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Frequency

Due to each country having different frequency spectrums available, GSM is deployed on several different frequencies. In North America it is on the 850/1900 MHz bands, while in Europe it is on the 900/1800 MHz bands.

The following table lists all currently used GSM frequencies:

Download 3GPP Spec 45.005 (R7): http://www.3gpp.org/ftp/Specs/latest/Rel-7/45_series/45005-7d0.zip

The UpLink (UL) refers to the transmission from the phone to the base station, and is always the lower frequency, since the phone has a lower output power than the base station, and lower frequencies help the signal travel farther.

The ARFCN (Absolute Radio Frequency Channel Number) refers to the number sequence of the 200 kHz carriers inside of the larger frequency block (each 200 kHz frequency carries 8 GSM time-slots, which can correspond to 7 voice calls plus 1 signaling)

Example: The standard GSM 900 block is 25 MHz full duplex (25MHz UL, 25MHz DL). When this 25,000 kHz is divided by the number of 200KHz carriers, the number equals 125, which reflects the ARFCN numbers 1-124 (plus gaurd band)

As these are the total frequencies available, if more than one GSM operator is operating in the same area and in the same band (eg. 900 MHz) then the total mount of frequencies is divided among them (ex: instead of one operator getting all 124, two operators would get 62 frequencies each). The awarding of frequencies is usually done by a government authority (ex. the FCC in the USA) and for a limited number of years. The operators in return pay the authorities, and must meet other requirements imposed on them as well (ex: population coverage, emergency locating, etc.)

Along international borders, countries must coordinate with each other which frequencies are used in this area, so as not to interfere with each others networks. The agreement may relate to a certain signal strength for a certain distance inside the country (ex: no foreign operator may have a signal higher than -90dBm further than 20 miles inside another countries border)