware Configurator

Go to File

Open and create the configuration according to the requirement

Save it after giving a file name

Close it

Select BTS in the Menu of BTS Manager

Send the file to BTS

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Select commissioning in BTS Manager

Go to Wizard

Select Manual commissioning

Give BCF ID, BSC ID, site Name etc

Click Next

Abis will be in LAPD State, continue, click OK

(Do You want to commission without Abis, click Yes)

Give EAC inputs, click Next

Give EAC outputs, click Next

Finish (This will show the summary of commissioning)

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Launch Ultra BTS Hub Manager in tools menu

Double Click on E1/T1 card or FXC/RRI

Give LIF settings

Enable Used interfaces

Apply

Go to configuration

Go to Traffic Manager

Give TCH, TRx signalling, OMU signalling

Select Topology (chain or loop)

OK

Go to synchronisation

Go to Loop bits, if site is in Loop

Close

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2 Mbps PCM Sharing by 1 BTS (Total 1 TRX)

Synchronization

Signaling

T00

T01

T02

T03

T04

…..

T28

T29

T30

TRX1_S

TRX2_S

2Mbps =32 X 64Kbps

TRX SIGNALLING 16Kbps/TRX

TRX_1

TRX_1

TRX_1

TRX_1

TRX_1 TRX_1

TRX_1TRX_1

OMU2_S

OMU1_ST25

T26

T27

T31

OMU SIGNALLING 16Kbps/BTS

TRX TRAFFIC 8X16Kbps/TRX

TRX_2TRX_2

TRX_2

TRX_2

TRX_2 TRX_2

TRX_2TRX_2

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2Mbps =32 X 64Kbps




Synchronization

Signaling

T00

T01

T02

T03

T04

…..

T28

T29

T30

TRX1_S

TRX2_S

TRX_1

TRX_1

TRX_1

TRX_1

TRX_1 TRX_1

TRX_1TRX_1

OMU1_ST25

T26

T27

T31

TRX_2TRX_2

TRX_2

TRX_2

TRX_2 TRX_2

TRX_2TRX_2

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Synchronization

Signaling

T00

T01

T02

T03

T04

…..

T28

T29

T30

TRX1_S

TRX2_S

2Mbps =32 X 64Kbps


TRX_1

TRX_1

TRX_1

TRX_1

TRX_1 TRX_1

TRX_1TRX_1

OMU2_S

OMU1_ST25

T26

T27

T31



TRX_2TRX_2

TRX_2

TRX_2

TRX_2 TRX_2

TRX_2TRX_2

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2Mbps =32 X 64Kbps





Synchronization

Signaling

T00

T01

T02

…...

T23

T24

T28

T29

T30

TRX1_S

TRX2_S

TRX_1

TRX_1

TRX_1

TRX_1

TRX_1 TRX_1

TRX_1TRX_1

TRX_12TRX_12

TRX_12

TRX_12

TRX_12 TRX_12

TRX_12TRX_12

TRX3_S

TRX4_S

TRX7_S

TRX5_S

TRX6_S

TRX8_STRX9_S

TRX10_S

TRX11_S

TRX12_S

OMU1_ST25

T26

T27

T31

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Synchronization

Signaling

T00

T01

T02

…...

T23

T24

T28

T29

T30

TRX1_S

TRX2_S

2Mbps =32 X 64Kbps


TRX_1

TRX_1

TRX_1

TRX_1

TRX_1 TRX_1

TRX_1TRX_1

TRX_12TRX_12

TRX_12

TRX_12

TRX_12 TRX_12

TRX_12TRX_12

TRX3_S

TRX4_S

TRX7_S

TRX5_S

TRX6_S

OMU8_SOMU9_S

OMU10_S

OMU11_S

OMU12_S

OMU7_S

TRX8_STRX9_S

TRX10_S

TRX11_S

TRX12_S

OMU2_SOMU3_S

OMU4_S

OMU5_S

OMU6_S

OMU1_ST25

T26

T27

T31




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GSM TRAFFIC CASES

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GSM TRAFFIC CASES

1. SUBSCRIBER RELATED IDENTITIES

Mobile Station ISDN Number (MSISDN) : The Mobile station ISDN Number (MSISDN) uniquely identifies a mobile telephone subscription in the PSTN Numbering plan. This is the number dialed when calling a mobile subscriber. As the MSISDN is the actual telephone number of the mobile subscriber, it is the only network identity that subscribers are aware of.

