CDMA (Code-Division Multiple Access) is a wireless communication protocols.It is called second-generation (2G) and third-generation (3G) wireless communications.CDMA is a form of wireless multiplexing, in which data can be sent over multiple frequencies simultaneously.In a CDMA system, data is broken into packets.Each of packets is given a unique identifier, so that they can be sent out over multiple frequencies and then re-built in the correct order by the receiver.The technology is used in ultra-high-frequency (UHF) cellular telephone systems in the 800-MHz and 1.9-GHz bands.
CDMA uses analog-to-digital conversion (ADC) along with spread spectrum technology. Audio input is first converted into binary elements. The frequency of the transmitted signal is then made compatible with receiver frequency so that it can be intercepted only by a defined receiver. There are trillions of possible frequency-sequencing codes, which enhances privacy and makes cloning difficult.
The CDMA channel is nominally 1.23 MHz wide. CDMA networks use a scheme called soft handoff.It minimizes signal breakup as a handset passes from one cell to another. The combination of digital and spread-spectrum modes of CDMA supports several times as many signals per unit bandwidth as analog modes. CDMA is compatible with other cellular technologies, that supports nationwide roaming.
The first CDMA standard, also known as CDMAone and still common in cellular telephones in the U.S.It offers a transmission speed of only up to 14.4 Kbps in its single channel form and up to 115 Kbps in an eight-channel form. CDMA2000 and wideband CDMA support data many times faster.
CDMA has been used in many communications systems, including the GSM and in the OmniTRACS satellite system for transportation logistics.
Usage in mobile telephony
CDMA has been implementationed with different termology. The original U.S. standard defined by QUALCOMM was known as IS-95.The ‘IS’ referring to an Interim Standard of the Telecommunications Industry Association (TIA). IS-95 is often referred to as second generation cellular(2G). The QUALCOMM brand name CDMAone may also be used to refer to the 2G CDMA standard.
Various companies use different form of CDMA to provide fixed-line networks using Wireless local loop (WLL) technology. This application of CDMA can be found in most parts of the world.