There are many different types of mobile communications networks, used in different places and for different purposes. This page explains some of the current networks and related technologies. Digital networks Analogue networks Cellular 3G ITU
Global System for Mobile Communications (GSM) is one of the leading digital cellular systems. GSM uses narrowband TDMA, which allows eight simultaneous calls on the same radio frequency.
GSM was first introduced in 1991. By the end of 1997, the GSM service was available in more than 100 countries. It has be
come the de facto standard in Europe and Asia.
Considered the most advanced digital cellular technology, GSM networks are leaders in many typically “digital” services including Short Message Service (SMS), Over the air (OTA) configuration and GSM positioning. Thanks to its technology and presence both in the Americas and the rest of the world, GSM is well positioned for global roaming. Many new GSM phones are called “global phones” because they can be used in virtually any country. The SIM card (“Subscriber Identification Module”) is a unique and essential component of GSM phones.
Where GSM is used:
> GSM 900 (transmitting on the 900 MHz frequency band) is Europe’s main digital network. It’s also used in the Asia-Pacific region.
> GSM 1800 (transmitting on the 1800 MHz frequency band) is also used in Europe and Asia, but has not been as widely adopted as GSM 900.
> GSM 1900 (transmitting on the 1900 MHz frequency band) is the GSM system used mainly in the Americas and Canada.
Time Division Multiple Access (TDMA) delivers
digital wireless service using time-division multiplexing (TDM). A radio frequency is divided into time slots, then slots are allocated to multiple calls. In this way, a single frequency can support multiple, simultaneous data channels. TDMA is used by the GSM digital cellular system.
One of the oldest digital cellular technologies, TDMA is also considered the least advanced digital technology, partly because of its comparative lack of flexibility.
TDMA is used primarily in the USA, but also in Latin America, New Zealand, parts of Russia and the Asia-Pacific region.
Short for Code-Division Multiple Access, this is a digital cellular technology that uses spread-spectrum techniques. Unlike competing systems that use TDMA, such as GSM, CDMA does not assign a specific frequency to each user. Instead, every channel uses the full available spectrum.
Individual conversations are encoded with a pseudo-random digital sequence. Many conversations are carried simultaneously by sending all communications in groups of bits mixed together, and tagging each group belongin
g to a specific communication with a different code. Each communication can therefore be reassembled in the correct order at the other end, using the unique codes attached to particular groups of bits.
CDMA is the most common and most recent digital cellular technology in North America.
Personal Digital Cellular (PDC) is one of the world’s three main digital wireless standards, ranking alongside GSM and TDMA. Although PDC is currently only used in Japan, it is the world’s second-largest digital standard, with over 48 million subscribers by July 2000; operators in other regions of the world are actively considering PDC. Like GSM, PDC is based on TDMA technology.
General Packet Radio Service (GPRS) is a step between GSM and 3G cellular networks. GPRS offers faster data transmission (9.6Kbits to 115Kbits) via a GSM network. This enables users to make telephone calls and transmit data at the same time. For example, if you have a GPRS mobile phone, you will be able to make calls and receive email messages simultaneously.
The main benefits of GPRS are that it reserves radio resources only when there is data to send, and reduces reliance on traditional circuit-switched network elements.
Short for wideband CDMA, this is a high-speed 3G mobile wireless technology that can offer higher data speeds than CDMA. WCDMA can reach speeds of up to 2
Mbps for voice, video, data and image transmission. WCDMA was adopted as a standard by the ITU under the name “IMT-2000 direct spread.”
Personal Communications Service (PCS) is the U.S. Federal Communications Commission (FCC) term used to describe a set of digital cellular technologies being deployed in the USA. PCS works over CDMA (also called IS-95), GSM and North American TDMA (also called IS-136) air interfaces.
Three of the most important distinguishing
features of PCS systems are:
> They are completely digital.
> They operate in the 1900 MHz frequency range.
> They can be used internationally.
PCS is a second-generation mobile communications technology.
There are three kinds of analogue networks: AMPS, ETACS and NMT.
AMPS is used mainly in the US. It’s also used in Latin America, Australia, New Zealand, parts of Russia and the Asia-Pacific region.
ETACS is used in Europe and the Asia-Pacific region.
NMT is used in Scandinavia and some E
uropean countries, as well as parts of Russia, the Middle East and Asia. Top
The term cellular refers to comm
unications systems – especially the Advance Mobile Phone Service (AMPS) – that divide a geographic region into sections called cells. The purpose of this division is to make the most efficient use of a limited number of transmission frequencies. Each connection, or
conversation, requires its own dedicated frequency, and the total number of available frequencies is about 1,000.
To support more than 1,000 simultaneous conversations, cellular systems allocate a set number of frequencies to each cell. Two ce
lls can then use the same frequency for different conversations, provided the cells are not adjacent.
3G is an ITU specification for the third generation of mobile communications technology (analogue cellular was the first generation, digital PCS the second).
3G promises increased bandwidth of up to 384 Kbps when a device is stationary or moving at pedestrian speed, 128 Kbps in a car and 2 Mbps in fixed applications. 3G will work over wireless air interfaces such as GSM, TDMA and CDMA. The new EDGE air interface has been developed specifically to meet the bandwidth needs of 3G.
The International Telecommunication Union (ITU) is an intergovernmental organisation through which public and private organisations develop telecommunications. The ITU was founded in 1865 and became a United Nations agency in 1947. It is responsible for adopting international treaties, regulations and standards governing telecommunications.