cellular communication report

Cellular Communication Department Of CSA

College of Engineering & Technology

Guided by : Mr. Manjit Kumar Nayak

Report

On

Presented By : Prashant Kumar Gajendra

Regd. No.- 1305106016

MCA 2nd Semester

Department of CSA College of Engineering & Technology

2 Cellular Communication

Acknowledgement

I have taken efforts in this seminar. However, it would not have been possible without the kind support and help of many books and websites. I would like to extend my sincere thanks to all of them.

I am highly indebted to Mr. Manjit Kumar Nayak for his guidance and constant supervision as well as for providing necessary information regarding the seminar & also for their support in completing the Seminar.

I would like to express my gratitude to Dr. Ranjan kumar Dash, head of department, for giving us this opportunity and encouraging in completion of this seminar.

I thanks and appreciations also goes to our colleague in developing this seminar and people who have willingly helped us out with their abilities.



Certificate

This is to certify that Prashant Kumar Gajendra having regd no. 1305106016 has submitted seminar report on “CELLULAR COMMUNICATION” under the supervision in partial fulfilment of the requirement of the Seminar in Master in Computer Application. This is an original piece of the report and it has not been submitted elsewhere.

He has found to be very regular , sincere, hardworking, students & have undertaken lot of effort for the completion of this seminar.

I wish him all the success in his future.

Mr. Manjit Kumar Nayak Dr. Manjit Kumar Nayak

(Seminar Guide) (Seminar Incharge)



Abstract

The Global System for Mobile communications, is a digital cellular communications system which has rapidly gained acceptance and market share worldwide, although it was initially developed in a European context. In addition to digital transmission, cellular communication incorporates many advanced services and features, including ISDN compatibility and worldwide roaming in other cellular networks. The advanced services and architecture of cellular technology have made it a model for future third-generation cellular systems, such as UMTS. This paper will give an overview of the services offered by GSM, the system architecture, the radio transmission structure, and the signalling functional architecture.

Cellular communication basically deals with cell phones and radio waves. It describes how communication process occurs in cell phones. What are the basic process for establishment of a call i.e. for outgoing call and reception of a call. This topic describes the concept of frequency reuse, the division of cell, types of cell. It also describes cellular services, cellular components i.e. Base Transceiver Station, Base Station Controller, Mobile Switching Canter etc. and also different type of Registers.



Contents

• History

• Generations

• Network Cells

• Frequency Reuse

• Cellular Network Components

• Setting & Making a Call

• Receiving a Call

• Cellular Components & Channels

• GSM & Features

• Cellular Services

• Conclusion



List of Figures Page no.

1 . Generation of Phones…………………………………………….7

2 . Cell………..………………………...……………………………10

3 . Cluster……………..……………………...………...……………11

4 . Cellular Network Components…………..……….…...…………12

5 . Path of Communication………………………………………….17

6 . Handover…………………………………………………………19

7 . Roaming………………………………………………………….21

8 . Control Channels………………………………………………...22

9 . TDMA……………………………………………………………22

10 . CDMA………………………………………………………….24

11 . FDMA…………………………………………………………..24



CELLULAR COMMUNICATION

INTRODUCTION :

A hand-held mobile radiotelephone is an old dream of radio engineering. A particularly vivid and in many ways accurate prediction was presented by Arthur C. Clarke in a 1959 essay, where he envisioned a "personal transceiver, so small and compact that every man carries one." He wrote: "the time will come when we will be able to call a person anywhere on Earth merely by dialing a number." Such a device would also, in Clarke's vision, include means for global positioning so that "no one need ever again be lost." Later, in Profiles of the Future, he predicted the advent of such a device taking place in the mid-1980's.

Early predecessors of cellular phones included analog radio communications from ships and trains. The race to create truly portable telephone devices began after World War II, with developments taking place in many countries. The advances in mobile telephony have been traced in successive generations from the early "0G" (zeroth generation) services like the Bell System's Mobile Telephone Service and its successor, Improved Mobile Telephone Service. These "0G" systems were not cellular, supported few simultaneous calls, and were very expensive.

