User talk:Marudubshinki/Archive 54 and 2G: Difference between pages
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{{unreferenced|date=January 2007}}
{{Table Mobile phone standards}}
'''2G''' (or 2-G) is short for second-generation [[wireless]] [[telephone]] [[technology]].
The main differentiator to previous mobile telephone systems, retrospectively dubbed [[1G]], is that the radio signals that 1G networks use are [[Analog signal|analog]], while 2G networks are [[digital]]. Note that both systems use digital signaling to connect the radio towers (which listen to the handsets) to the rest of the telephone system.
== Flavours of 2G ==
2G technologies can be divided into [[Time division multiple access|TDMA]]-based and [[Code division multiple access|CDMA]]-based standards depending on the type of [[multiplexing]] used. The main 2G standards are:
* [[GSM]] (TDMA-based), originally from Europe but used worldwide (Time Division Multiple Access)
* [[iDEN]] (TDMA-based), proprietary network used by [[Nextel]] in the [[United States]] and [[Telus Mobility]] in [[Canada]]
* [[IS-136]] ''aka'' [[D-AMPS]], (TDMA-based, commonly referred as simply [[Time division multiple access|TDMA]] in the US), used in the Americas
* [[IS-95]] ''aka'' [[IS-95|cdmaOne]], (CDMA-based, commonly referred as simply [[CDMA]] in the US), used in the Americas and parts of Asia
* [[Personal Digital Cellular|PDC]] (TDMA-based), used exclusively in Japan
2G services are frequently referred as [[Personal Communications Service]], or '''PCS''', in the US.
[[2.5G]] services enable high-speed data transfer over upgraded existing 2G networks. Beyond 2G, there's [[3G]], with higher data speeds, and [[4G]], with even higher data speeds, to enable new services for subscribers, such as picture messaging and video telephony.
== Capacities, Advantages, Disadvantages ==
=== Capacity ===
Using digital signals between the handsets and the towers increases [[system capacity]] in two key ways:
* Digital voice data can be compressed and [[Multiplexing|multiplexed]] much more effectively than analog voice encodings through the use of various [[CODEC]]s, 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 [[Cellular network|cell]]s could be smaller, so more cells could be placed in the same amount of space. This was also made possible by [[cell tower]]s and related equipment getting less expensive.
=== Advantages ===
Digital systems were embraced by consumers for several reasons.
* The lower powered radio signals require less battery power, so phones last much longer between charges, and batteries can be smaller.
* The digital voice encoding allowed digital [[ECC|error checking]] which could increase sound quality by reducing [[dynamic]] and lowering the [[noise floor]].
* The lower power emissions helped address health concerns.
* Going all-digital allowed for the introduction of digital data services, such as [[Short message service|SMS]] and [[email]].
A key digital advantage not often mentioned is that digital cellular calls are much harder to [[eavesdrop]] on by use of [[radio scanner]]s. While the [[security algorithm]]s used have proved to not be as secure as initially advertised, 2G phones are immensely more private than 1G phones, which have no protection whatsoever against eavesdropping.
=== Disadvantages ===
The downsides of 2G systems, not often well publicized, are:
* In less populous areas, the weaker digital signal will not be sufficient to reach a cell tower.
* 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.
* Despite the coverage maps provided by major phone companies, as of 2006 digital coverage in many areas is spotty at best.
* With analog systems it was possible to have two or more [[Clone (cellphone)|"cloned"]] handsets that had the same phone number. This was widely abused for [[Fraud|fraudulent purposes]]. It was, however, of great advantage in many legitimate situations. One could have a backup handset in case of damage or loss, a permanently installed handset in a car or remote workshop, and so on. With digital systems, this is no longer possible.
* 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'll hear less of the tonality of someone's voice talking on a digital cellphone, but you will hear it more clearly.
[[Category:mobile telephony standards]]
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[[es:Telefonía móvil 2G]]
[[ja:第二世代携帯電話]]
[[vi:2G]]
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[[zh:2G]]
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