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Abstract

GSM (Global System for Mobile Communications) is the most popular standard for mobile phones in the world. GSM enables subscribers to use their phones in many parts of the world. GSM is a cellular network, which means that mobile phones connect to it by searching for cells. There are five different cell sizes in a GSM network, macro. micro, pico, femto and umbrella cells. The coverage area of each cell varies according to the implementation environment. Macro cells can be regarded as cells where the base station antenna is installed on a mast or a building above average roof top level. Micro cells are cells whose antenna height is under average roof top level; they are typically used in urban areas. Picocells are small cells whose coverage diameter is a few dozen metres; they are mainly used indoors. Femtocells are cells designed for use in residential or small business environments and connect to the service provider’s network via a broadband internet connection. Umbrella cells are used to cover shadowed regions of smaller cells and fill in gaps in coverage between those cells.
Mobile services based on GSM technology were first launched in Finland in 1991. Today, more than 690 mobile networks provide GSM services across 213 countries and GSM represents 82.4% of all global mobile connections. According to GSM World, there are now more than 2 billion GSM mobile phone users worldwide. GSM World references China as "the largest single GSM market, with more than 370 million users, followed by Russia with 145 million, India with 83 million and the USA with 78 million users."
GSM Versions : GSM versions are :
 GSM 900
 GSM 1800 - Also called DCS (Digital Cellular System)
 GSM 1900 - Also called PCS (Personal Communication System)
 GSM Rail
GSM Network: GSM provides recommendations, not requirements. The GSM specifications define the functions and interface requirements in detail but do not address the hardware. The reason for this is to limit the designers as little as possible but still to make it possible for the operators to buy equipment from different suppliers. The GSM network is divided into three major systems:
 Switching system (SS),
 The base station system (BSS),
 The operation and support system (OSS).
The Switching System
The switching system (SS) is responsible for performing call processing and subscriber-related functions. The switching system includes the following functional units.
• home location register (HLR)—The HLR is a database used for storage and management of subscriptions. The HLR is considered the most important database, as it stores permanent data about subscribers, including a subscriber's service profile, location information, and activity status. When an individual buys a subscription from one of the PCS operators, he or she is registered in the HLR of that operator.
• mobile services switching center (MSC)—The MSC performs the telephony switching functions of the system. It controls calls to and from other telephone and data systems. It also performs such functions as toll ticketing, network interfacing, common channel signaling, and others.
• visitor location register (VLR)—The VLR is a database that contains temporary information about subscribers that is needed by the MSC in order to service visiting subscribers. The VLR is always integrated with the MSC. When a mobile station roams into a new MSC area, the VLR connected to that MSC will request data about the mobile station from the HLR. Later, if the mobile station makes a call, the VLR will have the information needed for call setup without having to interrogate the HLR each time.
• authentication center (AUC)—A unit called the AUC provides authentication and encryption parameters that verify the user's identity and ensure the confidentiality of each call. The AUC protects network operators from different types of fraud found in today's cellular world.
• equipment identity register (EIR)—The EIR is a database that contains information about the identity of mobile equipment that prevents calls from stolen, unauthorized, or defective mobile stations. The AUC and EIR are implemented as stand-alone nodes or as a combined AUC/EIR node.
The Base Station System (BSS)
All radio-related functions are performed in the BSS, which consists of base station controllers (BSCs) and the base transceiver stations (BTSs).
• BSC—The BSC provides all the control functions and physical links between the MSC and BTS. It is a high-capacity switch that provides functions such as handover, cell configuration data, and control of radio frequency (RF) power levels in base transceiver stations. A number of BSCs are served by an MSC.
• BTS—The BTS handles the radio interface to the mobile station. The BTS is the radio equipment (transceivers and antennas) needed to service each cell in the network. A group of BTSs are controlled by a BSC.
The Operation and Support System
The operations and maintenance center (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 the network 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.

GSM Services :

 GSM System provides integration of voice and data services.
 Integration with PSTN and ISDN.
 Services are what customer care about.
 GSM services are categorized into three :
 Bearer Services
 Tele Services
 Supplementary Services

Bearer Services : Bearer services enable transmission of data and voice.