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The MSISDN consists of the following: CC: Country code NDC: National Destination Code SN: Subscriber Number

International Mobile Station ISDN number

CC NDC SN

National Mobile Number

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International Mobile Subscriber Identity (IMSI): The International Mobile Subscriber Identity (IMSI) is a unique identity allocated to each subscriber that facilitates correct subscriber information over the radio path and through the network. It is used for all signaling in the PLMN. All Network related subscriber information is connected to an IMSI. The IMSI is stored in the SIM, the HLR and in the serving VLR.

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IMSI

National MSI

MCC(3 digits)

MNC(2-3 digits)

MSIN

The IMSI consists of three different parts.MCC: Mobile Country CodeMNC: Mobile Network CodeMSIN: Mobile Station Identification Number

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Temporary Mobile Subscriber Identity (TMSI):

The Temporary Mobile Subscriber Identity (TMSI) is a temporary IMSI number made known to an MS at registration. It is used to protect the subscriber’s identity on the air interface. The TMSI has local significance only (that is, within the MSC/VLR area) and is changed when certain events occur.

Every operator can chose TMSI structure, but should not consist of more than 8 digits.

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2. EQUIPMENT RELATED IDENTITIES

International Mobile Equipment Identity (IMEI):

The International Mobile Equipment Identity (IMEI) is used to uniquely identify MS equipment to the network. The IMEI is used for security procedures such as identifying stolen equipment and preventing unauthorized access to the network. According to the GSM specifications, IMEI has a total length of 15 digits, and consists of the following.

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IMEI

TAC(6 digits)

FAC(2 digits)

SNR(6 digits)

SPARE(1 digit)

TAC: Type Approval code, determined by a central GSMFAC: Final Assembly code, identifies the manufacturerSNR: Serial Number, an individual serial number of six digits uniquely identifies all equipment within each TAC and FAC.Spare: A spare Digit for future use. When transmitted by the MS, this digit should always be zero.

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International mobile Equipment Identity and Software Version Number (IMEISV):

The International Mobile Equipment Identity and Software Version Number (IMEISV) provide a unique identity for every MS and also refers to the version of software, which is installed in the MS. The version of software is important as it may affect the services offered by the MS or its speech coding capabilities.

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IMEISV

TAC(6 digits)

FAC(2 digits)

SNR( 6 digits)

SVN(2 digits)

TAC : Type Approval CodeFAC : Final Assembly codeSNR : Serial Number SVN : Software Version Number allows the mobile equipment manufacturer to identify different Software versions of a given type approved mobile. SVN value 99 is reserved for future use.

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3. LOCATION RELATED IDENTITIES

Mobile Station Roaming Number (MSRN)

The Mobile Station Roaming Number (MSRN) is a temporary network identity, which is assigned during the establishment of a call to a roaming subscriber. The MSRN consists of three parts.

190


CC NDC SN

CC : Country CodeNDC: National Destination CodeSN : Serving Node (in this case, SN is the address to serving MSC/VLR.

191


Location Area Identity:

The Location Area Identity (LAI) is a temporary network identity, which is also required for routing.

The two main purposes of the LAI are:

1.Paging, which is used to inform the MSC of the LA in which the MS is currently situated.

2.Location updating of mobile Subscribers.

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The LAI contains the following:

LAC: Location Area code, the maximum length of LAC is 16 bits, enabling 65,536 different location areas to be defined in one PLMN

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BASE STATION IDENTITY CODE (BSIC)

The Base Station Identity Code (BSIC) enables MS’s to distinguish between different base stations sending on the same frequency.

