Like HowStuffWorks on Facebook!

What are CDMA phones?


Digital 2G (second generation) cell phone technology transmits information in several different ways, with different access methods. FDMA, or frequency division multiple access, means that each call is placed on a different frequency. This is usually used for analog transmissions, and is not considered as efficient for digital transmission. In TDMA, or time division multiple access, each call is given a certain portion of time on a specific frequency. TDMA compresses information so it takes up less space, and it has three times more capacity than the analog system using the same number of channels. It uses a narrow band split into three time slots. TDMA is also the access method used for GSM, which is used in Europe, Australia, Asia and Africa. GSM phones in the United States are not internationally compatible and do not provide access while traveling abroad.

The CDMA system is different than TDMA. Digitized data is sent spread out in different frequencies over the whole available bandwidth. The data from each phone is sent out and received using a unique code sequence, and data from all users is sent out over the same wide bandwidth. The data is sent out in small pieces, each of which is given a time stamp. The GPS system is accessed for this information. In the CDMA transmission method, calls can overlap on the same band because they have their specific recognition codes. Up to ten digitized CDMA calls can take up the space of one analog call. CDMA can operate in 800-MHz and 1900-MHz frequency bands. CDMA and TDMA both use high-power signals that can interfere with each other's reception.