GENERATION :

1G (First generation):

The first automatic analog cellular systems deployed were NTT's system first used in Tokyo in 1979, later spreading to the whole of Japan, and NMT in the Nordic countries in 1981.

The first analog cellular system widely deployed in North America was the Advanced Mobile Phone System (AMPS). It was commercially introduced in the Americas in October 1983, Israel in 1986, and Australia in 1987. AMPS was a pioneering technology that helped drive mass market usage of cellular technology, but it had several serious issues by modern standards. It was unencrypted and easily vulnerable to eavesdropping via a scanner; it was susceptible to cell phone "cloning;" and it used a Frequency-division multiple access (FDMA) scheme and required significant amounts of wireless spectrum to support.



On 6 March 1983, the DynaTAc mobile phone launched on the first US 1G network by Ameritech. It cost $100m to develop, and took over a decade to reach the market. The phone had a talk time of just half an hour and took ten hours to charge. Consumer demand was strong despite the battery life, weight, and low talk time, and waiting lists were in the thousands.

Many of the iconic early commercial cell phones such as the Motorola DynaTAc Analog AMPS were eventually superseded by Digital AMPS (D-AMPS) in 1990, and AMPS service was shut down by most North American carriers by 2008

2G (Second Generation):

The second generation introduced a new variant of communication called SMS or text messaging. It was initially available only on GSM networks but spread eventually on all digital networks. The first machine-generated SMS message was sent in the UK on 3 December 1992 followed in 1993 by the first person-to-person SMS sent in Finland. The advent of prepaid services in the late 1990s soon made SMS the communication method of choice amongst the young, a trend which spread across all ages.

2G also introduced the ability to access media content on mobile phones. In 1998 the first downloadable content sold to mobile phones was the ring tone, launched by Finland's Radiolinja (now Elisa). Advertising on the mobile phone first appeared in Finland when a free daily SMS news headline service was launched in 2000, sponsored by advertising.

3G (Third Generation):

3G telecommunication networks support services that provide an information transfer rate of at least 200 kbit/s. Later 3G releases, often denoted 3.5G and 3.75G, also provide mobile broadbandaccess of several Mbit/s to smartphones and mobile modems in laptop computers.

3G finds application in wireless voice telephony, mobile Internet access, fixed wireless Internet access, video calls and mobile TV.

This is a set of standards used for mobile devices and mobile telecommunication use services and networks that comply with the International Mobile Telecommunications-2000 (IMT-2000)specifications by the International Telecommunication Union. 3G finds application in wireless voice telephony, mobile Internet access, fixed wireless Internet access, video calls and mobile TV.

A new generation of cellular standards has appeared approximately every tenth year since 1G systems were introduced in 1981/1982. Each generation is characterized by new frequency bands, higher data rates and non-backwards compatible transmission technology. The first release of the 3GPP Long Term Evolution (LTE) standard does not completely fulfill the ITU 4G requirements called IMT-Advanced. First release LTE is not backwards compatible with 3G, but is a pre-4G or 3.9G technology, however sometimes branded 4G by the service providers. Its evolution LTE Advanced is a 4G technology. WiMAX is another technology verging on or marketed as 4G.



4G (Fourth Generation):

In telecommunication systems, 4G is the fourth generation of mobile phone mobile communication technology standards. It is a successor to the third generation (3G) standards. A 4G system provides mobile ultra-broadband Internet access, for example to laptops with USB wireless modems, to smartphones, and to other mobile devices. Conceivable applications include amendedmobile web access, IP telephony, gaming services, high-definition mobile TV, video conferencing, 3D television, and cloud computing.

Two 4G candidate systems are commercially deployed: the Mobile WiMAX standard (first used in South Korea in 2006), and the first-release Long Term Evolution (LTE) standard (in Oslo, Norway and Stockholm, Sweden since 2009). It has however been debated if these first-release versions should be considered to be 4G or not, as discussed in the technical definition section below.

In the United States, Sprint (previously Clearwire) has deployed Mobile WiMAX networks since 2008, and MetroPCS was the first operator to offer LTE service in 2010. USB wireless modems have been available since the start, while WiMAX smartphones have been available since 2010, and LTE smartphones since 2011. Equipment made for different continents is not always compatible, because of different frequency bands. Mobile WiMAX is currently (April 2012) not available for the European market.

