GSM (Global System for Mobile)

The GSM standard (Global System for Mobile Communications) for mobile telephony was introduced in the mid-1980s and is the European initiative for creating a new cellular radio interface. The GSM system uses a TDMA radio access system employed in 135 countries, operating in 200 KHz channels with eight users per channel. It is the most widely deployed digital network in the world today, used by 10.5 million people in more than 200 countries.
GSM 450: GSM 450 supports very large cells in the 450 MHz band. It was designed for countries with a low user density such as in Africa. It may also replace the original 1981 NMT 450 (Nordic Mobile Telephone) analog networks used in the 450 MHz band. NMT is a firstgeneration wireless technology. GSM 900: When speaking of GSM, the original GSM system was called GSM 900 because the original frequency band was represented by 900 MHz. To provide additional capacity and to enable higher subscriber densities, two other systems were added afterward: GSM 1800: GSM 1800 (or DCS 1800) is an adapted version of GSM 900 operating in the 1800 MHz frequency range. Any GSM system operating in a higher frequency band requires a large number of base stations than for an original GSM system. The availability of a wider band of spectrum and a reduction in cell size will enable GSM 1800 to handle more subscribers than GSM 900. The smaller cells, in fact, give improved indoor coverage and low power requirements. GSM 1900 (or PCS 1900): PCS 1900 (Personal Communications System) is a GSM 1800 variation designed for use on the North American Continent, which uses the 1900 MHz band. Since 1993, phase 2 of the specifications has included both the GSM 900 and DCS 1800 (Digital Cellular System) in common documents.