TDMA stands for Time division multiple access. It is a channel access method for shared medium networks.IT is digital transmission technology that allows a number of users to access a single radio-frequency (RF) channel without interference by allocating unique time slots to each user within each channel. The TDMA digital transmission scheme multiplexes three signals over a single channel. It allows several users to share the same frequency channel by dividing the signal into different timeslots. The users transmit in rapid succession, one after the other, each using his own timeslot. This allows multiple stations to share the same transmission medium (e.g. radio frequency channel) while using only the part of its bandwidth they require. TDMA is used in the digital 2G cellular systems such as GSM, IS-136, PDC and iDEN, and in the Digital Enhanced Cordless Telecommunications (DECT) . It is also used extensively in satellite systems, and combat-net radio systems. TDMA frame structure showing a data stream divided into frames and those frames divided into timeslots. The current TDMA standard for cellular divides a single channel into six time slots, with each signal using two slots, providing a 3 to 1 gain in capacity over advanced mobile-phone service (AMPS). Each caller is assigned a specific time slot for transmission.
TDMA is a type of Time-division multiplexing, with the special point that instead of having one transmitter connected to one receiver, there are multiple transmitters. In the case of the uplink from a mobile phone to a base station this becomes particularly difficult because the mobile phone can move around and vary the timing advance required to make its transmission match the gap in transmission from its peers.
CDMA stands for Code Division Multiple Access, but was originally known as IS-95. Qualcomm was the first to created this technology and by 1993 it was adopted by the Telecommunication Industry Association. Later this technology was enhanced and refined by Ericsson.Since the development of CDMA technology there has been many new releases and platforms. The original CDMA is now referred to as CDMAone. Several different variants of CDMA technology been developed continuously improving quality and data transfer speeds. Third generation CDMA technology, commonly referred to as CDMA2000 encompasses a wide variety of different standards, each continually improving upon the first including; 1X EV, 1XEV-DO, and MC 3X. CDMA2000 is the current standard used by most US carriers today. The first release of CDMA2000 was refereed to as either 3G1X, 1XRTT, or 1X. Designed to provide data transmissions of ten times faster then the previous technology and double the voice capacity of CDMAone.Depending on the phone you have and its capabilities you will notice symbols in the default screen of your phone reading either 1X, 1XEV-DO or some variation of the two. This symbol defines the CDMA2000 standards your phone is operating on. Newer phones will display EV or EV-DO using the newer faster, more reliable CDMA technology. Enhanced data transfer provides for the new technologies released by companies like Verizon. Including data transfer for files, music, games and the Internet.
WCDMA technology, standing for Wideband Code Division Multiple access, is the most developed and advanced form of the third generation CDMA2000 technology. It encompasses higher data transfer rates and provides wireless connections in markets world wide. Many existing GSM 2G (GSM/GPRS) operators have slowly began the switch to using WCDMA technology.Qualcomm the original developer of CDMA owns patents of this technology. They have granted royalty-bearing licenses to over 100 network operators. The chart below displays the number of operators, vendors, subscribers and countries each technology is used in.
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