GSM modulation

we use 0.3 GMSK(Gaussian minimum shift keying) in GSM service.

0.3 describes that the 3db bandwidth and bit-rate product BT=0.3

we know that in BPSK we have to shift the phase by 180 degree for each change of 1-0 or 0-1.this periodically changes brings high frequency components and induce higher harmonics in modulating bit stream.GMSK is continuous phase-shift keying modulation scheme.

so,if we use Gaussian low pass filter and some minimizations (we have to overlook a bit of ISI-Inter Symbol Interference problem),then BPSK becomes GMSK.

GMSK also reduce side-lobes in transmitted spectrum.

in GSM we represent binary 1 and 0 by shifting RF carrier by +/- 67.7khz

where the channel data rate is 270.8(=67.7*4), four times of RF shift,

so,the channel capacity will be increased.

I give you the link for GMSK as a brief overview-

http://en.wikipedia.org/wiki/Minimum-shift_keying

Google it Have a good time

http://science.jrank.org/pages/5677/Radio-Waves-Modulating-sound-wave.html

https://en.wikipedia.org/wiki/Frequency_modulation

https://www.infoplease.com/ce6/sci/A0860618.html

https://www.cybercollege.com/frtv/frtv017.htm

https://en.wikipedia.org/wiki/Antenna_(radio)

https://www.howstuffworks.com/radio.htm

I think that you know how the basic modulation takes place.

like, amplitude modulation or freqency modulation,PCM etc

if you don't know those then I think the another person has given you the proper links.