1G, 2G and 3G

1G:

Radio signals on 1G networks are analog.While It uses digital signaling to connect the radio towers (which listen to the handsets) to the rest of the telephone system, the voice itself during a call is modulated to higher frequency, typically 150 MHz and up in 1G.

2G:

Digital signals, speed upto

It uses digital signaling to connect the radio towers (which listen to the handsets) to the rest of the telephone system, the voice itself during a call is encoded to digital signals in 2G.

2G technologies can be divided into TDMA-based and CDMA-based standards depending on the type of multiplexing used.

(1) TDMA (Time division multiple access): It allows several users to share the samefrequency channel by dividing the signal into different time slots. It is used in GSM (Global system for mobile communications).

(2) CDMA (Code division multiple access): CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same physical channel

Another type is FDMA: frequency division multiple access.

3G:

3G system must provide peak data rates of at least 200 kbit/s according to the IMT-2000 (International mobile telecommunications) specification. Application services include wide-area wireless voice telephone, mobile Internet access, video calls and mobile TV, all in a mobile environment.

It is based on kindred spread spectrum radio transmission technology.

Spread-spectrum techniques are methods by which a signal (e.g. an electrical, electromagnetic, or acoustic signal) generated in a particular bandwidth is deliberately spread in the frequency domain, resulting in a signal with a wider bandwidth.

2.5G (GPRS):

GPRS could provide data rates from 56 kbit/s up to 115 kbit/s. It can be used for services such as Wireless Application Protocol (WAP) access, Multimedia Messaging Service (MMS), and for Internet communication services such as email and World Wide Web access, It has Implemented a packet switched domain in addition to the circuit switched domain. It does not necessarily provide faster services because bundling of timeslots is used for circuit switched data services (HSCSD) as well.

2.75G (EDGE):

GPRS networks evolved to EDGE networks with the introduction of 8PSK encoding. Enhanced Data rates for GSM Evolution (EDGE), Enhanced GPRS (EGPRS), or IMT Single Carrier (IMT-SC) is a backward-compatible digital mobile phone technology that allows improved data transmission rates, as an extension on top of standard GSM.

Note:

Each generation is characterized by new frequency bands, higher data rates and non backwards compatible transmission technology