6 cellular communication technologies

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Cellular Communication Technologies

P.Sree Ram M.R.KTeja P.V.Dixit

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Email: [email protected],[email protected],[email protected]

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This presentation involves the two hot

telecom technologies fighting out in the markets,

namely GSM and GPRS. It also includes a detailexplanation of the advantages they offer, how

they work, and their limitations. Also explained

are some of the possible applications that can be

made possible with them. Before going in detail

into these technologies, a look towards the Basic

Cellular Architecture has been made. This paper

will outline the Mobile Communication

Principles with a clear depiction. Additionally,the concept of packet switching and circuit

switching is mentioned. A greater emphasis is

laid on highlighting the credibilities of both

these network mechanisms

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The success of any technology largely

depends upon its widespread usage, which in

turn depends upon the number of applications

that can be made from it. A cellular mobile

communication system uses a large number of

low-power wireless transmitters to create cells

the basic geographic service area of a wireless

communication system. Variable power levels

allow cells to be sized according to the

subscriber density and demand within a particular region. As mobile users travel from

cell to cell, their conversations are handed off

between cells in order to maintain seamless

service. Channels (frequencies) used in one cell

can be reused in another cell some distance

away. Cells can be added to accommodate

growth, creating new cells in un served areas or

overlaying cells in existing areas.

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Each mobile uses a separate, temporary

radio channel to talk to the cell site. The cell site

talks to many mobiles at once, using one channel

per mobile. Channels use a pair off frequencies

for communication one frequency, the forward

link, for transmitting from the cell site and one

frequency, the reverse link, for the cell site to

receive calls from the users. Radio energy

dissipates over distance, so mobiles must stay

near the base station to maintain


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communications. The basic structure of mobile

networks includes telephone systems and radio

services.

3. MOBILE TELEPHONE SYSTEM USING

THE CELLULARCONCEPT

Inference problems caused by mobile

units using the same channel in adjacent areas

proved that all channels could not be reused in

every cell. Areas had to be skipped before the

same channel could be reused. Even though this

affected the efficiency to the original concept,

frequency reuse was still a viable solution to the

problems of mobile telephony systems.

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Increases in demand and the poor

quality of existing service led mobile service

providers to research ways to improve the

quality of service and to support more users in

their systems. Because the amount of frequency

spectrum available for mobile cellular use was

limited, efficient use of the required frequencies

was needed for mobile cellular coverage.

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Cell is the basic geographic unit of a

cellular system. The term cellular comes from

the honeycomb shape of the areas into which a

coverage region is divided. Cells are base station

transmitting over small geographic areas that are

represented are hexagons.

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A cluster is a group of cells. No channels are

reused within a cluster. The below figure

illustrates a seven- cell cluster.

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While using circuit switching the sender

seeks a connection right unto the receiver before

it begins transmitting. Data transmission begins

only after the sender has verified that a

dedicated connection to the receiver exists. 5.2

Packet Switching:


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Using packet switching,

however, eliminates the need to establish a

connection before transmission can begin. The

information to be sent is broken down into

packets (of fixed size) and sent on to the

network one after the other.

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1. Packet Switching Networks hasdynamic allocation of bandwidth -

packets are sent to the physical medium

as and when there is data to be sent

2. It allows the bandwidth to be used forother purposes during pauses between

conversations. Contrast this with the

circuit switching technique where in the

path between the sender and receiver is

reserved for their exclusive use, which

means that the bandwidth is wasted

during moments of silence.

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On the telecom front, numerous wireless

technologies have been introduced in the

country. It started with GSM based mobile

phones The developers of GSM choose an

unproven digital system and provided 8000

pages of recommendations that had enough

flexibility to allow competitive innovation but at

the same time ensured proper internetworking

between the components of the system

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A GSM based PLMN (Public Land Mobile

Network) can broadly be broken up into 3 parts

y The Mobile Station.y The Base Station Subsystem, andy The Network Subsystem.

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The Mobile Station (MS) is the

subscriber end of the network and consists of the

GSM device (cell phone) and the SIM

(Subscriber Entity Module). Each mobile devicehas a globally unique IMEI (International

Mobile Equipment Identity) and each SIM has

an IMSI (International Mobile Subscriber

Identity).

6.3BASE STATION SUBSYSTEM (BSS)

Mobile networks consist of many BTS

(Base Transceiver Stations), each of whichforms a cell covering a certain geographical

area. The BTSs are the ones responsible for

directly communicating with mobile devices.

Several BTSs are controlled together by a BSC

(Base Station Controller). The BSC provides

connectivity to the network subsystem.


