I attached the Ppt of GSM system, this PowerPoint slides is useful for those who want to know in-depth GSM system.

1. Global System for Mobile
Communications
Prepared by: Sanat Varasada
Florida Polytechnic University,
Lakeland, Florida

2. About GSM
Global System for Mobile communication
(GSM) is a cellular standard developed to
improve voice services and data delivery.

3. GSM Specifications
GSM 900
Mobile to BTS (uplink): 890-915 MHz
BTS to Mobile(downlink):935-960 MHz
Bandwidth : 25 MHz
GSM 1800
Mobile to BTS (uplink): 1710-1785 MHz
BTS to Mobile(downlink) 1805-1880 MHz
Bandwidth : 75 MHz

4. GSM architecture….
1. MSS (Mobile Station Sub-system)
# ME (Mobile Equipment)
# SIM (Subscriber Identity Module)
2. BSS (Base Station Sub-system)
# BTS (Base Transceiver Station)
# BSC (Base Station Controller)
3. NSS (Network Station Sub-system)
# MSC (Main Switching Center) & more….

5. GSM System Architecture

6. 1. Mobile Station Subsystem(MSS)
 The Mobile Station is made up of two entities:
i. Mobile Equipment (ME)
ii. Subscriber Identity Module (SIM)

7. .
i. Mobile Equipment (ME):-
The ME is the hardware used by the subscriber to access the
network. The hardware has an identity number associated with it,
which is unique for that particular device and permanently stored in it.
This identity number is called the International Mobile Equipment
Identity (IMEI)

8. • IMEI Structure
TAC: It indicated that the particular device was approved by a national
GSM approval body.
FAC: It identified the company that had built and assembled the device.
SNR: It assigned by manufacturer
SP: Check digit
It uniquely characterizes a mobile station and gives clues about the
manufacturer and the date of manufacturing.

9. The SIM is a card which plugs into the ME. This card identifies the MS
subscriber and also provides other information regarding the service
that subscriber should receive. The subscriber is identified by an
identity number called the International Mobile Subscriber Identity
(IMSI). SIM also contain PIN, PUK and ICCID number. Mobile Equipment
may be purchased from any store but the
SIM must be obtained from the GSM network provider. Without the
SIM inserted, the ME will only be able to make emergency calls.
ii. Subscriber Identity Module(SIM):-

10. 2. BSS(Base Station Subsystem)
 Base Station Subsystem is composed of two parts:
i. Base Transceiver Station (BTS)
ii. Base Station Controller (BSC)

11. i. Base Transceiver Station (BTS):-
A base transceiver station (BTS) is a piece of equipment that
facilitates wireless communication between user equipment (UE)
and a network. It transmits and receives RF signals from & to MS.
The area covered by one BTS is called as cell.

12. Cell concept
• Areas divided into cells
– Each cells served by its own antenna
– Served by base station consisting of transmitter, receiver,
and control unit
– Band of frequencies allocated
– Cells set up in hexagonal pattern

13. Why hexagonal cell ?

14. Cell planning
Macro cell: 1 – 20 mile. Normally the
site location is on a hilltop or rooftop.
Micro cell: 0.5 – 1.5 mile. Normally site
location is on the building or under a
roof.
Pico cell: Up to 0.3 mile. It’s use for
small coverage area. Normally located
inside the building.

16. Approaches to cope with Increasing
capacity
• Cell Splitting
• Cell Sectoring
Why cell splitting and sectoring?
As users increases channel capacity decreases
Both techniques are needed to provide extra channels

17. • Cell sectoring
The sectoring is done by Replacing a single Omni-directional
antenna with 3 direction antennas (120 degree) or with 6
directional antennas (60 degree) at the base station by several
directional antenna.

18. • Cell splitting
Cell splitting is the process of splitting a cell into smaller cells.
The splitting is usually done on demand, when in a certain cell there is
too much blocking of calls.

19. ii. Base Station Controller (BSC)
The Base Station Controller (BSC) controls the working of one or more
Base Transceivers. It handles radio-channel setup, handovers etc.
Numbers of BSCs are connected to MSC. Thus BSC is the connection
between the mobile station and the Mobile Switching Center (MSC).

20. BSS Configurations
• chain Configurations
• Star configurations
• Loop configurations

21. Chain Configuration

22. Star Configuration

23. Loop configuration

24. Handover
- Changing the point of connection while communicating.
- In other words, when mobile users travel from one cell to another cell.

