Mani Raj Paul - GSM

Global System for Mobile Communication Technology

Global system for mobile communication (GSM) is a globally accepted standard for digital cellular communication. GSM is the name of a standardization group established in 1982 to create a common European mobile telephone standard that would formulate specifications for a pan-European mobile cellular radio system operating at 900 MHz. It is estimated that many countries outside of Europe will join the GSM partnership.

Introduction: The Evolution of Mobile Telephone Systems


Cellular is one of the fastest growing and most demanding telecommunications applications. Today, it represents a continuously increasing percentage of all new telephone subscriptions around the world. Currently there are more than 45 million cellular subscribers worldwide, and nearly 50 percent of those subscribers are located in the United States. It is forecasted that cellular systems using a digital technology will become the universal method of telecommunications. By the year 2005, forecasters predict that there will be more than 100 million cellular subscribers worldwide. It has even been estimated that
some countries may have more mobile phones than fixed phones by the year
2000

The GSM Network

GSM provides recommendations, not requirements. The GSM specifications define the functions and interface requirements in detail but do not address the hardware. The reason for this is to limit the designers as little as possible but still to make it possible for the operators to buy equipment from different suppliers. The GSM network is divided into three major systems: the switching system (SS), the base station system (BSS), and the operation and support system (OSS). The basic GSM network elements

GSM Specifications

• bandwidth—the range of a channel's limits; the broader the bandwidth, the faster data can be sent

• bits per second (bps)—a single on-off pulse of data; eight bits are equivalent to one byte

• frequency—the number of cycles per unit of time; frequency is measured in hertz (Hz)

• kilo (k)—kilo is the designation for 1,000; the abbreviation kbps represents 1,000 bits per second

• megahertz (MHz)—1,000,000 hertz (cycles per second)

• milliseconds (ms)—one-thousandth of a second

• watt (W)—a measure of power of a transmitter

• frequency band—The frequency range specified for GSM is 1,850 to 1,990 MHz (mobile station to base station).

• duplex distance—The duplex distance is 80 MHz. Duplex distance is the distance between the uplink and downlink frequencies. A channel has two frequencies, 80 MHz apart.

• channel separation—The separation between adjacent carrier frequencies. In GSM, this is 200 kHz.

• modulation—Modulation is the process of sending a signal by changing the characteristics of a carrier frequency. This is done in GSM via Gaussian minimum shift keying (GMSK).

• transmission rate—GSM is a digital system with an over-the-air bit rate of 270 kbps
.
• access method—GSM utilizes the time division multiple access
(TDMA) concept. TDMA is a technique in which several different calls
may share the same carrier. Each call is assigned a particular time slot.

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