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The MSC (Mobile Services Switching

Center) is the central component of the network

subsystem. It communicates with all the BSCs

and is responsible for providing all the

functionalities to mobile devices like,

registration, authentication, call routing etc. a

network also, usually, has GMSC (gateway

MSCs) to communicate with external (land line)

networks like ISDN, PSTN etc.

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When a mobile unit is switched on, it

tries to contact a BTS i.e., in range and logs onto

the network. The BTS also transmits the

frequencies of neighboring BTSs to the mobile

unit so it can determine if its getting better

reception from any one of them. It transmits

these measurements back to the BTS, which in

turn passes this information to the BSC.

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SMS (Short Text Messages): SMS was

the killer application on GSM networks, which

allowed Short Text Messages to be sent through

mobile phone. The capability to send short text

messages from one phone to another.

6.7 DATA TRANSFER RATE AS A

LIMITATION

One limitation of GSM is that currently

it has a maximum data transfer rate of only 9

kbps, but new developments like HSCSD (high

speed circuit switched data) andGPRS

(general packet switched radio) are pushing this

up quite a bit.

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General Packet Radio Service or GPRS is

relatively a new technology that offers packet

based radio service to mobile networks.

Designed to supplement the existing mobile

technologies, like GSM, CDMA, TDMA etc,

GPRS aims to provide anytime-anywhere

always-on network connections to mobile

devices.

GPRS (General Packet Radio Service)

It is a packet switched wireless protocol for

global system for mobile communications

(GSM) that mirrors the Internet model and

enables seamless transition towards 3G

networks..

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Its main features can be categorized from user

perspective and networking perspective.

y User features :The real advantage of GPRS is that it

provides an ALWAYS ON connection

between mobile terminal and the network.

Always on does not mean that there is

always a steady stream data connection; It just

means that, because data packets can be

transmitted almost immediately.

y Network features :


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Packet switching replaces the circuit

switched transfer mechanism of GSM. Just like

data transfers over internet, GPRS splits

information into separate related data packets

that are transmitted and reassembled at the

termination. This allows the operators to

implement IP (Internet Protocol) based

infrastructure for tomorrows 3G voice and data

applications.

Working of GPRS :Since the main goal of GPRS is to

provide an intermediate step towards 3G, it

needs to be both straightforward so that it can

deploy on existing systems and also provide a

logical upgrade path to 3G. However it is very

important to note that GPRS signaling and data

transfer does not in fact travel through GSM

networks.

GPRS NETWORKING

GPRS network nodes :

Since existing network nodes use circuit

switch technology, they cannot handle

packet traffic. Base stations for instance,

would have to be upgraded to include packet

control units, mobility management, and

security features. In addition to deploy

GPRS on GSM, two kinds of network nodes

are needed :

7.1 Why GPRS?

Though GSM uses circuit switching

like a telephone line, data transfer over GSM is

not quite the same as that over the PSTN line.

For each of our data requests (Over GSM), first,

a connection is established without network, our

request sent, the data received and then, and this

is important, that call is disconnected. Thus, we

have a dedicated connection as long as a

transaction lasts, but not in between

transactions..

PUBLIC

INTERNET

OPERATOR IP

NETWORK

GRPS

NETWORK

RADIO ACCESS

NETWORK(GSM


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7.2 IMPLEMENTING GPRS

Integrating GPRS into a GSM network

does not involve any major changes to the GSM

architecture. A new class of nodes, GSN (GPRS

support nodes) has been introduced two types of

GSNs defined. A SGSN (serving GPRS support

node) interacts with the mobile devices and is

responsible for delivery packets from and to

these devices.

8. CONCLUSION

GPRS, which uses packet switching

network, offers a better data transfer rate and proved to be a better communication system

than circuit switched GSM. GPRS enables an

existing GSM network to communicate with any

applications and/or network that uses packet

switching. Thus it allows mobile networks to

connect to the INTERNET (and other IP and

X.25 networks).

2.5GGPRS is considered to be the next

step towards the 3G networks. As it offers pretty

good speeds GPRS has the potential to move

beyond cell phones and move into the PC world.

Laptops connected to GPRS phones would offer

speeds fast, and may be even faster, than ourPC

connected to our landline.

9. REFERENCES:

[1]. Comm. ACM, special issue on Intelligent

Agents, vol. 37, no. 7, 1994.

[2]. IEEE Internet Computing, special issue on

Internet-Based Agents, vol. 1, 1997.

[3]. PC quest 2003 (edition February 2003).

[4]. Computer Networks by Andrew .S.

Tenenbaum.

[5]. G.H. Forman and J. Zahorjan, The

Challenges of Mobile Computing, Computer,

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