CDMA uses a “spread-spectrum” technique whereby electromagnetic energy is spread to allow for a signal with a wider bandwidth. This allows multiple people on multiple cell phones to be “multiplexed” over the same channel to share a bandwidth of frequencies.
With CDMA technology, data and voice packets are separated using codes and then transmitted using a wide frequency range. Since more space is often allocated for data with CDMA, this standard became attractive for 3G high-speed mobile Internet use.
The CDMA standard was originally designed by Qualcomm in the U.S. and is primarily used in the U.S. and portions of Asia by other carriers. Sprint, Virgin Mobile and Verizon Wireless use CDMA while T-Mobile and AT&T use GSM.
While CDMA and GSM compete head on in terms of higher bandwidth speed (i.e. for surfing the mobile Web), GSM has more complete global coverage due to roaming and international roaming contracts.
GSM technology tends to cover rural areas in the U.S. more completely than CDMA. Over time, CDMA won out over less advanced TDMA technology, which was incorporated into more advanced GSM.