kamal kiran

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  • 7/29/2019 Kamal Kiran





    Submitted in the partial fulfillment of the requirement for the award of degree of

    Bachelors of Technology


    Electronics & communication Engineering

    Department of Electronics & communication Engineering

    Swami Vivekanand Institute of Engineering & Technology

    Ramnagar, Banur

    Under the Guidance ofEr. Gaganpreet Singh

    Submitted byNavjeet Singh


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    The successful completion of any task would be incomplete without accomplishing the

    people who made it all possible and whose constant guidance and encouragement secured

    us the success

    This seems to be a fitting moment for me to express my heartfelt gratitude towards all those who

    helped me tirelessly and patiently in my training work. It gives me a great sense of pleasure to

    present this report on my Two month industrial training. Training in an organization like A

    TRAFFIC LIGHT which is fuelled by the individuals with so much zest & energy, teaming up

    to form a formidable force, was in itself a true learning experience which is going to help usimmensely in our career.

    To begin with, I express my sincere thanks to Mr. Gagandeep Singh Walia(Managing

    Director).)to my training coordinators for allowing me to avail all the available amenities in the

    division. They kept faith in me and made me an active member of my team. I am thankful to

    them for sharing their vast resource of knowledge and experience with me.

    Last but not the least I would like to express my heartfelt thanks to my teammates, who with

    their thought provoking views, veracity and whole hearted co-operation supported me throughout

    the duration of the training. I am thankful to The Institution of Electronics and

    Telecommunication Engineers (IETE) for giving me an opportunity to undertake my Two

    Months Industrial Training.


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    Telcoma Technologies Pvt. Ltd (ISO 9001:2008 Certified) is a provider ofTelecommunication and IT based solutions, including software, equipment and systemsintegration services.

    Telcoma Technologies develops and provides products, solutions, and professional services

    primarily for Telecommunications/IT companies.

    The business paradigm of Telcoma Technologies includes the following areas


    Network Solutions

    Next Generation Networks

    Wireless Broadband Service

    Data TransmissionMobile Networks

    Value-added Systems and Intelligent Networks

    Network Deployment and Integration

    New Technologies

    Operation & Business Support

    Network Monitoring

    Network and Service Management Fulfillment

    Billing and Customer Care Management

    Customized software development

    Telcoma Technologies develops customized software solutions for its clients. Our expertise

    includes Java programming, Apple iPhone/Google Android applications, PHP/MySQL, Ajax and

    Ruby on Rails.

    Web development and Internet/Intranet based Solutions

    Telcoma Technologies has completed many web projects catering to niche segment of internet

    fraternity, which include social networking sites, content management portals, dynamic websites,

    multimedia rich interactive websites with Flash and Intranet based solutions for Business

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    Automation. The sites and portalsgenerate a run-of-the-network traffic and a significantbusiness every month for our clients

    Corporate Training and IT/Telecom Education

    Telcoma Technologies has also launched various initiatives in the area of corporate trainingand IT education introducing the emerging technologies training solutions at affordable price.

    The team at Telcoma Technologies is well-qualified and strongly motivated and committed to

    providing the high level of personal service and customer satisfaction. All processes withinTelcoma Technologies are aligned towards the highest quality standards and formally certified

    to ISO 9001:2008. We "Believe in the Best", be it people, products or services. Our approach toeverything emanates from this corporate philosophy. With every new day the quest for acquiring

    new competencies continues. Forever searching, experimenting, innovating, learning, movingahead with our sincere efforts and dedication, shaping the future, and challenging our

    competencies to create new opportunities, is a never-ending proces

    100% PlacementsThe company has tie-ups with all the major companies of India such asNOKIA-SIEMENS, TATA, IDEA, ZTE, CONNECT, TATA-DOCOMO, VODAFONE, etc. The

    company assures 100% placement assistance

    Personality Development

    The company recently collaborated with IIPM, Mohali for overall personality development andcommunication skills


    Company Name: Telcoma Technologies.Faculty Members: Mr.Gagandeep Singh Walia

    Mr. Pawanjeet singh

    Mr.Kapil Bhutani

    Mrs.Rashi Gupta.Company Address: Telcoma Technologies pvt. limitedSCO 123, Phase 3B2, Mohali.

    Contact: Phone: 0172-4010731, 09814145471Website: Web:http://www.telcoma.inEmail: info@telcoma

  • 7/29/2019 Kamal Kiran



    With the ongoing telecom revolution where the innovations are taking place at the blink of an

    eye, it is impossible to keep pace with the emerging trends. Excellence is an attitude that whole

    of the human race is born with. It is the environment that makes sure that whether the result of

    this attitude is visible or otherwise. A well planned properly executed and evaluated Industrial

    Training helps a lot in inculcating a professional attitude.

    During this period, the students get the real, firsthand experience for working in the actual

    environment. Most of the theoretical knowledge that has been gained during the course of their

    studies is put to test here. I had the opportunity to have a real experience, which increased my

    sphere of telecom knowledge to a great extent. I was entrusted with projectDRIVE TEST.

    I was entrusted with a real life project, working on which had finally made me step into the

    ongoing telecom revolution and gradually become a part of it. And all the credit goes to

    organization TELCOMA TECHNOLOGIES PVT. LIMITED which in true self made the

    telecom revolution happen.


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    Brief History

    The Global System for Mobile communication (GSM) is an ETSI (European Telecommunication

    Standard Institute) standard for 2G pan European digital cellular with international roaming.

    The main purpose of the group was to develop a 2G standard to resolve the roaming problem in

    the six existing different 1G analog systems in Europe. In 1986, the task force was formed, and

    in 1987 a memorandum of understanding (MoU) was signed. In 1989, ETSI included GSM in its

    domain. In 1991, the specification of the standard was completed, and in 1992, the first

    deployment started. By the year 1993, thirty two operators in 22 countries adopted the GSM

    standard, and by 2001, close to 150 countries had adopted GSM for cellular adaptation

    Frequency BandsThis GSM system is a frequency and time division system. Each physical channel is characterized

    by a carrier frequency and a time slot number. GSM system frequencies include two bands at

    900 MHZ and 1800 MHz commonly referred to as the GSM 900 and DCS 1800 systems.

    For the primary band in the GSM 900 system, 124 radio carriers have been defined and

    assigned in two sub-bands of 25 MHz each in the 890 915 MHz and 935-960 MHz ranges with

    channel width of 200 kHz (these sub-bands are always referred as downlink as well as uplink

    respectively, we will see this concept in detailed in channel concepts later in this module).

    Each carrier (a total channel width of 200 KHz) is divided into frames of 8 time slots.

    For DCS1800, there are two sub bands of 75 MHz in the 1710 1785 MHz and 18051880

    MHz ranges

    GSM Services

    To study any system, it is very important to know the services, which the system supports or

    provides. Analog cellular systems were developed for a single application that is voice and in a

    manner similar to analog access to PSTN, other data services such as fax and voice-band

    modems were defined as overlay services on top of the analog voice service. GSM is an

    integrated voice-data service that provides a number of services beyond cellular telephone.

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    These services are divided into three major categories. They are Teleservices, Bearer services

    and supplementary services.

    Features of GSM

    1. The GSM system provides a greater subscriber capacity than analogue systems.

    2. GSM allows 25 kHz per user, that is, eight conversations per 200 kHz channel pair (a pair

    comprising one transmit channel and one receive channel).

    3.Digital channel coding and the modulation used makes the signal resistant to interference from

    cells where the same frequencies are re-used (co-channel interference); a Carrier to Interference

    Ratio (C/I) level of 12 dB is achieved, as opposed to the 18 dB typical with analogue cellular.

    4. This allows increased geographic reuse by permitting a reduction in the number of cells in the

    reuse pattern.


    It provide communication between two end user applications according to a standard protocol.

    These services are telephony, emergency, speech calls, group 3 facsimile, telex, short messages,

    and videotext. The upper most layer of the protocol stack of the standard should be specified so

    that it could communicate with protocols used in these applications.

    Bearer services

    It provide capabilities to transmit information among user network interfaces. Traditional bearer

    services include a variety of asynchronous and synchronous data access to PSTN/ISDN and

    packet switched public data network. To implement bearer services, the lower layers and the

    frame format of the standard should specify how these transmission would be implemented over

    the air-interface

    Supplementary services

    GSM supports a wide range of supplementary (complementary and is not mandatory) services.

