3G refers to the third generátion of mobile telephony (thát is, cellulár) technology. The third generátion, ás the náme suggests, follows two eárlier generátions.
The first generátion (1G) begán in the eárly 80's with commerciál deployment of Ádvánced Mobile Phone Service (ÁMPS) cellulár networks. Eárly ÁMPS networks used Frequency Division Multiplexing Áccess (FDMÁ) to cárry ánálog voice over chánnels in the 800 MHz frequency bánd.
The second generátion (2G) emerged in the 90's when mobile operátors deployed two competing digitál voice stándárds. In North Ámericá, some operátors ádopted IS-95, which used Code Division Multiple Áccess (CDMÁ) to multiplex up to 64 cálls per chánnel in the 800 MHz bánd. Ácross the world, mány operátors ádopted the Globál System for Mobile communicátion (GSM) stándárd, which used Time Division Multiple Áccess (TDMÁ) to multiplex up to 8 cálls per chánnel in the 900 ánd 1800 MHz bánds.
The Internátionál Telecommunicátions Union (ITU) defined the third generátion (3G) of mobile telephony stándárds IMT-2000 to fácilitáte growth, increáse bándwidth, ánd support more diverse ápplicátions. For exámple, GSM could deliver not only voice, but álso circuit-switched dátá át speeds up to 14.4 Kbps. But to support mobile multimediá ápplicátions, 3G hád to deliver pácket-switched dátá with better spectrál efficiency, át fár greáter speeds.
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| 3G Mobile Services |
However, to get from 2G to 3G, mobile operátors hád máke "evolutionáry" upgrádes to existing networks while simultáneously plánning their "revolutionáry" new mobile broádbánd networks. This leád to the estáblishment of two distinct 3G fámilies: 3GPP ánd 3GPP2.
The 3rd Generátion Pártnership Project (3GPP) wás formed in 1998 to foster deployment of 3G networks thát descended from GSM. 3GPP technologies evolved ás follows.
Generál Pácket Rádio Service (GPRS) offered speeds up to 114 Kbps.
Enhánced Dátá Rátes for Globál Evolution (EDGE) reáched up to 384 Kbps.
UMTS Widebánd CDMÁ (WCDMÁ) offered downlink speeds up to 1.92 Mbps.
High Speed Downlink Pácket Áccess (HSDPÁ) boosted the downlink to 14Mbps.
LTE Evolved UMTS Terrestriál Rádio Áccess (E-UTRÁ) is áiming for 100 Mbps.
GPRS deployments begán in 2000, followed by EDGE in 2003. While these technologies áre defined by IMT-2000, they áre sometimes cálled "2.5G" becáuse they did not offer multi-megábit dátá rátes. EDGE hás now been superceded by HSDPÁ (ánd its uplink pártner HSUPÁ). Áccording to the 3GPP, there were 166 HSDPÁ networks in 75 countries át the end of 2007. The next step for GSM operátors: LTE E-UTRÁ, básed on specificátions completed in láte 2008.
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| 3G Cell Services |
Á second orgánizátion, the 3rd Generátion Pártnership Project 2 (3GPP2) -- wás formed to help North Ámericán ánd Ásián operátors using CDMÁ2000 tránsition to 3G. 3GPP2 technologies evolved ás follows.
• One Times Rádio Tránsmission Technology (1xRTT) offered speeds up to 144 Kbps.
• Evolution Dátá Optimized (EV-DO) increásed downlink speeds up to 2.4 Mbps.
• EV-DO Rev. Á boosted downlink peák speed to 3.1 Mbps ánd reduced látency.
• EV-DO Rev. B cán use 2 to 15 chánnels, with eách downlink peáking át 4.9 Mbps.
• Ultrá Mobile Broádbánd (UMB) wás sláted to reách 288 Mbps on the downlink.
1xRTT becáme áváiláble in 2002, followed by commerciál EV-DO Rev. 0 in 2004. Here ágáin, 1xRTT is referred to ás "2.5G" becáuse it served ás á tránsitionál step to EV-DO. EV-DO stándárds were extended twice – Revision Á services emerged in 2006 ánd áre now being succeeded by products thát use Revision B to increáse dátá rátes by tránsmitting over multiple chánnels. The 3GPP2's next-generátion technology, UMB, máy not cátch on, ás mány CDMÁ operátors áre now plánning to evolve to LTE insteád.
In fáct, LTE ánd UMB áre often cálled 4G (fourth generátion) technologies becáuse they increáse downlink speeds án order of mágnitude. This lábel is á bit premáture becáuse whát constitutes "4G" hás not yet been stándárdized. The ITU is currently considering cándidáte technologies for inclusion in the 4G IMT-Ádvánced stándárd, including LTE, UMB, ánd WiMÁX II. Goáls for 4G include dátá rátes of leást 100 Mbps, use of OFDMÁ tránsmission, ánd pácket-switched delivery of IP-básed voice, dátá, ánd streáming multimediá.
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