GSM

Prepared by: Eng. Samir Jasim Ahmed Page 1

GSM Global System for Mobile

Communication

Fourth stage

Prepared by:

Eng. Samir Jasim Ahmed

GSM

Prepared by: Eng. Samir Jasim Ahmed Page 2

1- GSM Overview:

GSM stands for (Global System for Mobile Communication). It is a

digital cellular technology used for transmitting mobile voice and data

services. The concept of GSM emerged from a cell-based mobile

radio system at Bell Laboratories in the early 1970s.

GSM is the name of a standardization group established in 1982 to

create a common European mobile telephone standard, is the most

widely accepted standard in telecommunications and it is implemented

globally.

The GSM system was designed as a second generation (2G) cellular

phone technology. One of the basic aims was to provide a system that

would enable greater capacity to be achieved than the previous first

generation analogue systems. GSM achieved this by using a digital

TDMA (time division multiple access approach).

GSM is a circuit-switched system that divides each 200 kHz channel

into eight 25 kHz time-slots, is operates on the mobile communication

bands 900 MHz and 1800 MHz in most parts of the world.

GSM makes use of narrowband Time Division Multiple Access

(TDMA) technique for transmitting signals, it was developed using

digital technology. It has an ability to carry 64 kbps to 120 Mbps of

data rates.

GSM provides basic to advanced voice and data services including

roaming service. Roaming is the ability to use your GSM phone

number in another GSM network.

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2- Circuit Switching System:

Is a method of implementing a telecommunications network in which

two network nodes establish a dedicated communications channel

(circuit) through the network before the nodes may communicate, for

example when a call is made from one telephone to another, switches

within the telephone exchanges create a continuous wire circuit

between the two telephones, for as long as the call lasts.

Circuit Switching System

3- Mobile Device:

The term mobile device refers to any electronic device that be easily

moved from one location to another. Over time, this category has

expanded to include cell phones, laptops, smartphones, smart watches,

and other portable devices.

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4- Fundamentals of GSM

4.1- Frequency-Division Multiplexing (FDM):

FDM is a scheme in which numerous signals are combined for

transmission on a single communications line or channel. It is analog

multiplexing technique. Each signal is assigned a different frequency

(sub channel) within the main channel. Its requires channel

synchronization.

FDM requires that the bandwidth of a link should be greater than the

combined bandwidths of the various signals to be transmitted. Thus

each signal having different frequency forms a particular logical

channel on the link and follows this channel only. These channels are

then separated by the strips of unused bandwidth called guard bands.

These guard bands prevent the signals from overlapping.

In FDM, signals to be transmitted must be analog signals. Thus digital

signals need to be converted to analog form, if they are to use FDM.

Frequency-Division Multiplexing

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4.2- Time-division multiple Multiplexing (TDM):

Is a channel access method for shared-medium networks, It allows

several users to share the same frequency channel by dividing the

signal into different time slots. It use with digital and analog

signals. The users transmit in rapid succession, one after the other,

each using its own time slot. This allows multiple stations to share the

same transmission medium while using only a part of its channel

capacity.

TDMA

4.3- Code-Division Multiplexing (CDM):

Code division multiplexing (CDM) is a multiplexing technique that

uses spread spectrum communication. In spread spectrum

communications, a narrowband signal is spread over a larger band of

frequency or across multiple channels via division. It does not

constrict bandwidth‟s digital signals or frequencies. It is less

susceptible to interference, thus providing better data communication

capability and a more secure private line.

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5- Cellular Network:

A cellular network is a communication network where the last link

is wireless. The network is distributed over land areas called "cells",

each served by at least one fixed-location transceiver, but more

normally, three cell sites or base transceiver stations. These base

stations provide the cell with the network coverage which can be used

for transmission of voice, data, and other types of content. A cell

typically uses a different set of frequencies from neighbouring cells, to

avoid interference and provide guaranteed service quality within each

cell.

When joined together, these cells provide radio coverage over a wide

geographic area. This enables numerous portable transceivers

(e.g., mobile phones, tablets and laptops equipped with mobile

broadband modems, pagers, etc.) to communicate with each other and

with fixed transceivers and telephones anywhere in the network, via

base stations, even if some of the transceivers are moving through

more than one cell during transmission.

A cell is the geographic zone covered by one radio transmitter and

receiver.

Cellular network

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6- Evolution of Cellular Network:

6.1- 0G:

This is actually called “mobile radio telephone.” that‟s why the

system referred in retroactive terms like „zero generation‟ or we

can say „pre-cellular.‟ This system begins with technology like Motorola and the Bell

system. The commercial telecommunication the system was

introduced by it.

6.2- 1G:

The first generation of wireless cellular technology. It refers to

first generation of wireless technology. 1G network were analog.

It simply makes phone calls, this is all it was able to do.

This telecommunication standard remains until the advent of 2G.

The USA introduces its first 1G network for the Motorola

DynaTAC cellular phone.

