Thursday, 26 June 2014

GSM Frequency Bands

GSM Frequency Bands

  • GSM system is a frequency and time division system.
  • GSM system frequencies include two bands:-
                      1. At 900 MHZ commonly referred to as GSM 900.
                      2. At 1800 MHz commonly referred as DCS 1800.
                      3. 1900 MHZ is used by Defense.



    1.  In GSM 900 system:- 
      • 124 carriers have been defined.
      • Frequencies are assigned in two sub-bands of 25
      • MHz each.
      • The sub-bands are 890-915 MHz and 935-960 MHz.
      • Channel width is 200 KHz.
      • 890-915 MHz is referred as uplink.
      • 935-960 MHz is referred as downlink.

      NOTE:-  Uplink is the transmission from Mobile to BTS.
                            Downlink is the transmission from BTS to Mobile.
    2. In DCS 1800 system:-

    • Frequencies are assigned in two sub-bands of 75 MHz each.
    • The sub bands are 1710 – 1785 MHz and 1805 – 1880 MHz.
    • 1710 – 1785 MHz is referred as uplink.
    • 1805 – 1880 MHz is referred as down link.  


    NOTE : - 
    • Channel width for GSM is 200 KHz. constant.


                                  In  900MHz 

    uplink frequency                            downlink frequency 
      890 - 915 MHz                                                           935 - 960 MHz

    1. Buffer :-  ( 935-915) = 20 MHz
    2. Bandwidth :- ( 915- 890) or ( 960- 935) = 25 MHz.
    3. Duplexing Space :- ( 935- 890) or ( 960 - 915) = 45 MHz
    4. Total Channel :- ( Bandwidth)/( width of a single channel)
                                  (25 MHz)/(200 KHz) = 125
    5. ARFCN ( Absolute Radio Frequency Channel) :-
                       ( total channel) - 1 = (125) - 1= 124 that means
    124 carriers have been defined



                                 In  1800MHz 

    uplink frequency                            downlink frequency 
      1710 - 1785 MHz                                                           1805 - 1880 MHz

    1. Buffer :-  ( 1805 - 1785) = 20 MHz
    2. Bandwidth :- ( 1785- 1710) or ( 1880- 1805) = 75 MHz.
    3. Duplexing Space :- ( 1805- 1710) or ( 1880 - 1785) = 95 MHz
    4. Total Channel :- ( Bandwidth)/( width of a single channel)
                                  (75 MHz)/(200 KHz) = 375
    5. ARFCN ( Absolute Radio Frequency Channel) :-
                       ( total channel) - 1 = (375) - 1= 374 that means
    374 carriers have been defined


                                   In  1900MHz 

    uplink frequency                            downlink frequency 
      1850 - 1910 MHz                                                           1930 - 1990 MHz

    1. Buffer :-   20 MHz
    2. Bandwidth :-  60 MHz.
    3. Duplexing Space :- 80 MHz
    4. Total Channel :- 300
    5. ARFCN :- 299
    299 carriers have been defined