Bearer services are divided into two parts :
 Transparent services
 Non-transparent services

Transparent Services :

 Make only use of functions of physical layer (PHY).
 Data transmission has constant delay and constant throughput
 Use only FEC
 No retransmissions
 Data rates: 2.4, 4.8, 9.6 Kbps (depending on FEC used)

Non-transparent Services :

 Make only use of functions of layers two and three
 Can have retransmission
 Can implement flow control
 Very low error rate
 Delay and throughput may vary depending on quality

Tele Services : Main focus of tele services is on voice and encrypted voice.

Other services include :
 Message Services :
 Short messaging service (message <= 160 chars)
 SMS Applications : road conditions, stock quotes, news, e-mail header etc.
 EMS : Enhanced messaging service (message <= 760 chars)
 Small images, animated pictures can be used.
 MMS : Multimedia messaging service
 Large pictures : GIF, JPEG
 Short video clips
 Fax service


Supplementary Services : Supplementary services include :
 Caller identification
 Call forwarding
 Multi-party communication

Features Of GSM :

Localisation & Calling Of GSM :

One of the main features of GSM system is the automatic, worldwide localisation of it’s users. The GSM system always knows where a user is currently located, and the same phone number is valid worldwide. To have this ability the GSM system performs periodic location updates.
The HLR (home location register) contains information about the current location, and the VLR that is currently responsible for the MS informs the HLR about the location of the MS when it changes. Changing VLRs (visitor location register) with uninterrupted availability of all services is also called roaming.

To locate an MS and to address the MS, several numbers are needed:
MSISDN (Mobile Station International ISDN Number) : The only important number for the user of GSM is the phone number, due to the fact that the phone number is only associated with the SIM, rather than a certain MS.
IMSI (International Mobile Subscriber Identity) : GSM uses the IMSI for internal unique identification of a subscriber.
TMSI (Temporary Mobile Subscriber Identity) : To disguise the IMSI that would give the exact identity of the user which is signaling over the radio air interface, GSM uses the 4 byte TMSI for local subscriber identification. The TMSI is selected by the VLR and only has temporary validity within the location area of the VLR. In addition to that the VLR will change the TMSI periodically.
MSRN (Mobile Station [Subscriber] Roaming Number) : This is another temporary address that disguises the identity and location of the subscriber. The VLR generates this address upon request from the MSC and the address is also stored in the HLR. The MSRN is comprised of the current VCC (Visitor Country Code), the VNDC (Visitor National Destination Code) and the identification of the current MSC together with the subscriber number, hence the MSRN is essential to help the HLR to find a subscriber for an incoming call.
All the numbers are needed to find a user within the GSM system, and to maintain the connection with a mobile station.

[attachment=6084]
DSP/MATLAB GSM SIMULATION

Description:
Global system for mobile communication (GSM) network is composed of several functional entities, whose functions and interfaces are specified. The GSM network can be divided into three broad parts. The Mobile Station is carried by the subscriber. The Base Station Subsystem controls the radio page link with the Mobile Station. The Network Subsystem, the main part of which is the Mobile services Switching Center (MSC), performs the switching of calls between the mobile users, and between mobile and fixed network users. The MSC also handles the mobility management operations.

[attachment=6354]
[attachment=6355]

GSM Traffic Channel

Traffic Channels carries Speech and data.
Types of traffic channels :
Full Rate, EFR and Half rate
Full rate
TCH/FS: Speech (13 kbit/s net, 22.8 kbit/s gross)
TCH/EFR: Speech (12.2 kbit/s net, 22.8 kbit/s gross)
TCH/F9.6: 9.6 kbit/s – data
TCH/F4.8: 4.8 kbit/s – data
TCH/F2.4 2.4 kbit/s – data
Half rate
TCH/HS: speech (6.5 kbit/s net, 11.4 kbit/s gross)
TCH/H4.8 4.8 kbit/s – data
TCH/H2.4 2.4 kbit/s – data

Control channel groups(Contd)


