401 Cellular Systems

8/2/2019 401 Cellular Systems

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CELLULAR SYSTEMS


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ABSTRACT

In todays world of technology its really

exciting and enthusiastic to know that a

frequency band of 800MHz or 1900 MHz is

used for mobile communication. Technologies

that we are using for mobile communication

are known as cellular access technologies

GSM, FDMA,TDMA and CDMA.


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1.1 INTRODUCTION

The cellular concept was developed andintroduce by the bell laboratories in the early1970.One of the successful initial implementationof the cellular concept was the advanced mobile

phone system (AMPS). One of many reasons for developing a cellular

mobile telephone system and developing it inmany cities is the operational limitations of

conventional mobile telephone systems: limitedservices capability, poor service performance,and inefficient frequency spectrum utilization


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1.2 Multiple access technologies for

cellular system

Generally a fixed amount of frequency

spectrum is allocated to a cellular system by

the national regulator.

Multiple access technique are the deployed so

that many user can share the available

spectrum in an efficient manner.


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The three basic multiple access method

currently in use in cellular system are:

1. Frequency division multiple access (FDMA).

2. Time division multiple access (TDMA).

3. Code division multiple access (CDMA).


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FDMA

It separates the spectrum into distinct voice

channels by splitting it into uniform chunks of

bandwidth. To better understand FDMA, think

of radio stations: Each station sends its signal

at a different frequency within the available

band.

FDMA is used mainly for analog transmission


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TDMA

In TDMA, a narrow band that is 30 kHz wideand 6.7milliseconds long is split Time wise intothree time slots. Narrow band means

"channels" in the traditional sense. Eachconversation gets the radio for one-third ofthe time.

TDMA is also used as the access technologyfor Global System for Mobile communications(GSM).


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CDMA

The bandwidth is spread by means of the codewhich is independent of the data . Theindependence of the code distinguishes this fromstandard modulation schemes in which the data

modulation will always spread the spectrumsome what.

The receiver synchronizes to the code to recoverthe data. The use of an independent code and

synchronous reception allows multiple users toaccess the same frequency band at the sametime.


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1.3 Analog vs. digital cellular system

In an analog system, the signals applied totransmission media are continuous function ofthe message waveform. In the analog system,

either the amplitude, the phase, or the frequencyof a sinusoidal carrier can be continuously variedin accordance with the voice or the message

In digital transmission systems, the transmitted

signals are discrete in time, amplitude, phase orfrequency or in a combination of any two ofthese parameters


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1.4 Introduction to digital system

In digital transmission systems, thetransmitted signals are discrete in time,

amplitude, phase or frequency or in a

combination of any two of these parameters.

The digital cellular system employ TDMA

technique for communication.

Some examples of DC systems are

GSM,CDMA, PDC, NA-TDMA, 1800-DCS.

Out of these GSM is most popular DC S being

used world wide.


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Advantages of digital cellular system

Provide the effective data transmission . Reduced RF transmission power and longer

battery life.

International and wide-area roaming capability.

Encryption capability for information securityand privacy.

These systems require very less transmit power

this property increase battery life. These systems also provide powerful error

detection and error correction techniques


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1.5 Digital mobile Telephony

Since voice communication is the key service in

cellular mobile systems, when we think of the

digital systems, we must think of a digital voice. The major consideration in implementing digital

voice in cellular mobile systems is stated below.

Digital transmission rate. Relationship between carrier and noise.

Word error rate.


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INTRODUCTION OF GSM

GSM represents Global System for Mobile

communications. The main service provided

by the GSM system is a worldwide wireless

(mobile) communication.

CEPT implemented the first GSM system in

1982.


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Characteristics of the initial GSM

standard

Fully digital system utilizing the 900mhz frequency band

TDMA over radio carriers (200 kHz carrier spacing).

8 full rates or 16 half-rate TDMA channels per carrier.

Encryption of speech and data transmission over the radio path.

Full international roaming capability.

Low speed data services.


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The GSM sub systems are

1. Mobile station

2. Base station subsystem3. Network and switching subsystem

4. Operation subsystem


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Architecture of the GSM network


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Application of GSM

Good subjective speech quality

Low terminal and service cost

Support for international roaming Ability to support handheld terminals


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Conclusion:

Telecommunications are evolving towards

personal communication networks, whose

objective can be stated as the availability of all

communication services anytime, anywhere,

to anyone, by a single identity number and a

pocket able communication terminal. Having a

multitude of incompatible systems throughoutthe world moves us farther away from this

ideal.

Documents

401 Cellular Systems