The BSIC consists of

BSIC

NCC BCC

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NCC: Network Color Code (3 bits) identifies the PLMN. Note that it does not uniquely identify the operator. NCC is primarily used to distinguish between operators on each side of the border.

BCC: Base Station color Code (3 bits), identifies the Base Station to help distinguish between BTS using the same control frequencies

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Different States of an MS

An MS can have one of the following states:

Idle: The MS is ON, but a call is not in progress.

Active: the MS is On and a call is in Progress.

Detached: The MS is OFF.

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Mode Term Description

Idle Mode Registration This is the process, which an MS informs a network that it is attached.

Roaming When am MS moves around a network in idle mode, it is referred to as roaming.

International Roaming

When an MS moves into a network, which is not, its home network, it is referred to as international roaming. MSs can only roam into networks with which the home network has a roaming agreement.

Location Updating An MS roaming around the network must inform the network when it enters a new LA. This is called location Updating.

Paging This is the process whereby a network attempts to contact a particular MS. This is achieved by broadcasting a paging message containing the identity of that MS.

Active Mode Handover This is the process in which control of a call is passed from one cell to another while the MS moves between cells.

Detached Mode

In this mode no traffic cases are present. MS is switched OFF in this case.

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Attaching to the Network IMSI Attach:

When an MS is switched ON, the IMSI attach procedure is executed. This involves the following steps:

The MS sends an IMSI attach message to the network, indicating that it has changed state to idle.

The VLR determines whether there is a record for the subscriber already present. If not, the VLR contacts the subscriber’s HLR for a copy of the subscription information.

The VLR updates the MS status to idle.

Acknowledgement is sent to the MS.

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4

32

BSC/TRC MSC/VLRR

199


Location Updating type IMSI Attach:

If the MS has changed LA while powered off, the IMSI attach procedure may lead to an update to the location of the MS.

During IMSI attach, the VLR may determine that the current LAI of the MS is different from the LAI stored in the MS’s subscription information. If so, the VLR updates the LAI of the MS.

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IMSI DETACH

IMSI detach enables the MS to indicate to the network that it is switched ff. At power off, the MS sends an IMSI detach message to the network. On reception, the VLR marks the corresponding IMSI detached. The HLR is not informed. No acknowledgement is sent to the MS.

201


TRAFFIC ENGINEERING

202


Telecommunications Traffic, Tele Traffic:

A Process of events related to demands for the utilization of resources in a telecommunication network.

203


Traffic Intensity :

The instantaneous traffic in a pool of resources is the number of busy resources at a given instant of time. Traffic intensity is a measure of the average occupancy of a facility during a specified period of time, normally a busy hour, measured in traffic units (erlangs) and defined as the ratio of the time during which a facility is occupied (continuously or cumulatively) to the time. This facility is available for occupancy.

Traffic Intensity = Call Request Rate X Holding Time.

Au = H, Where = Average Number of Call requests per unit time for each user.

H = Average Duration of a call.

204


Calling Rate : The number of times a route or traffic path is used per unit time, more properly defined, the call intensity per traffic path during busy hour.

Holding time : The average duration of occupancy of a traffic path by a call.

Traffic intensity : It is the average number of calls simultaneously in progress during a particular period of time. It is measured either in units of Erlangs or CCS.

205


An average of one call in progress during an hour represents a traffic intensity of 1 Erlang or 1 Erlang=1X3600 call seconds=36 CCS.

Traffic intensity can be obtained as:

Traffic intensity = (The sum of circuit holding time)/(the duration of the monitoring period)

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1. If the carried load for a component is 2900 CCS at 5% blocking, what is the offered load?

Sol: Offered load = 2900/(1-0.05)=3050 CCS.

2. In a voice network, each subscriber generates two calls/hour on average and a typical call holding time is 120 seconds. What is the traffic intensity?

