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CDMA Presentation

CDMA is a channel access method that separates both data and voice signals using codes that are then transmitted over a wide frequency range. It allows many users to share the same frequency by using pseudo-random number codes or Walsh codes to distinguish different transmissions. Some key advantages are that it allows a base station to communicate with multiple mobiles on a single channel and can provide very high channel data rates. CDMA2000 is an evolution of the original IS-95 standard and includes specifications like 1X and EV-DO that support higher data rates.

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162 views15 pages

CDMA Presentation

CDMA is a channel access method that separates both data and voice signals using codes that are then transmitted over a wide frequency range. It allows many users to share the same frequency by using pseudo-random number codes or Walsh codes to distinguish different transmissions. Some key advantages are that it allows a base station to communicate with multiple mobiles on a single channel and can provide very high channel data rates. CDMA2000 is an evolution of the original IS-95 standard and includes specifications like 1X and EV-DO that support higher data rates.

Uploaded by

shriniwas ghadyalji
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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CDMA PPT

-Rishabh Tripathi
-Shriniwas Ghadyalji
CDMA
oCode Division Multiple Access.
ois a channel access method

oBoth data and voice are separated from signals


using codes and then transmitted using a wide
frequency range.
oCDMA is the preferred technology for the 3G
generation.
FDMA: Division by frequency
each pair of communicators is allocated part of the spectrum
for all of the time
TDMA: Division by time
each pair of communicators is allocated all of the spectrum for
part of the time
CDMA: every communicator will be allocated the entire
spectrum all of the time.
CODE TYPES
PN codes: Pseudo-random number codes (pseudo-noise or
PN code) can be generated very easily.
A feature of PN codes is that if the same versions of the PN
code are time shifted, then they become almost orthogonal,
and can be used as virtually orthogonal codes within a CDMA
system.
Truly orthogonal codes: Two codes are said to be
orthogonal if when they are multiplied together the result is
added over a period of time they sum to zero. For example a
codes 1 -1 -1 1 and 1 -1 1 -1 when multiplied together give 1 1
-1 -1 which gives the sum zero. An example of an orthogonal
code set is the Walsh codes used within the IS95 / CDMA2000
system.
FEATURES
Many users share the same frequency
There is no absolute limit on the number of users .
System performance is inversely proportional to the
no. of users
Channel data rates are very high in CDMA systems
A RAKE receiver is used to improve reception by
collecting time delayed versions of required signal.
Self jamming is a problem
The near-far problems at receiver
CDMA system showing use of
spreading codes
CDMA spread spectrum
CDMA spreading

•the data is multiplied using the XOR function.


•Each bit in the spreading sequence is called a chip
CDMA spread spectrum
generation
CDMA spread spectrum
decoding
CDMA spreading gain

Spreading gain = W / R
w - the bandwidth of the CDMA spread spectrum signal
R - the input data bit length
System performance is proportional to the spreading gain of
CDMA
spreading factor - chip rate/ data rate
ADVANTAGES
o using this CDMA technique, it is possible to transmit
several sets of data independently on the same carrier
and then reconstitute them at the receiver without
mutual interference.
o In this way a base station can communicate with
several mobiles on a single channel.
CDMA IS-95
Interim Standard 95 (IS-95) is the first CDMA-based digital
cellular standard
also known as TIA-EIA-95
It is described as a 3 layer stack.
The speech coder is Qualcomm 9600 Code Excited Linear
Predictive (QCELP)coder.
That vocoder is detects voice activity,
Reduces data rate to 1200 bps during silent periods
CDMA2000 
known as IMT Multi‑Carrier (IMT‑MC)
The set of standards includes:
CDMA2000 1X,
CDMA2000 EV-DO Rev. 0,
CDMA2000 EV-DO Rev. A,
CDMA2000 EV-DO Rev.
CDMA2000 1X EV-DV
1x-meaning 1 times Radio Transmission Technology
THANK YOU

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