Mobile Computing – Global System for Mobile Communications Prof. Rajesh M. More*, Lecturer, GSMCOE, MCA, Pune-45
(Abstract - Global System for Mobile Communications (GSM) is a digital mobile telephone system which is widely used in Europe and other part of the world. In 1982 it was recognized as a standard for digital wireless communications adopted firstly by Europe and then by Asia, Africa etc.
To develop a standard for mobile telephone the European Conference of Postal and Telecommunication Administrations (CEPT) created the Groupe Spécial Mobile (GSM) which was used across Europe. The GSM standard has been an advantage to both consumers and network operator. Consumer can get benefit from the ability to roam and switch carriers without switching phones whereas Network Operators can choose equipment from any of the many vendors implementing GSM. GSM also pioneered a low-cost (for network carrier) alternative to voice calls. The Short Message Service (SMS), also called "text messaging", which is now also supported on other mobile standards were backward-compatible with the original GSM phones. For example, Release ‘97 of the standard added packet data capabilities, by means of General Packet Radio Service (GPRS). Release '99 introduced higher speed data transmission using Enhance Data Rates for GSM Evolution (EDGE).
GSM is a cellular network where each cell is connected or served by Base Transceiver Station (BTS). BTS is equipment which facilitates wireless connection between user equipment (mobile) and network. Several BSTs are connected to the Base Station Controller (BSC). BSC controls all the calls in all the connected base stations. Base Stations can be directly connected to BSC forms star configuration, in the form of chain i.e. one to another or in the form of loop configuration. The GSM network can be divided into three broad parts - The Mobile Station (which is carried by the subscriber), The Base Station Subsystem (which controls the radio link with the Mobile Station) and The Network Subsystem (which performs the switching of calls between the mobile and other fixed or mobile network users as well as management of mobile services). *email@example.com
The mobile station (MS) consists of the physical equipment (i.e. the radio transceiver, display and digital signal processors and a smart card called the Subscriber Identity Module (SIM). The SIM provides personal mobility, so that the user can have access to all subscribed services irrespective of both the location of the terminal. SIM card needs to be inserted into GSM cellular phone, so that the user is able to receive and make calls from that phone or receive other subscribed services. The mobile equipment is uniquely identified by the International Mobile Equipment Identity (IMEI). The SIM card contains the International Mobile Subscriber Identity (IMSI), identifying the subscriber, a secret key for authentication, and other user information. The IMEI and the IMSI are independent. The SIM card may be protected against unauthorized use by a password or personal identity number. Base Station Subsystem
The Base Station Subsystem is consisting of two parts - The Base Transceiver Station (BTS) and The Base Station Controller (BSC). The Base Transceiver Station houses the radio transceivers that define a cell and handles the radio-link protocols with the Mobile Station. Depending upon the area, there will potentially be a large number of BTSs deployed. The Base Station Controller manages the radio resources for one or more BTSs. It handles radio channel setup, frequency hopping, and handovers. The BSC is the connection between the mobile and the Mobile service Switching Center (MSC). The BSC can translate the 13 kbps voice channel used over the radio link to the standard 64 kbps channel used by the Public Switched Telephone Network or ISDN. Network Subsystem
The central component of the...
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