2G refers to second-generation wireless telephone technology that uses digital cellular networks. While 1G networks used analog signals, 2G networks transitioned to digital signals. This allowed for more efficient use of bandwidth and the introduction of data services like SMS. Common 2G standards include GSM, CDMA, and IS-136. 3G networks provided faster data speeds like 200kbps and introduced UMTS and CDMA2000. 4G aims to provide speeds up to 1Gbps for stationary users and 100Mbps for mobile through technologies like LTE Advanced.

2. 2G2G (or 2-G) is short for second-generation wireless telephone technology. Second generation 2G cellular telecom networks were commercially launched on the GSM standard in Finland by Radiolinja(now part of Elisa Oyj) in 1991. After 2G was launched, the previous mobile telephone systems were retrospectively dubbed 1G. While radio signals on 1G networks are analog, radio signals on 2G networks are digital. Both systems use digital signaling to connect the radio towers (which listen to the handsets) to the rest of the telephone system.

3. 2G technologies2G 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 in almost all countries on all six inhabited continents. Today accounts for over 80% of all subscribers around the world. Over 60 GSM operators are also using CDMA2000 in the 450 MHz frequency band (CDMA450).IS-95akacdmaOne (CDMA-based, commonly referred as simply CDMA in the US), used in the Americas and parts of Asia. Today accounts for about 17% of all subscribers globally PDC (TDMA-based), used exclusively in JapaniDEN (TDMA-based), proprietary network used by Nextel in the United States and Telus Mobility in CanadaIS-136 a.k.a. D-AMPS (TDMA-based, commonly referred as simply 'TDMA' in the US), was once prevalent in the Americas but most have migrated to GSM.

4. CapacityUsing digital signals between the handsets and the towers increases system capacity in two key ways:Digital voice data can be compressed and multiplexed much more effectively than analog voice encodings through the use of various codecs, allowing more calls to be packed into the same amount of radio bandwidth.The digital systems were designed to emit less radio power from the handsets. This meant that cells could be smaller, so more cells could be placed in the same amount of space. This was also made possible by cell towers and related equipment getting less expensive.

5. AdvantagesThe lower power emissions helped address health concerns.Going all-digital allowed for the introduction of digital data services, such as SMS and email.Greatly reduced fraud. With analog systems it was possible to have two or more "cloned" handsets that had the same phone number.Enhanced privacy. A key digital advantage not often mentioned is that digital cellular calls are much harder to eavesdrop on by use of radio scanners. While the security algorithms used have proved not to be as secure as initially advertised, 2G phones are immensely more private than 1G phones, which have no protection against eavesdropping.DisadvantagesIn less populous areas, the weaker digital signal may not be sufficient to reach a cell tower. This tends to be a particular problem on 2G systems deployed on higher frequencies, but is mostly not a problem on 2G systems deployed on lower frequencies. National regulations differ greatly among countries which dictate where 2G can be deployed.Analog has a smooth decay curve, digital a jagged steppy one. This can be both an advantage and a disadvantage. Under good conditions, digital will sound better. Under slightly worse conditions, analog will experience static, while digital has occasional dropouts. As conditions worsen, though, digital will start to completely fail, by dropping calls or being unintelligible, while analog slowly gets worse, generally holding a call longer and allowing at least a few words to get through.While digital calls tend to be free of static and background noise, the lossy compression used by the codecs takes a toll; the range of sound that they convey is reduced. You will hear less of the tonality of someone's voice talking on a digital cellphone, but you will hear it more clearly.

6. Some protocols, such as EDGE for GSM and 1x-RTT for CDMA2000, are defined as "3G" services (because they are defined in IMT-2000 specification documents), but are considered by the general public to be 2.5G or 2.75G services because they are several times slower than present-day 3G services.2.5 G(GPRS)2.75G(EDGE)

