GSM_All, WCDMA , LTE

7/28/2019 GSM_All, WCDMA , LTE

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Introduction into Communication

Eng./Mohamed Tarek


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2006-01-24 Lecture 1 2

Communication Introduction

Multiple Access Technique

GSM Network Architecture

Contents

Call scenario and call set up ,Hand over ,Location update

Radio planning and GSM coverage

GSM Network Interferences and Signaling

Access to 3G and New communication systems

Communication Companies and Different positions


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2006-01-24 Lecture 1 3

Introduction

Any Communication system consists of :-

source DestinationTransmission medium


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2006-01-24 Lecture 1 4

Introduction

The kinds of transmission medium :

Wired

Wireless

Wired transmission medium :

1- Twisted-pair

2- Coaxial cable

3-optical fibers


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2006-01-24 Lecture 1 5

Introduction

Communication Channels types:-

ApplicationsPropertiesChannel Type

FM radio, televisionOne-way onlySimplex

Police radio, push-to-talkTwo-way, only one at a timeHalf duplex

PSTN, Mobile systemsTwo-way, both at the same timeFull duplex


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2006-01-24 Lecture 1 6

Introduction

Communication system consists of :-

SourceSource

encoder

Channel

encoderModulator

DestinationSource

decoder

Channel

decoderDemodulator

Transmitter

Receiver

SOURCE

Info.Transmitter

Transmitted

signal

Received

signalReceiver

Received

info.

Noise

Channel

Source User


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2006-01-24 Lecture 1 7

Introduction

Encoding:-

Encoding is the process of transforming information from one format

into another. The opposite operation is called decoding.

Encoding is the process of putting a sequence of characters (letters,numbers, punctuation, and certain symbols)

into a specialized format for efficient transmission or storage.

Decoding is the opposite process Source Encoding

conversion from analog to digital is Encoding


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2006-01-24 Lecture 1 8

Introduction

Channel encoding deals with error control during the transmission

through the communication channel.

Error detection Codes

Parity check codes (Odd parity Even parity)

(Frame Protocols )??


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2006-01-24 Lecture 1 9

Introduction

Data Compressionis an important subject as more digital

information is required to be stored and transmitted.

Compression methods:

There are two main types of compression.

Lossless compression

Lossy compression


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2006-01-24 Lecture 1 10

Classification of signals

Periodic and non-periodic signals

Analog and discrete signals

A discrete signalAnalog signals

A non-periodic signalA periodic signal


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2006-01-24 Lecture 1 11

Classification of signals

Deterministic and random signals Deterministic signal: No uncertainty with

respect to the signal value at any time.

Random signal: Some degree of uncertainty in

signal values before it actually occurs.

Thermal noise in electronic circuits due to the

random movement of electrons

Reflection of radio waves from different layers of

ionosphere


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2006-01-24 Lecture 1 12

Noise


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2006-01-24 Lecture 1 13

Digital versus analog

Advantages of digital communications:

Regenerator receiver

Different kinds of digital signal are treated

identically.

Data

Voice

Media

Propagation distance

Original

pulse

Regenerated

pulse

A bit is a bit!


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2006-01-24 Lecture 1 14

Analog VS Digital

Digital Communication:-Advantages of Digital :-

Less noise effect

More reliable

Easy to manipulateFlexibleCompatibility with other digital systemsOnly digitized information can be transported

through a noisy channel without degradationIntegrated networks


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2006-01-24 Lecture 1 15

Introduction

Disadvantages of Digital -

Sampling Error

Digital communications require greater bandwidth than

analogue to transmit the same information.

We loss some of information due to sampling process


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2006-01-24 Lecture 1 16

Introduction

Definition of Analogue :-

Analogue is a transmission standard that uses electrical impulses to

emulate the audio waveform of sound. When you use a phone, the

variations in your voice are transformed by a microphone into similar

variations in an electrical signal and carried down the line to the

exchange

Advantages of Analogue -

Uses less bandwidth

More accurate

Disadvantages of Analogue -

The effects of random noise can make signal loss and distortion

impossible to recover and more effect by noise


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2006-01-24 Lecture 1 17

Circuit Switching VS Packet SwitchingCircuit Switching


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2006-01-24 Lecture 1 18

Circuit Switching VS Packet Switching

Packet Switching


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2006-01-24 Lecture 1 21

Multiple Acess TechniqeIt is used because the limitation of transmission resources comparing with the

number of users


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2006-01-24 Lecture 1 22

Multiple Acess Techniqe

Three types of Multiple Access Technique are available:

Frequency Division Multiple Access (FDMA)

Time Division Multiple Access (TDMA)

Code Division Multiple Access (CDMA)


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2006-01-24 Lecture 1 23

Frequency Division Multiple Access (FDMA)

Each FDMA user is assigned a specific frequency channel. No one else in the samecell or a neighboring cell can use the frequency channel while it is assigned to a

user. Although this technology will reduce signal interference, it also severely limits

the number of users able to transmit at a time.