    These services belong to both telephony as well as data services. These services are considered

    as revenue generating features. These are not stand-alone services but they are services that

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    supplement a bearer or teleservice. These services are call forwarding, call barring, call waiting,

    call hold, calling line identification, connected line identification, multiple communication (like

    conferencing, up to five ongoing calls can be included in one conversation), closed user group,

    Advice of charge, operator determined call barring etc.

    The important supplementary services are:-

    1. Call forwarding : gives the subscriber the ability to forward incoming calls to

    another number (either to the same network or even other network) with conditional or

    unconditional. The conditions are when the MS is not reachable, if it is busy or if there is

    no reply. While unconditional call forwarding is active, calls are forwarded without any

    condition that is the MS will be treated as a passive device.

    2. Barring of outgoing calls : This function makes it possible for a mobile subscriber

    to prevent all outgoing calls.

    3. Barring of incoming calls : This service exists with two conditions: barring of all

    incoming calls and barring of incoming calls when roaming outside the home PLMN.

    4. Advice of Charge (AoC): This service provides the mobile subscriber with an

    estimate of the call charges. There are two types of Aoc information: one provides the

    subscriber with an estimate of the bill and one that can be used for immediate charging


    5. Call hold: This service enables the subscriber to interrupt an ongoing call and then

    subsequently reestablish the call.

    6. Call waiting : This service enables the mobile subscriber to be notified of an incoming

    call during a conversation. The subscriber can answer, reject or ignore the incoming

    call. This functionality is applicable to all GSM telecommunications services using a

    circuit switched connection.

    7. Multiparty service: This service enables a mobile subscriber to establish a multiparty

    conversation. That is the subscriber can establish multiple conversations at a time (max


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    8. Calling line identification (CLI) presentation/restriction: These services

    supply the called party with the ISDN number of the calling party. These restriction

    services enable the calling party to restrict the presentation. The restriction overrides the



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    The information contained in the file is solely property of ZTE corporation. Any kind of disclosing without permission is prohibited.ZTE University univ.zte.com.cn


    7/16 Din Connector

    7/8 Cable


    1/2 Jumper



    Grounding clip

    Grounding bar

    1/2 Clamp

    Tower Top


    7/8 Cable

    Machine house

    1/2 Jumper


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    Feeder and J umper Cables

    Mount, Mechnical Tilt and GSM antenna

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    Electrical Tilt

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    Feeder and jumper cable

    When a new site is to be installed, firstly the right place for the site is planned by the planning

    department. It includes right height, TX and RX frequency of the microwave antenna. The site is

    installed mainly on top of the building so that the total height may be achieved by subtracting the

    height of the building from the total height from where the antenna is to be installed i.e. if we

    have planned to mount an antenna at a height of 30 meters and the height of the building selected

    is 18 meters, so we have to built an tower of (30mts -18mts) 12 meters.







    Unit BatteryBackup




    BTS Cabin/Shelter/Room

    A C


    GSM Antenna System

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    All the hardware installation (Tower, Antennas, DG, BTS, Shelter AC,) during site installation is

    done by different vendors (NOKIA, Kirloskar, Zeppelin etc). When they complete their job, the

    O&M Engineer comes and checks whether the installations are done properly or not. He checks

    the jumpers coming from antennas very carefully. After he is completely satisfied, he starts his

    job of integrating the site .

    A site mainly consists of following:


    2.DC Generator(DG)

    3.Tower (including antenna)

    Shelter :

    For the shelter, we use four cemented base which is raised from ground to a height

    approximately one and a halffeet with two metal rails running over this base. The shelter is

    mounted over this by metal nails. The Back side of the shelter has an AC exhaust fans mounted

    over by two metal nails. As the shelter is at a height of one and a half feet, we use 3 to 4 stairs

    for getting into the shelter conveniently.


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    Diesel Generator :

    It is one of the important components used in a site. It is used in case of power breakdown, in

    that case it starts automatically and when the mains are ok, it stops automatically. The

    specifications of the DG are :

    AC generator: 50Hz 1500 RPM, 240 V, 10 KVA or 15KVA or 25KVA

    DC Generator


    For constructing the tower, firstly a concrete square wall of 3 -4 feet is made. The thickness is

    such that it can withhold the weight of the antenna. It is painted by orange and white color as it

    the standard for any antenna using microwave frequency. The two antennas i.e. the GSM and the

    microwave antenna are installed on top of the tower using moulds. The jumper cables are

    connected from top of BTS &hen connected to the feeder cable which is routed through the cable

    tray on to the top of the tower, then further connected by the jumper to the antenna.

    There are basically two types of towers :

    1.Roof Top(RT) towers .

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    2.Ground Based towers.

    The main advantage of Roof Tower (RT) tower is that it reduces the height of the tower and

    therefore not only reduces the material required for constructing the tower but automatically

    saves the time required to erect a tower as well as reduces the cost required for construction.

    Ground Base Tower

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    Roof Top Tower


    Introduction to GSM (Global System for Mobile Communications)


    1.The Global System for Mobile Communications (GSM) is a set of recommendations and

    specifications for a digital cellular telephone network (known as a Public Land Mobile Network,

    or PLMN).

    2.These recommendations ensure the compatibility of equipment from different GSM

    manufacturers, and interconnectivity between different administrations, including operation

    across international boundaries.3.GSM networks are digital and can cater for high system capacities.

    4.They are consistent with the world-wide digitization of the telephone network, and are an

    extension of the Integrated Services Digital Network (ISDN), using a digital radio interface

    between the cellular network and the mobile subscriber equipment.

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    GSM (Global System for Mobile Communication)

    Definition :

    Global system for mobile communication (GSM) is a globally accepted standard for digital

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

    create a common European mobile telephone standard that would formulate specifications for a

    pan-European mobile cellular radio system operating at 900 MHz. It is estimated that many

    countries outside of Europe will join the GSM partnership.



    1. The GSM system provides a greater subscriber capacity than analogue systems.

    2. GSM allows 25 kHz per user, that is, eight conversations per 200 kHz channel pair (a pair

    comprising one transmit channel and one receive channel).

    3.Digital channel coding and the modulation used makes the signal resistant to interference from

    cells where the same frequencies are re-used (co-channel interference); a Carrier to InterferenceRatio (C/I) level of 12 dB is achieved, as opposed to the 18 dB typical with analogue cellular.

    4. This allows increased geographic reuse by permitting a reduction in the number of cells in the

    reuse pattern.


    1. Digital transmission of speech and high performance digital signal processors provides good

    quality speech transmission.

    2. 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.

    3. In regions of interference or noise-limited operation the speech quality is noticeably better

    than analogue.


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    1. GSM offers high speech and data confidentiality.Subscriber authentication can be performed

    by the system to check if a subscriber is a valid subscriber or not..

    2. The GSM system provides for high degree of confidentiality for the subscriber. Calls are

    encoded and ciphered when sent over air.

    3. The mobile equipment can be identified independently from the mobile subscriber. The mobile

    has an identity number hard coded into it when it is manufactured. This number is stored in a

    standard database and whenever a call is made the equipment can be checked to see if it has

    been reported stolen.


    1. GSM uses Mobile assisted handover technique.

    2. The mobile itself carries out the signal strength and quality measurement of its server and

    signal strength measurement of its neighbors.

    3. This data is passed on the Network which then uses sophisticated algorithms to determine the

    need of handover.


    1. In a GSM system the mobile station and the subscriber are identified separately.

    2. The subscriber is identified by means of a smart card known as a SIM.

    3. This enables the subscriber to use different mobile equipment while retaining the same

    subscriber number.


    1. Speech services for normal telephony.

    2. Short Message Service for point ot point transmission of text message.

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    3. Cell broadcast for transmission of text message from the cell to all MS in its coverage area.

    Message like traffic information or advertising can be transmitted.

    4. Fax and data services are provided. Data rates available are 2.4 Kb/s, 4.8 Kb/s and 9.6 Kb/s.

    5. Supplementary services like number identification, call barring, call forwarding, charging

    display etc can be provided.


    1. There are total 124 carriers in GSM ( additional 50 carriers are available if EGSM band is


    2. Each carrier has 8 timeslots and if 7 can be used for traffic then a maximum of 868 (124 X 7)

    calls can be made. This is not enough and hence frequencies have to be reused.

