Global System for Mobile Communication (GSM) is the most successful digital mobile telecommunication system in the world today. It is use by over 1000 million people in more than 190 countries.
The primary goal of GSM was to provide a mobile phone system that allows users to roam throughout Europe. It also provides voice service that is compatible to ISDN (Integrated Services Digital Network) and PSTN (Public Switched Telephone Network).
GSM Overview
Global System for Mobile Communication (GSM) is a globally accepted standard for digital cellular communication. It is an ETSI standard for 2G pan-European digital system with international roaming.
The basic version of GSM (i.e. GSM 900) was founded in 1982. Now it is most successful mobile communication system in the world and over 1.2 billion users use the system. The main goal of GSM is to provide voice services that are compatible to ISDN and other PSTN systems at the same time allowing users of the system to roam throughout Europe.
GSM is a second generation 2G system, replacing the first generation analog systems. The initial version of GSM was design in Europe using 890-915MHz for uplink and 935-960MHz for downlink. This system is called GSM 900.
Another version of GSM is Digital Cellular System 1800 (DCS 1800) uses 1710-1785 MHz for uplink and 1805-1880 MHz for downlink. GSM at 1900 MHz (1850-1910 MHz uplink and 1930-1990 MHz downlink) uses in US is PCS (Personal Communication Services) 1900.
Modifications and Derivatives of GSM
The system evolution of GSM can be divide into three phases:
- Phase 1 (1991-1994) : The basic version of GSM system was in operation.
- Phase 2 (1994-1995) : The system modification was verified in order to allow future gradual modifications and new improvements.
- Phase 3 (from 1995) : The modifications to the original GSM 900 are being introduce.
Following are the derivatives of the original GSM 900.
(1) DCS 1800
One important modification to the original GSM 900 was the development of Digital Cellular System (DCS 1800). DCS 1800 is primarily devote to the operation in areas with high traffic such as urban and suburban areas.
The main difference between GSM 900 and DCS 1800 was in the lower power of the base station and mobile station. As a result the cell size becomes smaller.
The bandwidth assign to the DCS 1800 was much higher than the GSM 900. This implies that up to 374 carrier frequency channels can be assign to the DCS 1800. Thus the capacity of DCS 1800 is much higher than the GSM 900.
Another essential enhancement of the DCS 1800 is the possibility of roaming inside the country. This was not possible with initial GSN 900 due to organization reason.
(2) GSM 400
Another promising modification and enhancement of the original GSM 900 system was 400. It has been observe that the analog systems operating in the 400 MHz bands are now becoming absolute. They are losing their customers as most of them move to the 2G systems.
After shutting this analog systems completely, this frequency range can be use for another GSM version. ETSI Standardizes the GSM system operating in the band around 450 and 480 MHz called GSM 400. The whole infrastructure will remain same however software needs to be change.
The basic features of GSM 400 are given below :
– Frequency allocation : Uplink : 450.4 – 457.6 MHz ; Downlink : 460.4 – 496.0 MHz.
– Duplex separation : 10 MHz.
– Carrier spacing : 200 KHz.
