CDMA

Also see CDMA One, CDMA2000, and W-CDMA.

CDMA (Code-Division Multiple Access) refers to any of several protocols used in so-called second-generation (2G) and third-generation (3G) wireless communications. As the term implies, CDMA is a form of multiplexing, which allows numerous signals to occupy a single transmission channel, optimizing the use of available bandwidth. The technology is used in ultra-high-frequency (UHF) cellular telephone systems in the 800-MHz and 1.9-GHz bands.

CDMA employs analog-to-digital conversion (ADC) in combination with spread spectrum technology. Audio input is first digitized into binary elements. The frequency of the transmitted signal is then made to vary according to a defined pattern (code), so it can be intercepted only by a receiver whose frequency response is programmed with the same code, so it follows exactly along with the transmitter frequency. 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, which minimizes signal breakup as a handset passes from one cell to another. The combination of digital and spread-spectrum modes supports several times as many signals per unit bandwidth as analog modes. CDMA is compatible with other cellular technologies; this allows for nationwide roaming.

The original CDMA standard, also known as CDMA One and still common in cellular telephones in the U.S., 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 deliver data many times faster.

Getting started with CDMA

To explore how CDMA is used in the enterprise, here are additional resources:

CDMA and GSM: What's the difference?: The differences between the two competing cell phone technologies are discussed in this article. The piece was inspired by a Brighthand.com reader's question.

3G: The CDMA alternative : CDMA2000 is a third-generation (3G) mobile wireless technology that can support mobile data communications at speeds ranging from 144 Kbps to 2 Mbps. This column discusses the history and specifications of CDMA and explores its benefits.

Ericsson's Nortel LTE, CDMA win gives it 4G advantage: Ericsson's winning bid for Nortel's CDMA and LTE business gives it a launchpad into the early North American 4G market and leaves loser Nokia Siemens Networks in a tricky position.

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More resources from around the web: - The CDMA Development Group has a Web site. - Ericsson describes its CDMA systems. - Tutorial - CDMA technology

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