Strength

f1 f2 f3

Frequency

User 1 User 2 User 3


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2006-01-24 Lecture 1 24


TDMA users share a common frequency channel, but use the channel foronly a very short amount of time. They are each given a time slot and

only allowed to transmit during that particular time slot. When all

available time slots in a given frequency are used, the next user must be

assigned a time slot on another frequency. The time slices are so small

that the human ear cannot perceive the time slicing, and thereforeassumes that they have the entire channel to transmit their signal.


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2006-01-24 Lecture 1 25


Frequency

Strength

User 1, time=0

User 2, time=t0


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2006-01-24 Lecture 1 26

TDMA VS FDMA

Strength

User 7User 2

User 1


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2006-01-24 Lecture 1 27

Code Division Multiple Access (CDMA)

CDMA users share a common frequency channel. All users are on the same

frequency at the same time. However, each pair of users is assigned a

special code that reduces interferences while increasing privacy.

Frequency

Strength


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2006-01-24 Lecture 1 28

TDMA VS FDMA VS CDMA


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What is the GSM?

GSM is the Global System for Mobile telecommunications.

It is the European standard for the Mobile telecommunications and it

is considered as one of the most popular standard worldwide.

It is known as the second generation mobile telecommunicationssystem 2G system.

It is used in Egypt by the two existing operators; Mobinil and Vodafone;

also it used as a part of the third operator in Egypt Etisalat.


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2006-01-24 Lecture 1 30

GSM Worldwide (darker areas)


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2006-01-24 Lecture 1 31

What is the GPRS?

GPRS is the General Packet Radio Service.

Within the GSM network it shares the network databases and radio access

network.

It is known as the 2.5generation mobile telecommunications system 2Gsystem.


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2006-01-24 Lecture 1 32

3G Systems

Universal Mobile Telecommunication Service (UMTS) is the marketing

name for the 3G has two standardization bodies:

1- 3GPP which uses the W-CDMA technology.

2- 3GPP2 which uses the CDMA2000 technology.


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2006-01-24 Lecture 1 33

Basic GSM Network Structure


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Mobile Station (MS) The Mobile Station (MS) is the interface between the user and the

network. The MS consists of two independent parts:

Subscriber Identity Module (SIM) card

Mobile Equipment (ME)

+


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2006-01-24 Lecture 1 35


Mobile Equipment (ME)

The ME is the only part of the GSM network which the subscriber will

really see.

Vehicle Mounted

These devices are mounted in a vehicle and the antenna is physically

mounted on the outside of the vehicle. Portable Mobile Unit

This equipment can be handheld when in operation, but the antenna is

not connected to the handset of the unit.

Handportable Unit

This equipment comprises of a small telephone handset not much bigger

than a calculator. The antenna is be connected to the handset.


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2006-01-24 Lecture 1 36


Mobile Equipment Capabilities:

RF power capability

Encryption capability

Frequency capability

Short message service capability

The ME is the hardware used by the subscriber to access the network. Thehardware has an identity number associated with it, which is unique forthat particular device and

permanently stored in it. This identity number is called The

International Mobile Equipment Identity (IMEI)

To guarantee that the mobile not to be stolen


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2006-01-24 Lecture 1 37


IMEI

6 Digits

TAC

2 Digits

FAC

6 Digits

SN

TAC: Type Approval Code,

The first two digits are the

code for the country approval

FAC: Final Assembly Code

SN: Serial Number



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2006-01-24 Lecture 1 38


IMEI

Short for International Mobile Equipment Identity, a unique number given

to every single mobile phone, typically found behind the battery.

IMEI numbers of cellular phones connected to a GSM network are stored

in a database (EIR - Equipment Identity Register) containing all validmobile phone equipment.

When a phone is reported stolen or is not type approved, the number is

marked invalid.

The number consists of four groups that looks this:

nnnnnn--nn-nnnnnn-n
http://wi-fiplanet.webopedia.com/TERM/I/GSM.htmhttp://wi-fiplanet.webopedia.com/TERM/I/GSM.htm


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2006-01-24 Lecture 1 39


The first set of numbers is the type approval code (TAC). The first two

digits represent the country code. The rest make up the final assembly

code. The second group of numbers identifies the manufacturer:

01 and 02 = AEG

07 and 40 = Motorola

10 and 20 = Nokia 41and 44 = Siemens

51= Sony, Siemens, Ericsson

The third set is the serial number and the last single digit is an

additional number (usually 0).


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2006-01-24 Lecture 1 40


Subscriber Identity Module (SIM)

The SIM as mentioned previously is a smart card which plugs into the

ME Mobile Equipment.

It contains a memory that contain information about the MSsubscriber hence the name Subscriber Identity Module.

This memory can store data by the user.


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2006-01-24 Lecture 1 41


The SIM contains several pieces of information:

International Mobile Subscriber Identity (IMSI)

This number identifies the MS subscriber. It is only transmitted over the

air during initialization.

Temporary Mobile Subscriber Identity (TMSI)

This number identifies the subscriber, it is periodically changed by thesystem.

Location Area Identity (LAI)

Identifies the current location of the subscriber.

Subscriber Authentication Key (Ki) This is used to authenticate the SIM card.