DEFINATION :

A mobile phone (also known as a cellular phone, cell phone, and a hand phone) is a device that can make and receive telephone calls over a radio link while moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile phone operator, allowing access to the public telephone network. By contrast, a cordless telephone is used only within the short range of a single, private base station.

In addition to telephony, modern mobile phones also support a wide variety of other services such as text messaging, MMS, email, Internet access, short-range wireless communications (infrared, Bluetooth), business applications, gaming and photography. Mobile phones that offer these and more general computing capabilities are referred to as smartphones.



CELL:

A cellular network or mobile network is a wireless network distributed over land areas called cells, each served by at least one fixed-locationtransceiver, known as a cell site or base station. In a cellular network, each cell uses a different set of frequencies from neighboring cells, to avoid interference and provide guaranteed bandwidth within each cell.

When joined together these cells provide radio coverage over a wide geographic area. This enables a large number of portable transceivers (e.g., mobile phones, pagers, etc.) to communicate with each other and with fixed transceivers and telephones anywhere in the network, via base stations, even if some of the transceivers are moving through more than one cell during transmission.

Cellular networks offer a number of desirable features:

• More capacity than a single large transmitter, since the same frequency can be used for multiple links as long as they are in different cells

• Mobile devices use less power than with a single transmitter or satellite since the cell towers are closer

• Larger coverage area than a single terrestrial transmitter, since additional cell towers can be added indefinitely and are not limited by the horizon

Major telecommunications providers have deployed voice and data cellular networks over most of the inhabited land area of the Earth. This allows mobile phones and mobile computing devices to be connected to the public switched telephone network and public Internet. Private cellular networks can be used for research or for large organizations and fleets, such as dispatch for local public safety agencies or a taxicab company.

CLUSTER :

The cells are grouped into clusters. The number of cells in a cluster must be determined so that the cluster can be repeated continuously within the covering area of an operator. Typical clusters contain 4, 7, 12 or 21 cells. The number of cells in each cluster is very important. The smaller the number of cells per cluster is, the bigger the number of channels per cell . The capacity of each cell will, therefore, increase. However, this must be balanced with the



reduction of to interference occuring between neighboring clusters. This interference is produced by the small size of the clusters (cluster size is defined as the number of cells/cluster). The total number of channels per cell depends on the number of available channels and the type of cluster used.

FREQUENCY REUSE :

It is a method used by service providers to improve the efficiency of a cellular network and to serve millions of subscribers using a limited radio spectrum. In the cellular concept, frequencies allocated to the service are re-used in a regular pattern of areas, called 'cells', each covered by one base station. In mobile-telephone nets these cells are usually hexagonal. In radio broadcasting, a similar concept has been developed based on rhombic cells.

To ensure that the mutual interference between users remains below a harmful level, adjacent cells use different frequencies. In fact, a set of C different frequencies {f1, ..., fC} are used for each cluster of C adjacent cells. Cluster patterns and the corresponding frequencies are re-used in a regular pattern over the entire service area.



TYPES OF CELL :

Macrocell – their coverage is large (aprox. 6 miles in diameter); used in remote areas, high-power transmitters and receivers are used. A macrocell is a cell in a mobile phone network that provides radio coverage served by a high power cellular base station (tower). Generally, macrocells provide coverage larger than microcell. The antennae for macrocells are mounted on ground-based masts, rooftops and other existing structures, at a height that provides a clear view over the surrounding buildings and terrain. Macrocell base stations have power outputs of typically tens of watt.

Microcell – Their coverage is small (half a mile in diameter) and are used in urban zones; low-powered transmitters and receivers are used to avoid interference with cells in another clusters. A microcell is a cell in a mobile phone network served by a low power cellular base station (tower), covering a limited area such as a mall, a hotel, or a transportation hub. A microcell is usually larger than a picocell, though the distinction is not always clear. A microcell uses power control to limit the radius of its coverage area.