6.3- 2G:

The second generation provided customers with the facility of

voice calling and text messaging. 2G networks are digital.

During 90s 2G was the first commercially launched network.

The important thing is that it was the first network that makes

use of data on phone calls. And also it was the first network that

offers SMS(short messaging service).

Because of this, the quality of phone calls was improved than

analogue data. It reduces the intricacies of data transmission.

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6.4- 2.75G:

It marks the evolution of GPRS to the EDGE network, which

offers fastest and improves data transmission rates than previous

ones.

But the EDGE was introduced in the pre-3G era, so the

ITU(International Telecommunication Union) officially

announced it as 3G technology.

6.5- 3G:

This technology sets the standard for most of the wireless

networks.

Third generation allowed the use of internet on the mobile

phone, while also enabling picture-sharing and Bluetooth

Connectivity.

Commercially it was launched in 2001. And it was the 1st

mobile broadband capable wireless network.

Data transmission rates of 3G networks are 200 kbps (2mbps).

It allows high data speed at low cost.

It enables different application like email, video streaming,

video call, voice call, downloading, sharing, etc.

6.6- 3.5G:

3.5G is five times faster than the 3G network.

It is a combination of two protocols HSDPA and HSUPA, i.e.

high-speed downlink packet access and high-speed uplink packet

access respectively.

It uses Wideband code division multiple access protocol.

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6.7- 3.75G:

3.75G comes with high packet access, also known as HSPA+.

It is another cellular technology which is a further evolution

of HSPA standard.

Data transmission rates are 168mbps for downloading and

22mbps for uploading it depends on condition.

These speeds were improved by using MIMO(multiple input and

multiple outputs).

6.8- 4G:

Fourth generation the latest technology till date – has completely

transformed the app and content ecosystem.

It offers first true internet broadband data transmission rates.

It was deployed in 2009 in Sweden and Norway.

Its data transmission rates are 10 times faster than 3G

technology.

It expanded over the past years to become more available for the

major metropolitan area and developed countries.

It not only gave immense speed to social media and video

streaming but also made booking movie tickets or ordering a taxi

through a few clicks on an app easy and fast! 1g 2g 3g 4g 5g technology | what is 1g | 1g 2g 3g 4g 5g | 1g 2g 3g 4g 5g

6.9- LTE:

LTE it means „long term evolution‟ this is the mobile evolution

standard for high-speed wireless internet connection for mobile

device and data terminals.

If you want to take advantage of this you have to choose the

right phone which supports LTE as it offers you more advantage

of the speed improvements. 2g 3g 4g 5g technology | what is 1g | 1g 2g 3g 4g 5g | 1g 2g 3g 4g 5g

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6.10- LTE plus:

We discussed above what is LTE! Now the LTE plus, It is the

same technology based on LTE platform as we saw above.

Except that the data transfer speeds are even fastest or we can

say triple than LTE in the LTE Plus.

6.11- 5G:

The next-generation telecom technology will bring higher speeds

to mobile phones, but it won‟t be limited only to that.

5G will be the network for millions of devices and not just for

the smartphone. It promises to enable fast (and secure)

connectivity between devices other than smartphones, such

as sensors, vehicles, robots, and drones.

Now, imagine the benefits of a technology like this.

It will change the game entirely for many industries!

Many companies come up with hardware and routers while

others have begun to the introduced 5G network.

It will have data speed up to 1 to 10 Gbps.

It is Expected that it would launch up to 2020 but the fates the

technology could come sooner than that.

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7- GSM System Architecture:

In GSM system the mobile handset is called Mobile Station (MS). A

cell is formed by the coverage area of a Base Transceiver Station

(BTS) which serves the MS in its coverage area. Several BTS together

are controlled by one Base Station Controller (BSC). The BTS and

BSC together form Base Station Subsystem (BSS). The combined

traffic of the mobile stations in their respective cells is routed through

a switch called Mobile Switching Center (MSC). Connection

originating or terminating from external telephone (PSTN) are

handled by a dedicated gateway Gateway Mobile Switching Center

(GMSC).

GSM System Architecture

GSM

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7.1- Mobile Station (MS):

A mobile station communicates across the air interface with a base

station transceiver in the same cell in which the mobile subscriber unit

is located. The MS communicates the information with the user and

modifies it to the transmission protocols if the air-interface to

communicate with the BSS. The user‟s voice information is interfaced

with the MS through a microphone and speaker for the speech,

keypad, and display for short messaging, and the cable connection for

other data terminals. The MS has two elements. The Mobile

Equipment (ME) refers to the physical device, which comprises of

transceiver, digital signal processors, and the antenna. The second

element of the MS is the GSM is the Subscriber Identity Module

(SIM). The SIM card is unique to the GSM system. It has a memory

of 32 KB.