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2006-01-24 Lecture 1 42


Mobile Station International Services Digital Network (MSISDN)

CC : Country Code

NDC : National Destination Code

SN : Subscriber Number

Vodafone Egypt MSISDN

20

CC

10

NDC

1100477

SN

Vodafone UK MSISDN

44

CC

385

NDC

196099

SN


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Base Station Subsystem (BSS)

MS

BTS BSC

BSS


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The Base Transceiver Station BTS The BTS contains the RF components that provide the air interface for a

particular cell. This is the part of the GSM network which

communicates with the MS. The antenna is included as part of the BTS.

Converts the GSM radio signals into a format that can be recognized by

the BSC.

Channel coding and interleaving.

Records and passes to the BSC the Signal strength measurements.


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The BSC is the central node within a BSS and co-ordinates the actions of

Base Stations. The BSC controls a major part of the radio network.

Its main functions can be divided into two types:

During Call Set Up:

Finding the called mobile station by paging.

Allocate the frequency for setting the call.During Call :

Monitoring the call quality.

Controlling the transmitted power to the MS depending

on the location of the MS.

Control the handover for the MS after receiving the

power measurements from the MS and from the BTS.


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One location area consists of more than one BTS.

One BSC controls more than one BTS.

One BTS covers 3 cells.

One cell is covered by one Antenna.

So, one Location Area consists of more than one cell.


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2006-01-24 Lecture 1 53


Transcoder (XCDR) The Transcoder (XCDR) is required to convert the speech or data output

from the MSC (64 kbit/s PCM), into the form specified by GSMspecifications for transmission over the air interface,

that is, between the BSS and MS

(64 kbit/s to 16 kbit/s and vice versa)

The 64 kbit/s Pulse Code Modulation (PCM) circuits from the MSC, iftransmitted on the air interface without modification, would occupy anexcessive amount of radio bandwidth.

This would use the available radio spectrum inefficiently. The requiredbandwidth is therefore reduced by processing the 64 kbit/s circuits sothat the amount of information

required to transmit digitized voice calls to a gross rate of 16 kbit/s. The transcoding function may be located at the

MSC, BSC, or BTS.

N t k S it hi S b t (NSS)


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2006-01-24 Lecture 1 54

Network Switching Subsystem (NSS)

MSC/VLR

HLR

AUC

BSC

NSS

BTS

BTS


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2006-01-24 Lecture 1 56

The primary node in a GSM network is the MSC. It is the node

which controls calls establishment. The primary functions of anMSC include the following: Switching and call routing to or from MS. Charging. Service providing. Control of connected BSCs.

Access to PSTN. Provides the gateway functionality to other networks. One MSC controls more than one BSC.

Mobile Switching Center (MSC)


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2006-01-24 Lecture 1 57

Mobile Switching Center (MSC)


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Types of the MSC

VMSC: Visited MSC

There are three types of the MSC, the difference just in the function.

GMSC: Gateway MSC

TMSC: Transit MSC


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Visited Mobile Switching CenterIts function is to switch in the level of BSCs and it is combined with a VLR.

MSC/VLR

BSC BSC


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Transit Mobile Switching CenterIts function is to switch between the different

VMSC. It is not combined with a VLR.

TMSC

VMSC VMSC

Gateway Mobile Switching Center (GMSC)


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Its function is to connect the PLMN to the PSTN or to the

other PLMN existing in the country.

Gateway Mobile Switching Center (GMSC)

TMSC

VMSCVMSC

TMSC

VMSCVMSC

Mobinil GMSC

PSTNVodafone


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Home Location Register (HLR)

The HLR is a centralized network database that stores and manages allmobile subscriptions belonging to a specific operator.

It acts as a permanent store for a persons subscription informationuntil that subscription is cancelled.

The primary functions of the HLR include:

Stores for each mobile subscriber:

Basic subscriber categories.

Supplementary services.

Current location.

Allowed/barred services.

Authentication data.

Subscription database management

Controls the routing of mobile terminated calls and SMS


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Visitor Location Register (VLR)

The role of a VLR in a GSM network is to act as a temporary storagelocation for subscription information for MSs, which are within a

particular MSC service area.

Thus, there is one VLR for each MSC service area. This means that theMSC does not have to contact the HLR (which may be located in

another country) every time the subscriber uses a service or changes

its status. The VLR is always integrated with the MSC.



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2006-01-24 Lecture 1 66

For the duration when the MS is within one MSC service area, then the VLRcontains a complete copy of the necessary subscription details, including

the following information:

Identity numbers for the subscriber

Supplementary service information (e.g. Does the subscriber has call

waiting activated or not)

Activity of MS (e.g. idle or busy)

Current Location Area of MS



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Authentication Center (AUC)


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To protect GSM systems, the following security functions have

been defined: Subscriber authentication: by performing authentication, the

network ensures that no unauthorized users can access thenetwork, including those that are attempting to impersonateothers.

Radio information ciphering: the information sent between thenetwork and an MS is ciphered. An MS can only decipherinformation intended for it.

Authentication Center (AUC)


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Equipment Identification Register(EIR) In order to block the stolen mobiles equipments; the EIR equipment

is used; also in case of the Mobile operator wants to block a certain

type of Mobile phones.

