Spectrum Allocation in UMTS and LTE

One of the main factors in any cellular system is the deployed frequency spectrum. 2G, 3G,
and 4G systems offer multiple band options. This depends on the regulator in each country
and the availability of spectrum sharing among multiple network operators in the same
country.
The device’s support of different frequency bands is driven by the hardware capabilities.
Therefore, not all bands are supported by a single device. The demand of multi-mode and
multi-band device depends on the market where the device is being commercialized.
Tables 1.1 and 1.2 list the FDD frequency bands defined in 3GPP for both UMTS and LTE.
LTE uses a variable channel bandwidth of 1.4, 3, 5, 10, 15, or 20 MHz. Most common worldwide
network deployments are in 5 or 10MHz, given the bandwidth available in the allocated
spectrum for the operator. LTE in 20MHz is being increasingly deployed, especially in bands
like 2.6 GHz as well as 1.8 GHz after frequency re-farming.
LTE-FDD requires two center frequencies, one for the downlink and one for the uplink.
These carrier frequencies are each given an EARFCN (E-UTRA absolute radio frequency
channel number). In contrast, LTE-TDD has only one EARFCN. The channel raster for
LTE is 100 kHz for all bands. The carrier center frequency must be an integer multiple
of 100 kHz.
In UMTS, the nominal channel spacing is 5MHz, but can be adjusted to optimize performance
in a particular deployment scenario, such as in UMTS900 to re-farm fewer carriers
from GSM900. The channel raster is 200 kHz, which means that the center frequency must
be an integer multiple of 200 kHz. The carrier frequency is designated by the UTRA absolute
radio frequency channel number (UARFCN).