    3. The same RF carrier can be used for many conversations in several different cells at the same


    4. The radio carriers available are allocated according to a regular pattern which repeats over

    the whole coverage area.

    5. The pattern to be used depends on traffic requirement and spectrum availability.

    6. Some typical repeat patterns are 4/12, 7/21 etc.


    1. A cellular telephone system links mobile subscribers into the public telephone system or to

    another cellular subscriber.

    2. Information between the mobile unit and the cellular network uses radio communication.

    Hence the subscriber is able to move around and become fully mobile.

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    3. The service area in which mobile communication is to be provided is divided into regions

    called cells.

    4. Each cell has the equipment to transmit and receive calls from any subscriber located within

    the borders of its radio coverage area.


    Radio spectrum is very limited, thats why we have only 10-25MHz dedicated to wireless

    communication. Such narrow bandwidth allows 100-400 channels of reasonable quality, which

    is not rational and commercially not profitable to develop network for such small number of

    mobile subscribers. Genius idea lead to division of the whole geographical area to relatively

    small cells, and each cell may reuse the same frequencies by reducing power of transmission.

    Each cell has its own antenna (base station), and all base stations are interconnected using

    microwave or cable communication.

    Every telephone network needs a specific structure to route incoming calls to the correct

    exchange and then on to the subscriber. In a mobile network, this structure is very important

    because the subscribers are mobile.




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    A cell is the basic unit of a cellular system and is defined as the area where radio coverage is

    given by one base station. Different cells are identified by a unique number called Cell Global

    Identity (CGI). In a complete network the number of cells is large.

    There are a limited number of frequencies available within the frequency band specified for

    cellular systems. Each operator licensed to run a cellular network, has been provided with a

    number of frequencies. A cell has one or several frequencies, depending on traffic load. To cover

    a country, for example, the available frequencies must be reused. The same frequency cannot be

    used in neighboring cells due to interference.

    Neighbouring cells cant have the same frequency.


    The Location Area (LA) is defined as a group of cells. The system uses LA to search for

    subscribers in active state. When there is a call for a mobile station, a paging message is

    broadcast to all cells belonging to a specific LA.

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    A LA is the part of the network in which a mobile station may move around freely without

    reporting its location to the network. Different location areas can be identified by the system

    using the Location Area Identity (LAI).

    Location Areas

    MSC/VLR SERVICE AREAThe mobile station is registered in a database called Visitor Location Register (VLR). MSC and

    VLR are always implemented in the same node in all Ericsson GSM networks, thus the area is

    often called MSC/VLR Service Area. A MSC/VLR Service Area is made up of a number of LAs. It

    represents the geographical part of the network that is covered by one MSC. To route a call to

    an MS, the subscribers MSC service area is also recorded and monitored.

    Network Areas

    PLMN SERVICE AREAThe Public Land Mobile Network (PLMN) is a geographical area served by one network

    operator and is defined as the area in which an operator offers radio coverage and possibility to

    access its network.

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    PLMN Service Area


    The GSM service area is the entire geographic areas in which a subscriber can gain access to

    the GSM network. The GSM service area increases as more operators sign contract agreeing to

    work together. As shown in Figure, these areas include cells, location areas (LAs), MSC/VLR

    service areas, and public land mobile network (PLMN) areas.

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    The GSM network can be divided into four main parts:

    1.Mobile Station (MS).

    2.Base Station Subsystem (BSS).

    3.The Network and Switching Subsystem (NSS).

    4.Operation and Support Subsystem (OSS).

    Mobile Station

    A Mobile Station consists of two main elements:

    1.The mobile equipment or terminal.

    2.The Subscriber Identity Module (SIM).


    There are different types of terminals/mobile equipment distinguished principally by their power

    and application:

    1.The `fixed' terminals are the ones installed in cars. Their maximum allowed output power is 20


    2.The GSM portable terminals can also be installed in vehicles. Their maximum allowed output

    power is 8W.

    3.The handheld terminals have experienced the biggest success thanks to their weight and

    volume, which are continuously decreasing. These terminals can emit up to 2 W. The evolution of

    technologies allows decreasing the maximum allowed power to 0.8W.


    The MS includes radio equipment and the man machine interface (MMI) that a subscribe needs

    in order to access the services provided by the GSM PLMN. MS can be installed in Vehicles or

    can be portable or handheld stations. The MS may include provisions for data communication as

    well as voice. A mobile transmits and receives message to and from the GSM system over the air

    interface to establish and continue connections through the system.

    Different type of MSs can provide different type of data interfaces. To provide a common modelfor describing these different MS configuration, reference configuration for MS, similar to

    those defined for ISDN land stations, has been defined.

    Each MS is identified by an IMEI that is permanently stored in the mobile unit. Upon request,

    the MS sends this number over the signaling channel to the MSC. The IMEI can be used to

    identify mobile units that are reported stolen or operating incorrectly.

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    Just as the IMEI identities the mobile equipment, other numbers are used to identity the mobile

    subscriber. Different subscriber identities are used in different phases of call setup. The Mobile

    Subscriber ISDN Number (MSISDN) is the number that the calling party dials in order to reach

    the subscriber. It is used by the land network to route calls toward an appropriate MSC. The

    international mobile subscribe identity (IMSI) is the primary function of the subscriber within

    the mobile network and is permanently assigned to him. The GSM system can also assign a

    Temporary Mobile Subscriber Identity (TMSI) to identity a mobile. This number can be

    periodically changed by the system and protect the subscriber from being identified by those

    attempting to monitor the radio channel.

    Functions of MS

    The primary functions of MS are to transmit and receive voice and data over the air interface of

    the GSM system. MS performs the signal processing function of digitizing, encoding, error

    protecting, encrypting, and modulating the transmitted signals. It also performs the inverse

    functions on the received signals from the BS.

    In order to transmit voice and data signals, the mobile must be in synchronization with the

    system so that the messages are the transmitted and received by the mobile at the correct instant.

    To achieve this, the MS automatically tunes and synchronizes to the frequency and TDMA

    timeslot specified by the BSC. This message is received over a dedicated timeslot several times

    within a multiframe period of 51 frames. The exact synchronization will also include adjusting

    the timing advance to compensate for varying distance of the mobile from the BTS.

    MS keeps the GSM network informed of its location during both national and international

    roaming, even when it is inactive. This enables the System to page in its present LA.

    Finally, the MS can store and display short received alphanumeric messages on the liquid

    crystal display (LCD) that is used to show call dialing and status in formation. These messages

    are limited to 160 characters in length (varies from mobile to mobile).

    Power Levels

    These are five different categories of mobile telephone units specified by the European GSM

    system: 20W, 8W, 5W, 2W, and 0.8W. These correspond to 43-dBm, 39-dBm, 37-dBm, 33-dBm,

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    and 29-dBm power levels. The 20-W and 8-W units (peak power) are either for vehicle-mounted

    or portable station use.

    The MS power is adjustable in 2-dB steps from its nominal value down to 20mW (13 dBm). This

    is done automatically under remote control from the BTS, which monitors the received power

    and adjusts the MS transmitter to the minimum power setting necessary for reliable


    The SIM

    The SIM is a smart card that identifies the terminal. By inserting the SIM card into the terminal,

    the user can have access to all the subscribed services. Without the SIM card, the terminal is notoperational.

    The SIM card is protected by a four-digit Personal Identification Number (PIN). In order to

    identify the subscriber to the system, the SIM card contains some parameters of the user such as

    its International Mobile Subscriber Identity (IMSI).

    Another advantage of the SIM card is the mobility of the users. In fact, the only element that

    personalizes a terminal is the SIM card. Therefore, the user can have access to its subscribed

    services in any terminal using its SIM card.

    Equipment identification

    The purpose of equipment identification is to ensure that no stolen or otherwise unauthorized

    mobiles are used in the network. To this end, every mobile is provided with a tamper-proof

    equipment number in the manufacturing process, in GSM an international mobile equipment

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    identity (IMEI). During the set-up phase, the MSC can request this number from the mobile and

    then send it on for checking in the network element called EIR (in GSM). If the number is barred

    or unknown, the set-up attempt is rejected.

    Subscriber identity confidentiality

    Subscriber identity confidentiality means that the operator tries to protect the user's telephone

    number (the IMSI) from unauthorized tapping. A temporary mobile subscriber number (TMSI in

    GSM) is used in the dialogue between the mobile and the network, except for the first contact

    attempt in a set-up phase. The MSC gives the mobile a random TMSI for each set-up.


