CDMA
(Code Division Multiple Access) A method for transmitting simultaneous signals over a shared portion of the spectrum. The foremost application of CDMA is the digital cellular phone technology from QUALCOMM that operates in the 800MHz band and 1.9GHz PCS band. CDMA phones are noted for their call quality.
CDMA Is Efficient
CDMA requires fewer cell sites than the GSM and TDMA digital cellphone systems and provides three to five times the calling capacity. Providing more than 10 times the capacity of the analog cell phone system (AMPS), CDMA has become widely used in North America and is also expected to become the third-generation (3G) technology for GSM. For example, in the U.S., the Verizon and Sprint cellphone , in India Reliance services are based on CDMA.
Spread Spectrum
Unlike the other digital systems that divide the spectrum into different time slots, CDMA's spread spectrum technique overlaps every transmission on the same carrier frequency by assigning a unique code to each conversation. The often-used analogy for this is your ability to detect your own language in a room full of people speaking other languages.
A Different Kind of Chip
After the speech codec converts voice to digital, CDMA spreads the voice stream over the full 1.25MHz bandwidth of the CDMA channel, coding each stream separately so it can be decoded at the receiving end. The rate of the spreading signal is known as the "chip rate," as each bit in the spreading signal is called a "chip" (no relation to an integrated circuit). All voice conversations use the full bandwidth at the same time. One bit from each conversation is multiplied into 128 coded bits by the spreading techniques, giving the receiving side an enormous amount of data it can average just to determine the value of one bit.
GSM | GPRS | EDGE | CDMA | UMTS | HSDPA | Mobile Standards