BCCH Group: DL only ---- every 30 secs,Continually broadcasts MS’s present cell information, surrounding cells information, information including base station identity, frequency allocations, and frequency-hopping sequences.
SCH:Frame Synchronization
FCCH:Carrier synchronization (Frequency locking)
CCCH:UL and DL.—call origination and call paging
RACH:MS uses to access the network for call setup or responds to a page.
AGCH:used to allocate an SDCCH to a mobile for signalling(in order to obtain a dedicated channel), following a request on RACH
PCH:Used to alert the mobile of an incoming call.
DCCH:UL and DL---for call setup an validation.
SDCCH:carries data to and from MS during call setup and validation.
SACCH:Link measurement and power control messages.
FACCH:to carry event type messages like handovers. used during call establishment.

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GLOBAL SYSTEM
FOR
MOBILE COMMUNICATION


Guided by:-
Satya Ranjan Biswal

Presented by:-
Suvendu Kumar Pani
Regd no. -0701289238
IT

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This article is presented by:Ravi Kesh Mishra
MIT, Manipal

GSM

INTRODUCTION
GSM (Global System for Mobile Communications):
The GSM is a set of recommendations and specifications for a digital cellular phone network (known as Public Land Mobile Network, PLMN). These recommendations ensure the compatibility of the equipment from different GSM manufacturers and interconnectivity between different administrations. GSM was designed with a moderate level of service security. The system was designed to authenticate the subscriber using a pre-shared key and challenge response. Communications between the subscriber and the base station can be encrypted.
CELLULAR TELEPHONY
• A cellular telephone system links mobile subscribers into the public telephone system or to another cellular subscriber.
• Information between the mobile unit and the cellular network uses radio communication. Hence the subscriber is able to move around and become fully mobile.
• The service area in which mobile communication is to be provided is divided into regions called cells.
• Each cell has the equipment to transmit and receive calls from any subscriber located within the borders of its radio coverage

GSM Phases:
The original version of GSM were released in various phases each adding on some features
on the existing phase. The various phases are:
1. Phase I:
This phase contains the most common services such as:
 Voice Telephony
 International Roaming
 Call forwarding
 Call barring
 Short Message Service(SMS)
Phase I also incorporated features like ciphering and Subscriber Identity Module (SIM).
Phase I features were then closed and cannot be modified.
2. Phase II:
Additional features included in Phase II are:
 Advice of charge
 Call line identification
 Call waiting
 Call hold
 Conference calling
 Additional data communication capabilities
3. Phase 2+:
The Phase 2+ program will cover multiple subscriber numbers and a variety of
business oriented features. Some of the enhancements include:
 Multiple service profiles
 Private numbering plan
 Access to Centrex services


Features of GSM:
 The GSM system provides a greater subscriber capacity than analogue systems.
 Digital transmission of speech and high performance digital signal processors provides good
quality speech transmission.
 Since GSM is a digital technology, the signals passed over a digital air interface can be
protected against errors by using better error detection and correction techniques.
 In regions of interference or noise-limited operation the speech quality is noticeably better
than analogue.
 GSM offers high data and speech confidentiality.
 In a GSM system the mobile station and the subscriber are identified separately
.
 The subscriber is identified by means of a smart card known as a SIM.
 This enables the subscriber to use different mobile equipment while retaining the same
subscriber number.
GSM carrier frequencies:
GSM networks operate in a number of different carrier frequency ranges (separated into
GSM frequency ranges for 2G and UMTS frequency bands for 3G), with most 2G GSM networks
operating in the 900 MHz or 1800 MHz bands. Where these bands were already allocated, the
850 MHz and 1900 MHz bands were used instead.
Regardless of the frequency selected by an operator, it is divided into timeslots individual phones to
use. This allows eight full-rate or sixteen half-rate speech channels per radio frequencies. These eight
radio timeslots are grouped into a TDMA frame. Half rate channels use alternate frames in the same
timeslot. The channel data rate for all 8 channels is 270.833 Kbit/s, and the frame duration is
4.615 ms.
The transmission power in the handset is limited to a maximum of 2 watts in GSM850/900 and 1
watt in GSM1800/19.