12 March 2008

GSM (Global System for Mobile) communications is the most popular standard communications system for mobiles all around the world and it`s believed to be incorporated into 82% of all mobile phones worldwide. It`s a cellular network which means that mobile phones search for `cells` in the immediate vicinity to access the phone networks. Cells are like servers which take information and pass it on.


Because of GSM`s popularity most of us can `roam` to other countries and still use our mobiles there without having to buy new handsets or join new network plans.


One way that GSM is different from other systems is that information such as the `voices` of those communicating are transmitted digitally. There`s also an emergency telephone number integrated into the GSM system which means that if you call 112 from anywhere in the world you`ll connect with the closest branch of emergency services. This is useful because it means you don`t need to memorise emergency service codes for everywhere that you go!


As with digital radio, frequency bands are used send information. In the UK we use 900 MHz or 1800 MHz bands but in the US and Canada 850 MHz and 1900 MHz bands are used because the 900 and 1800 MHz frequency bands were already allocated for other uses.

A voice codec would originally record our voices and other ambient sounds when we communicate on a mobile phone and then compact this information from 3.1 kHz audio to between 5.6 and 13 kbit/s of digital information. However, in 1997 `Enhanced Full Rates` were created which streamlined this process even further.

`Modulations` are used to reduce interference on the from other frequency channels and the very technical sounding term `Gaussian minimum-shift keying` or GMSK is used to smooth information and make voices on mobile phones sound clearer and less `fuzzy`.

There are five different sizes of cell in a GSM network; macro, micro, pico, femto and umbrella cells. Depending on where each cell is located and how it`s used it has a different coverage area. Macro cells are generally speaking, a base station antenna and they`re usually above roof level.

Micro cells are similar but smaller and tend to be in suburban areas and Pico cells are smaller still. These offer smaller amounts of coverage which is often less than 100 metres, they are often indoors. Femtocells are generally for use in industry and business and they connect people in a building to a network service provider through a broadband internet connection. Umbrella cells meanwhile are used to provide over-arching cover for a small cluster of scattered cells and they fill the gaps in network cover.


Because GSM is so popular the world over it is thought to be a technology that will continue to evolve many more times before being replaced.


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