Overview on GSM Technology

GSM Technology

GSM is the leading mobile standard commercially used worldwide. GSM provides easy interoperability, international roaming operations. It operates through SIM (Subscriber Identification Module) card. Same handset can be used for different handset. More than one SIM can be used in a handset.

In 1987, 13 European countries signed a memorandum of understanding to develop a common uniform interoperable telephone standard lead to formation of GSM standard in 1990 and further on later period. GSM technologies were all digital and address most of tele communication requirement expected by consumers.

GSM Standard was further updated in 1993 to enable SMS communication between mobiles. Another update to GSM standards was done to include general radio packet services now called GPRS. This lead to advancement of mobile features by letting person to access internet through mobile while traveling. The 3rd major update to GSM standard was made to enhance data rates for GSM evolution called EDGE.


How GSM Operates?

As like cells collectively form a living being. The GSM which only could communicate within a cellular bordered area, soon covered with many such cellular station covered signal distance of very long range.  When user makes a call, the mobile phones at any location  first searches for the nearest cellular station of highest strength. While the user on move, the mobile will

automatically changes the communication station from one cellular border to another without disconnecting the call, commonly called handing over process.

GSM had some limitation to cope with second generation standards which to allow multiple mobiles to use same available spectrum. This let to adoption of new technique called TDMA (Time division Multiple Access). In this technique, the conversion of one user for small finite duration is recorded, encoded and transmitted in a burst that lasts much shorter than duration of a second. Though GSM could handle only one call at a time, the quick conversion, signal transmission lets a impression to users that their call is single continuous call. This signal processing is done within a given range of frequencies.

The maximum number of simultaneous calls a cellular station can handle is based on  length of finite duration of conversion by burst factors which in turn depends on station techniques and  efficient standards used.

As said that GSM operates within a given range of frequencies, this range is defined by government of each country or by communication governing bodies, in some cases association of tele communication private company itself. European networks operate at 2100 MHz while Canada and USA uses frequency range of 950MHz spectrum. The range of frequency the GSM operators use are termed as Operation frequency bands. Hansets operates more than one band specifically termed as TriBand, Quad Bang which operate in all assigned frequencies.
 

A mobile user could find two uniqueness in their device. One is uniqueness of SIM card number and other is the unique number found in handset itself which is used for security reason (just to track down its origin, usage, locality definition etc..).  This handset number is called International Mobile Equipment Identification (IMEI) number. Encryption of the signal is also possible based on the IMEI once phone is authenticated by the base unit.



We will look at CDMA technology in next post.