Picocell – A picocell is a small cellular base station typically covering a small area, such as in-building (offices, shopping malls, train stations, stock exchanges, etc.), or more recently in-aircraft. In cellular networks, picocells are typically used to extend coverage to indoor areas where outdoor signals do not reach well, or to add network capacity in areas with very dense phone usage, such as train stations. Picocells provide coverage and capacity in areas difficult or expensive to reach using the more traditional Macrocell approach.

CELLULAR NETWORK COMPONENTS:



BTS (Base Transceiver System):

A base transceiver station (BTS) is a piece of equipment that facilitates wireless communication between user equipment (UE) and a network. UEs are devices like mobile phones (handsets), WLL phones, computers with wireless Internet connectivity. BTS is also referred to as the radio base station (RBS), node B (in 3G Networks) or, simply, the base station (BS). For discussion of the LTE standard the abbreviation eNB for evolved node B is widely used. Though the term BTS can be applicable to any of the wireless communication standards, it is generally associated with mobile communication technologies like GSM and CDMA. In this regard, a BTS forms part of the base station subsystem (BSS) developments for system management. It may also have equipment for encrypting and decrypting communications, spectrum filtering tools (band pass filters), etc. antennas may also be considered as components of BTS in general sense as they facilitate the functioning of BTS. Typically a BTS will have several transceivers (TRXs) which allow it to serve several different frequencies and different sectors of the cell (in the case of sectorised base stations). A BTS is controlled by a parent base station controller via the base station control function (BCF).

BSC (Base Station Controller):

The base station controller (BSC) provides, classically, the intelligence behind the BTSs. Typically a BSC has tens or even hundreds of BTSs under its control. The BSC handles allocation of radio channels, receives measurements from the mobile phones, and controls handovers from BTS to BTS (except in the case of an inter-BSC handover in which case control is in part the responsibility of the anchor MSC). A key function of the BSC is to act as a concentrator where many different low capacity connections to BTSs (with relatively low utilisation) become reduced to a smaller number of connections towards the mobile switching center (MSC) (with a high level of utilisation). Overall, this means that networks are often structured to have many BSCs distributed into regions near their BTSs which are then connected to large centralised MSC sites.

MSC (Mobile Switching Center):

The coordinator of a cellular network, it is connected to several BSCs, it routes calls between BSCs; links the cellular network with other networks like PSTN through fiber optics, microwave or copper cable.The mobile switching centre server is a soft-switch variant of the mobile switching centre, which provides circuit-switched calling mobility management, and GSM services to the mobile phonesroaming within the area that it serves. MSS functionality enables split between control (signalling) and user plane (bearer in network element called as



media gateway/MG), which guarantees better placement of network elements within the network.

HLR (Home Location Register):

The home location register (HLR) is a central database that contains details of each mobile phone subscriber that is authorized to use the GSM core network. There can be several logical, and physical, HLRs per public land mobile network (PLMN),though one international mobile subscribe identity (IMSI)/MSISDN pair can be associated with only one logical HLR (which can span several physical nodes) at a time. The HLRs store 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.

VLR (Visitor Location Registor):

A visitor location register (VLR) is a database that contains information about the subscribers roaming within a mobile switching center’s (MSC) location area. The primary role of the VLR is to minimize the number of queries that MSCs have to make to the home location register (HLR), which holds permanent data regarding the cellular network’s subscribers. Ideally, there should be only one visitor location register per MSC, but it is also possible for a single VLR to serve multiple MSCs. the VLR also holds the international mobile subscriber identity (IMSI) and the mobile subscriber integrated services digital network (MSISDN), the services allowed for a particular IMSI/MSISDN pair, and authentication data, all of which correspond to a particular subscription.

EIR (Equipment Identity Registor):

Equipment Identity Register (EIR) consults a database to determine if the service of a GSM mobile station is authorized, unauthorized, or if it should be monitored. EIR allows for the programming of the decision-making logic and the definition of the course of action to be taken in each case, taking into consideration e-mail and/or SMS notifications, in addition to the response required by the MSC. Moreover, it stores information records for their subsequent processing.



