What is Code Division Multiple Access

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Introduction :
The world is more demanding of wireless communication technologies than ever. More popular in the world are subscribing to wireless services and consumers use their phones more often. Add on the characteristics of third generation (3G) wireless data services and applications - such as email, wireless Internet, digital photo taking / sending and position location Assisted-GPS. CDMA consistently provides better capacity for voice and data communications than other commercial mobile technologies, allowing more subscribers to connect at some point, and it is the common platform on which 3G technologies are built.


CDMA Multiple Access: The concept of multiple access is to allow a certain number of users to share a common channel. The two traditional ways of multiple access Frequency Division Multiple Access (FDMA) and Time Division Multiple Access (TDMA).

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FDMA:
Frequency Division Multiple Access in the frequency band is divided into slots. Each user receives a frequency slot. assigned that is used at will. It could be compared to AM or FM radio broadcast in which each station has an assigned frequency. FDMA good filtering requirements.


TDMA:
In Time Division Multiple Access, the band is not partitioned but users are allowed to use only in predefined time intervals. one at a time. And TDMA synchronization requests between users.


CDMA:
CDMA, for Code Division Multiple Access, is different from traditional methods in that it does not allocate frequency or time slots in the user, but shall be entitled to use both simultaneously to all users. To do this, it uses a technique called spread spectrum. Indeed, each user is assigned a code can recover at the end of the receiver. This method has the property that the unwanted signals with codes different spread even more by the process, make them like the sound of the receiver.


Techniques :
For mobile telephony, three techniques are possible to spend several channels on the same frequency carrier: the multiplexing time (TDMA, English TDMA), frequency division multiplexing (FDMA, English FDMA) and code multiplexing (CDMA, English CDMA).

- Standard GSM does not use CDMA, but TDMA and FDMA.
The current standard is CDMA-2000.


Standards :
CDMA2000 (Code Division Multiple Access) is an evolution of cdmaOne systems used in the United States of America. It allows data rates up theoretically up to 2 Mbps

- The CDMA-2000 standard is based on the CDMA air interface originally developed by the U.S. Army.
- CDMA-2000 was developed by the 3GPP2 (3rd Generation Partnership Project # 2) which includes the American TIA, ARIB, TTA and - CWTS the Asia Pacific and inclusive international forum.
- The ETSI European and the American T1P1 are not part and focus only onUMTS.
- The CDMA-2000 is an American standard TIA IS-under reference 2000.


Advantages of CDMA 2000
CDMA 2000 has benefited from the vast experience gained by several years of operation of CDMA-One. Accordingly. CDMA 2000 is a highly effective and robust. Support both voice and data, the standard has been designed and tested in different frequency bands, including the new IMT-2000 allocations. There is a strong demand for new services and operators seek to offer these subscribers to many other reasonably priced. Thanks to its optimized radio technology, CDMA 2000 enables operators to invest in fewer cell sites and deploy them more quickly, ultimately allowinf service providers to increase their earnings with return on investment (ROI) . Rising incomes, with a wider range of services, ensure CDMA2000 the technology of choice for service providers. Other advantages of CDMA technology are increased voice capacity, higher data throughput, increase battery life, timing, transmit diversity.