2G
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| Mobile phone and data standards |
| GSM / UMTS Family
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| 2G |
| 3G |
| Pre-4G |
| cdmaOne / CDMA2000 Family
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| 2G |
| 3G |
| Pre-4G |
| Other Technologies
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| 0G |
| 1G |
| 2G |
| Pre-4G |
| Frequency bands
|
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, while 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.
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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 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 TDMA in the US), used in the Americas
- IS-95 aka cdmaOne, (CDMA-based, commonly referred as simply CDMA in the US), used in the Americas and parts of Asia
- PDC (TDMA-based), used exclusively in Japan
2G services are frequently referred as Personal Communications Service, or PCS, in the United States.
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.
[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 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.
[edit] 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 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 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 scanners. While the security algorithms 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.
[edit] 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.
- With analog systems it was possible to have two or more "cloned" handsets that had the same phone number. This was widely abused for 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.
