Cellular Telephony (CDMA Technique + Data)

Presented byMd. Mazed Rayhan ShuvoRoll: 1309023

&Ashikur RahmanRoll: 1309024

2 Key Points

Cellular Telephony SystemsCellular Telephony System TechniquesWhy CDMA technique?What is CDMA ?Spread Spectrum Technique in CDMACDMA Data transmission and reconstructionAdvantages of CDMADisadvantages of CDMA

3 Cellular Telephony SystemBoth wire and wireless telecommunication of voice, video, and data

Based on large number of subscribers and MSC-CO

Introduced by Bell Telephone Laboratories in 1971, as Advanced Mobile Phone System

Usage of different multiple access technique like TDMA, FDMA , CDMA

Evolution of 1G, 2G, 3G and 4G

4

5 Cellular Telephony System Techniques

• Time Division Multiple Access (TDMA): Most 2G cellular systems are based on TDMA. TDMA technology was popular in Europe, Japan and Asian countries.

• Frequency Division Multiple Access (FDMA): FDMA is a channel access method used in multiple-access protocols as a channelization protocol.

• Code Division Multiple Access (CDMA): CDMA is an example of multiple access, where several subscribers can send information simultaneously over a single communication channel. This allows several users to share a band of frequencies.

6 Why CDMA technique?

FDMA vs TDMA vs CDMA Techniques

7What is CDMA ?

A digital wireless technology that uses spread-spectrum techniques.

CDMA does not assign a specific frequency to each user. Instead, every channel uses the full available spectrum.

Individual conversations are encoded with a pseudo-random digital sequence.

Provides better capacity for voice and data communications than other commercial mobile technologies, allowing more subscribers to connect at any given time.

It is the common platform on which 3G technologies are built.

8

Code Division Multiple Access Technique

9 Spread Spectrum Technique in CDMA

10CDMA Data transmission and reconstruction (using spread spectrum)

11 Advantages of CDMA High spectral capacity.

Reusing the same frequency in every cell eliminates the need for frequency planning.

Rejection of narrow band interference (i.e. in FDMA)

Usage of the soft hand off, which is undetectable and provides a more reliable and higher quality signal.

Call dropout occurrence is very rare.

Covers more area than GSM.

12 Disadvantages of CDMA Lack of international roaming capabilities compared to GSM

Limited variety of the handset e.g. Citycell in Bangladesh

The ability to upgrade or change to another handset is not easy

Near-far problem

After a certain number of users, in the same area audio quality degrades.

13

Thanks to all