25. Types of handover
• Soft handover: Mobile users
move from one BTS to other BTS
• Softer handover: Mobile users
move from one sector to
another sector within one cell.
When will a handover occur?
When received signal level drops below a certain signal level.

26. Improper and Proper handovers
Improper handover
Proper handover

27. Handover signaling

28. 3. NSS(Network Switching Subsystem)
 The Network switching system (NSS), the main part of which is the
Mobile Switching Center (MSC), performs the switching of calls
between the mobile and other fixed or mobile network users, as
well as the management of mobile services such as authentication.

29. i. Mobile Switching Centre (MSC)
The MSC is included in the GSM system for call-switching.
The functions carried out by the MSC are listed below:-
 Manages communication between GSM and other networks
 Call setup function and basic switching
 Call routing
 Billing information and collection
 Mobility management
- Registration
- Location Updating
- Handovers

30. • permanent database about mobile subscribers in a large service
area.
• Any administrative action by the service provider or changes made
by subscriber is first carried out on the HLR and then update the
VLR.
 data in HLR:-
– IMSI number.
– Roaming restriction (allowed or not).
-- Supplementary services like call forwarding
-- Messages waiting data used for SMS
ii. Home Location Register (HLR)

31. The only way via which HLR communicates with other GSM nodes is
Mobile Access Protocol. Other functions defined on the MAP are:
- Update HLR and VLR
- Fault Recovery
- Retrieval of subscriber data during call setup.
- Security related data

32. iii. Visitor Location Register (VLR)
 It is a subscriber database containing the information about all the
MS currently located in the MSC service area. If MS moves into a
new service area, VLR requests the HLR to provide the relevant data
and store it, for making the calls for that MS.
 VLR is always integrated with MSC to avoid the signaling load on the
system.
 The additional data stored in the VLR is listed below:
Location updating and registration
Updating the mobile subscriber data.
Maintain the security of the subscriber by allocating TMSI.
Receiving and delivering short messages

33. Location update

34. iv. Authentication Centre (AUC)
Authentication is required at each registration, at each call setup
attempt, at the time of location updating, before supplementary
service activation, de-activation , registration.
-- Providing the authentication key used for authorizing the
subscriber access to the associated GSM Network.
-- it is linked to the MSC and checks the identity of each user trying
to connect.
-- Stores IMSI number

35. v. Equipment Identity Register (EIR)
-- The Equipment Identity Register (EIR) is a database that contains a
list of all valid mobile equipment on the network, where its
International Mobile Equipment Identity (IMEI) identifies each
mobile station.
1. White List
Contains those IMEIs which are
known to have been assigned to
valid MS equipment.
2. Grey List
Contains IMEIs of MS which have problems.
3. Black List
Contains IMEIs of MS which are to be denied
service for some other reason.

37. Public Switched Telephone Network (PSTN)
The PSTN consists of telephone lines, fiber optic
cables, microwave transmission links, cellular networks,
communications satellites, and undersea telephone cables, all
interconnected by switching centers, thus allowing most
telephones to communicate with each other.

38. Operation and Maintenance Centre
• The centralized operation of the various units in the system
and functions needed to maintain the subsystems.
• Fault report & alarm handling
• Storage of systems software and data
• Traffic monitoring
• Status reports of networks
• Configuration management

40. GSM network protocols
1. MAP: Mobile Access Protocol
2. BSSAP: BSS Access Protocol
3. LAP: Link Access Protocol

41. GSM control channels
BCCH Broadcast Control Channel – Continuously transmitted from the BTS. Contains information
about cell identity, frequency etc.
FCCH
SCH
Frequency Correction Channel / Synchronisation Channel – Used to correct/synchronise the
frequency (FCCH) + time synchronise to the frame structure. Each cell has a FCCH and a
SCH
RACH Random Access Channel – Used by the mobile to send a request to the network for access.
AGCH Access Grant CHannel – Used by the network to inform the mobile that access has been
granted and information about which channel to use
PCH Paging Channel – Used by the network to notify users about incoming calls.

42. Handover system
Between 1 and 2
Inter BTS / Intra BSC ( Soft
handover)
Between 1 and 3
Inter BSC/ Intra MSC
Between 1 and 4
Inter MSC

43. Call Detail Recorders
• CDRs contain the following information:
- Subscriber Identity
- Number called
- Call Length
- Route of call

44. Mobile Originated Call

45. Mobile Terminated Call

46. 1. GSM in US