401 cellular systems
TRANSCRIPT
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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.