    It identifies the current location of the subscriber.



    MCC= Mobile Country Code

    MNC= Mobile Network Code (2 digit). Identifies the GSM PLMN in that country and takes the

    same value as the MNC in IMSI.

    LAC= Location Area Code (max. 16 bits). Identifies a location area within a GSM PLMN

    Network & enabling 65536 different location areas to be defined in one GSM PLMN.


    It is used to authenticate the SIM card.


    It is used to unlock the MS. If one enters the wrong PIN three times it will lock the SIM. The SIM

    can be protected by use of PIN password.


    In case of PIN, the PUK is needed for unlocking the SIM again. PUK is numeric only, with eight

    digits. If a correct PUK is entered, an indication is given to the user. After 10 consecutive

    incorrect entries the SIM is blocked. Either the IMSI or the MSISDN Number may access the

    subscriber data. Some of the parameters like IAI will be continuously updated to reflect the

    current location of the subscriber. The SIM is capable of storing additional information such as

    accumulated call charges. This information will be accessible to the customer via handset key


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    Technical department has four main streams:

    1. Network Switching System (NSS) & Base Station Subsystem (BSS)

    3. Network Planning

    4. Operation Maintenance & controlling (OMC)

    5. Operation and Maintenance (O&M)

    Base Station Subsystem (BSS)

    The BSS connects the Mobile Station and the NSS. It is in charge of the transmission and

    reception. The BSS can be divided into two parts:

    1.The Base Transceiver Station (BTS) or Base Station.

    2.The Base Station Controller (BSC).

    Base Transceiver Station (BTS)

    The BTS controls the radio interface to the MS. The BTS comprises the radio equipment such as

    transceivers and antennas which are needed to serve each cell of the network. A BTS is usually

    placed in the centre of a cell. Its transmitting power defines the size of a cell. Each BTS has

    between one and sixteen transceivers depending on the density of users in the cell.

    BTS has 4 functional parts:

    1. Transmission unit

    2. Control functions

    3. TRX





    NSS & BSS

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    4. Combiner

    1.Transmission unit

    The task of the transmission unit is to connect the BTS to the Abis interface and, in doing so,

    create different types of transmission configuration possibilities. All of the Nokia BTSs have

    integrated transmission units. Certain Talk-family models offer additional integrated radio relay

    links. Transmission units are monitored by the operation and maintenance unit by means of an

    internal Q1 bus.

    2.Control functions

    Control functions can be split into four individual functions:

    1. Operation and maintenance

    2. Master clock function

    3. Frequency hopping control

    4. External alarms and controls

    That being said, depending on the type of BTS this could mean from one integrated unit to up to

    four individual plug-in units.

    a.Operation and maintenance

    The O&M processor controls and supervises the operation of all BTS units alone or in co-

    operation with other processors. It is the main interface for local O&M and controls and

    supervises the other units as well as delivers all status information to the BSC by means of the

    O&M signalling link , which it manages. It stores SW as well as downloads SW to the other

    units. It also downloads the software and configuration information received from the BSC or

    the MMI to other processors.

    b. External alarms and controls

    External alarms and controls are programmable interfaces to other devices in the BTS , which

    can be used to monitor environmental conditions at the BTS site as well as monitor the state of

    units, which do not have a processor of their own. An example of external alarm might be an

    intruder alarm or a smoke detector.

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    C. Frequency hopping control

    The frequency hopping control processor controls the frequency hopping functions of the BTS by

    calculating the frequency hopping algorithm and controls the transceivers through a specific

    parallel bus.

    3.Transceiver (TRX)

    The TRX can also contain a varying number of plug-in units depending on the type of BTS. The

    TRX can basically be thought of in terms of two functional parts: the base band part and the

    radio part. The radio part can also be split into a transmitter part(Tx) and a receiver part(Rx).

    The Rx part may also be configured to support antenna diversity , which is supported by all of

    the BTS products.

    The functions of the TRX can be divided into two categories: O&M and telecommunication

    control. One of the most important functions relative to O&M is to download the software and

    configuration information received from the main O&M processor to its slave processors


    In terms of telecommunication control, we can apply many of the functions examined in the

    previous section directly to the TRX.

    Apart from digitising and source coding, all of these are in fact performed in the TRX, speech

    coding being performed in the transcoder. It is important to remember that in the uplink

    direction the mobile will perform the same functions as well as digitising and speech coding.

    Relative to the other functions of the TRX, we could also mention channel equalisation, adaptive

    frame alignment, RACH channel detection and measurements as TRX functions.

    TRX software is also designed to handle a number of signalling scenarios including call set-up

    and release, handovers, TX power control, Air-interface measurements and short messages.

    Functionality of the BSC

    The BSC manages a variety of tasks ranging from channel administration to short messaging

    service. Furthermore the BSC provides interfaces to other network elements. The main

    functionalities are explained in brief below.

    The following BSC functionalities consist of basic and optional functionalities. These

    functionalities and options are described in more detail in BSS feature descriptions.

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    General functionalities

    A. Management of terrestrial channels

    1. Indication of blocking on the A interface channels between the BSC and the MSC

    2. Allocation of traffic channels between the BSC and the BTSs3. Pool support for A interface circuits

    4. concept support for flexible channel assignments, for example, half rate and high speed circuit

    switched data

    B. Management of radio channels

    1.Management of channel configurations, that is, how many traffic channels and signallingchannels can be used in the BSS. This is done in connection with radio network configuration.

    2.Management of traffic channels (TCH) and stand-alone dedicated control channels (SDCCH).

    This function can be subdivided into the following tasks:

    - resource management

    - channel allocation

    - link supervision

    - channel release

    - power control

    3. Management of broadcast control channels (BCCH) and common control channels (CCCH).

    This function can be subdivided into the following tasks:

    - channel management

    - random access

    - access grant

    - paging

    - Management of PCCCH/PBCCH for (E)GRPS

    C. Management of frequency hopping:

    The BSC is in charge of frequency hopping management which enables effective use of radio

    resources and enhanced voice quality for a GSM subscriber.

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    1. Handovers

    The frequency of the mobile is changed in connection with handovers which are executed and

    controlled by the BSC. Such a handover can be one of the following three types:

    a. Intra-BSC, intra-cell (both intra-TRX and inter-TRX), which means that the handover takes

    place within the area controlled by the BSC and the mobile stays in the same cell

    b. Intra-BSC, inter-cell, which means that the mobile stays in the area of the BSC but moves from

    one cell to another

    c. Inter-BSC, both outgoing and incoming, which means that the mobile moves into the area of

    another BSC

    Management of signalling channels between the BSC and the BTSs

    The BSC supervises all 16, 32 or 64 kbit/s permanent point-to-point LAPD signalling

    connections, consisting of one connection per Transceiver Unit (TRX) and BTS Operation and

    Maintenance Unit (OMU).


    The BSC offers the possibility for the following maintenance procedures:

    Fault localization for the BSC

    Reconfiguration of the BSC

    Reconfiguration support to the BTS

    Updating of the software in the BSC, TCSM2 and BTS


    During normal operation, the BSC offers various possibilities for the operator:

    modification of the parameters of the BSC and the BTS

    modification of the radio network parameters

    configuration of the BSC hardware administration of the BSC equipment

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    Network and Switching Subsystem (NSS)

    The switching system (SS) is responsible for performing call processing and subscriber-


    The different components of the NSS are described below:

    Mobile services Switching Centre (MSC)

    The MSC performs the telephony switching functions for the mobile network. It controls calls to

    and from other telephone and data systems such as Public Switched Telephone Network (PSTN),

    Integrated Services Digital Network (ISDN), public data networks, private networks and other

    mobile networks.


    The Mobile Switching Center or MSC is the primary service delivery node for GSM, responsible

    for handling voice calls and SMS as well as other services (such as conference calls, FAX and

    circuit switched data). The MSC sets up and releases the end-to-end connection, handles

    mobility and hand-over requirements during the call and takes care of charging and real time

    pre-paid account monitoring.

    In the GSM mobile phone system, in contrast with earlier analogue services, fax and datainformation is sent directly digitally encoded to the MSC. Only at the MSC is this re-coded into

    an "analogue" signal .

    There are various different names for MSCs in different contexts which reflects their complex

    role in the network, all of these terms though could refer to the same MSC, but doing different

    things at different times.