COMPONENTS OF CELLULAR NETWORK: Radio transceiver – low power radio transmitter and receiver Antenna - which is usually located inside the phone Control circuitry – formats the data sent to and from the BTS; controls signal transmission and reception Man-machine interface – consists from a keypad and a display; is managed by the control circuitry SIM – integrated circuit card that stores the identity information of subscriber Battery - usually Li-ion, the power unit of the phone

SETTING UP A CALL PROGRESS:

In order to gain access to GSM services, a user needs three things:

• A billing relationship with a mobile phone operator. This is usually either where services are paid for in advance of them being consumed (prepaid), or where bills are issued and settled after the service has been consumed (postpaid).

• A mobile phone that is GSM compliant and operates at the same frequency as the operator. Most phone companies sell phones from third-party manufacturers.

• A Subscriber Identity Module (SIM) card, which is activated by the operator once the billing relationship is established. After activation the card is then programmed with the subscriber's Mobile Subscriber Integrated Services Digital Network Number (MSISDN) (the telephone number). Personal information such as contact numbers of friends and family can also be stored on the SIM by the subscriber.

After subscribers sign up, information about their identity (telephone number) and what services they are allowed to access are stored in a "SIM record" in the Home Location Register (HLR).

Once the SIM card is loaded into the phone and the phone is powered on, it will search for the nearest mobile phone mast (also called a Base Transceiver Station/BTS) with the strongest signal in the operator's frequency band. If a mast can be successfully contacted, then there is said to be coverage in the area. The phone then identifies itself to the network through the control channel. Once this is successfully completed, the phone is said to be attached to the network.

The key feature of a mobile phone is the ability to receive and make calls in any area where coverage is available. This is generally called roaming from a customer perspective, but also called visiting when describing the underlying technical process. Each geographic area has a database called the Visitor Location Register (VLR), which contains details of all the mobiles currently in that area. Whenever a phone attaches, or visits, a new area, the Visitor Location Register must contact the Home Location Register to obtain the details for that phone. The



current cellular location of the phone (i.e., which BTS it is at) is entered into the VLR record and will be used during a process called paging when the GSM network wishes to locate the mobile phone.

Every SIM card contains a secret key, called the Ki, which is used to provide authentication and encryption services. This is useful to prevent theft of service, and also to prevent "over the air" snooping of a user's activity. The network does this by utilising the Authentication Center and is accomplished without transmitting the key directly.

Every GSM phone contains a unique identifier (different from the phone number), called the International Mobile Equipment Identity (IMEI). This can be found by dialing *#06#. When a phone contacts the network, its IMEI may be checked against the Equipment Identity Register to locate stolen phones and facilitate monitoring.

MAKING A CALL:

Once a mobile phone has successfully attached to a GSM network as described above, calls may be made from the phone to any other phone on the global Public Switched Telephone Network.

The user dials the telephone number, presses the send or talk key, and the mobile phone sends a call setup request message to the mobile phone network via the nearest mobile phone base transceiver station (BTS).

The call setup request message is handled next by the Mobile Switching Center, which checks the subscriber's record held in the Visitor Location Register to see if the outgoing call is allowed. If so, the MSC then routes the call in the same way that a telephone exchange does in a fixed network.

If the subscriber is on a prepaid tariff (sometimes known as Pay As You Go (PAYG) or Pay & Go), then an additional check is made to see if the subscriber has enough credit to proceed. If not, the call is rejected. If the call is allowed to continue, then it is continually monitored and the appropriate amount is decremented from the subscriber's account. When the credit reaches zero, the call is cut off by the network. The systems that monitor and provide the prepaid services are not part of the GSM standard services, but instead an example of intelligent network services that amobile phone operator may decide to implement in addition to the standard GSM ones.

When the HLR receives this query message, it determines whether the call should be routed to another number (called a divert), or if it is to be routed directly to the mobile.

• If the owner of the phone has previously requested that all incoming calls be diverted to another number, known as the Call Forward Unconditional (CFU) Number, then this number is stored in the Home Location Register. If that is the case, then the CFU number is returned to the Gateway MSC for immediate routing to that destination.

• If the mobile phone is not currently associated with a Visited Location Register (because the phone has been turned off) then the Home Location Register returns a number known as the Call Forward Not Reachable (CFNRc) number to the Gateway MSC, and the call is forwarded there. Many operators may set this value automatically to the phone's voice



mail number, so that callers may leave a message. The mobile phone may sometimes override the default setting.

