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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.
However, unlike TDMA, there are no time slots, and all CDMA radios can be active all the time to deliver up to 14.4 kbit/s data transmission speeds. With the evolution of CDMA to CDMA2000 and 1xRTT, the use of IS-95 CDMA Circuit Switched Data declined in favour of the faster data transmission speeds available with the newer technologies.
CDMA is analogous to the last example where people speaking the same language can understand each other, but other languages are perceived as noise and rejected. Similarly, in radio CDMA, each group of users is given a shared code. Many codes occupy the same channel, but only users associated with a particular code can communicate.
The Universal Mobile Telecommunications System (UMTS) is a 3G mobile cellular system for networks based on the GSM standard. Developed and maintained by the 3GPP (3rd Generation Partnership Project), UMTS is a component of the International Telecommunication Union IMT-2000 standard set and compares with the CDMA2000 standard set for networks based on the competing cdmaOne technology.
IS-95 was the first ever CDMA-based digital cellular technology. It was developed by Qualcomm using Code Division Multiple Access and later adopted as a standard by the Telecommunications Industry Association in TIA/EIA/IS-95 release published in 1995.
The name TDMA is based on the abbreviation for time-division multiple access, a common multiple access technique which is used in most 2G standards, including GSM, as well as in IS-54 and IS-136. D-AMPS competed against GSM and systems based on code-division multiple access (CDMA).
Most 2G cellular systems, with the notable exception of IS-95, are based on TDMA. GSM, D-AMPS, PDC, iDEN, and PHS are examples of TDMA cellular systems.. In the GSM system, the synchronization of the mobile phones is achieved by sending timing advance commands from the base station which instruct the mobile phone to transmit earlier and by how much.
CDMA frequency bands or frequency ranges are the cellular frequencies designated by the ITU for the operation of cdmaOne ... GSM frequency bands; UMTS frequency bands ...
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