Sol : Intensity = 2X120/3600 = 0.0667 Erlangs = 2.4 CCS.

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3. To determine voice traffic on a line, the following data was collected during a period of 90 minutes (refer the table below). Calculate the traffic intensity in Erlangs and CCS

Call Number Duration of call

1 60

2 74

3 80

4 90

5 92

6 70

7 96

8 48

9 64

10 126

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Sol: Call arrival Rate : 10 calls/1.5 hours =6.667 calls/Hour

Average holding time : (60+74+80+90+92+70+96+48+64+126) / 10 = 80 seconds

Intensity = 6.667X80/3600=0.148 Erlangs = 5.53 CCS.

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4. The data in the table below was recorded by observing the activity of a single customer line during the eight hour period from 9.00 A.M. to 5.00 P.M. Determine the traffic intensity during the eight hour period, during the Busy Hour (which is assumed to be between 4:00 PM. And 5:00 P.M).

210


Call Number Call started Call ended

1 9:15 9:18

2 9:31 9:41

3 10:17 10:24

4 10:24 10:34

5 10:37 10:42

6 10:55 11:00

7 12:01 12:02

8 2:09 2:14

9 3:15 3:30

10 4:01 4:35

11 4:38 4:43

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Sol: Call arrival Rate : 11 calls/ 8Hrs = 1.375 Calls/Hour

Total call minutes = 3+10+7+10+5+5+1+5+15+34+5 = 100 minutes

Call holding time = (100 minutes/11 calls)X 1Hr/60 mnts = 0.515 hour/call

The traffic intensity I = 1.375 X 0.1515 = 0.208 Erlangs = 7.5 CCS.

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The busy hour is 4:00 P.M to 5:00 P.M. Since there are only two calls between this period, the call arrival rate = 2 calls/Hr

The average call holding time during busy hour :

(34+5) min/2 calls = 19.5 minutes/call =0.325 hour/call

The traffic load in the BH is I= 2X0.325 = 0.65 Erlang =23.4 CCS.

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GSM SERVICES

214


Types of GSM services

Basic Services: These are available to all subscribers to a mobile network. For example, the ability to make voice telephone calls is a basic service.

Supplementary Services: These are additional services that are available by subscription only. Call forwarding is an example of a supplementary service

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Basic Services can be divided into 2 types:

Tele services:

A tele service allows the subscriber to communicate (usually via voice, fax, data or SMS) with another subscriber. It is a complete system including necessary terminal equipment.

Basic Services

216


Bearer Services:A bearer service transports speech

and data as digital information within the network between user interfaces.

A bearer service is the capability to transfer information and does not include the end user equipment.

Every tele service is associated with a bearer service. For example, a bearer service associated with the speech telephony tele service is the timeslot assigned to a call on a TDMA frame over the air interface.

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The following are the major tele services supported by GSM System.

1. Speech

2. Emergency Calls

3. Dual Tone Multi Frequency (DTMF)

4. Alternate Speech/Fax

5. Short Message Service

6. SMS Cell Broadcast (SMSCB)

7. Voice Mail

8. Fax Mail

TELE SERVICES:

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BEARER SERVICES:

1. Traffic to PSTN

2. Traffic to ISDN

3. Traffic to Packet Switched Public Data Networks (PSPDN)

4. Traffic to Circuit Switched Public Data Networks (CSPDN)

5. Traffic to Internet

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SUPPLEMENTARY SERVICES

1. Call Forwarding

2. Barring of outgoing calls

3. Bar all outgoing calls

4. Bar all outgoing international calls

5. Bar all outgoing international calls except those directed to the home PLMN

6. Call waiting

7. Multi party service

8. Closed User Group (CUG)

220


BATTERY LIFE

221


One of the main factors, which restrict reducing the size of a MS, is the battery.

A battery must be large enough to maintain a telephone call for an acceptable amount of time without needing to be recharged.

Since there is demand for MSs to become smaller and lighter the battery must also become smaller and lighter.