Example, In Turkey all the mobile phones bought from outside Turkeyare blocked and can not be used before paying fees.

The Mobile equipment is identified by a number called InternationalMobile Equipment Identity (IMEI). This number is uniquely identifiesthe MS worldwide.


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Because the subscriber and equipment are separate in GSM, it is

necessary to have a separate authentication process for the MSequipment.

The equipment identification procedure uses the identity of theequipment itself (IMEI) to ensure that the MS terminal equipment isvalid.

EIR

1. IMEI Request

2. IMEI3. IMEI Check

4. Access/ Barring Data

MSC / VLR

Equipment Identification Register (EIR)



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IMEI

6 Digits

TAC

2 Digits

FAC

6 Digits

SN

TAC: Type Approval Code,

The first two digits are the

code for the countryapproval

FAC: Final Assembly Code

SN: Serial Number




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Interworking Function (IWF)

Interworking Function (IWF)The IWF provides the function to enable the GSM system to

interface with the various

forms of public and private data networks currently available.

The basic features of the IWF are listed below.

Data rate adaption.Protocol conversion.


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Echo Canceller (EC)

An EC is used on the PSTN side of the MSC for all voice circuits. Echocontrol is required at the switch because the incoherent GSM system

delay can cause an unacceptable echo condition, even on short

distance PSTN circuit connections.


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OSS

The operation and Maintenance center (OMC) is connected to all equipment(the GMSC, MSC, HLR, VLR, AUC, EIR and the BSC).

It can be viewed as a computerized monitoring center were staff canmonitor and control the network remotely.

MSC

SMSCBSC

HLR

OMC

LAN


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Operation and Support Subsystem (OSS)


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Operations and maintenance center (OMC)

(OMC) is connected to all equipment in the switching system and to

the BSC. The implementation of OMC is called the operation and

support system (OSS). The OSS is the functional entity from which thenetwork operator monitors and controls the system. The purpose of

OSS is to offer the customer cost-effective support for centralized,

regional, and local operational and maintenance activities that are

required for a GSM network. An important function of OSS is to

provide a network overview and support the maintenance activities of

different operation and maintenance organizations.


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Mobile Originated Call


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1. The MS ask for a signaling channel.

2. The BSC/TRC allocates a signaling channel.

3. The MS sends a call set-up request via MSC/VLR.all signaling preceding a call takes place. This

includes:

Marking the MS as active in the VLR

The authentication procedure

Equipment identification

Sending the B-subscribers number to the

network

Checking if the subscriber has the service

Barring of outgoing calls activated

4. The MSC/VLR instructs the BSC/TRC to allocate .

The BTS and MS.5. The MSC/VLR forwards the Bnumber to an

exchange in the PSTN, which establishes a

connection to the subscriber.

6. If the B-subscriber answers, the connection is

established.

PSTN

g

BSC

MSC

Mobile Terminating call


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PSTN

HLR

GMSC MSC

1

3

2

5

4

7

6

8

9

Mobile Terminating call

BSC

Roaming: Location Update


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g p

HLR

Attached

VLR ADD=

Egypt Airport

Roaming & Int.

Allowed

Detached

Roaming & Int.

Allowed

MSC/VLR

Is a roaming agreement present ?IMSI

60202..

Isroaming

andInt.

callsallowed?

Attached

VLR ADD=

Stock. Airport

Roaming & Int.

Allowed

Copy of the HLR Profile will

be stored in Stock. VLR

Roaming: Call to HPLMN

H P bli L ti M bil N t k


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HLR

Attached

VLR ADD=

xyz

GWMSC

MSC/VLR

MSISDN

+2010.

Home Public Location Mobile Network

Roaming: Call from HPLMN


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HLR

Attached

VLR ADD=Stock. Airport

Roaming & Int.

AllowedGWMSC

MSISDN

010

MSC/VLR

Roaming: Call from another Roamer


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HLR

GWMSC

MSC/VLR

A

MSC/VLR

B

Attached

VLR ADD=

Stock. B

Roaming & Int.

Allowed

MSISDN

+2010.

g


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Location Update

Why do we need to update our location data ?

Actually, the location update process is done in aim to exactlyidentify the location of the subscribers within the network so thatany incoming call goes directly to the called subscriber.

To fulfill this aim, one can say that we may update the system withthe cell ID each time the subscriber changes his serving cell. TheMSC/VLR will now know the exact cell you are roaming in. This willresult in a huge amount of location update messages.

An extreme is never to make a location update and to be paged inall the network. This will cause huge amount of paging messages.

Location Update


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Types of Location Update


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1. Normal Location update within same MSC/VLR service area

2. Normal Location update between 2 different MSC/VLR service areas

3. IMSI attach/detach

4. Periodic Location Update

Normal Location within the same MSC/VLR Service area


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BSC

1. The Mobile sends an allocation request

message to the BTS

2. The BTS responds with the allocation

message

3. The mobile sends a location update request

message with its IMSI to the MSC/VLR

4

4. The MSC/VLR updates the location

information and sends a Location Update

confirmation message

MSC/VLR

UpdatesLA Record

Normal Location Update between 2 different MSC/VLR service areas


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Old MSC/VLR New MSC/VLR

NEW BSCOld BSC

LA 1

LA 2

1. The mobile sends a location update

request to the MSC.2. The new MSC/VLR receives the IMSI and

conclude the its HLR address.

