Introduction of Global system for Mobile communications ( GSM ) Lesson 1

GSM is a Digital wireless Mobile telephony system that is widely used in the world. GSM use a combination of both the FDMA ( frequency division multiple access ) and TDMA (  Time division multiple access ). using this both combination can be transmit more channel of same time.

GSM used frequency Bands 

GSM System	Band	Up link ( MHz )	Down link ( MHz )	Channel numbers
T-GSM-380	380	380.2–389.8	390.2–399.8	Dynamic
T-GSM-410	410	410.2–419.8	420.2–429.8	Dynamic
GSM-450	450	450.6–457.6	460.6–467.6	259–293
GSM-480	480	479.0–486	489.0–496	306–340
GSM-710	710	698.2–716.2	728.2–746.2	Dynamic
GSM-750	750	747.2–762.2	777.2–792.2	438–511
T-GSM-810	810	806.2–821.2	851.2–866.2	Dynamic
GSM-850	850	824.2–849.2	869.2–894.2	128–251
P-GSM-900	900	890.0–915	935.0–960	1–124
E-GSM-900	900	880.0–915	925.0–960	975–1023, 0-124
R-GSM-900	900	876.0–915	921.0–960	955–1023 & 0-124
T-GSM-900	900	870.4–876	915.4–921	Dynamic
DCS-1800	1800	1,710.2–1,784.8	1,805.2–1,879.8	512–885
PCS-1900	1900	1,850.2–1,909.8	1,930.2–1,989.8	512–810

Most popular standard for mobile phones in the world

• GSM 900 and GSM 1800 MHz are used in most parts of the world  Europe, Asia, Australia, Middle East, Africa.
• GSM 850 and GSM 1900 MHz are used in the United States, Canada, Mexico and most countries of South America

E-GSM 900

E-GSM 900 Band include primary GSM 900 band and addition of 10 MHz at the lower side of the primary GSM 900 MHz band. This extension Up link ranges from 880 - 890 MHz and Down link range from 925 - 960 MHz.

R-GSM 900

R-GSM 900 ( Railway GSM )  This is used for communication between train and railway regulation control centers. The system is based on GSM and EIRENE MORANE specifications which guarantee performance at speeds up to 500 km/h without any communication loss.

Up Link
Up link frequency is used for a band of frequencies dedicated for transmitting data from mobile phones to the BTS ( Tower sector  Antenna ). This band contains frequencies range from 890 MHz to 915 MHz (for GSM  900).

Down Link 

Down link frequency in a GSM network refers to the transmitting frequency from BTS sector antenna to a mobile phone. This band contains frequencies range from 935 MHz to 960 MHz (for GSM  900).

Up Link and Down Link band Gap

Up link and Down Link band gap is 20 MHz (such as 915 to 935 MHz). This band width gap is avoid any interference between up link and down link data transmission sessions.

Down link frequency is greater than Up link frequency

we need definitely more power for transmits high frequency and we can transmits distance same power low frequency than same power high frequency. Mobile phone transmitting power is lower as compared to BTS. BTS has a commercial power and very big battery bank compared to mobile. therefor mobile phone used low frequency transmits data to BTS antenna. this helps to save battery in mobile phone.