Global System for Mobile communications (GSM)

is an open architecture digital cellular technology having application in transmitting and receiving voice and data.

This technology differs from the first generation wireless systems which used analog technology for communication, while GSM uses digital technology and time division multiple Access (TDMA) transmission methods.

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GSM technology is a circuit-switched system, and works by dividing each 200 KHz frequency channel into 25 KHz slots and operates on 900MHz and 1.8GHz bands in Europe and the 1.9GHz and 850MHz bands in the US.

In Australia, Canada and many South American countries, 850MHz is used for GSM and 3GSM. GSM satellite services enables users to access the service from areas where terrestrial coverage is not available.

At the very beginning, these so called mobile phones were fixed in the cars, being permanently installed. As the mobile phone evolved, the first generation systems, 1G, came into commercial operation, based on analog switched circuits.

The system used a technology called Advanced Mobile Phone Service (AMPS), which operated in the 800MHz band. Japan launched AMPS in 1979 and the Europeans had their own technology, which they called Nordic Mobile Telephony (NMT), operating in the 450-MHz band. There are about 2 million GSM mobile phone users in the world today, with China being the largest user of mobile phones.

GSM operates on the following frequencies -

850 MHz (824.2 – 848.8 MHz Tx; 869.2 – 893.8 MHz Rx)

900 MHz (880-2 – 914.8 MHz Tx; 925.2 – 959.8 MHz Rx)

1800 MHz (1710.2 – 1784.8 MHz Tx; 1805.2 – 1879.8 MH Rx)

1900 MHz (1850.2 – 1909.8 MHz Tx; 1930.2 – 1989.8 MHz Rx)

The quad band mobile handset is compatible with all the frequencies illustrated above. The Tri band phones work operate on 800MHz, 900MHz and 1800MHz frequency bands, which would mean,that it will work in only those countries which operates on those frequency bands.

A Dual band mobile operates on 800 MHz and 1900 MHz. GSM phones are not only capable of voice transmission, but it allows Short Messaging System (SMS) and also supports General Packet Radio Services (GPRS), which is basically a data service available to GSM phone users.

It uses the unused Time Division Multiple Access (TDMA) communication channels in the GSM network to transmit data at a fairly moderate speed. As GSM evolved, it retained the backward compatibility. In some countries, GSM offers Enhanced Data rates for GSM Evolution (EDGE).

GSM phones work with a Subscriber Identity Module (SIM) card. GSM mobile phones are at times are SIM locked. With any other SIM card the phone would not work. GSM offers its subscribers the ‘roaming’ facility.

Mobile phones are available on rent and pre-paid SIM cards are available for specific countries, where you get a local number of that country and you do not pay for your incoming calls, unlike roaming.

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