3. The MSC/VLR sends a subscriber

information request with the IMSI

to the proper HLR

4. The HLR stores the address of

the new MSC/VLR

VLR Address

=

Old MSC

VLR Address

=

New VLR

5. The HLR sends the data to the

new MSC/VLR and it is kept there

6. The HLR sends a location

cancellation message to the old

MSC/VLR to remove the data

HLR

7. The new MSC/VLR sends a location

updating confirmation message to

the mobile

IMSI Attach


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IMSI attach is a complement to the IMSI detach procedure. It is used by the

mobile subscriber to inform the network that it has re-entered an active state

and is still in the same location area. If the MS changes location area while

being switched off, a normal location update takes place.

1. The MS requests a signaling channel.

2. The MSC/VLR receives the IMSI attach message from the MS.

3. The MSC/VLR sets the IMSI attach in the VLR. The mobile is now ready for

normal call handling.

4. The VLR returns an acknowledgment to the MS.

MSC/VLRBSC

1

2 3

4

Periodic Location Update


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Periodic location update is a routine task performed by the network if

the MS doesnt make any network action (sets a call, sends

SMS, location update, receives a call,. etc)

If the MS doesnt respond to this periodic location update, it will be

marked

as implicitly detached. ( Temporarily out of service )

Handover


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Handover is to keep continuity of the call when the subscriber is roaming

along the network moving from one cell to another and moving betweendifferent nodes in the network.

During call, the MS is continuously measuring transmission quality ofneighboring cells and reports this results to the BSC through the BTS.

The BSC, being responsible on supervising the cells, is responsible ofhandover initiation.

Good neighbor relations between cells is an important factor in keepingthe network performance in the accepted level.

Types of Handover


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1. Intra BSC Handover:

When the cell to which the call will be handed over belongs to the same BSC of theserving cell.

2. Inter BSC / Intra MSC Handover:

When the cell to which the call will be handed over belongs to the different BSCs butto the same serving MSC.

3. Inter MSC

When the cell to which the call will be handed over belongs to the different BSC anddifferent MSC.

Intra BSC Handover


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BSC

Serving Cell New Cell

1. The BSC decides from the power measurement reports

that the call must be handed over to another cell

2

2. The BSC checks the new cell and ordersthis cell to activate the TCH

3

3. The BSC orders the serving cell to senda message to the MS telling the information

of new TCH4. The MS tunes to the new frequency andSends handover access burst

45. The new cell detects the handover burstand sends information about the suitable

timing advance to the MS56. The MS sends complete message to the new cell

6

7. The new cell sends a message to the BSC that thehandover is successful

7

8.The BSC orders the old Cell to release the TCH

8

Inter BSC /Intra MSC Handover


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Old BSC New BSC

MSC/VLR

Inter MSC Handover


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Old MSC

Old BSC

New MSC

New BSC

Air Interface Layers


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Air Interface Layers

RadioTransmission

Logical

Channels

Messages

RadioTransmission

Logical

Channels

Messages

Terminal BaseStation

Layer 1Bits

Layer 2

Packets

Layer 3

Messages

Frequency Allocation


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99

GSM 1900GSM 1800GSM 900

1850-1910 MHz710-1785MHz890-915 MHzUplinkFrequency

1930-1990 MHz1805-1880 MHz935-960 MHzDownlink

60 MHz75 MHz25 MHzBandwidth

80 MHz95 MHz45 MHzDuplex Distance

200 KHz200 KHz200 KHzCarrier Separation299374124Radio Channels

system

space

Spectrum Allocation (GSM 900)


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GSM 900 Frequency Allocation

F (MHz)915890

Uplink1 2 3 4 121 122 123 124

F (MHz)

Downlink

960935

1 2 3 4 121 122 123 124

890.2

890.4

890.6

935.2

935.4

935.6

200 KHz

1

1

121

121

Downlink 935 960 MHz

Uplink 890 915 MHz

FDMA in GSM


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101

FDMA in GSM

Separation between carriers Frequency gap must be sufficient to eliminateinterference between adjacent channels.

Where The more the separation the less the co-channel interference but the lessthe available channels suited in the bandwidth.

It is found that a 200 kHz channel separation is suitable for all systems.

TDMA in GSM


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TDMA in GSM

With TDMA, one carrier is used to carry a number of calls, each call using that

carrier at designated periods in time .

These periods of time are referred to as time slots .

Each MS on a call is assigned one time slot on the uplink frequency and one on thedownlink frequency, and both the same.

It is found that a 8 Time Slots per carrier, called physical channels is suitable forall systems.

Information sent during one time slot is called a burst, and depending on

information sent we named what called logical Channels

Channel Type


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Traffic ChannelTransmit voice and data

Signaling Channel

transmit the signaling and synchronous data between

BTS and MS.

