There is a whole overview of CDMA.

1. CDMACDMA
Submitted By
Shuvangkar Dhar (Id No: WUB09/12/51/2002)
Dept: EEE Batch: 51-B
World University of Bangladesh
Submitted To
Rajib Mondal
Senior Lecturer, Dept. of EEE

2. Introduction to CDMA
• CDMA – Code Division Multiple Access
• Fully digital wireless data transmission system
• Uses special random numbers to encode bits
of information.
• Allows multiple access by assigning different
users different random numbers on the same
channel.
• Users have control of a very wide channel
bandwidth 1.5 to 5 MHz
• Built-in interference minimization.

3. Background
• 1993, the first CDMA standard IS-95 was issued;1993, the first CDMA standard IS-95 was issued;
• In 1995, CDMA technology was put intoIn 1995, CDMA technology was put into
commercialization in Hong Kong and America oncommercialization in Hong Kong and America on
large scale.large scale.
• In April, 2001, China Unicom began to constructIn April, 2001, China Unicom began to construct
CDMA networks—the largest in the world (aboutCDMA networks—the largest in the world (about
70Million line now).70Million line now).
• At present, CDMA commercial networks areAt present, CDMA commercial networks are
established in about 40 countries or area, almostestablished in about 40 countries or area, almost
20% of all users in the world20% of all users in the world..

4. Executive Summary
• CDMA stands for Code Division Multiple Access.
• It provides a new dimension which represent the
Code.
• It works in two method which are Direct
sequence and Frequency Hopping.
• It has a huge application in cellular network.
• There are three evolution for CDMA:
1. IS-95
2. CDMA2000
3. WCDMA
• Soft handoff increases reliability of handovers.

5. Objective
•Introduce to CDMA Networks
• What is CDMA?
• How it works?
• To know about types of CDMA.
• To find the Advantages and
Disadvantages of CDMA.
• To know about application

6. Methodology
• Collection of information from books as
well as different websites such as
Wikipedia, Slideshare.com.
• Got help from the communication theory
classes taken by Rajib Mondal sir.

7. Basic diagram of CDMA
• There exist a new
dimension with time
and frequency.
• The new dimension
represent the code
which provided by
the operator for the
user.

8. Working Principle of CDMA
CDMA transmitter:
• The voice has to be digitalize (Pulse Code
Modulation (PCM) then compressed)
• Each user is given a unique PN code.
• The Codes must have low cross-correlation
• The transmitter multiplies the code by the data
to get the coded massage (bit)

9. Working Principle of CDMA
CDMA Transmitter:

10. Working Principle of CDMA
-5000 -4000 -3000 -2000 -1000 0 1000 2000 3000 4000 5000
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0.1
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0.9
1
noise
massege
After SpredingChipDurationis0.4
ms.
Bit Durationis6.4ms.
ProcessingGainis16
Spectrum of the CDMA:

11. Working Principle of CDMA
CDMA Receiver:
• The received signal is multiplied again by the same
code that used in the transmitter.
• Integrate over bit duration and, then using a hard
decision to get the transmitted massage (bit)

12. Working Principle of CDMA
CDMA Receiver:

13. Working Principle of CDMA

14. Types of CDMA
1. Frequency Hopping
• Fixed sequence of frequency values & Time is
divided into slots .
• In the first time slot, a given user transmit to the
base station using the first frequency in its
frequency hopping sequence.
• In the next time interval, it transmits using the
second frequency value in its frequency hopping
sequence, and so on.
• This way, the transmit frequency keeps changing in
time.

15. Types of CDMA
2. Direct Sequence
• Each user transmits its message to the base station
using the same frequency, at the same time.
• Here signals from different users interfere with each
other.
• But the user distinguishes its message by using a
special, unique code. This code serves as a special
language that only the transmitter and receiver
understand.

16. CDMA Application in Mobile Network
• IS-95
• Mainly used in U.S.A
• Standard was finished in 1993 and first
commercially launched in 1996
• Basic data rate is 9.6 kbps
• Chip rate of 1.2288 Mchip/s
• Allocated bandwidth is 1.25 MHz
• Fixed spreading code of length 64

17. CDMA Application in Mobile Network
• CDMA2000
• CDMA2000 1x
• Use same 1.25 MHz as IS-95
• CDMA2000 1xEV-DO
• CDMA2000 1xEV-DO delivers peak data speeds of 2.4Mbps
and supports
• Applications such as MP3 transfers and video conferencing
• CDMA2000 1xEV-DV
• CDMA2000 1xEV-DV provides integrated voice and
simultaneous high speed
• Packet data multimedia services at speeds of up to 3.09
Mbps.

18. CDMA Application in Mobile Network
• WCDMA
• The faster chip rate of 3,84 Mchips/s
• 5 MHz bandwidth
• Wider bandwidth implies greater frequency
diversity Rake Receiver
• Data rates
• Up to 2 Mbps for packet switched data

19. Advantages of CDMA
• Capacity is CDMA's biggest asset. It can
accommodate more users per MHz of bandwidth
than any other technology.
• 3 to 5 times more than GSM
• CDMA consumes less power and covers large areas
so cell size in CDMA is larger.
• CDMA is able to produce a reasonable call with lower
signal (cell phone reception) levels.
• CDMA uses Soft Handoff, reducing the likelihood of
dropped calls.
• Has a well-defined path to higher data rates.

20. Disadvantages of CDMA
• Most technologies are patented and must be
licensed from Qualcomm.
• Breathing of base stations, where coverage area
shrinks under load. As the number of subscribers
using a particular site goes up, the range of that
site goes down.
• Currently CDMA covers a smaller portion of the
world as compared to GSM which has more
subscribers and is in more countries overall
worldwide.

21. Conclusion
• The CDMA will allow many signals to be
transmitted at the same channel at the same
time. This done by giving each user a Pseudo-
Noise code which is a binary sequence. This code
should have low cross-correlation between each
other.
• Multiple access interference has bad effect on
the CDMA system so the multiple user detection
is used to reduce the MAI.

22. Recommendation
• To produce of the application of optical CDMA,
adhoc networks, dense wireless LANs.
• Now a days CDMA has lost its popularity in our
country though it has much better
communication system from the other
technologies. So if it provides the 4G network it
will be a masterpiece of mobile communication.