Page 231 - From GMS to LTE

Long Term Evolution (LTE) and LTE-Advanced Pro 217

downlink direction and 832 and 862 MHz in the uplink direction was put into use as LTE
band 20 for rural coverage and better in‐house coverage in cities. This band is also
referred to as the digital dividend band, because the spectrum became available when
terrestrial TV broadcasting switched from analog to digital. For a number of years, these
three bands remained the main pillars for LTE coverage in Europe. Due to rising demand,
network operators then started to deploy LTE in additional bands. Due to the reduced
importance of GSM a number of network operators are now using up to 10 MHz of
spectrum in the 900 MHz band that was previously dedicated to GSM, as 5 MHz seems
sufficient for 2G voice calls and GPRS data with the bulk of voice calls now handled by
UMTS and Voice over LTE. A number of network operators have also started using band
38 for TDD‐LTE operation with one or more 20 MHz carriers. It is also likely that some
network operators will also use spectrum in band 1 (2100 MHz), which was initially
dedicated to UMTS. In addition, licensing of two additional bands has started in a num-
ber of European countries. In addition to 30 MHz of FDD spectrum in the 800 MHz
band that is already used today, an additional 30 MHz of spectrum has been assigned for
use by LTE networks in the 700 MHz region between 758 and 788 MHz in the downlink
direction and between 703 and 733 MHz in the uplink direction. This band, also referred
to as the digital dividend 2 band, is made available once digital terrestrial television
broadcast channels are converted to a newer and more resource‐efficient digital broad-
cast standard. In addition a 40 MHz downlink‐only channel has been made available as
band 32 from 1452 to 1492 MHz for carrier aggregation purposes. The two bands are not
included in Table 4.2 but their use is very likely in the near future.
To keep the table compact, bands used in several regions are only listed once. In
China, for example, in addition to the TDD bands, a number of the FDD bands such as
band 3 are also used but are not mentioned. In the US, many different frequency band
numbers are used. On closer inspection it can be seen, however, that many are exten-
sions of initially smaller bandwidth assignments or are directly adjacent to each other.
Most LTE‐capable devices also support other radio technologies such as GSM and
UMTS. As a consequence, a typical high‐end LTE device today not only supports more
than 20 LTE frequency bands between 700 and 2600 MHz but also supports those for
the other radio technologies. A device sold in Europe usually also supports 900 and
1800 MHz for GSM, 900 and 2100 MHz for UMTS and, in addition, the 850 MHz and
1900 MHz bands for international GSM and UMTS roaming. This is a challenge for
antenna design as the sensitivity of a device’s antennas must be equally good in all
supported non‐roaming bands. Furthermore, supporting an increasing number of
bands is a challenge for receiver chips as adding more input ports decreases their overall
sensitivity, which needs to be compensated for by advances in receiver technology.

4.2.2 The eNode‐B and the S1 and X2 Interfaces
The most complex device in the LTE network is the radio base station, referred to as
eNode‐B in the specification documents. The name is derived from the name originally
given to the UMTS base station (Node‐B) with an ‘e’ referring to ‘evolved’. The leading
‘e’ has also been added to numerous other abbreviations already used in UMTS. For
example, while the UMTS radio network is referred to as the UTRAN (Universal Mobile
Telecommunications System Terrestrial Radio Access Network), the LTE radio network
is referred to as the E‐UTRAN.