• Finally, if the Home Location Register knows that the phone is roaming in a particular Visited Location Register area, then it will request a temporary number (called an MSRN) from that VLR. This number is relayed back to the Gateway MSC, and then used to route the call to the MSC where the called phone is roaming.

How speech is encoded during mobile phone calls :

During a GSM call, speech is converted from analogue sound waves to digital data by the phone itself, and transmitted through the mobile phone network by digital means. (Though older parts of the fixed Public Switched Telephone Network may use analog transmission.)

The digital algorithm used to encode speech signals is called a codec. The speech codecs used in GSM are called Half-Rate (HR), Full-Rate (FR), Enhanced Full-Rate (EFR) and Adaptive Multirate (AMR). All codecs except AMR operate with a fixed data rate and error correction level.

RECEIVING A CALL :

� When the receiver’s phone is in an idle state it listens for the control channel of its

BTS � if there is an incoming call the BSC and BTS sends a message to the cells in the area

where the receiver’s phone is located � the phone monitors its message and compares the number from the message with its

own � if the numbers matches the cell phone sends an acknowledgement to the BTS

after authentication, the communication is established between the caller and the receiver.



AUC (AUTHENTICATION CENTER):

� It is a database that stores the list of authorized subscribers of a GSM network � it is linked to the MSC and checks the identity of each user trying to connect also

provides encryption parameters to secure a call made in the network. � The AuC connects to the following elements:

• 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:

• the Ki • 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 the signed response (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 K i (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 is allowed 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.

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.

A3 Algorithm is used to encrypt Global System for Mobile Communications (GSM) cellular communications. In practice, A3 and A8 algorithms are generally implemented together (known as A3/A8, see COMP128). An A3/A8 algorithm is implemented in Subscriber Identity Module (SIM) cards and in GSM network Authentication Centres. It is used to authenticate the customer and generate a key for encrypting voice and data traffic, as defined in 3GPP TS 43.020 (03.20 before Rel-4). Development of A3 and A8 algorithms is considered a matter for individual GSM network operators, although example implementations are available.

HANDOVER :

Moving an ongoing call from one CELL to another CELL due to subscriber’s mobility.

In telecommunications there may be different reasons why a handover might be conducted:

• when the phone is moving away from the area covered by one cell and entering the area covered by another cell the call is transferred to the second cell in order to avoid call termination when the phone gets outside the range of the first cell;

• when the capacity for connecting new calls of a given cell is used up and an existing or new call from a phone, which is located in an area overlapped by another cell, is



transferred to that cell in order to free-up some capacity in the first cell for other users, who can only be connected to that cell;

• in non-CDMA networks when the channel used by the phone becomes interfered by another phone using the same channel in a different cell, the call is transferred to a different channel in the same cell or to a different channel in another cell in order to avoid the interference;

• again in non-CDMA networks when the user behaviour changes, e.g. when a fast-travelling user, connected to a large, umbrella-type of cell, stops then the call may be transferred to a smaller macro cell or even to a micro cell in order to free capacity on the umbrella cell for other fast-travelling users and to reduce the potential interference to other cells or users (this works in reverse too, when a user is detected to be moving faster than a certain threshold, the call can be transferred to a larger umbrella-type of cell in order to minimize the frequency of the handovers due to this movement);

• in CDMA networks a handover (see further down) may be induced in order to reduce the interference to a smaller neighbouring cell due to the "near-far" effect even when the phone still has an excellent connection to its current cell;

• etc.

The most basic form of handover is when a phone call in progress is redirected from its current cell (called source) to a new cell (called target). In terrestrial networks the source and the target cells may be served from two different cell sites or from one and the same cell site (in the latter case the two cells are usually referred to as two sectors on that cell site). Such a handover, in which the source and the target are different cells (even if they are on the same cell site) is called inter-cell handover. The purpose of inter-cell handover is to maintain the call as the subscriber is moving out of the area covered by the source cell and entering the area of the target cell.

A special case is possible, in which the source and the target are one and the same cell and only the used channel is changed during the handover. Such a handover, in which the cell is not changed, is called intra-cell handover. The purpose of intra-cell handover is to change one channel, which may be interfered or fading with a new clearer or less fading channel.

