2G
From Wikipedia, the free encyclopedia
2G (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.[1] Three primary benefits of 2G networks over their predecessors were that phone conversations were digitally encrypted; 2G systems were significantly more efficient on the spectrum allowing for far greater mobile phone penetration levels; and 2G introduced data services for mobile, starting with SMS text messages.
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.
2G has been superseded by newer technologies such as 2.5G, 2.75G, 3G, and 4G; however, 2G networks are still used in many parts of the world.
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[edit] 2G technologies
2G 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).[2]
- IS-95 aka cdmaOne (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. Over a dozen CDMA operators have migrated to GSM including operators in Mexico, India, Australia and South Korea.
- PDC (TDMA-based), used exclusively in Japan
- iDEN (TDMA-based), proprietary network used by Nextel in the United States and Telus Mobility in Canada
- IS-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.
[edit] Capacities, advantages, and disadvantages
[edit] Capacity
Using 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 had to be smaller, so more cells had to be placed in the same amount of space. This was made possible by cell towers and related equipment getting less expensive.
[edit] Disadvantages
- In 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.
[edit] Evolution
2G networks were built mainly for voice services and slow data transmission.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 service.
[edit] 2.5G (GPRS)
2.5G ("second and a half generation") is used to describe 2G-systems that have 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.The first major step in the evolution of GSM networks to 3G occurred with the introduction of General Packet Radio Service (GPRS). CDMA2000 networks similarly evolved through the introduction of 1xRTT. The combination of these capabilities came to be known as 2.5G.
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. GPRS data transfer is typically charged per megabyte of traffic transferred, while data communication via traditional circuit switching is billed per minute of connection time, independent of whether the user actually is utilizing the capacity or is in an idle state.
1xRTT supports bi-directional (up and downlink) peak data rates up to 153.6 kbit/s, delivering an average user data throughput of 80-100 kbit/s in commercial networks.[3] It can also be used for WAP, SMS & MMS services, as well as Internet access.
[edit] 2.75G (EDGE)
GPRS1 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. EDGE was deployed on GSM networks beginning in 2003—initially by Cingular (now AT&T) in the United States.EDGE is standardized by 3GPP as part of the GSM family and it is an upgrade that provides a potential three-fold increase in capacity of GSM/GPRS networks. The specification achieves higher data-rates (up to 236.8 kbit/s) by switching to more sophisticated methods of coding (8PSK), within existing GSM timeslots.
[edit] See also
- Mobile radio telephone, also known as 0G
- 1G
- 3G
- 4G
- 2G spectrum scam, India
[edit] References
- ^ "Radiolinja's History". April 20, 2004. http://www.elisa.com/english/index.cfm?t=6&o=6532.50. Retrieved December 23, 2009.
- ^ "CDMA Worldwide". Archived from the original on 30 January 2010. http://www.cdg.org/worldwide/index.asp?h_area=0&h_technology=999&h_frequency=1. Retrieved December 23, 2009.
- ^ "CDMA2000 1X". CDG.org. CDMA Development Group. Archived from the original on 25 July 2011. http://www.cdg.org/technology/cdma20001x.asp. Retrieved July 31, 2011.
| Preceded by 1st Generation (1G) | Mobile Telephony Generations | Succeeded by 3rd Generation (3G) |
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http://zh.wikipedia.org/zh-hk/2G
2G
維基百科，自由的百科全書
2G，是第二代手機通訊技術規格的簡稱，一般定義為無法直接傳送如電子郵件、軟件等資訊；只具有通話、和一些如時間日期等傳送的手機通訊技術規格。手機短訊SMS（Short message service）在2G的某些規格中能夠被執行。
2G在美國通常稱為PCS（Personal Communications Service）。
2G技術基本可被切為兩種，一種是基於TDMA所發展出來的以GSM為代表，另一種則是基於CDMA規格所發展出來的cdmaOne，復用（Multiplexing）形式的一種。
主要的第二代手機通訊技術規格標準有：
- GSM：基於TDMA所發展、源於歐洲、目前已全球化。
- IS-95（也叫做cdmaOne）：基於CDMA所發展、是美國最簡單的CDMA系統、用於美洲和亞洲一些國家。
- IS-136（也叫做D-AMPS）：基於TDMA所發展，是美國最簡單的TDMA系統，用於美洲。
- IDEN：基於TDMA所發展、美國獨有的系統。被美國電信系統商Nextell使用。
- PDC（Personal Digital Cellular）：基於TDMA所發展，僅在日本普及。
[編輯] 參看
流動通訊標準
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| 0G (無線電話) | |||||||||
| 1G | |||||||||
| 2G |
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| 2G的過渡 (2.5G, 2.75G) |
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| 3G (IMT-2000) |
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| 3G的過渡 (3.5G, 3.9G) |
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| 4G (IMT-Advanced) |
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| 5G |
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| Links |
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