7. 3G3G or 3rd generation mobile telecommunications is a generation of standards for mobile phones and mobile telecommunication services fulfilling the International Mobile Telecommunications-2000 (IMT-2000) specific. To meet the IMT-2000 standards, a system is required to provide peak data rates of at least 200 kbit/s by the ITUThe following standards are typically branded 3G:the UMTS system, first offered in 2001, standardized by 3GPP, used primarily in Europe, Japan, China and other regions predominated by GSM2G system infrastructure. The cell phones are typically UMTS and GSM hybrids. Several radio interfaces are offered, sharing the same infrastructure: The original and most widespread radio interface is called W-CDMA.The latest UMTS release, HSPA+, can provide peak data rates up to 56 Mbit/s in the downlink in theory and 22 Mbit/s in the uplink.the CDMA2000 system, first offered in 2002, standardized by 3GPP2, used especially in North America and South Korea, sharing infrastructure with the IS-95 2G standard. The cell phones are typically CDMA2000 and IS-95 hybrids.

8. Adoption3G was relatively slow to be adopted globally. In some instances, 3G networks do not use the same radio frequencies as 2G so mobile operators must build entirely new networks and license entirely new frequencies, especially so to achieve high-end data transmission rates. Other delays were due to the expenses of upgrading transmission hardware, especially for UMTS, whose deployment required the replacement of most broadcast towers. Due to these issues and difficulties with deployment, many carriers were not able to or delayed acquisition of these updated capabilities.In December 2007, 190 3G networks were operating in 40 countries and 154 HSDPA networks were operating in 71 countries, according to the Global Mobile Suppliers Association (GSA). In Asia, Europe, Canada and the USA, telecommunication companies use W-CDMA technology with the support of around 100 terminal designs to operate 3G mobile networks

9. ADOPTION IN India11 December 2008, India entered the 3G arena with the launch of 3G enabled Mobile and Data services by Government owned Mahanagar Telephone Nigam Ltd MTNL in Delhi and later in Mumbai.MTNL becomes the first 3G Mobile service provider in India. After MTNL, another state opertaor Bharat Sanchar Nigam Ltd. (BSNL)launched 3G services on 22 Feb 2009 in Chennai and later launched 3G as Nationwide. The auction of 3G wireless spectrum was announced in April 2010 and 3G Spectrum allocated to all private operators on 1 September 2010.The first Private-sector service provider that launched 3G services is Tata DoCoMo, on November 5, 2010.The other companies providing 3g services are bhartiairtel, vodafone, reliance, idea.

10. FeaturesData ratesa minimum data rate of 2 Mbit/s for stationary or walking users, and 384 kbit/s in a moving vehicleSecurity3G networks offer greater security than their 2G predecessors. By allowing the UE (User Equipment) to authenticate the network it is attaching to, the user can be sure the network is the intended one and not an impersonator. 3G networks use the KASUMIblock crypto instead of the older A5/1stream cipher

11. Applications of 3GThe bandwidth and location information available to 3G devices gives rise to applications not previously available to mobile phone users. Some of the applications are:Mobile TVVideo on demandVideoconferencingTelemedicineLocation-based services

12. 4GIn telecommunications, 4G is the fourth generation of cellularwireless standards. It is a successor to the 3G and 2G families of standards. In 2009, the ITU-R organization specified the IMT-Advanced (International Mobile Telecommunications Advanced) requirements for 4G standards, setting peak speed requirements for 4G service at 100 Mbit/s for high mobility communication (such as from trains and cars) and 1 Gbit/s for low mobility communication (such as pedestrians and stationary users).[1]A 4G system is expected to provide a comprehensive and secure all-IP based mobile broadband solution to laptop computer wireless modems, smartphones, and other mobile devices. Facilities such as ultra-broadband Internet access, IP telephony, gaming services, and streamed multimedia may be provided to users.

13. ITU Requirements and 4G wireless standardsBased on an all-IP packet switched network.Peak data rates of up to approximately 100 Mbit/s for high mobility such as mobile access and up to approximately 1 Gbit/s for low mobility such as nomadic/local wireless access Scalable channel bandwidth 5–20 MHz, optionally up to 40 MHz.[9][9][10]Smooth handovers across heterogeneous networks.Ability to offer high quality of service for next generation multimedia support.

14. 4G candidate systemsData speeds of LTE Advanced LTE Advanced Peak Download 1 Gbit/s Peak Upload 500 Mbit/sIEEE 802.16m or WirelessMAN-Advanced 1 Gbit/s for stationary reception and 100 Mbit/s for mobile reception.