Widely used in 90s-2000allows multiple users on a single channel.Supports voice as well as data.radio signals on 2G networks are digital, which can be compressed and multiplexed easily.2G technologies can be divided into TDMA-based and CDMA-based standards depending on the type of multiplexing used.Speed 9.6 Kbps .Carrier frequency is of 200 KHz.

Used in 2001-2004In addition to circuit switched data, packet switched data was also implemented.Enhanced multimedia and streaming video are possible. Supports web browsing2.5G is General Packet Radio Service (GPRS), which is evolution from GSM.GPRS could provide data rates from 56Kbps up to 115Kbps. 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.carrier frequency is same as that of 2G.

Came into picture during 2004-2005.High speed (2Mbps) and increased bandwidth (2GHz).Carrier frequency is 5 MHz.3G networks offer greater security than their 2G predecessors because 3G networks permit validation measures when communicating with other devices.This technology is much more flexible as it can support 5 major radio technologies that operate under CDMA, TDMA and FDMA. CDMA accounts for IMT-DS (direct speed), IMT-MC (multi carrier). TDMA holds for IMT-TC (time code), IMT-SC (single carrier).Applications of 3G are: Mobile TV, Video on Demand, Video Conferencing, Location-based services and Global Positioning System(GPS)Drawback of 3G is that it is simply not available in certain regions.

Figure: Evolution of Mobile system from 2G to 3G

LTE is a standard for wireless communication of high-speed data for mobile phones and data terminals.Supports at least 200 active data clients in every 5MHz cell.It is based on the GSM/EDGE and UMTS/HSPA network technologies, increasing the capacity and speed using new modulation techniques.Ability to manage fast moving mobiles and supports MBSFN (Multicast Broadcast Single Frequency Network).It can deliver services such as Mobile TV

Formally submitted as a candidate 4G system to ITU-T in late 2009, was approved into ITU, International Telecommunications Union, IMT-Advanced and was finalized by 3GPP in March 2011.Data rate is 2Gbps.It targets faster switching between power states and improved performance at the cell edge.Improves the capacity and coverage, and ensures user fairness.Also introduces multicarrier to be able to use ultra wide bandwidth, up to 100MHz of spectrum supporting very high data rates.