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In 3G, the most prevalent technology was UMTS with CDMA-2000 in close contention. All radio access technologies have to solve the same problems: to divide the finite RF spectrum among multiple users as efficiently as possible. GSM uses TDMA and FDMA for user and cell separation. UMTS, IS-95 and CDMA-2000 use CDMA. WiMAX and LTE use OFDM.
In theory CDMA, TDMA and FDMA have exactly the same spectral efficiency, but, in practice, each has its own challenges – power control in the case of CDMA, timing in the case of TDMA, and frequency generation/filtering in the case of FDMA. TDMA systems must carefully synchronize the transmission times of all the users to ensure that they are ...
As users take turns using the channel, the system can more easily manage timing and coordination compared to more complex methods like CDMA (Code Division Multiple Access), where signals overlap. [12] Scalability: TDMA systems can be scaled effectively to accommodate a growing number of users. As demand increases, additional time slots can be ...
DAMA and PAMA are related only to channel/resource allocation and should not be confused with the multiple access/multiplexing methods (such as FDMA frequencies, TDMA slots, CDMA codes, or others) intended to divide a single communication channel into multiple virtual channels.
IMT-2000 CDMA Direct Spread. also known as W-CDMA, used in UMTS, the successor to GSM; IMT-2000 CDMA Multi-Carrier. also known as CDMA2000, the successor to 2G CDMA ; IMT-2000 CDMA TDD. also known as TD-SCDMA; IMT-2000 TDMA Single Carrier. also known as EDGE, an intermediate 2.5G technology; IMT-2000 FDMA/TDMA. also known as DECT
MC-CDMA spreads each user symbol in the frequency domain. That is, each user symbol is carried over multiple parallel subcarriers, but it is phase-shifted (typically 0 or 180 degrees) according to a code value. The code values differ per subcarrier and per user.
W-CDMA (WCDMA; Wideband Code-Division Multiple Access), along with UMTS-FDD, UTRA-FDD, or IMT-2000 CDMA Direct Spread is an air interface standard found in 3G mobile telecommunications networks. It supports conventional cellular voice, text and MMS services, but can also carry data at high speeds, allowing mobile operators to deliver higher ...
Frequency-division multiple access (FDMA) is a channel access method used in some multiple-access protocols. FDMA allows multiple users to send data through a single communication channel, such as a coaxial cable or microwave beam, by dividing the bandwidth of the channel into separate non-overlapping frequency sub-channels and allocating each sub-channel to a separate user.