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    A Gateway MSC is the MSC that determines which visited MSC the subscriber who is being

    called is currently located. It also interfaces with the Public Switched Telephone Network. All

    mobile to mobile calls and PSTN to mobile calls are routed through a GMSC. The term is only

    valid in the context of one call since any MSC may provide both the gateway function and the

    Visited MSC function, however, some manufacturers design dedicated high capacity MSCs

    which do not have any BSSes connected to them. These MSCs will then be the Gateway MSC for

    many of the calls they handle.

    The Visited MSC is the MSC where a customer is currently located. The VLR associated with this

    MSC will have the subscriber's data in it.

    The Anchor MSC is the MSC from which a handover has been initiated. The Target MSC is the

    MSC toward which a Handover should take place.

    Mobile Switching Centre Server (MSS)

    The Mobile Switching Centre Server or MSC Server is a soft switch variant of Mobile Switching

    Centre, which provides circuit-switched calling, mobility management, and GSM services to the

    mobile phones roaming within the area that it serves. MSC Server functionality enables split

    between control (signalling) and user plane (bearer in network element called as Media

    Gateway), which guarantees more optimal placement of network elements within the network.

    Other GSM Core Network Elements connected to the MSCThe MSC connects to the following elements:

    1. The HLR for obtaining data about the SIM and MSISDN

    2. The Base Station Subsystem which handles the radio communication with 2G and 2.5G mobile


    3. The UTRAN which handles the radio communication with 3G mobile phones.

    4. The VLR for determining where other mobile subscribers are located.

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    Tasks of the MSC include

    1. Delivering calls to subscribers as they arrive based on information from the

    VLR .

    2. Connecting outgoing calls to other mobile subscribers or the PSTN.

    3. DeliveringSMSsfrom subscribers to the SMSCand vice versa.

    4. Arranginghandoversfrom BSC to BSC.

    5. Carrying out handovers from this MSC to another.

    6. Supportingsupplementary servicessuch as conference calls or call hold.

    7. Generating billing information.

    Home Location Register (HLR)

    The HLR is a centralized network database that stores and manages all mobile subscriptions

    belonging to a specific operator. It acts as a permanent store for a persons subscription

    information until that subscription is canceled. The information stored includes:

    1. Subscriber identity.

    2. Subscriber supplementary services.

    3. Subscriber location information.

    4. Subscriber authentication information.

    The 'Home Location Register' or HLR is a central database that contains details of each mobile

    phone subscriber that is authorized to use the GSM core network. There is one logical HLR per

    PLMN, although there may be multiple physical platforms.

    The HLR stores details of every SIM card issued by the mobile phone operator. Each SIM has a

    unique identifier called an IMSI which is the primary key to each HLR record.

    The next important items of data associated with the SIM are the MSISDNs, which are the

    telephone numbers used by mobile phones to make and receive calls. The primary MSISDN is the

    number used for making and receiving voice calls and SMS, but it is possible for a SIM to have

    other secondary MSISDNs associated with it for fax and data calls. Each MSISDN is also a

    primary key to the HLR record.

    Examples of other data stored in the HLR against an IMSI record are:

    1. GSM services that the subscriber has requested or been given

    2. GPRS settings to allow the subscriber to access packet services

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    3. Current Location of subscriber (VLR and SGSN)

    4. Call divertsettings applicable for each associated MSISDN.

    5. The HLR data is stored for as long as a subscriber remains with the mobile phone operator.

    The HLR is a system which directly receives and processes MAP transactions and messages from

    elements in the GSM network, for example, the Location Update messages received as mobile

    phones roam around.

    The HLR connects to the following elements:

    1. The Gateway MSC (G-MSC) for handling incoming calls2. The VLR for handling requests from mobile phones to attach to the network

    3. The SMSC for handling incoming SMS

    4. The voice mail system for delivering notifications to the mobile phone that a message is


    Procedures implemented The main function of the HLR is to manage the fact that SIMs and

    phones move around a lot. The following procedures are implemented to deal with this:

    Manage the mobility of subscribers by means of updating their position in administrative areas

    called 'location areas', which are identified with a LAC. The action of a user of moving from one

    LA to another is followed by the HLR with a Location area update while retrieving information

    from BSS as BSIC (cell identifier).

    Send the subscriber data to a VLR or SGSN when a subscriber first roams there.

    Broker between the GMSC or SMSC and the subscriber's current VLR in order to allow

    incoming calls or text messages to be delivered. Remove subscriber data from the previous VLR

    when a subscriber has roamed away from it.

    Visitor Location Register (VLR)

    The VLR database contains information about all the mobile subscribers currently located in the

    MSC service area. Thus, there is one VLR for each MSC in a network. The VLR temporarily

    stores subscription information so that the MSC can service all the subscribers currently visiting

    that MSC service area. The VLR can be regarded as a distributed HLR as it holds a copy of the

    HLR information stored about the subscriber.

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    When a subscriber roams into a new MSC service area, the VLR connected to that MSC requests

    information about the subscriber from the subscribers HLR. The HLR sends a copy of the

    information to the VLR and updates its own location information. When the subscriber makes a

    call, the VLR will already have the information required for call set-up.

    Authentication Center (AUC)

    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. The AUC is a database connected to the HLR which

    provides it with the authentication parameters and ciphering keys used to ensure network


    The 'Authentication Centre' or AUC is a function to authenticate each SIM card that attempts to

    connect to the GSM core network (typically when the phone is powered on). Once the

    authentication is successful, the HLR is allowed to manage the SIM and services described

    above. An encryption key is also generated that is subsequently used to encrypt all wireless

    communications (voice, SMS, etc.) between the mobile phone and the GSM core network.

    If the authentication fails, then no services are possible from that particular combination of SIM

    card and mobile phone operator attempted. There is an additional form of identification check

    performed on the serial number of the mobile phone described in the EIR section below, but this

    is not relevant to the AUC processing.Proper implementation of security in and around the AUC is a key part of an operator's strategy

    to avoid SIM cloning.

    The AUC does not engage directly in the authentication process, but instead generates data

    known as triplets for the MSC to use during the procedure. The security of the process depends

    upon a shared secret between the AUC and the SIM called the Ki. The Ki is securely burned into

    the SIM during manufacture and is also securely replicated onto the AUC. This Ki is never

    transmitted between the AUC and SIM, but is combined with the IMSI to produce a

    challenge/response for identification purposes and an encryption key called Kc for use in over

    the air communications.

    Other GSM Core Network Elements connected to the AUC

    The AUC connects to the following elements:

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    The MSC which requests a new batch of triplet data for an IMSI after the previous data have

    been used. This ensures that same keys and challenge responses are not used twice for a

    particular mobile.

    Procedures implemented

    The AUC stores the following data for each IMSI:

    1. The Ki

    2. Algorithm id (the standard algorithms are called A3 or A8, but an operator may choose a

    proprietary one).

    When the MSC asks the AUC for a new set of triplets for a particular IMSI, the AUC first

    generates a random number known as RAND. This RAND is then combined with the Ki to

    produce two numbers as follows:

    The Ki and RAND are fed into the A3 algorithm and a number known as Signed response or

    SRES is calculated.

    The Ki and RAND are fed into the A8 algorithm and a session key called Kc is calculated.

    The numbers (RAND, SRES, KC) form the triplet sent back to the MSC. When a particular IMSI

    requests access to the GSM core network, the MSC sends the RAND part of the triplet to the

    SIM. The SIM then feeds this number and the Ki (which is burned onto the SIM) into the A3

    algorithm as appropriate and an SRES is calculated and sent back to the MSC. If this SRES

    matches with the SRES in the triplet (which it should if it is a valid SIM), then the mobile isallowed to attach and proceed with GSM services.

    After successful authentication, the MSC sends the encryption key Kc to the Base Station

    Controller (BSC) so that all communications can be encrypted and decrypted. Of course, the

    mobile phone can generate the Kc itself by feeding the same RAND supplied during

    authentication and the Ki into the A8 algorithm.

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    The AUC is usually collocated with the HLR, although this is not necessary. Whilst the

    procedure is secure for most everyday use, it is by no means crack proof. Therefore a new set

    of security methods was designed for 3G phones.

    Radio Interface

    Radio interface is the interface between the MS and the RBS. It is also called as Um interface.

