1G - Using analog signals based on Advanced Mobile Phone System (AMPS) standard operating in the range of 824Mhz to 894MHz (also dubbed as 800Mhz band)
2G - Converted to use digital signals to cram more calls into the available frequency. There are 2 competing standards - CDMA (Code Division Multiple Access) which operates in the same 800Mhz band, and GSM (Global System for Mobile Communication) which operates in 1900MHz. These 2 standards are not interoperatable. 2G allows transmission of data in form of SMS (Short Message Service) and MMS (Multimedia Message Service). Transfer speed is around 144Kbps.
3G - For smartphone with transfer speed to around 2Mbps. Standards include CDMA2000 which evolved from CDMA and UMTS (Universal Mobile Telecommunication System) which evolved from GSM.
4G - Transmission speed up exceeds 1Gbps. Competing standards are:
(1) LTE (Long Term Evolution) with download rate up to 300Mbps
(2) HSPA+ (Evolved High Speed Packet Access) with download rate up to 168Mbps. Current rate is around 42Mbps
(3) WiMax (Worldwide Operability for Microwave Access) with download rate of 128Mbps
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