Channels


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Channels

Physical Channels Traffic Associated with frequency bands, time slots, codes

Physical channels transfer bits from one network element to another

Logical Channels Control

Distinguished by the nature of carried information and the way to assemblebits into data units

Three types

one-to-one: traffic channels between a BTS and a MS

one-to-many: synchronization signals from BTS to MSs in a cell

many-to-one: from MSs to the same BTS

Physical Channels


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GSM band is divided into 124 RF channels, and each channel is

divided into 8 time slots using TDMA. Thesetime slots are called physical channels.

CH 1 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

CH 2 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

CH 3 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

CH 1240 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

Traffic Channel


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106

Carries either encoded speech or user data up and down link

between a single mobile and a single BTS.

Types of traffic channel:

Full rate (TCH)

Transmits full rate speech (13 Kbits/s). A full rate TCHoccupies one physical channel.

Half rate (TCH/2)

Transmits half rate speech (6.5 Kbits/s).

Two half rate TCHs can share one physical channel, thus doubling

the capacity of a cell.

Traffic Channel


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Traffic Channel

Control Channels


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Control Channels

These are used to carry signaling or synchronization data. They are divided

into three types:-

Broadcast CHannels (BCH)

Common Control CHannels (CCCH)

Dedicated Control CHannels (DCCH)

1.Broadcast Channels


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109

From Single BTS to all the mobiles in the area

Frequency Correction Control CHannel (FCCH) Carries information for frequency correction of the mobile

Synchronization CHannel (SCH) Carries 2 important pieces of information

TDMA frame number (max = 2715684 ) Base station identity Code (BSIC)

Broadcast Control CHannel (BCCH) Broadcasts some general cell information such as:

Location Area Identity (LAI), maximum output power allowed in the cell and the identity of BCCH carriers for neighboring cells.

2.Common Control Channels


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110

2.Common Control Channels

To or from a certain BTS to a single mobile

Paging CHannel (PCH)

BTS Transmits a paging message to indicate an incoming call or short message.The paging message contains the identity number of the mobile subscriberthat the network wishes to contact.

Random Access CHannel (RACH)

MS Answers paging message on the RACH by requesting a signaling channel ofSDCCH.

Access Grant CHannel (AGCH)

Assigns a signaling channel (SDCCH) to the MS.

3.Dedicated Control Channels


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111

3.Dedicated Control Channels

Stand alone Dedicated Control Channel (SDCCH) The BTS switches to the assigned SDCCH. The call set-up procedure is

performed in idle mode. The BSC assigns a TCH (carrier and time slot) and theMS switches to the assigned SDCCH.

SDCCH is also used to Registration & Authentication

Slow Associated Control Channel (SACCH)

BTS Instructs the MS the transmitting power to use and gives instructions ontiming advance (TA).

MS Sends averaged measurements on its own BTS (signal strength and quality)and neighboring BTSs (signal strength). The MS continues to use SACCH forthis purpose during a call.

Fast Associated Control Channel (FACCH) Transmits handover information.

Transmits necessary handover information

Control Channels


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Control Channels

Channel Type-Summary


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channel

TCH

CCH

Voice CH

Data CH

FR Voice Traffic Channel (TCH/FS)

HR Traffic Channel (TCH/HS)

4.8Kbit/s HR TCH (TCH/H4.8)

9.6Kbit/s FR TCH(TCH/F9.6)

4.8Kbit/s FR TCH (TCH/F4.8)

BCH

FCCH (down)SCH (down)

BCCH (down)

CCCH

RACH (up)

AGCH (down)

PCH (down)

DCCH

SDCCH

FACCH

SACCH

14.4Kbit/s FR TCH (TCH/F14.4)

Enhanced FR Traffic Channel (TCH/EFR)

Power Measurements Performed by the Mobile


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114

Power measurements represent one of the important functions carried out by

a mobile station in both of its modes: idle mode

active mode

in order for the mobile to tune to the best cell.

Power Measurements in Active Mode


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1. To enable the mobile from making power measurements during a call,the uplink time slot will be delayed by an offset of three time slots fromthe down link time slot. (The mobile will try to measure the signalstrength of these carriers one by one during the time betweentransmission and reception of the allocated traffic channel)

2. The mobile is informed on the SACCH channel which BCCH frequenciesto be measured.

3. To make sure that the measured carriers do not belong to co-channel

cells, the mobile will have to check the identity of the adjacent cells byreading the BSIC value sent on the SCH of each cell. This will take placeduring the idle frame number 26.

(Note) The signal strength of the serving cell is measured duringreception of the allocated traffic channel.

4. The mobile will make a list of the strongest six carriers and their BSICvalues along with the signal strength of its cell, and reports this list tothe BSC via the uplink SACCH channel which is repeated once every 26frame.

GSM Coverage Plan


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116

g

To provide coverage for a large service area of a mobile networkwe have two Options:

(A) Install one transceiver with high radio power at the center of

the service area

Drawbacks:

The mobile equipments used in this network should have

high output power in order to be able to transmit signals

across the coverage area.

The usage of the radio resources would be limited.

GSM Coverage Plan


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117

g

(B) Divide the service area into smaller areas (cells) Advantages:

Each cell as well as the mobile handsets will have relatively

small power transceivers.

The frequency spectrum might be reused in two far

separated cells. This yields:1- Unlimited capacity of the system.

