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GSM Network
Posted Date: 24 Feb 2008 Resource Type: Articles/Knowledge Sharing Category: How things work
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Posted By: Moncy Member Level: Silver
Rating:  Points: 5
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GSM Background
GSM Network Overview
At a high level, GSM is a mobile telephony network based on the cellular concept. Users can place and receive calls without being fixed to a specific location or wired to a physical connection. To supply this capability, a GSM network consists of three basic components:
. Subscriber Terminal Devices — Today, these devices are typically cell phones, but there are other devices such as personal digital assistants (PDAs) with various input/output capabilities. All have integrated radio transceivers.
• Radio Base Station Network — Cellular networks are composed of small, low-powered, terrestrial radio cells that typically range in coverage area from tens of kilometers in sparsely populated rural areas to less than 500 meters in densely populated urban areas. The frequencies used by the network are reused again and again in different cells throughout the network to increase network capacity.
• Network Switching and Services Infrastructure — The traffic to and from the radio network is concentrated at a set of switching nodes that interface to other fixed public or private networks. These nodes handle the call setup, channel resource allocation, and the administration of subscriber services. These components allow the GSM network to provide coverage as a user moves from an area covered by one cell to an area covered by another cell. The network terminates the old cell connection and immediately establishes a new cell connection. This process is designed to be transparent to the user. In addition, users can “roam” or travel outside of a “home” coverage area to a new city, region, or country. The arrival of the visitor is detected by the new system through an automatic registration process. The new system informs the user's home system of the new location so that calls can be delivered.
GSM Technology Characteristics
The GSM radio technology is based on 200-kHz wide radio channels with a gross data rate of 270 Kbps. Each radio channel is divided into eight time slots using TDMA. Several users can efficiently share these radio channels. Separate radio channels are used from the mobile devices to the network and the network to the mobile devices through the frequency division duplex
(FDD) technique. In GSM, voice calls are supported by sampling the user’s voice and compressing the data using digital encoding algorithms. GSM is currently defined for three major frequency bands, including blocks of radio spectrum within the 900-, 1800-, and 1900-MHz bands. The 900- and 1800- MHz bands are the principal bands used in Europe and Asia, and the 1900-MHz band is used in North America. North American TDMA operators are also considering
the deployment of GSM within the 850-MHz band as well. The 450-MHz band is used in some Eastern European countries. There are terminal devices that support multiple bands, allowing them to operate in different countries and networks.
GSM Data Services
Today, in addition to circuit-switched voice services, GSM supports the following data services:
• Circuit-Switched Data — A GSM circuit-switched data call is similar to a landline modem dial-up call. A dedicated connection is set up for the duration of the call, regardless of whether data is being transferred. The data throughput rate is 9.6 or 14.4 Kbps, depending on the coding scheme supported by the network and terminal device. Support for highspeed circuit-switched data services (HSCSD) was recently added. HSCSD can support the concatenation of multiple time slots for data rates of up to 38 Kbps.
• SMS — GSM also supports sending and receiving short text messages (approximately 160 characters) known as SMS on a signaling channel. SMS is widely popular for person-to-person messaging, pushing stock quotes and sports scores, and so forth. Billions of these messages are sent per month and the numbers are growing. The circuit-switched services provided by the GSM technology are augmented by packet-switched services provided by the GPRS overlay.
Wide-area1 cellular networks have enjoyed phenomenal
growth worldwide since they were first deployed in the
early 1980s, and this growth is expected to continue. Already,
in a number of countries, wireless users
outnumber wired landline phone users. Today, most
use the wide-area wireless networks for voice calls on
cell phones, but there is a growing trend in nonvoice
data and messaging applications such as the short
message service (SMS).
There are several major second-generation (or 2G) digital
cellular standards used throughout the world. The
most widespread are GSM, the Code Division Multiple
Access (CDMA) standard called cdmaOne, Time Division
Multiple Access (TDMA), and Personal Digital
Communications (PDC) used mainly in Japan. Over the
next few years, there will be a transition to 2.5G and 3G
technologies that, in addition to voice services, will add
support for “always on” packet data access and, eventually,
new multimedia types of wireless service. In
some countries such as the U.S., there is a complementary
trend to deploy localized wireless local area
networks (WLANs) in public places such as hotels, airports,
and cafes. These wireless LANs allow users to
access the Internet and intranets through broadband
service providers.
More than two out of three digital cellular subscribers
worldwide connect using GSM, making GSM the dominant
worldwide standard. Additionally, a number of
major North American TDMA service providers have decided
to deploy GSM/GPRS overlays, rather than
continuing on a separate and unique evolution path towards
3G networks. Figure 1 shows the evolution paths
of current technologies to 2.5G and 3G.
The ARC Group forecasts that by the end of 2003, GPRS
will account for 68 percent (or approximately 138 million)
of the worldwide mobile data subscribers. By the
end of 2006, GPRS worldwide subscribers are forecast
to grow to almost 600 million.2
Figure 1. Wide-Area Cellular Network Evolution to 3G
1. In this context, “wide area” refers to wireless networks that offer broad metropolitan, regional, or national coverage, both indoors and outdoors.
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Responses
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| Author: Shanthi M 29 May 2008 | Member Level: Diamond Points : 2 | useful information.
| | Author: helpu 31 May 2008 | Member Level: Gold Points : 0 | Very Nice Article.This is very good.
| | Author: helpu 31 May 2008 | Member Level: Gold Points : 0 | Very Nice Article.This is very good.
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