GSM Main Features

------------------ 1-Modulation technique (GMSK)

The Modulation used in GSM is Gaussian minimum-shift keying

(GMSK),a kind of continuous-phase frequency shift keying.

In GMSK, the signal to be modulated onto the carrier is first

smoothed with a Gaussian low-pass filter prior to being fed to a

frequency modulator, which greatly reduces the interference to

neighboring channels (adjacent-channel interference).

2-Frequency Bands (900/1800/1900 MHz)

GSM networks operate in a number of different carrier frequency

ranges (separated into GSM frequency ranges for 2G and UMTS

frequency bands for 3G), with most 2G GSM networks operating in

the 900 MHz or 1800 MHz bands.

Where these bands were already allocated, the 850 MHz and 1900

MHz bands were used instead (for example in Canada and the

United States).

In rare cases the 400 and 450 MHz frequency bands are assigned

in some countries because they were previously used for first-

generation systems.

3-Multiple access technique (TDMA/FDMA)

GSM combines TDMA with Frequency Hopping and wideband

transmission to minimize common types of interference.

4-Duplexing technique (FDD)

Frequency-division duplexing (FDD) means that the transmitter

and receiver operate at different carrier frequencies.

5-Channel coding

GSM uses:

a. Block code.

b. Convolutional code.