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Cellular Networks QuickStart: Getting up to Speed on Cellular, from 1G to 3G

Get the basics on cellular infrastructure and transport protocols.


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ireless networks are slowly evolving from yesterday's 1G analog systems to tomorrow's 3G high-speed, digital networks. Throughout the world, every country is at a different phase of building networks to support 3G's next-generation, data-centric applications, such as games, multimedia messaging, and online shopping. European and Japanese subscribers, the mobile industry's early adopters, are already enjoying these next-generation applications. U.S. subscribers, though, are just now being introduced to the advantages of mobile data applications.

The U.S. mobile market is challenged because it supports multiple 2G cellular standards—CDMA, GSM, and TDMA. Rather than regulate the cellular market, the FCC decided to open the sector to competition and let the winning standard be chosen by market forces.

With a free market environment, all the key players—operators, handheld device manufacturers, and network infrastructure providers—began developing their products to support their chosen network transport layer.



In hindsight, the decision to support a free market created an extremely competitive environment, but it also stalled the introduction of innovative mobile applications. Europe, on the other hand, made an early decision to standardize on GSM, which has led to a more integrated mobile network because each operator supports GSM-based infrastructure elements, GSM standard formats, and GSM handsets. Because of this commonality, European subscribers are well versed in sending simple text messages and multimedia messages, as well as making small transaction purchases via their phones.

Japanese subscribers are also familiar with data services and accustomed to using their phone for much more than talking. NTT DoCoMo led the move to next-generation applications when its iMode network launched in February 1999. Subscribers downloaded cartoons and searched Web sites at such a pace that analysts and the media heralded DoCoMo's mobility model as the one to match.

Unfortunately, U.S. operators were unable to build an environment that attracted content and application developers. DoCoMo was able to lure droves of developers with its revenue-sharing model. For every application downloaded, DoCoMo kept 10 percent of the fees leaving 90 percent to the content developer. U.S. operators haven't been as generous as DoCoMo, but they are moving toward an 80/20 split.

With these events as the backdrop, U.S. developers enter a confusing mobile scene where they face multiple transport technologies, a dizzying number of handsets, and competing development tools.

Operators support any number of mobile networks. AT&T Wireless supports GSM. Cingular supports TDMA and GSM. Nextel relies on iDEN. T-Mobile supports GSM. ATT Wireless supports TDMA and GSM networks. And Verizon Wireless uses CDMA. Within these 2G environments, the operators are at different stages of adding 2.5G capabilities. In most cases they are adding GPRS as an overlay to support data applications.

Handset Incompatibility
Interoperable handsets are another factor that complicates the mobile environment. Handsets work on some networks but not others. For example, Motorola's C331 is compatible with Cingular's GSM network, but cannot be used on Verizon's CDMA network. Handset makers have attempted to ease interoperability issues by creating dual-band handsets. These devices support calls in the 900 mHZ and 1800 mHZ frequencies and differing technologies, such as GSM, GPRS, and TDMA. These phones are especially convenient for subscribers that move between areas covered by different networks.

And lastly, J2ME and BREW's battle for supremacy is keeping many developers on the sideline, waiting for the market to shakeout. Keep in mind that J2ME and BREW applications will run on a small subset of the most recently released handsets. (For a listing of Java devices, visit www.microjava.com/devices. Visit Qualcomm's site to see all the BREW phones.) With a few exceptions, BREW applications work only on CDMA networks. Qualcomm intends to extend BREW to other networks and has had tests to GSM, but for now it is generally confined to CDMA.

Both Sun and Nokia want to separate the application development environment from the network. They want to hide the underlying network transport layer from a developer and create an environment where applications run on all networks regardless of the transport technology. With that in mind, developers don't need to know all the dirty details about network transport technology, but a general knowledge and familiarity with the acronyms is helpful.

1G networks, or the original analog, circuit-switched systems, include AMPS, ETACS and TACS.

  • AMPS (Advanced Mobile Phone System) is the original standard for analog cellular phone service. It is used primarily in North America, Latin America, Australia, and parts of Russia and Asia.
  • ETACS (Extended Total Access Communication System) was developed in the UK and is available in Europe and Asia.
  • TACS (Total Access Communication System) was used in Britain for the 900 MHz frequency band. TACS was based on the United States AMPS system and was later adopted in other countries, including Hong Kong and Japan.

2G networks use digital encoding and include CDMA, TDMA and GSM. Text messages can be sent on 2G networks, but more bandwidth hungry applications require 2.5G.

  • CDMA (Code Division Multiple Access) uses a spread spectrum technique to scatter a radio signal across a wide range of frequencies.
  • IDEN, from Motorola, is an enhanced specialized mobile radio network technology that combines two-way radio, telephone, text messaging and data transmission into one network.
  • GSM (Global System for Mobile Communications) is the digital transmission technique widely adopted in Europe and supported in North America. GSM uses 900 MHz and 1800 MHz in Europe. In North America, GSM uses the 1900 MHz.
  • TDMA (Time Division Multiple Access) divides each cellular channel into three time slots in order to increase the amount of data that can be carried. GSM and D-AMPS use TDMA in one form or another. It is also generally used to describe what was formerly known as D-AMPS. TDMA networks are operated in the United States, Latin America, New Zealand, parts of Russia and Asia Pacific.

2.5G networks incorporate 2G technology with GPRS' higher speeds to support data transport. 2.5G is a bridge from the voice-centric 2G networks to the data-centric 3G networks.

  • GPRS (General Packet Radio Service) is a radio technology for GSM networks that adds packet-switching protocols. As a 2.5G technology, GPRS enables high-speed wireless Internet and other data communications. GPRS networks can deliver SMS, MMS, email, games, and WAP applications.

3G networks promise next-generation service with transmission rates of 144Kbps and higher that can support multimedia applications, such as video, video conferencing and Internet access. Both UMTS (WCDMA) and EDGE will support 3G services. 3G networks operate on a different frequency than 2G networks.

  • UMTS (Universal Mobile Telecommunications System) or WCDM (Wideband Code Division Multiple Access) was selected as the successor to GSM. It is the European standard for 3G wideband digital radio communications, and it utilizes one 5 MHz channel for both voice and data, offering data speeds up to 2 Mbps.
  • EDGE is a mobile network radio technology that allows current GSM networks to offer 3G services within existing frequencies. As an evolution of GSM/GPRS, EDGE is an upgrade to GPRS' data and GSM's voice networks. EDGE provides data speed three times that of GPRS.



   
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