CDMA WIRELESS SYSTEM

CDMA WIRELESS SYSTEM

ABSTRACT:

With the emerging technologies in the wireless communication, various access methods have been emerged so far. One of the most important access methods includes TDMA, FDMA and CDMA. The most of the mobile operator companies are using either TDMA or CDMA access methods. The GSM and CDMA are one of the important technologies that are being used widespread the modern day wireless communication. The main difference in the GSM and CDMA is in media access protocol in the Data link sub layer, MAC (Media Access Control) layer in the OSI (Open System Interconnection) stack. There are many companies in India using these technologies to provide services such as GPRS, WAP, SMS, and MMS etc. In India, the communication market is growing like wild mushroom. At present India has full potential that it has earned from companies like TATA Indicomm, Reliance Infocomm, etc.

For radio systems there are two resources, frequency and time. Division by frequency, so that each pair of communicators is allocated part of the spectrum for all of the time, results in Frequency Division Multiple Access (FDMA). Division by time, so that each pair of communicators is allocated all (or at least a large part) of the spectrum for part of the time results in Time Division Multiple Access (TDMA). In Code Division Multiple Access (CDMA), every communicator will be allocated the entire spectrum all of the time. CDMA uses codes to identify connections.

CDMA uses unique spreading codes to spread the baseband data before transmission. The signal is transmitted in a channel, which is below noise level. The receiver then uses a correlator to despread the wanted signal, which is passed through a narrow bandpass filter. Unwanted signals will not be despread and will not pass through the filter.

INTRODUCTION:

Code Division Multiple Access (CDMA) is now in widespread use for Cellular Telecommunications. It also uses the cellular concept, in which a geographical area is divided into small geographical areas called “radio cell” or simply “cell”. The channel allocation is achieved by the DSSS technique. It was first used for the North American CDMA standard or IS-95 cellular system also known by the trade name cdmaOne, and in its later 3G developments as CDMA2000. It is also being used in the other major 3G system, Wideband-CDMA. The technology is based on a form of transmission known as Direct Sequence Spread Spectrum (DSSS). This form of transmission was originally used for military and police communications because the transmissions were difficult to detect in many instances, and even if they were received, they were very difficult to decipher without the correct codes. Previous cellular telecommunications technologies used either frequency division multiple access (FDMA) where different users were allocated different frequencies, or time division multiple access (TDMA) where they were allotted different time slots on a channel. Code Division Multiple Access technology emerged as an alternative to the GSM cellular architecture and has shared in the past decade’s explosive growth in the wireless market. CDMA, like GSM, has seen incremental improvements in capacity throughout this period. Now both types of networks are making a transition to third-generation (3G) systems around the globe, offering yet more capacity and data services.


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