Battery Life

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The features which enable the life of a GSM MS battery to be extended are :

1.Power Control

2.Voice Activity Detection (VAD)

3.Discontinuous Transmission (DTX)

4.Discontinuous Reception (DRX)

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1. Power Control:

This is a feature of the GSM air interface which allows the network provider to not only compensate for the distance from MS to BTS as regards timing, but can also cause the BTS and MS to adjust their power output to take account of that distance also.

224


The closer the MS is to the BTS, the less the power it and the BTS will be required to transmit. This feature saves radio battery power at the MS, and helps to reduce co-channel and adjacent channel interference

225


Power Control

226


2. Voice Activity Detection (VAD):VAD is a mechanism whereby the source

transmitter equipment identifies the presence or absence of speech.

VAD implementation is effected in speech mode by encoding the speech pattern silences at a rate of 500 bit/s rather than the full 13 kbit/s.

This results in a data transmission rate for background noise, known as “comfort” noise, which is regenerated in the receiver. Without “comfort” noise the total silence between the speeches would be considered to be disturbing by the listener.

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3. Discontinuous Transmission (DTX) :

DTX increases the efficiency of the system through a decrease in the possible radio transmission interference level. It does this by ensuring that the MS does not transmit unnecessary message data.

DTX can be implemented, as necessary, on a call-by-call basis. The effects will be most noticeable in communications between two MS.

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4. Discontinuous Reception (DRX):

DRX allows the MS to effectively “switch off” during times when reception is deemed unnecessary.

This allows the MS to ‘go to sleep’ and listen-in only when necessary, with the effective saving in power usage. DRX may only be used when a MS is not in a call.

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GSM Basic Call Sequence

230


Call from Land Line to a GSM network

231


Call flow :

1. The incoming call is passed from the fixed network to the gateway MSC (GMSC).

2. Then, based on the IMSI numbers of the called party, its HLR is determined.

3. The HLR checks for the existence of the called number. Then the relevant VLR is requested to provide a mobile station roaming number (MSRN).

232


4. This is transmitted back to the GMSC.

5. Then the connection is through from GMSC to the responsible MSC.

6. Now the MSC queries the VLR for the location range and reachability status of the mobile subscriber.

7. If the MS is marked reachable, VLR asks the MSC to go ahead with necessary paging message.

8. MSC asks the BSC for the same, then the BSC asks the BTS to send a paging message.

233


9. Then the particular mobile subscriber telephone responds to the page request through RACH. This will be forwarded to the BSC and MSC.

10.SDCCH will be provided through AGCH by the BSC with the instructions from MSC. SDCCH handles all necessary security procedures like authentication, IMEI check etc.

11.If this is successful, the VLR indicates to the MSC to go ahead with the call.

12. The traffic channel will be provided and the call can be completed.

234


Call from Mobile Station to land line

235


Call Flow from MS to PSTN

1. MS after dialing a number and press send key uses RACH to ask for a signaling channel.

2. The BSC allocates a signaling channel, using AGCH.

3. The MS sends a call setup request through SDCCH, to the MSC/VLR. Over SDCCH, all signaling takes place. This includes:

236


Marking the MS status as active in the VLR (if the MS status is not updated earlier).

The Authentication Procedure

Ciphering

Equipment Identification

Sending the called Subscriber number to the network

Checking if the subscriber has service barring of outgoing calls activated.

237


4. The MSC/VLR instructs the BSC to allocate an idle TCH. The BTS and MS are told to tune to the TCH.

5. The MSC/VLR forwards the called number to an exchange in the PSTN, which establishes a connection to the subscriber.

6. If the called subscriber answers, the connection is established.

238


Case Study 9:

How Call flow happens in reality from the cell site? (PSTN Demo and BTS Video)

239


Handover between Cells Controlled by the Same BSC

240


1. The BSC orders the new BTS to activate a TCH.

2. The BSC sends a message to the MS, via the old BTS, containing information about the frequency and time slot to change to and also the output power to use. This information is sent to the MS using FACCH.

