2G
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2G hay 2-G (viết tắt của tiếng Anh second generation, "thế hệ thứ hai") là công nghệ thông tin thứ hai có ứng dụng nhiều đặc tính kỹ thuật số.
The main differentiator to previous mobile telephones, retroactively dubbed 1G, is that 1G networks process analog data but 2G networks are digital. This allowed a considerable improvement in voice quality, as digital information is not subject to distortions in the same way as analog information, and also increased capacity as calls can be multiplexed more efficiently. 2G networks may offer an optional service to transfer low-speed data, such as email or software, in addition to the digital voice call itself. SMS messaging is also available as a form of data transmission for some standards.
2G services are frequently referred as Personal Communications Service or PCS in the US.
2G technologies can be divided into TDMA-based and CDMA-based standards depending on the type of multiplexing used. The main 2G standards are:
- GSM (TDMA-based), originally from Europe but used worldwide
- IDEN (TDMA-based), proprietary network used by Nextel in the United States and Telus Mobility in Canada
- IS-136 aka D-AMPS, (TDMA-based, commonly referred as simply TDMA in the US), used in the Americas
- IS-95 aka cdmaOne, (CDMA-based, commonly referred as simply CDMA in the US), used in the Americas and parts of Asia
- PDC (TDMA-based), used exclusively in Japan
2.5G services, which enable high-speed data transfer over upgraded existing 2G networks, are widely deployed worldwide. Next-generation 3G, designed to allow the transmission of very large quantities of data, is also becoming increasingly popular. Work on 4G has already started although its scope is not clear yet. Higher data speeds enable new services for subscribers, such as picture messaging and video telephony.