    This interface has three layers (OSI). They are Physical Layer (Layer1), Data Link Layer (Layer2)

    and Network Layer (Layer3)Network Layer (Layer3):

    This layer provides the Mobile Network Signaling (MNS) service to the user application.

    The basic functions of this layer are to establish, maintain and terminate circuit switched

    connections across a GSM PLMN and other networks to which the PLMN is connected.

    Also it supports functions for supplementary services and short message service

    This layer consists of three-sub layer which are basically protocol control entities. They

    are a. Connection Management (CM) b. Mobility Management (MM) c. Radio Resource

    Management (RR)

    In the MS, entities from all three sub layers are present however on the network sidethere is a distribution of the signaling functions between different network equipment.

    The RR function resides mainly in the BSC. The MM and CM functions are located in the

    MSC. In the BTS most of the RR messages are handled as transparent message. However

    some of them must be interpreted by the BTS.

    a. Mobility Management:The following functions are being carried out by this Mobility management MM sub layer.

    All the functions regarding the location of the MS, which includes location updating type

    normal, location update type periodic registration and location updating type IMSI attach.

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    It provides the user identity procedures. These procedures are authentication, TMSI

    reallocation, IMSI detach and identification of the MS by requesting either IMSI or IMEI.

    c. Radio Resource Management:

    The main purpose of this sub layer is to establish, maintain and release a dedicated

    connection between the MS and the network. This includes handover procedures, cell

    selection at power on and cell re-selection in idle mode, recovery from lack of coverage in

    idle mode. The following are the basic RR functions.

    On the downlink, the RR sub layer sends system information to the busy MS.

    On the uplink, the MS transmits measurement reports.

    The network may use the RR ciphering mode-setting procedure for setting the ciphering


    The class mark change procedure is used by the MS to provide the system with additional MS

    class mark information. It is also used to indicate to the network a change in class mark. For

    example, when the power capabilities of a hand held MS are changed because the MS is

    connected to external power in a vehicle.

    Equipment Identity Register (EIR)The EIR is also used for security purposes. It is a register containing information about the

    mobile equipments. More particularly, it contains a list of all valid terminals. A terminal is

    identified by its International Mobile Equipment Identity (IMEI). The EIR allows then to forbid

    calls from stolen or unauthorized terminals (e.g., a terminal which does not respect the

    specifications concerning the output RF power).

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    1. UmThe air interface between the MS (Mobile Station) and the BTS. This interface uses

    LAPDm protocol for signaling, to conduct call control, measurement reporting, Handover,

    Power control, Authentication, Authorization, Location Update and so on. Traffic and Signaling

    are sent in bursts of 0.577 ms at intervals of 4.615 ms, to form data blocks each 20 ms.

    The traffic channels in the Air interface are allocated onto a TDMA frame. The TDMA frame

    consists of 8 time slots. Generally, all time slots are used for traffic channels. Time slot 0 and

    sometimes also time slot 1 can be used for the signaling between the BTS (BSC, MSC) and the


    0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

    TDMA Frame = 8time slots

    2. Abis The interface between the Base Transceiver Station and Base Station Controller.

    Generally carried by a DS-1, ES-1, or E1 TDM circuit. Uses TDM sub channels for traffic

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    (TCH), LAPD protocol for BTS supervision and telecom signaling, and carries synchronization

    from the BSC to the BTS and MS.

    It is a 2 Mbit/s interface which can carry up to 96 channels. The capacity of the Abis depends on

    the type of signaling used between the BSC and the BTS. When using 64 kbit/s signaling, the 2

    Mbit/s link capacity is 80 traffic channels. Using 16 kbit/s signaling, the 2 Mbit/s link capacity is

    96 traffic channels.

    3. A The interface between the BSC and Mobile Switching Center. It is used for carrying

    Traffic channels and the BSSAP user part of the SS7 stack. Although there are usually

    transcoding units between BSC and MSC, the signaling communication takes place between

    these two ending points and the transcoder unit doesn't touch the SS7 information, only the voice

    or CS data are transcoded or rate adapted.

    4. AterThe interface between the Base Station Controller and Transcoder. It is a proprietary

    interface whose name depends on the vendor (for example Ater by Nokia), it carries the A

    interface information from the BSC leaving it untouched.

    5.Gb Connects the BSS to the Serving GPRS Support Node (SGSN) in the GPRS Core


    6. B-Interface b/w MSC-VLR

    7. C-Interface b/w MSC-HLR

    8. E-Interface b/w MSC-MSC

    9. F-Interface b/w MSC-EIR

    Channel structure

    A total of 156.25 bits is transmitted in 0.577 milliseconds, giving a gross bit rate of 270.833

    kbps. There are three other types of burst structure for frame and carrier synchronization and

    frequency correction. The 26bit training sequence is used for equalization, as described above.

    The 8.25 bit guard time allows for some propagation time delay in the arrival of bursts.

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    Physical channels

    In the air interface, frequency channel C0 and time slots TS0 and TS1 on that channel constitute

    the physical channels. Each cell has a dedicated C0 channel. Most logical control channels for

    signaling across the air interface are carried by LAPDm.

    In the interface between the base station and the BSC, all signaling is carried by LAPD links,

    which in turn use PCM channels. Signaling that is also transported across the air interface is

    carried by links having 0 as the service access point identifier (SAPI) address. Since a BSC is

    responsible for the maintenance of its base stations, BSC-BTS communication is extensive. The

    maintenance signals are carried by LAPD links having 62 as the SAPI address for base station

    maintenance and 63 for maintenance of LAPD. The LAPD links are in turn carried by a time slot

    (usually TS1) on the PCM link connecting a base station to its BSC.

    In the interface between a BSC and its MSC, there are three levels of physical channels. The

    topmost level is the discrimination mechanism of the BSSAP protocol, which distinguishes

    between signals to be transported between a mobile and the MSC and signals that are to be

    transported only between the MSC and the BSC. In both cases, BSSAP signals are carried by the

    SCCP in SS7. All call-related signaling uses SCCP's connection-oriented service, while the

    connectionless service is used in all other cases. SS7 normally uses one or more time slots in a

    PCM system.The physical channels - together with the relay functions - are used to create logical channels

    through all or part of the access network. In the air interface, these logical channels are divided

    into nine types of control channel and two types of traffic channel, all of which are mapped onto

    the time slots of the physical channels.

    Control channels

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    Control channels are divided into three classes, based on how and when they are used:

    broadcast channels (BCH); common control channels (CCCH); and dedicated control channels


    The GSM system has 11 logical channels

    Broadcast channels

    Class BCH channels continuously send information about cell and network parameters to the

    mobiles. They are unidirectional (from base station to mobile) and used jointly by all mobiles.

    There are three types of broadcast channel:

    A frequency correction channel (FCCH) carries frequency correction information.

    A synchronization channel (SCH) carries frame synchronization information and information for

    identifying the base station.

    A broadcast control channel (BCCH) carries cell-specific information.

    These channels are shown in the lower part ofFigure.

    Common control channels

    Class CCCH channels are used for access to the network. These three channels, too, are

    common to all mobiles.

    A paging channel (PCH) is used by the network to call terminals.A random access channel (RACH) is used by a mobile to answer paging calls and call the

    network when the mobile initiates set-up.

    An access granted channel (AGCH) is used by the network to allocate a dedicated control

    channel (SDCCH - see below) for continued signaling or some other channel (FACCH - see

    below) for handover.

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    All these logical channels are unidirectional: PCH and AGCH from network to mobile and

    RACH from mobile to network. The signals sent on RACH, AGCH and PCH are relayed via the

    base station and transferred to and from the BSC on LAPD links.

    Dedicated control channels

    Class DCCH channels are used for signaling between a mobile and the network before and

    during a call. These three channels are allocated to individual connections and are always


    A stand-alone dedicated control channel (SDCCH) is used for signaling during the set-up phase;

    that is, before traffic channel has been allocated. This channel is also used for registration,

    authentication and signaling in connection with clearing.

    A slow associated control channel (SACCH) is a locating channel that the mobile uses to

    continuously report received signal strength in the visited cell and from surrounding cells. The

    channel can also be used for controlling the output power of the mobile. Note, however, that

    SACCH does not have the signaling capacity required to control handover.

    A fast associated control channel (FACCH) - only available in conversation state - is used for

    handover operations. FACCH is allocated 20 ms of the traffic channel when rapid signaling is

    required. The listening party does not notice the loss of 20 ms conversation because the

    receiving unit repeats the last 20 ms. There is one FACCH for each traffic channel.

