Page 343 - From GMS to LTE

Long Term Evolution (LTE) and LTE-Advanced Pro 329

In the uplink direction, beamforming is also a challenge, especially when a device
is currently not connected to the network and needs to use a Random Access mes-
sage to connect to a cell. If only cells that use high‐frequency spectrum are available,
uplink beamforming might be required to reach the base station. To resolve the fact
that the mobile device is not aware in which direction to send the beam, one idea is
to send random access messages in several beams, each one directed in a different
direction.
mmWaves: To further increase datarates, 5G NR must use spectrum that goes far
beyond the spectrum below 3 GHz that is typically used for LTE today. While spectrum
below 6 GHz can be used similarly to spectrum use today, it requires additional meas-
ures such as beamforming to extend its useful range. Spectrum above 6 GHz, also
referred to as millimeter waves (mmWave), is abundant in the frequency ranges dis-
cussed for 5G use, which are 26, 28, 38 and 73 GHz. In these frequency ranges, large
amounts of spectrum are available and individual channel bandwidths of several hun-
dred MHz are possible. As signal attenuation is very high in these bands, even more
advanced beamforming techniques will be required. However, due to the very high
frequencies used, individual antennas are very small and antenna arrays with 256 indi-
vidual antennas on the network side per base station sector and arrays with 32 small
antennas in small mobile devices can be envisaged.
A political and administrative problem that was still unresolved in early 2017 was
that none of these frequency ranges was yet assigned globally for use in 5G cellular
networks. Only the US, Korea and Japan have so far assigned spectrum in the 28 GHz
range for cellular networks. This is problematic as frequency bands for cellular use
should be globally harmonized to avoid a fractured device landscape that inhibits
production of devices for a global market and also negatively impacts intercontinental
roaming.

4.21.2 Radio Network Evolution for 5G
As described in the introduction to this section, 5G wireless networks will address a
number of very different applications. Depending on which uses cases are to be
addressed by individual network operators, radio networks will be structured in differ-
ent ways.
Network operators interested in using a 5G air interface as an alternative to fiber,
copper or cable connectivity to homes in rural areas are likely to deploy standalone (SA)
5G base stations, referred to as gNBs in the 3GPP 38 series of documents, and connect
them to an enhanced LTE core network. This is shown in Figure 4.34(a). In the core
network, a software enhancement of the MME and S‐GW is required to allow communication
with the gNBs.
Network operators that are interested in using 5G to increase capacity of their mobile
networks are likely to deploy 5G gNBs alongside LTE eNBs, as shown in Figure 4.34(b).
The LTE eNBs then act as a mobility and control plane anchor as they operate on lower
frequencies and hence have a wider coverage area than the gNBs operating on higher
frequencies. In a way this is similar to aggregating several LTE carriers today, and the
eNB becomes responsible for aggregating traditional LTE carriers that it controls and
5G carriers handled by the gNB. This option is also referred to as the non‐standalone
(NSA) configuration.