wireless video services on cdma

8/13/2019 wireless video services on cdma

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LAKPA BITTU TAMANG (ECE-01/08)

JITENDRA KUMAR RAI (ECE-50/08)

PRESENTED BY:


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INTRODUCTION:

CDMA is a new technology in wirelesscommunication.

Spread Spectrum technique is used.

Mathematical codes are used to transmit &distinguish the users. The great attraction of CDMA technology has been

because of the extraordinary increase in the systemcapacity and the service capacity.

CDMA is extremely robust and provides excellentaudio quality.


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HISTORY:

1 st generation cellular system introduced in 1980,uses Analog frequency modulation.

Due to some drawbacks, increase in marketdemands led to the foundation of 2 nd generationcellular system.

2 nd generation cellular system uses Digitalmodulation technique which includes CDMA, GSM &

TDMA. CDMA was introduced by QUALCOMM in 1994. CDMA provides 10 times more capacity than other

Analog system.


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BASIS OF CDMA:

Based on Spread Spectrum Technology.Spread Spectrum is independent of datasequence.

It provides secure communication which is noteasily detectable.It rejects unwanted interference that may beintentional or unintentional.Number of independent users can share acommon channel without externalSYNCHRONIZING mechanism.


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COMPETITION:

The Euro-Asian biggest competitive toCDMA is the GSM.

CDMA is more advantageous to GSM dueto less interference, low radiation level &more security.

GSM uses modified version of TDMA. GSM increases the network strength

using SIM card. CDMA is the fastest growing technology

in wireless communication than GSM.


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MOST POPULAR MULTIPLE ACCESS TECHNOLOGIESTHAT ESTABLISHED CHANNELS:

FDMA (Frequency Division Multiplex Access) Each user on a different frequency A channel is a frequency

TDMA (Time Division Multiplex Access)each user on a different window periodin time (time slot)

a channel is a specific time slot on a specific frequency

CDMA (Code Division Multiplex Access)each user uses the same frequency all the

time but mixed With different distinguishingcode patterns

a channel is a unique set of code patterns

Power

Power

Power

FDMA

TDMA

CDMA


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1. A wireless communications technology that uses the principle of spread spectrumcommunication( a method of wireless communications thattakes a narrowband signal and spreads it over a broader portion of theavailable radio frequency band)

2.All users use same frequency and may transmit simultaneously

3.Narrowband message signal multiplied by wideband spreading signal, or codeword

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

5.Receivers detect only the desired codeword. All others appear

as noise.

6.Receivers must know transmitters codeword.

CDMA FEATURES:


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GENERAL THEORY OF CDMA: Let us consider arbitrary signal with rectangular frequency spectrum.

It is multiplied by the cosine function to shift the spectrum as shown in fig. below:

Fig.: Frequency spectrum

Fig.: Shifted frequency spectrum


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In receiver end, the signal is once again multiplied by the cosine function as shown in fig.

Fig.: Frequency Spectrum of the signalbefore filtering

LPF (Low Pass Filter) is used at receiver end to recover the signal.

The bandwidth of the signal should not exceed 1/3 rd of whole frequency spectrum. Sampling should be done at 44.1kHz to prevent ALIASING.

Transmitted signal:

The transmitted signal is represented by squaring pulse which corresponds Sine functionin the frequency.

100 200 300 400 500 600

2

4

6

8

10

12

14

Fig.: Sine function occupying theLowest part of Spectrum.


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GENERATING THECDMA SIGNAL:


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Working Principle:

b(t)=data signal

a(t)=PN sequence

s(t)=Modulated signal
http://en.wikipedia.org/wiki/File:Generation_of_CDMA.svg


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DECODING PROCESS:

STEPS:

Conversion of R.F signal to Digital signal.

Decoding & dispreading the users signal. Deinterleaving & decoding. Decompression of the voice signals.

Digital to Analog converter.


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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 bitis the inter-cell interference factor.

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

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


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CDMA BELONGS TO TWO BASICCATEGORIES:

1 . S YNC H RO NO US( O RT H O G O N AL C O D E S )

2 . A S Y N C H R O N O U S( P S E U D O R A N D O M C O D E S )


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1 . SYNCHRONOUS (ORTHOGONAL CODES) CDMA

E a c h u s e r i n s y n c h r o n o u s C D M A u s e s a c o d e o r t h o g o n a l

t o t h e o t h e r s ' c o d e s t o m o d u l a t e t h e i r s i g n a l . O r t h o g o n a l c o d e s h a v e a c r o s s - c o r r e l a t i o n e q u a l t o z e r o ;i n o t h e r w o r d s , t h e y d o n o t i n t e r f e r e w i t h e a c h o t h e r .

Fig : An example of fourmutually orthogonal digitalsignals.
http://en.wikipedia.org/wiki/File:Cdma_orthogonal_signals.png


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2 . ASYNCHRONOUS (PSEUDORANDOM CODES)

Each user is assigned a pseudo-noise code (PN code) insteadof a vector code.

Occupy a very large bandwidth.

Generated at random at the transmitter side.

Appears as a noise into the background.

Very low cross-correlation with other sequences.

Spreads the narrow-band message signal into a wide-bandsignal.


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MULTI-CARRIER SYSTEM IN CDMA:o Is a Data transmission technique where several sub-carriers are used

to transmit data signal.o Modulation & Demodulation is done by IDFT and DFT.o It increases the spectral density and reduces frequency selectivefading.o

All sub-carriers uses the same information offering better frequencydiversity.

FEATURES: Low interchannel interference. Sensitivity to non-linear amplification. Robust against multi-path fading. Robust against narrow band interference or jamming

signal.


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CDMA IN MOBILE COMMUNICATION

CDMA was used earlier in militaryapplication like anti-jamming andsecure communication.CDMA in mobile communication

have made evolutionarydevelopment.

Availability of low cost, high densedigital integrated circuit.

Reduced size, weight and cost ofsubscriber station.Lower transmission power.


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MULTI-PATH FADING INCDMA SYSTEM: Fading in CDMA system is mostly due to the random variation in

received signal or undesired variation in intensity and loudness of radiowaves.

It can be eliminated using dispreading correlator at receiver end. Multi-path fading cannot be eliminated if multi-path components are

separated by less than the correlated time producing flat fading.

A B


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ADVANTAGES:

DISADVANTAGES:

Capacity increase.

No frequency management or assignment. Reduce average transmitted power. Improves telephone traffic capacity. Reduce the effects of Multi-path fading Improves voice quality. Provides reliable transport mechanism for data communication.

Multi-path fading. Multi-user interference or Multiple access interference (MAI).


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CONCLUSION:

CDMA is radically new concept in wirelesscommunication. It has gained wide spreadacceptance in cellular system and hasdominated worldwide wireless market,increase in system capacity and servicequality. Though there is some limitation inCDMA like multiple access interference,multi-path fading which makes CDMAunderdog of 4G but still it may win.


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BIBLIOGRAPHY:

http://www.cellular.co.za/cdma.htm

http://www.authorstream.com

http://www.altera.com

http://www.wikipedia.org

http://images.google.co.in

http://www.wisegeek.com


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THANK YOU

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wireless video services on cdma

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