2- Good interference characteristics

Cell Geometry


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118

y

Problem of omni directional antennas

Dead Spots

Cell Geometrical Shape


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Differentiation between these three shapes will be in order tooptimize the number of cells required to cover a given service area

against the cell transceiver power. By some calculations, you will find

that using hexagonal shaped cells achieves the optimum.

R R R



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p

Umbrella Cell

Normal Cell Normal Cell

Macro Cell



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p

Umbrella cell

Macro cell

Slow moving subscribers

Fast moving subscribers

Pico cell

In building

coverage

Clusters


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122

Clusters

Cluster is a set of cells where the

frequency is not being reusedwithin this cluster.

Cluster can be 3, 4, 7 and 9 cells.

Sectorization


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123

sectroized CellsOmni-Directional Cell

3/9 Cluster


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A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

4 / 12 Cluster


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A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2A1

B3

B2B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

E3

E2

7 / 21 Cluster


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A3

A2

A1

C3

C2

C1

D3

D2

D1

B3

B2

B1

E3

E2

E1

F3

F2

F1

G3

G2

G1

A3

A2

A1

C3

C2

C1

D3

D2

D1

B3

B2

B1

E3

E2

E1

F3

F2

F1

G3

G2

G1

A3

A2

A1

C3

C2

C1

D3

D2

D1

B3

B2

B1

E3

E2

E1

F3

F2

F1

G3

G2

G1

A3

A2

A1

C3

C2

C1

D3

D2

D1

B3

B2

B1

E3

E2

E1

F3

F2

F1

G3

G2

G1

A1

C3

C2

C1

D3

D2

D1

B3

B2

B1

E1

F3

F2

F1

G3

G2

G1

Frequency Reuse


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127

If the GSM900 system has 124 Absolute Radio Frequency TrafficChannels, and if we are using only in our network 60 of them, thenwe can only serve 8 x 60 = 480 Calls if we only use the frequencyonce.

However, a cellular network overcome this constraint andmaximizes the number of subscribers that it can serve by usingfrequency re-use.

The frequency reuse is performed by dividing the whole availablefrequencies between a group of neighboring cells which is calledfrequency reuse patternor a Cluster, and then repeat this cluster

over the whole network

Frequency Reuse


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128

3/9 cluster in which the available frequencies are divided into 9groups and distributed between 3 sites

4/12 cluster in which the available frequencies are divided into 12groups and distributed between 4 sites

7 / 21 cluster in which the available frequencies are divided into 21groups and distributed between 7 sites

But we must take into consideration two types of interference:

1- Co- Channel Interference

2- Adjacent Channel Interference

Co- Channel Interference


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129

Co-channel interference is caused by short distance between the cell and other cell thatuse the same frequency.

To overcome this type of interference. Each frequency is reused after the same distanceD

Reuse Plan = (D/R)2 = 3N. Where N is the number of cells per cluster

Adjacent Channel Interference

d f h f h f d k f h


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130

Adjacent frequencies, that are frequencies shifted 200kHz from the carrierfrequency, must be avoided in the same cell and preferably in neighboring cellsalso .

To overcome this type we must make good planning for the frequencies in thecluster

Frequency Planning


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131

A3A2

A1

B3B2

B1C3

C2C1

A3A2

A1

B3B2

B1C3

C2C1

B3

B2B1

C3 C2C1

A3A2

A1

B3B2

B1C3

C2C1

A3A2

A1

C3B3A3C2B2A2C1B1A1Frequency

group

727170696867666564

Channels818079787776757473

878685848382

Frequency Planning


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132

In a real network the allocation of channels to cells will not be asuniform as in table, as some cells will require more channels and

some will require less.

In this case, a channel may be taken from a cell with low traffic

load and moved to one with a higher traffic load.

However, if doing so, it is important to ensure that interference is

still minimized.

Which Cluster Size to use?


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133

Carrier to interference ratio Its the difference in power level between the carrier in a given cell and the same

carrier received from the nearest cell that reuses the same frequency.

Number of frequenciesper site

Traffic ChannelsC/I Ratio

3/9 High High Low

4/12 Medium Medium Medium

7/21 Low Low High

Introduction to Cell Planning


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134


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2006-01-24 Lecture 1 135

Radio Transmission problems


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1

As it was stated before that the mobile telecommunications will use

radio transmission as the transmission technique; the radio transmissionis suffering from many problems which causing unacceptable degradation

of the service quality.

We will discuss these problems in details during our course.



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2

1. Path Loss

2. Multipath Fading

a. Rayleigh Fading

b. Time Dispersion

3. Time Alignment



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3

1. Path Loss

Cause

Due to Increasing distance between MS, and BTS.

Solution

Handover

p



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5

2. Multipath Fading

Cause

Due to different paths of signals between MS, and BTS.

Which cause fading dips as a result of different in phase and amplitude

Solution

Diversity

a. Space Diversity

b. Polarization Diversity

c. Frequency Diversity ( Frequency Hopping)



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3. Time AlignmentCauseDue to different distance of different MSs from BTS (Near-Far)

Solution

Time Advance

7



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2006-01-24 Lecture 1 141

GSM Terrestrial Interfaces


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142

The standard interfaces used are as follows: 2 Mbit/s.

