global system for mobile communications (gsm)
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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
Introduction to Mobile Communication Systems
– Duplexing• Frequency Division Duplexing• TimeDivision Duplexing
Introduction to Mobile Communication Systems
• 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.
GSM Network Planning
• 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.
GSM Network Planning
• 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
GSM Network Planning
• 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
GSM Network Planning
• 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
GSM Network Planning
• 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.
GSM Operation & Performance
• 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
GSM Operation & Performance
• 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
GSM Operation & Performance
• 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
GSM Operation & Performance
– 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
GSM Operation & Performance
• 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
System simulationPart I
• 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
System simulationPart I
• 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
System simulationPart I
• 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
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