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