ROAMING :

Roaming helps ensure that a traveling wireless device (typically a cell phone) is kept connected to a network without breaking the connection. In wireless telecommunications, Traditional Roaming is a general term referring to the ability for a cellular customer to automatically make and receive voice calls, send and receive data, or access other services, including home data services, when travelling outside the geographical coverage area of the home network, by means of using a visited network. For example; should you travel beyond of your cell phone company's transmitter range, your cell phone would automatically hop onto another phone company's service, if available.



Roaming is divided into "SIM-based roaming" and "Username/password-based roaming", whereby the technical term "roaming" also encompasses roaming between networks of different network standards, e.g. WLAN (Wireless Local Area Network) or GSM. Device equipment and functionality, such as SIM card capability, antenna and network interfaces, and power management, determine the access possibilities.

Using the example of WLAN/GSM roaming, the following scenarios can be differentiated (cf. GSM Association Permanent Reference Document AA.39):

• SIM-based (roaming): GSM subscriber roams onto a Public WLAN operated by:

• their GSM Operator, or

• another Operator who has a roaming agreement with their GSM Operator. • Username/password based roaming: GSM subscriber roams onto a Public WLAN

operated by:

• their GSM Operator, or

• another Operator who has a roaming agreement with their GSM Operator.

Although these user/network scenarios focus on roaming from GSM Network Operator's network(s), clearly roaming can be bi-directional, i.e. from Public WLAN Operators to GSM Networks. Traditional roaming in networks of the same standard, e.g. from a WLAN to a WLAN or a GSM network to a GSM network, has already been described above and is likewise defined by the foreignness of the network based on the type of subscriber entry in the home subscriber register. In the case of session continuity, seamless access to these services across different access types is provided.

GSM Control Channels:

� Time Division Multiple Access (TDMA) � Code Division Multiple Access (CDMA) � Frequency Division Multiple Access (FDMA)



TDMA :

Time division multiple access (TDMA) is a channel access method for shared medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession, one after the other, each using its own time slot. This allows multiple stations to share the same transmission medium (e.g. radio frequency channel) while using only a part of its channel capacity. TDMA is used in the digital 2G cellular systems such as Global System for Mobile Communications (GSM), IS-136, Personal Digital Cellular (PDC) and iDEN, and in the Digital Enhanced Cordless Telecommunications (DECT) standard for portable phones. It is also used extensively in satellite systems, combat-net radiosystems, and PON networks for upstream traffic from premises to the operator.

TDMA is a type of Time-division multiplexing, with the special point that instead of having one transmitter connected to onereceiver, there are multiple transmitters. In the case of the uplink from a mobile phone to a base station this becomes particularly difficult because the mobile phone can move around and vary the timing advance required to make its transmission match the gap in transmission from its peers.


CDMA :

CDMA is an example of multiple accessinformation simultaneously over a single communication channel. This allows several users to share a band of frequencies (seeinterference between the users, CDMA employscoding scheme (where each transmitter is assigned a code

CDMA is used as the access method in manyas cdmaOne, CDMA2000 (theused by GSM carriers), which are often referred to as simply

CDMA is a spread-spectrum multiple accessthe bandwidth of the data uniformly for the same pseudo-random code that has a narrowIn CDMA a locally generated code runs aData for transmission is combined via bitwisefigure shows how a spread spectrof (symbol period) is XOR’ed with the code signal with pulse duration of

period). (Note: bandwidth is proportional to

bandwidth of the data signal is

is . Since is much smaller than

much larger than the bandwidth of the original signal. The ratiospreading factor or processing gain and determines to a certain extent the upper limit of the total number of users supported simultaneously by a base station.

FDMA :

Frequency Division Multiple Accessaccess protocols as a channelization protocol. FDMA gives users an individual allocatioone or several frequency bands

College of Engineering & Technology

lar Communication

multiple access, which is where several transmitters can send information simultaneously over a single communication channel. This allows several users to share a band of frequencies (see bandwidth). To permit this to be achieved without undue interference between the users, CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code).

