Global System for Mobile Communications (GSM)

Study Global System for Mobile Communications (GSM)

and Simulate the Communication Process

Implemented In comprehensive professions Institute

Using WATS 2002 ModulePrepared by

SAMUEL OCHIENG

BDO

Overview

• Global System for Mobile Communications definition• Main project chapters– Introduction to Mobile Communication Systems– GSM Overview– GSM Network Planning– Operation & Performance– system simulation

GSM Definition

• Global System for Mobile (GSM) is a second generation cellular standard developed to cater voice services and data delivery using digital modulation

• Is defined as a digital mobile telephony system that is widely used in Europe and other parts of the world

Introduction to Mobile Communication Systems

• Introduction• Definition in Mobile Communication systems– Multiple Access

• Frequency Division Multiple Access • Time Division Multiple Access• Code Division Multiple Access


– Duplexing• Frequency Division Duplexing• TimeDivision Duplexing


• Cellular concept

• Evolution of Mobile Systems– First Generation 1G– Second Generation 2G– 2.5 Generation 2.5G– Third Generation 3G– Fourth Generation 4G

GSM Overview

• GSM History– In the early 1980s, stimulated by the authorities, the CEPT

administrations created the group special mobile with the aim of developing a Pan-European standard for digital cellular communications.

– In 1986 the European Commission proposed to reserve the 900 MHz spectrum band for GSM

– Phase I of the GSM specifications were published in 1990.– the first 1900 MHz GSM network in the world became

operational in the United States

GSM Overview• GSM Architecture– The Base Station Subsystem (BSS).– The Network and Switching Subsystem (NSS). – The operation support subsystem(OSS)

GSM Overview

• GSM Frequency Spectrum Allocation– GSM uses Frequency Division Duplexing (FDD) where the

uplink and downlink of each channel operates on a different frequency

GSM Overview• GSM Channels– Physical Channel

• The physical channel is defined as the combination of Time Slot (TS) number and an Absolute Radio Frequency Channel Numbers (ARFCNs)

– Logical Channel• Each physical channel in a GSM system can be mapped into different logical channels at different times.

• There are two types of GSM logical channels.– Traffic channels (TCHs)– Control channels (CCHs)

GSM Network Planning

• Radio Wave Propagation– Most cellular radio systems operate in urban areas where

there is no direct line-of-sight path between the transmitter and the receiver

– Due to multiple reflections from various objects, the electromagnetic waves travel along different paths of varying lengths.

– The interaction between these waves causes multipath fading at a specific location, and the strengths of the waves decrease as the distance between the transmitter and receiver increases.


• Mobile Environment and Signal Fading – The mobile environment plays a key role to the mobile

communication link (mobile channels). – The main factors that determine the propagating

environment are: • Natural landforms (mountains, hills, plains or water area, etc. )• Number, height, allocation and surface material of buildings• Local vegetation• Climate• Natural and man-made electromagnetic environment and noise

condition.

GSM Network Planning• Radio Line of Sight– Radio transmission requires a clear path between

antennas known as radio line of sight.– Line of sight is the direct free-space path that exists

between two points.– The following obstructions might obscure a visual link:

• Topographic features, such as mountains.• The curvature of the Earth.• Buildings and other man-made objects.• Trees.

GSM Network Planning• Radio Line of Sight– The Fresnel zone for a radio beam is an elliptical area

immediately surrounding the visual path– The necessary clearance for the Fresnel zone can be

calculated, and it must be taken into account when designing a wireless links.

– when a hard object protrudes into the signal path within the Fresnel zone, knife-edge diffraction can deflect part of the signal and cause it to reach the receiving antenna slightly later than the direct signal.


• Radio Line of Sight– There are several options to establish or improve the line

of sight:• Raise the antenna mounting point on the existing structure.• Build a new structure, i.e. radio tower, which is tall enough to

mount the antenna.• Increase the height of an existing tower.• Locate a different mounting point, i.e. building or tower, for the

antenna.• Cut down problem trees

GSM Network Planning• Handovers– One of the key elements of a mobile phone is that it is able

to move and still remain connected. – Handover is: an automatic change of the responsible BTS

without influence on the quality of a connection.– Process

• Measurement• Initiation of handover• Switching to new BTS

– Handover Types• Intracell handover• Handover between two cells of the same BSC area (intercell)• Handover between two cells of different BSC areas (intercell)• Handover between different MSCs


• Radio Wave Propagation Loss Prediction and Calculation – In free space, there is no reflection, refraction, scattering,

diffraction, absorption, etc. to the radio wave, there is only the fading caused by diffusion.