3. The MS tunes to the new frequency, and transmits handover access burst in the correct time slot. Since the MS had no information yet on TA, the handover burst are very short (only 8 bits of information).

241


4. When the new BTS detects the hand over bursts, it sends the information about TA. This is also sent through FACCH.

5. The MS sends a handover complete message to the BSC through the new BTS.

6. The BSC tells the old BTS to release the old TCH

242


.Hand over between cells controlled by different BSC’s but the same MSC/VLR :

243


1. The serving BSC sends a Hand over Required Message to the MSC containing the identity of the target cell

2. The MSC knows which BSC controls this cell and sends a Hand over Request to this BSC.

3. The new BSC orders the target BTS to activate a TCH.

4. The new BSC sends a message to the MS through the MSC and the old BTS.

244


5. MS tunes to the new frequency and transmits handover access bursts in the correct time slot.

6. When the new BTS sends information about TA.

7. MS sends a handover complete message to MSC through the new BSC.

8. MSC sends the old BSC an order to release the old TCH.

9. The old BSC tells the old BTS to release the TCH.

245


Hand over between cells controlled by different MSC/VLRs:

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1. The serving (old) BSC sends a Hand over required message to the serving MSC (MSC-A), with the identity of the target cell.

2. MSC-A identifies that this cell belongs to another MSC (MSC-B), and requests help.

3. MSC-B allocates a hand over number to reroute the call. A Hand over Request is then sent to the new BSC.

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4. The new BSC orders the target BTS to activate a TCH.

5. MSC-B receives the information, and passes it on to MSC-A together with the handover number.

6. A link is set up to MSC-B, possibly, though PSTN.

7. MSC-A sends a handover command to the MS, through the old BSC.

8. The MS tunes to the new frequency and transmits hand over access burst in the correct time slot.

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9. When the new BTS detects the hand over burst it sends information about TA.

10. The MS sends hand over complete message to the old MSC, through the new BSC and the new MSC/VLR.

11. A new path in the group switches in MSC-A is established, and the call is switched through.

12. The old TCH is deactivated by the old BSC.

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SHORT MESSAGE SERVICE

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The point-to-point SMS provides a mechanism for transmitting "short" messages to and from wireless handsets. The service makes use of a short message service center (SMSC), which acts as a store and forward system for short messages.

The wireless network provides for the transport of short messages between the SMSCs and wireless handsets.

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A distinguishing characteristic of the service is that an active mobile handset is able to receive or submit a short message at any time, independent of whether or not a voice or data call is in progress. SMS also guarantees delivery of the short message by the network. Temporary failures are identified, and the short message is stored in the network until the destination becomes available.

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Network Elements and Architecture

SME Short Message EntitySMS Short Message ServiceSMSC Short Message Service Center

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SMS-GMSC Gateway Mobile Switching Center

SMS-IWMSC SMS Inter working Mobile Switching Center

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Short Messaging Entities

Short messaging entity (SME) is an entity which may receive or send short messages. The SME may be located in the fixed network, a mobile station, or another service center.

Short Message Service Center

Short message service center (SMSC) is responsible for the relaying and store-and forwarding of a short message between an SME and mobile station.

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SMS-Gateway/Inter working Mobile Switching Center

The SMS gateway MSC (SMS-GMSC) is an MSC capable of receiving a short message from an SMSC, interrogating a home location register (HLR) for routing information, and delivering the short message to the "visited" MSC of the recipient mobile station.

The SMS inter working MSC (SMS-IWMSC) is an MSC capable of receiving a short message from the mobile network and submitting it to the appropriate SMSC. The SMSGMSC/ SMS-IWMSC are typically integrated with the SMSC.

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Mobile Switching Center

The mobile switching center (MSC) performs the switching functions of the system and controls calls to and from other telephone and data systems.