    Signals on SACCH, FACCH and SDCCH are relayed to the BSC via the base station. Signalsrelated to call handling; authentication and registration are relayed via SDCCH and then sent to

    the MSC. Connection handling is performed in both the BSC and the MSC.

    All control channels except SCH and FCCH use LAPDm.

    The following comments complete the information given in figure:

    Between the BSC and base stations, LAPD links are used for maintenance of base stations (base

    control function, BCF, in GSM).

    Between the BSC and the MSC, BSSAP (discrim.) signaling is used for paging (in the case of a

    call to a mobile) and for handover, if the MSC is involved in this handover.

    Traffic channels

    A traffic channel (TCH) is used to carry speech and data traffic. Traffic channels are defined

    using a 26-frame multiframe, or group of 26 TDMA frames. The length of a 26-frame multiframe

    is 120 ms, which is how the length of a burst period is defined (120 ms divided by 26 frames

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    divided by 8 burst periods per frame). Out of the 26 frames, 24 are used for traffic, 1 is used for

    the Slow Associated Control Channel (SACCH) and 1 is currently unused (see Figure). TCHs for

    the uplink and downlink are separated in time by 3 burst periods, so that the mobile station does

    not have to transmit and receive simultaneously, thus simplifying the electronics.

    In addition to these full-rate TCHs, there are also half-rate TCHs defined, although they are

    not yet implemented. Half-rate TCHs will effectively double the capacity of a system once half-

    rate speech coders are specified (i.e., speech coding at around 7 kbps, instead of 13 kbps).

    Eighth-rate TCHs are also specified, and are used for signaling. In the recommendations, they

    are called Stand-alone Dedicated Control Channels (SDCCH).

    CALL SETUPCall set up can be classified into two major categories, they are (i) Call From MS (Mobile

    Originated call) (ii) Call to MS (Mobile Terminated call)

    (i) Call From MS (Mobile Originated Call)

    Mobile Originated call is possible when the MS is attached with the MSC/VLR and is

    listening to the system information.

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    1. The MS requests a SDCCH using RACH2. The MS indicates that it wants to set up a call. The identity of the MS, IMSI is

    analyzed and the MS is marked as busy in the VLR

    3. Authentication is performed4. Ciphering may be initiated.5. The MSC receives a setup message from the MS. This includes the kind of service the

    MS wants and the B-number. MSC verify that the MS doesnt have services like

    barring of outgoing calls. If the MS is not barred, the setup of call proceeds.

    6. Between the MSC and the BSC a link is established and a PCM time slot is seized.The MSC sends a request to the BSC to assign a TCH. The BSC assigns a TCH to the

    call (if there is an idle TCH available) and tells the BTS to activate the channel. The

    BTS sends an acknowledgement when the activation is completed and the BSC orders

    the MS to switch over to the TCH. The BSC informs the MSC when the assignment is


    7. An alert message is sent to the MS indicating that a ringing tone has been generatedon the other side. The ringing tone generated in the exchange on the B- subscriber

    side is sent t the MS via the group switch in the MSC.

    8. When the B subscriber answers, the network sends a connect message to the MSindicating that the call is accepted . The MS returns a connect acknowledgement

    which completes the call set-up.

    Call to MS (Mobile Terminated Call)

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    Figure : Call to MS from PSTN.

    1. The number dialed by the calling party is called the Mobile station ISDN number(MSISDN). If the call is being made from a PSTN exchange, the exchange analyses

    the number and decides that the call is for a GSM subscriber

    2. From PSTN, the call is routed to the GMSC in the home PLMN of the called MS.3. By analyzing the MSISDN, the GMSC finds out which HLR the subscriber is

    registered in. GMSC asks the HLR for information so the call can be routed to the

    MSC/VLR where the MS is temporarily registered.

    4. The HLR contacts the VLR and gets the roaming number.

    5. The HLR forwards the roaming number to the GMSC.

    6a. With the help of the roaming number, the GMSC can route the call to the

    appropriate MSC.

    6b. The call is routed to the MSC

    7. The MSC knows which location area the MS is located in and sends a paging

    message to the BSCs handling this location area.

    8. The BSC distributes the paging message to the BTSs in the LA


    Exchange GMSC




    (2) (3)

    (6a) (5)




    (8) (8)

    Signaling connectionSpeech path





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    9. The BTSs page the MS using IMSIThe MS sends a request for a SDCCH when it detects its identity in the paging message.

    The MSC performs authentication and starts ciphering. The MSC may send information

    to the MS about requested services like speech, data, fax etc.,

    The BSC orders the BTS to activate a TCH and release the SDCCH. The MS is ordered to

    tune to the frequency of the TCH. An alerting message is sent from the MS indicate that a

    ring tone has been generated in the MS. The ringing tone for the calling subscriber is

    generated in the MSC. When the mobile subscriber answers, the MS sends a connect

    message. The network completes the through connection path and sends a connection

    acknowledgement to the MS. The duplex path for traffic is open now.

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    GSM is a digital mobile standard But radio frequencies are analogue. So the question is how do

    we transmit digital information in an analogue signal ?

    It looks difficult, but if we think about the values that must be transmitted (0 and 1), suppose thatthe frequency varies between two values, one representing 0 and the other representing 1. By

    altering the value of a certain characteristic of frequency at every specified interval (the bit

    duration), we can translate an analogue signal into a bit stream in the frequency domain. This

    technique is called modulation. The characteristics that can be varied is the frequency, the

    amplitude or the phase shift. The modulation technique used in GSM is the Gaussian Minimum

    Shift Keying (GMSK).


    In telecommunications and computer networks, multiplexing (known as muxing) is a term used to

    refer to a process where multiple analog message signals or digital data streams are combinedinto one signal over a shared medium. The aim is to share an expensive resource. For example,

    in telecommunications, several phone calls may be transferred using one wire.

    The multiplexed signal is transmitted over a communication channel, which may be a physical

    transmission medium. The multiplexing divides the capacity of the low-level communication

    channel into several higher-level logical channels, one for each message signal or data stream

    1 Bit duration

    Phase ModulationAM Amplitude ModulationFM Frequency Modulation


    M Modulation Signal

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    to be transferred. A reverse process, known as demultiplexing, can extract the original channels

    on the receiver side.

    A device that performs the multiplexing is called a multiplexer (MUX), and a device that

    performs the reverse process is called a demultiplexer(DEMUX).

    Inverse multiplexing (IMUX) has the opposite aim as multiplexing, namely to break one data

    stream into several streams, transfer them simultaneously over several communication channels,

    and recreate the original data stream.

    Categories of multiplexing

    The two most basic forms of multiplexing are time-division multiplexing (TDM) and frequency-

    division multiplexing (FDM), both either in analog or digital form. FDM requires modulation of

    each signal.

    Variable bit rate digital bit streams may be transferred efficiently over a fixed bandwidth

    channel by means of statistical multiplexing, for example packet mode communication. Packet

    mode communication is an asynchronous mode time-domain multiplexing, which resembles but

    should not be considered as time-division multiplexing.

    Digital bit streams can be transferred over an analog channel by means of code-division

    multiplexing (CDM) techniques such as frequency-hopping spread spectrum (FHSS) and direct-

    sequence spread spectrum (DSSS).


    HANDOVER:1. The GSM handover process uses a mobile assisted technique for accurate and fast

    handovers, in order to:

    Maintain the user connection link quality.

    Manage traffic distribution

    2. The overall handover process is implemented in the MS,BSS & MSC.

    3. Measurement of radio subsystem downlink performance and signal strengths received

    from surrounding cells, is made in the MS.

    4. These measurements are sent to the BSS for assessment.

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    5. The BSS measures the uplink performance for the MS being served and also assesses the

    signal strength of interference on its idle traffic channels.

    6. Initial assessment of the measurements in conjunction with defined thresholds and

    handover strategy may be performed in the BSS. Assessment requiring measurement

    results from other BSS or other information resident in the MSC, may be perform. in the


    7. The MS assists the handover decision process by performing certain measurements.

    8. When the MS is engaged in a speech conversation, a portion of the TDMA frame is idle

    while the rest of the frame is used for uplink (BTS receive) and downlink (BTS transmit)


    9. During the idle time period of the frame, the MS changes radio channel frequency and

    monitors and measures the signal level of the six best neighbor cells.