Signaling System ITU-TSS #7 (C7 or SS#7).

X.25 (packet switched data); (LAPB).

Abis using the LAPD protocol (Link Access Procedure D). Whatever the interfaces and whatever their function, they will often share a

common

physical bearer (cable) between two points, for example, the MSC and a

BSS.



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/


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145

2 Mbit/s Trunk 30-channel PCM

This diagram opposite shows the logical GSM system with the 2 Mbit/s interfaces

highlighted.

They carry traffic from the PSTN to the MSC, between MSCs, from an MSC to a BSC

and from a BSC to remotely sited BTSs.

These links are also used between the MSC and IWF. Each 2.048Mbit/s link provides thirty 64 kbit/s channels available to carry speech, data, or

control information.

The control information may contain C7, LAPD or X.25 formatted information.

These 2 Mbit/s links commonly act as the physical bearer for the interfaces used

between the GSM system entities.



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146

X.25 Interfaces


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147

The X.25 packets provide the OMC with communications to all the entities over

which it has control and oversight.

Note that the X.25 connection from the OMC to the BSS may be nailed through

or (permanently connected by software) at the MSC, or may be supported by a

completely independent physical route.

X.25 Interfaces


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Signaling System #7


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C7 Interfaces SS7 Signaling System #7

The diagram opposite illustrates the use of C7 in the GSM system; carrying signalingand control information between most major entities, and to and from the PSTN.

Used to communicate between the different GSM network entities.

Between the MSC and the BSC, the Base Station System Management

Is used between the MSC and the VLR, EIR, and HLR.

Signaling System #7


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A-bis (LAPD) Interfaces


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151

a different type of interface is required. To Communicate between BTS and BSC

GSM has specified the use of LAPD A-bis.

The GSM specifications for this interface (termed A-bis) are not very specific and

therefore interpretations of the interface vary. This means that one manufacturers

BTS will not work with another manufacturers BSC.

As we have already mentioned, the functionality split between the BTS and BSC is

also largely in the hands of the manufacturer and therefore it is unlikely that they

would operate together, even if this interface were rigidly enforced by the

specifications.

A-bis (LAPD) Interfaces


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Interface Names


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The GSM System Interface Names


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154

GSM Transmission Process


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Segmentation

Speech Coding

Channel Coding

Interleaving

Encryption

A/D Conversion

Burst Formatting

Modulation and

Transmission

Analog to Digital Conversion


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Analog to digital conversion takesplace in 3 steps:

1. Sampling2. Quantization3. Coding

1. Sampling

Telecommunication systems use Sampling rate = 8 Ksample/s

Segmentation

Segmentation refers to the process of partitioning a digital information into


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1 2 3 4 5 6 7 8 9 10 11 12 13 0 1 2 3 4 5 6 7 8 9 10

1 2 3 4 . . . . . . . . . . . . . . . 160

160 sample in 20 ms = 1 Segment

Segmentation refers to the process of partitioning a digital information into

multiple regions . The goal of segmentation is to simplify and/or change the

representation of an image into something that is more meaningful and easierto analyze.

Interleaving

Interleaving in computer science is a way to arrange data in a non-contiguous way


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158

Interleaving in computer science is a way to arrange data in a non-contiguous way

in order to increase performance.

It is used in:

time-division multiplexing (TDM) in telecommunications .

computer memory.

disk storage.

Interleaving


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Second Level Interleaving

1 A T

2 A T

3 A T

4 A T

1 B T 5 A

2 B T 6 A

3 B T 7 A

4 B T 8 A

1 C T 5 B

2 C T 6 B

3 C T 7 B

4 C T 8 B

1 D T 5 C

2 D T 6 C

3 D T 7 C

4 D T 8 C

1

2

3

4

5

6

7

8

20 ms Block A

1

2

3

4

5

6

7

8

20 ms Block A

1

2

3

4

5

6

7

8

20 ms Block D1

2

3

4

5

6

7

8

20 ms Block D

1

2

3

4

5

6

7

8

20 ms Block c

1

2

3

4

5

6

7

8

20 ms Block c

1

2

3

4

56

7

8

20 ms Block B

1

2

3

4

56

7

8

20 ms Block B

Modulation / Demodulation in GSM


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GSM uses the Gaussian Minimum Shift Keying (GMSK)

Gaussian minimum-shift keying

Modulation / Demodulation in GSM

Gaussian minimum shift keying or GMSK is a continuous-phase frequency-shift


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keying modulation scheme. It is similar to standard minimum-shift keying (MSK);

however the digital data stream is first shaped with a Gaussian filter before beingapplied to a frequency modulator. This has the advantage of reducing sideband

power, which in turn reduces out-of-band interference between signal carriers in

adjacent frequency channels.


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Open

Discussion

Vendors :-

Communication Companies


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Communication Companies


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Services and subcontractors

CIVIL Telecom

Different kinds of engineers


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Telecom Civil

Power Mechanical

Target Job


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Good Luck

Eng / Mohamed [email protected]

01004758147

Documents

GSM_All, WCDMA , LTE