CDMA is used as the access method in many mobile phone standards(the 3G evolution of cdmaOne), and WCDMA

carriers), which are often referred to as simply CDMA.

spectrum multiple access technique. A spread spectrum technique spreads the bandwidth of the data uniformly for the same transmitted power. A spreading code is a

random code that has a narrow ambiguity function, unlike other narrow pulse codes. In CDMA a locally generated code runs at a much higher rate than the data to be transmitted. Data for transmission is combined via bitwise XOR (exclusive OR) with the faster code. The figure shows how a spread spectrum signal is generated. The data signal with pulse duration

(symbol period) is XOR’ed with the code signal with pulse duration of

is proportional to , where = bit time.) Therefore, the

bandwidth of the data signal is and the bandwidth of the spread spectrum signal

is much smaller than , the bandwidth of the spread spectrum signal is

r than the bandwidth of the original signal. The ratio spreading factor or processing gain and determines to a certain extent the upper limit of the total number of users supported simultaneously by a base station.

Division Multiple Access or FDMA is a channel access methodaccess protocols as a channelization protocol. FDMA gives users an individual allocatio

frequency bands, or channels. It is particularly commonplace


, which is where several transmitters can send information simultaneously over a single communication channel. This allows several users

this to be achieved without undue technology and a special

mobile phone standards such WCDMA(the 3G standard

technique. A spread spectrum technique spreads transmitted power. A spreading code is a

, unlike other narrow pulse codes. t a much higher rate than the data to be transmitted.

(exclusive OR) with the faster code. The um signal is generated. The data signal with pulse duration

(symbol period) is XOR’ed with the code signal with pulse duration of (chip

= bit time.) Therefore, the

and the bandwidth of the spread spectrum signal

, the bandwidth of the spread spectrum signal is

is called the spreading factor or processing gain and determines to a certain extent the upper limit of the

channel access method used in multiple-access protocols as a channelization protocol. FDMA gives users an individual allocation of

. It is particularly commonplace in satellite



communication. FDMA, like other Multiple Access systems, coordinates access between multiple users. Alternatives include TDMA, CDMA, or SDMA. These protocols are utilized differently, at different levels of the theoretical OSI model.

GSM:

GSM (Global System for Mobile Communications, originally Group Spécial Mobile), is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe protocols for second generation (2G) digital cellular networks used by mobile phones. It became the de facto global standard for mobile communications with over 80% market share.

The GSM standard was developed as a replacement for first generation (1G) analog cellular networks, and originally described a digital, circuit-switched network optimized for full duplex voice telephony. This was expanded over time to include data communications, first by circuit-switched transport, thenpacket data transport via GPRS (General Packet Radio Services) and EDGE (Enhanced Data rates for GSM Evolution or EGPRS).

Subsequently, the 3GPP developed third generation (3G) UMTS standards followed by fourth generation (4G) LTE Advanced standards, which are not part of the ETSI GSM standard.

Subscriber Identity Module (SIM)

Main article: Subscriber Identity Module

One of the key features of GSM is the Subscriber Identity Module, commonly known as a SIM card. The SIM is a detachable smart card containing the user's subscription information and phone book. This allows the user to retain his or her information after switching handsets. Alternatively, the user can also change operators while retaining the handset simply by changing the SIM. Some operators will block this by allowing the phone to use only a single SIM, or only a SIM issued by them; this practice is known as SIM locking.



CELLULAR SERVICES : • Voice Communication

• Short Message Service

• Multimedia Messaging Service

• Global Positioning System

• Wireless Application Protocol

• Security

CONCLUSION :

The development of GSM is the first step towards a true personal communication system that will allow communication anywhere, anytime, and with anyone. The functional architecture of GSM, employing intelligent networking principles, and its ideology, which provides enough standardization to ensure compatibility, but still allows manufacturers and operators freedom, has been widely adopted in the development of future wireless systems.

BIBLIOGRATHY:

M. Mouly and M.-B. Pautet, The GSM System for Mobile Communications, 1992.

M. Mouly and M.-B. Pautet, GSM Protocol Architecture: Radio Sub-system Signalling, IEEE 41st Vehicular Technology Conference, 1991.

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