7.2- Base Station Subsystem (BSS):

A base station subsystem consists of a base station controller and one

or more base transceiver station. Each Base Transceiver Station

defines a single cell. A cell can have a radius of between 100m to

35km, depending on the environment. A Base Station Controller may

be connected with a BTS. It may control multiple BTS units and

hence multiple cells. There are two main architectural elements in the

BSS – the Base Transceiver Subsystem (BTS) and the Base Station

Controller (BSC). The interface that connects a BTS to a BSC is

called the A-bis interface. The interface between the BSC and the

MSC is called the A interface, which is standardised within GSM.

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7.3- Network and switching subsystem (NSS):

A base station subsystem consists of a base station controller and one

or more base transceiver station. Each Base Transceiver Station

defines a single cell. A cell can have a radius of between 100m to

35km, depending on the environment. A Base Station Controller may

be connected with a BTS. It may control multiple BTS units and

hence multiple cells. There are two main architectural elements in the

BSS – the Base Transceiver Subsystem (BTS) and the Base Station

Controller (BSC). The interface that connects a BTS to a BSC is

called the A-bis interface. The interface between the BSC and the

MSC is called the A interface, which is standardised within GSM.

The NSS is responsible for the network operation. It provides the link

between the cellular network and the Public switched

telecommunicates Networks (PSTN or ISDN or Data Networks). The

NSS controls handoffs between cells in different BSSs, authenticates

user and validates their accounts, and includes functions for enabling

worldwide roaming of mobile subscribers.

In particular the switching subsystem consists of:

1. Mobile switch center (MSC)

2. Home location register (HLR)

3. Visitor location Register (VLR)

4. Authentications center (Auc)

5. Equipment Identity Register (EIR)

6. Interworking Functions (IWF)

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7.3.1 HLR:

The HLR is database software that handles the management of the

mobile subscriber account. It stores the subscriber address, service

type, current locations, forwarding address, authentication / ciphering

keys, and billings information. In addition to the ISDN telephone

number for the terminal, the SIM card is identified with an

International Mobile Subscribes Identity (IMSI) number that is totally

different from the ISDN telephone number. The HLR is the reference

database that permanently stores data related to subscribers, including

subscriber‟s service profile, location information, and activity status.

7.3.2 VLR:

The VLR is temporary database software similar to the HLR

identifying the mobile subscribers visiting inside the coverage area of

an MSC. The VLR assigns a Temporary mobile subscriber Identity

(TMSI) that is used to avoid using IMSI on the air. The visitor

location register maintains information about mobile subscriber that is

currently physically in the range covered by the switching center.

When a mobile subscriber roams from one LA (Local Area) to

another, current location is automatically updated in the VLR. When a

mobile station roams into anew MSC area, if the old and new LA‟s are

under the control of two different VLRs, the VLR connected to the

MSC will request data about the mobile stations from the HLR. The

entry on the old VLR is deleted and an entry is created in the new

VLR by copying the database from the HLR.

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7.3.3 AuC:

The AuC database holds different algorithms that are used for

authentication and encryptions of the mobile subscribers that verify

the mobile user‟s identity and ensure the confidentiality of each call.

The AuC holds the authentication and encryption keys for all the

subscribers in both the home and visitor location register.

7.3.4 EIR:

The EIR is another database that keeps the information about the

identity of mobile equipment such the International mobile Equipment

Identity (IMEI) that reveals the details about the manufacturer,

country of production, and device type. This information is used to

prevent calls from being misused, to prevent unauthorised or defective

MSs, to report stolen mobile phones or check if the mobile phone is

operating according to the specification of its type.

White list:

This list contains the IMEI of the phones who are allowed to enter in

the network.

Black list:

This list on the contrary contains the IMEI of the phones who are not

allowed to enter in the network, for example because they are stolen.

Grey list:

This list contains the IMEI of the phones momentarily not allowed to

enter in the network, for example because the software version is too

old or because they are in repair.

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7.3.5 IWF:

Interworking Function: It is a system in the PLMN that allows for non

speech communication between the GSM and the other networks. The

tasks of an IWF are particularly to adapt transmission parameters and

protocol conversions. The physical manifestations of an IWF may be

through a modem which is activated by the MSC dependent on the

bearer service and the destination network. The OSS (Operational

Support Systems) supports operation and maintenance of the system

and allows engineers to monitor, diagnose, and troubleshoot every

aspect of the GSM network.

7.4 Operation and Support Subsystem (OSS):

The OSS or operation support subsystem is an element within the

overall GSM network architecture that is connected to components of

the NSS and the BSC. It is used to control and monitor the overall

GSM network and it is also used to control the traffic load of the BSS.

It must be noted that as the number of BS increases with the scaling of

the subscriber population some of the maintenance tasks are

transferred to the BTS, allowing savings in the cost of ownership of

the system.

Public land mobile network (PLMN):

In telecommunication, a Public Land Mobile Network (PLMN) is a

combination of wireless communication services offered by a specific

operator in a specific country. A PLMN typically consists of several

cellular technologies like GSM/2G, UMTS/3G, LTE/4G, offered by a

single operator within a given country.