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OutlineOutline

IntroductionType of MultiplexingFDMATDMACDMAFuture Work

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IntroductionIntroduction

The multiplexing is used to combined a number of independent signals The multiplexing is used to combined a number of independent signals into a composite signal suitable for transmission over a common channelinto a composite signal suitable for transmission over a common channel

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Type of Multiplexing:Type of Multiplexing:

1. Frequency-Division Multiple Access (FDMA). 1. Frequency-Division Multiple Access (FDMA).

3. Code-division Multiple-Access (CDMA)3. Code-division Multiple-Access (CDMA)

2. Time-Division Multiple Access (TDMA). 2. Time-Division Multiple Access (TDMA).

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Frequency-Division Multiple Access (FDMA)Frequency-Division Multiple Access (FDMA)

It is a communications technique that divides a communications It is a communications technique that divides a communications channel into a number of equally spaced frequency bandschannel into a number of equally spaced frequency bands

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Time-Division Multiple Access (TDMA) Time-Division Multiple Access (TDMA)

It is a digital transmission technology that allows a number of users to It is a digital transmission technology that allows a number of users to access a single radio-frequency (RF) channel without interference by access a single radio-frequency (RF) channel without interference by allocating unique time slots to each user within each channel. allocating unique time slots to each user within each channel.

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Code Division Multiple Access (CDMA) Code Division Multiple Access (CDMA)

is a wireless communications technology that uses the is a wireless communications technology that uses the principle of spread spectrum communication.principle of spread spectrum communication.

There are three ways to spread the bandwidth of the signal: Frequency hopping Time hopping Direct sequence

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Code Division Multiple Access (CDMA)Code Division Multiple Access (CDMA)

CDMA Features:CDMA Features:o All users use same frequency and may transmit simultaneouslyAll users use same frequency and may transmit simultaneously

o Narrowband message signal multiplied by wideband spreading Narrowband message signal multiplied by wideband spreading signal, or codewordsignal, or codeword

o Each user has its own pseudo-codeword (orthogonal to others).Each user has its own pseudo-codeword (orthogonal to others).

o Receivers detect only the desired codeword. All others appearReceivers detect only the desired codeword. All others appear

as noise.as noise.

o Receivers must know transmitter’s codeword.Receivers must know transmitter’s codeword.

CDMA is a Direct Sequence Spread Spectrum systemCDMA is a Direct Sequence Spread Spectrum system

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Code Division Multiple Access (CDMA) Code Division Multiple Access (CDMA)

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Code Division Multiple Access (CDMA) Code Division Multiple Access (CDMA)

Pseudo-Noise Spreading

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Code Division Multiple Access (CDMA)Code Division Multiple Access (CDMA)

Direct Sequence Spread Spectrum System

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Code Division Multiple Access (CDMA)Code Division Multiple Access (CDMA)

Processing Gain:

is the processing gain

is Chipping Frequency (the bit rate of the PN code).

is Information Frequency (the bit rate of the digital data).

=

fc

fi

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Code Division Multiple Access (CDMA)Code Division Multiple Access (CDMA)

System Capacity: The capacity of a system is approximated by :

is the maximum number of simultaneous calls

is the processing gain

is the total signal to noise ratio per bit

is the inter-cell interference factor.

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Code Division Multiple Access (CDMA)Code Division Multiple Access (CDMA)

Advantages:Advantages:oIncreased capacityIncreased capacity

oImproved voice qualityImproved voice quality

oEliminating the audible effects of multipath fadingEliminating the audible effects of multipath fading

oEnhanced privacy and securityEnhanced privacy and security

oReduced average transmitted powerReduced average transmitted power

oReduced interference to other electronic devices Reduced interference to other electronic devices

Disadvantages:Disadvantages:oWide bandwidth per user requiredWide bandwidth per user required

oPrecision code synchronization neededPrecision code synchronization needed

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Code Division Multiple Access (CDMA)Code Division Multiple Access (CDMA)

The Future Planning For Next Semester The Future Planning For Next Semester

We will evaluate interference and capacity in We will evaluate interference and capacity in CDMA system and analysize them using CDMA system and analysize them using

MatLab simulator MatLab simulator

Study the capacity of CDMA Study the capacity of CDMA

Study the interference rises from the increasing of Study the interference rises from the increasing of capacity and how to reduce its effect.capacity and how to reduce its effect.

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Than you for attendance

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