Visitor Location Register The visitor location register (VLR) is a database

that contains temporary information about subscribers. This information is needed by the MSC in order to service visiting subscribers.

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The Base Station System

All radio-related functions are performed in the base station system (BSS). The BSS consists of base station controllers (BSCs) and the base transceiver stations (BTSs), and its primary responsibility is to transmit voice and data traffic between the mobile stations.

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Service Elements

SMS comprises several service elements relevant to the reception and submission of short messages:

Validity period: The validity period indicates how long the SMSC shall guarantee the storage of the short message before delivery to the intended recipient.

Priority: Priority is the information element provided by an SME to indicate the priority message.

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Mobile-Terminated Short Message Example

Figure 3 depicts the successful MT-SM scenario. For convenience, the GSM method is illustrated.

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1. The short message is submitted from the SME to the SMSC.

2. After completing its internal processing, the SMSC interrogates the HLR and receives the routing information for the mobile subscriber.

3. The SMSC sends the short message to the MSC using the forward Short Message operation.

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4. The MSC retrieves the subscriber information from the VLR. This operation may include an authentication procedure.

5. The MSC transfers the short message to the MS.

6. The MSC returns to the SMSC the outcome of the forward Short Message operation.

7. If requested by the SME, the SMSC returns a status report indicating delivery of the short message.

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Mobile-Originated Short Message Example

Figure 4 depicts the successful MO-SM scenario. For convenience, the GSM method is shown.

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1. The MS transfers the SM to the MSC.

2. The MSC interrogates the VLR to verify that the message transfer does not violate the supplementary services invoked or the restrictions imposed.

3. The MSC sends the short message to the SMSC using the forward Short Message operation.

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4. The SMSC delivers the short message to the SME.

5. The SMSC acknowledges to the MSC the successful outcome of the forward Short Message operation.

6. The MSC returns to the MS the outcome of the MO-SM operation.

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SHORT MESSAGE SERVICE

The Short Message Service (SMS) provides a means of sending text messages containing up to 160 alphanumerical characters to and from MS’s. SMS makes use of a SMS Center (SMS-C), which acts as a store and forward center for short messages.

SMS consists of two basic services

Mobile Originated SMS : From an SMS-C to an MS.

Mobile Terminated SMS: From an MS to an SMS-C.

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In the two cases described below, the MS is in idle mode. If the MS is in active mode, short message is transmitted on the SACCH.

No paging, Call set up, authentication, etc needs to be performed in that case.

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Mobile Originated SMS

Mobile Originated SMS transfers a short message submitted by the MS to an SMS-C. It also provides information about the delivery of the short message, either by a delivery report or failure report.

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1. An MS establishes a connection to the network, as in the case of a normal call set-up. This step is not performed if the MS is in active mode, since the connection already exists.

2. If authentication is successful, the MS sends the short message using SDCCH to the SMS-C via the MSC/VLR. The SMS-C in turn forwards the short message to its destination. This could be an MS or a terminal in the fixed network such as a PC.

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Mobile Terminated SMS Mobile Terminated SMS has the capability to

transfer a short message from the SMS-C to an MS.

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1. A User sends a message to a SMS-C.

2. The SMS-C sends the message to the SMS-GMSC.

3. The SMS-GMSC queries the HLR for routing information

4. The HLR returns routing information to the SMS-GMSC.

5. The SMS-GMSC reroutes the message to the MSC/VLR.

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6. The MS is paged and a connection is set up between the MS and the network, as in the normal call set up case.

7. If authentication is successful, the MSC/VLR delivers the message to the MS. Short Messages are transmitted on the allocated signalling channel, SDCCH.

8. If the delivery was successful, a report is sent from the MSC/VLR to the SMS-C, if not, the HLR is informed by the MSC/VLR, and a failure report is sent to SMS-C.

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In the case of an unsuccessful delivery, the SMS-C informs the HLR and VLR that there is a message waiting to be delivered to the MS. The HLR then informs the SMS-C when the MS becomes available.

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