Duplex Spacing (MHz)
3GPP Band 1, also known as the IMT band, is the world's most popular 3G UMTS frequency band. As a Frequency Division Duplex (FDD) band, communication with the cellular network is conducted over split frequencies - the cell tower transmits to the mobile device over frequencies 2110 to 2170 MHz, and receives from the mobile device on frequencies 1920 to 1980 MHz.
The global popularity of Band 1 (2100 MHz) is primarily attributed to harmonised spectrum arrangements, with regulators having set aside the 2100 MHz band for cellular services in the early 2000s. Residing in the upper cellular band, cell coverage is typically 5 to 20 km from a base station, depending on environmental characteristics. While having a more limited range and penetration than lower band carriers, such as Band 5 (850 MHz) and Band 8 (900 MHz) 3G services, the short range of 2100 MHz provided superior spectrum re-use, allowing more base stations to be packed into a geographical area.
With the significantly increased spectral efficiency of LTE and NR protocols, many operators have begun refarming their valuable 2100 MHz spectrum into 4G and 5G networks, a trend which will only accelerate throughout the 2020s.