– the basic propagation loss Lbf can be calculated with the formula below:

– Common propagation models used in GSM network planning are Okumura-Hata and COST231

kmMHzbf dfL log20log205.32


• Radio Wave Propagation Loss Prediction and Calculation – Okumura proposed an experience-oriented propagation

loss formula, which is -Hata Model• HATA so-called Okumura-Hata model.

– COST-231 Model • For 1,800MHz, use COST -231 model.• The propagation loss formula:

t))(lglg55.69.44()(lg82.13lg16.2655.69 dhhahfL bmb -+--+=b cities

r))(lglg55.69.44()(lg82.13lg9.333.46 dhhahfL bmb -+--+=b cities


• Determining Various Types of Losses– Breakthrough loss of the building – Human Body Loss– In-vehicle Loss

GSM Operation & Performance

• Operations– Initialization

• The mobile needs to connect to the network so it can be ready to make and receive calls.

– Call initiation• When a call is made from a mobile the network will request

authentication and, if successful, the call can commence.

– Receiving a call• The mobile receives the paging message, which alert it that he

have a call.

– Ending a call• A call may be terminated by either end of the connection.


• Mobile Terminated Call– 1: Calling a GSM subscribers– 2: Forwarding call to GSMC– 3: Signal Setup to HLR– 4,5: Request MSRN from VLR– 6: Forward responsible MSC to

GMSC– 7: Forward Call to current MSC– 8,9: Get current status of MS– 10,11: Paging of MS– 12,13: MS answers– 14,15: Security checks– 16,17: Set up connection


• Performance characteristics of GSM– Communication– Total mobility– Worldwide connectivity– High capacity– High transmission quality– Security functions

• Disadvantages of GSM– Reduced concentration while driving– Electromagnetic radiation– High complexity of the system– Abuse of private data possible


• Mobile Services– There are three service domains

• Bearer Services• Tele Services• Supplementary Services

– Bearer Services• Include various data services for information transfer between

GSM and other networks• Telecommunication services to transfer data between access

points


– Tele Services• Telecommunication services that enable voice communication via

mobile phones.• Offered services

– Mobile telephony– Emergency calling

• Short Message Service (SMS) • Voice mailbox• Electronic mail

– Supplementary services• Call related services

– Call Waiting- Notification of an incoming call while on the handset– Call Hold- Put a caller on hold to take another call– Call Barring- All calls, outgoing calls, or incoming calls– Automatic call-back


• Security in GSM– Security services

• Access control/authentication• Confidentiality• Anonymity• 3 algorithms specified in GSM

System simulationPart I

• In this part, various wave characteristics occurring under the mobile communication wave environment will be tested.• Phase Delay• Attenuation Characteristics• Multipath Fading


• Phase Delay:

NO

Phase Delay [degre

e]

Fading Level [dBm]

Direct Received Level [dBm]

1 0 -7 -10

2 40 -8.4 -9.8

3 60 -10 -9.8

4 90 -12.5 -10

5 120 -16.2 -10

6 150 -22.7 -10.2

7 180 -40.3 -10.6


• Attenuation Characteristics :

NO

Attenuation Value[dB]

Combined level [dBm]

Direct Received Level [dBm]

1 0 -7.4 -12.3

2 -4 -10.4 -12.5

3 -10 -11.1 -12.5

4 -16 -11.7 -12.3

5 -20 -11.8 -12.5


• Multipath Fading:

NO

Path1Attenuati

on

Path1Phase

Path2Attenuati

on

Path2Phase

FadingLevel

Direct Receiv

ing Level

1 -10 dB 0 -8 dB 45 -13.9 -9.8

2 -10 dB 0 -8 dB 135 -17.2 -9.8

3 -10 dB 60 -8 dB 45 -15.4 -9.8

4 -10 dB 60 -8 dB 135 -19.4 -10

5 -10 dB 120 -8 dB 45 -17.8 -10

6 -10 dB 120 -8 dB 135 -24.2 -9.8

7 -10 dB 180 -8 dB 45 -17 -9.8

8 -10 dB 180 -8 dB 135 -40.4 -10

System simulationPart II

• Simulate the communication process– In this process we will follow the stages of the connection

between the two phones in two different networks, and will use Flash technology to simulate the connection process.

Conclusion

• GSM system is basically designed as a combination of three major subsystems (BSS, NSS, OSS) that interact between themselves and with the users through certain network interface.

• The mobile environment and the line of sight plays a key role to the mobile communication link (mobile channels).

• As a result of rapid development in telecommunications, GSM system does not fully satisfy the people needs. considering that there's other systems which already in use like UMTS and for now 4G systems.

Thanks to all of you for baring with me

I hope you enjoyed this

presentation

Thank you

السالم عليكم

Business

Global System for Mobile Communications (GSM)