Truncated square tiling and 2G: Difference between pages

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Revision as of 20:51, 6 February 2007

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{{Infobox Polyhedron_with_vertfig |

Image_File=Tile 488.svg |

Polyhedron_Type=[[Tilings of regular polygons|Semiregular tiling]]|

Face_List=[[Square (geometry)|squares]], [[octagon]]s|

Edge_Count=Infinite|

Vertex_Count=Infinite|

Wythoff_Symbol=2 4 | 4|

Symmetry_Group=p4m|

Vertex_List=4.8.8|

Dual=[[Tetrakis square tiling]]|

Property_List=[[planar]], [[vertex-uniform]]|

VertexImage_File=Truncated square tiling vertfig.png }}

{{Table Mobile phone standards}}

In [[geometry]], the '''truncated square tiling''' is a semiregular tiling of the Euclidean plane. There is one square and two octagons on each [[vertex]]. This is the only edge-to-edge tiling by regular convex polygons which contains an octagon.

'''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.

It is topologically related to the polyhedron [[truncated octahedron]], 4.6.6[[image:Truncated octahedron.png|50px]]

== Flavours of 2G ==

There are 3 regular and 8 semiregular tilings in the plane.

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:

There are two distinct [[vertex-uniform]] colorings of a truncated square tiling. (Naming the colors by indices around a vertex (4.8.8): 122, 123.)

* [[GSM]] (TDMA-based), originally from Europe but used worldwide (Time Division Multiple Access)

== See also ==

* [[iDEN]] (TDMA-based), proprietary network used by [[Nextel]] in the [[United States]] and [[Telus Mobility]] in [[Canada]]

* [[Tilings of regular polygons]]

* [[IS-136]] ''aka'' [[D-AMPS]], (TDMA-based, commonly referred as simply [[Time division multiple access|TDMA]] in the US), used in the Americas

* [[List of uniform planar tilings]]

* [[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.

[[Category:Tiling]]

[[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 ==

{{geometry-stub}}

=== 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]]

[[cs:2G]]

[[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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