Presentation on CDMA

CDMACDMASubmitted By

Shuvangkar Dhar (Id No: WUB09/12/51/2002)Dept: EEE Batch: 51-BWorld University of Bangladesh

Submitted To

Rajib MondalSenior Lecturer, Dept. of EEE

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.

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 into In 1995, CDMA technology was put into

commercialization in Hong Kong and America on commercialization in Hong Kong and America on large scale.large scale.

• In April, 2001, China Unicom began to construct In April, 2001, China Unicom began to construct CDMA networks—the largest in the world (about CDMA networks—the largest in the world (about 70Million line now).70Million line now).

• At present, CDMA commercial networks are At present, CDMA commercial networks are established in about 40 countries or area, almost established in about 40 countries or area, almost 20% of all users in the world20% of all users in the world..

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-952. CDMA20003. WCDMA

• Soft handoff increases reliability of handovers.

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

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.

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.

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)


CDMA Transmitter:


-5000 -4000 -3000 -2000 -1000 0 1000 2000 3000 4000 50000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1noisemassegeAfter SpredingChip Duration is 0.4

ms.Bit Duration is 6.4 ms.Processing Gain is 16

Spectrum of the 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)


CDMA Receiver:


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.

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.

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


• 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.


• 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

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.

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.

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.

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.

Engineering

Presentation on CDMA