    10.Measurements which feed the handover decision algorithm are made at both ends of

    the radio link.

    MS END:

    1. At the MS end, measurements are continuously signaled, via the associated control

    channel, to the BSS where the decision for handover is ultimately made.

    2. MS measurements include:

    Serving cell downlink quality (bit error rate (BER) estimate).

    Serving cell downlink received signal level, and six best neighbor cells downlink

    received signal level.

    3. The MS also decodes the Base Station ID Code (BSIC) from the six best neighbor cells,

    and reports the BSICs and the measurement information to the BSS.

    BTS END:

    1. The BTS measures the uplink link quality, received signal level, and MS to BTS site


    2. The MS RF transmit output power budget is also considered in the handover decision.

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    3. If the MS can be served by a neighbor cell at a lower power, the handover is


    4. From a system perspective, handover may be considered due to loading or congestion

    conditions. In this case, the MSC or BSC tries to balance channel usage among cells.


    1. During the conversation, the MS only transmits and receives for one eighth of the time,

    that is during one timeslot in each frame.

    2. During its idle time (the remaining seven timeslots), the MS switches to the BCCH of the

    surrounding cells and measures its signal strength.

    3. The signal strength measurements of the surrounding cells, and the signal strength and

    quality measurements of the serving cell, are reported back to the serving cell via the

    SACCH once in every SACCH multiframe.

    4. This information is evaluated by the BSS for use in deciding when the MS should be

    handed over to another traffic channel.

    5. This reporting is the basis for MS assisted handovers

    The following measurements is be continuously processed in the BSS:

    1. Measurements reported by MS on SACCH

    Down link RXLEV

    Down link RXQUAL

    Down link neighbor cell RXLEV

    2. Measurements performed in BSS

    Uplink RXLEV

    Uplink RXQUAL

    MS-BS distance

    Interference level in unallocated time slots

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    Every SACCH multiframe (480 ms) a new processed value for each of the measurements

    is calculated.


    Handover is done on five conditions:

    1. Interference

    2. RXQUAL

    3. RXLEV

    4. Distance or Timing Advance

    5. Power Budget

    Interference - If signal level is high and still there is RXQUAL problem, then the RXQUAL

    problem is because of interference.

    RXQUAL - It is the receive quality. It ranges from 0 to 7 , 0 being the best and 7 the


    RXLEV - It is the receive level. It varies from -47dBm to -110dBm.

    Timing Advance - Ranges from 0 to 63.

    Power budget - It is used to save the power of the MS.

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    1. Handover takes place in the same cell from one timeslot to another timeslot of the same

    carrier or different carriers (but the same cell).

    2. Intra-cell handover is triggered only if the cause is interference.

    3. Intra-cell handover can be enabled or disabled in a cell.


    Handover takes place between different cells which are controlled by the different


    HANDOVER TYPESInter-BSC Handover


    BTS1 Call is handed from timeslot 3of cell1 to timeslot 1 of cell2 .

    Both the cells are controlled

    by the different BSC.

    0 1 2 3 4 5 6 7



    0 1 2 3 4 5 6 7



    Call is handed

    from timeslot 3 to timeslot 5

    0 1 2 3 4 5 6 7


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    Handover Priority1.Up Link Interference ---- Intra cell handover

    2.Down Link Interference ---- Intra cell handover

    3.Up Link Quality Poor ---- Inter cell handover

    4.Down Link Quality Poor ---- Inter cell handover

    5.Up Link Strength Poor ---- Inter cell handover

    6.Down Link Strength Poor ---- Inter cell handover

    7.MS-BS Distance exceed TA ---- Inter cell handover

    8.Better Cell ---- Inter cell handover

    9.Macro-Micro delay handover ---- Intra cell handover

    10.GOOD C/I handover ---- Intra cell handover11.Directed Retry ---- Inter cell handover

    Base Station Identity CodeProblem defination

    A problem could arise when the mobile station in a given position is performing a

    handover, but is receiving two cells using the same BCCH frequency. This can happen

    when the mobile station is moving along the national borders, where on each side of theborder the different PLMN operators have some frequencies in common.

    In order to discriminate between cells transmitting the BCCH channels at the same

    frequency, the mobile station uses the Base Station Identify Code (BSIC). The BSIC is

    broadcast on the SCH (Synchronization Channel) of each cell.

    Definition of BSICThe BSIC is a local color code that allows a mobile station to distinguish between different

    neighboring base stations. However, it is not an unambiguous identification of a basestation. Many cells bear the same BSIC. The scheme of BSIC values to be used are

    normally laid down in a bilateral agreement between the concerned PLMN operators to


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    FREQUENCY HOPPINGThe Frequency Hopping function permits the dynamic switching of radio links from one carrier

    frequency to another. Frequency Hopping changes the frequency used by a radio link every new

    TDMA frame in a regular pattern. Frequency Hopping is a GSM feature which can be enabledor disabled on a per cell basis.

    Reasons for frequency hopping Decreasing the probability of interference

    Frequency Hopping will spread the annoyance of interference over different mobile

    stations in a particular cell

    Suppressing the effect of Rayleigh fadingRayleigh fading (or multipath fading) is caused by different paths followed by the radio

    signal. Rayleigh fading can cause coverage holes.

    Rayleigh fading is location and frequency dependent. When the mobile station is stationary

    or moves at a slow speed, Frequency Hopping will significantly improve the level of theair-interface performance. However, when the mobile station moves at a high speed,

    Frequency Hopping does not harm, but does not help much either. The more frequencies

    are used in a particular cell, the more Frequency Hopping can gain in suppressing the

    effect of Rayleigh fading.

    In GSM, the frequency hopping is implemented through:

    Baseband hopping (BH)

    Divert a call to different transceiver on a frame basis

    Synthesiser hopping (SH)

    Fix a call on a transceiver which re-tunes the frequency on a frame basis

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    Baseband Hopping (BH)

    Number of transceiver units in place equals number of hopping frequencies in the


    Each transceiver unit is tuned to a fixed frequency

    A call is routed to different transceivers on a frame basis

    Hopping spectrum is limited by the number of transceiver units

    Combining loss is independent of number transceiver units in place

    1. Tuned cavity combiners used 2. BH introducing high EIRP

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    Synthesiser Hopping (SH)

    Transceivers are tuned to new frequencies on a frame basis

    Number of hopping frequencies is not limited by the number of transceivers in place

    A call is always routed to a given transceiver

    Hybrid combining is required for SH

    High carrier numbers reduces EIRP

    Air combining is recommended to recover EIRP

    Key Differences (BH ~ SH) Both can be used to improve quality or increase capacity

    BHs effectiveness is limited by the number of transceivers equipped

    SH can hop over a wide range of frequencies and is independent of number of

    transceivers equipped

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    Key AdvantagesSH SH is more effective to provide frequency diversity and interference diversity

    Extending coverage area - frequency diversity

    Improving quality - frequency diversity

    Enabling aggressive reuse - interference diversity

    Realising the potential benefits to operators, the synthesiser frequency hopping capability

    has been made available since the first generation of Motorolas BTS equipment

    Frequency Hopping Parameters Cell Allocation (CA):Refer to all available frequency carriers in a cell. The allocation

    should be consecutive starting from effective frequency carrier 0.

    Mobile Allocation (MA): Set of frequencies to hop over. Maximum of 63 frequencies can

    be defined in the MA list.

    Hopping Sequence Number (HSN): Order used to hop over the frequencies. There are

    64 different sequences:

    Hopping Sequence Number (HSN): Order used to hop over the frequencies. There are

    64 different sequences:

    1. 0 is cyclic2.1 - 63 are pseudo random

    Mobile Allocation Index Offset (MAIO): used to define initial frequency of hopping. The

    value of MAIO ranges between 0 to (N-1) where N is the number of frequencies defined

    in the MA list. MAIO of all channel of one hopping TRX must be identical but of different

    hopping TRX in same cell must be different.

    Frequency Hopping Indicator (FHI): Defines a hopping system, made up by an

    associated set of frequencies (MA) to hop over and sequence of hopping (HSN).

    Training Sequence Code (TSC): Used for delay equalization at RX end. TSC must be the

    same as BTS code.

    Planning for frequency hoppingThe plan depends upon the type of Frequency Hopping system used. As in case of