CDMA, CdmaOne, Cdma2000

Code division multiple access (CDMA) is a channel access method utilized by various radio communication technologies. It should not be confused with the mobile phone standards called cdmaOne and CDMA2000 (which are often referred to as simply "CDMA"), which use CDMA as an underlying channel access method..

One of the basic concepts in data communication is the idea of allowing several transmitters to send information simultaneously over a single communication channel. This allows several users to share a bandwidth of different frequencies. This concept is called multiplexing.

CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same physical channel. By contrast, time division multiple access (TDMA) divides access by time, while frequency-division multiple access (FDMA) divides it by frequency. CDMA is a form of "spread-spectrum" signaling, since the modulated coded signal has a much higher data bandwidth than the data being communicated.

CDMA is a spread spectrum multiple access technique. A spread spectrum technique is one which spreads the bandwidth of the data uniformly for the same transmitted power.  In CDMA a locally generated code runs at a much higher rate than the data to be transmitted. Data for transmission is simply logically XOR (exclusive OR) added with the faster code.CDMA employs analog-to-digital conversion  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.

Spread Spectrum Modulation is distinguished from wideband modulation schemes such as wideband Frequency Modulation (FM) by noting that in spread spectrum the waveform causing the spreading is independent of the data being transmitted. This permits the spreading waveform to be selected based on improving system performance in some way. In IS-95, PN sequences(A  sequence is a sequence of binary numbers, e.g. ±1, which appears to be random; but is in fact perfectly deterministic). are selected as the spreading signals since they uniformly spread the signal power over the available bandwidth and provide other critical advantages such as permitting universal frequency reuse.

PN Spreading and De-spreading:

PN spreading is the use of a PN sequence to distribute or spread the power of a signal over a bandwidth which is much greater than the bandwidth of the signal itself. PN despreading is the process of tasking a signal in its wide PN spread bandwidth and reconstituting it in its own much narrower bandwidth.
PN sequences can be used in at least two ways to spread the signal power over a wide bandwidth. One is called Frequency Hopping (FH) in which the center frequency of a narrowband signal is shifted pseudo randomly using the PN code. A second method is called Direct Sequence (DS). In DS the signal power is spread over a wide bandwidth by in effect multiplying the narrow-band signal by a wideband PN sequence. When a wideband signal and a narrowband signal are multiplied together, the resulting product signal has a bandwidth about equal to the bandwidth of the wideband signal.

CdmaOne:

Interim Standard 95 (IS-95) is the first CDMA-based digital cellular standard pioneered by Qualcomm(a wireless telecommunications research and development company). The brand name for IS-95 is cdmaOne. 
It is a 2G Mobile Telecommunications Standard that uses CDMA, a multiple access scheme for digital radio, to send voice, data and signaling data (such as a dialed telephone number) between mobile telephones and cell sites.
There are two versions of IS-95, called IS-95A and IS-95B. The IS-95A protocol employs a 1.25-MHz carrier, operates in radio-frequency bands at either 800 MHz or 1.9 GHz, and supports data speeds of up to 14.4 Kbps. IS-95B can support data speeds of up to 115 kbps by bundling up to eight channels. 

Cdma2000:
CDMA2000 (also known as IMT Multi‑Carrier (IMT‑MC)) is a family of 3G mobile technology standards, which use CDMA channel access, to send voice, data, and signaling data between mobile phones and cell sites. The set of standards includes: CDMA2000 1X, CDMA2000 EV-DO Rev. 0, CDMA2000 EV-DO Rev. A, and CDMA2000 EV-DO Rev. B.  CDMA2000 has a relatively long technical history and is backward-compatible with its previous 2G iteration IS-95 (cdmaOne). CDMA2000 can support mobile data communications at speeds ranging from 144 Kbps to 2 Mbps.