Page 296 - From GMS to LTE

282 From GSM to LTE-Advanced Pro and 5G

Transferring data in different parts of the spectrum is straightforward on the base
station side. Here, different bands such as 800 MHz and 1800 MHz were already used
simultaneously but separately before carrier aggregation was introduced. Hence, carrier
aggregation mainly requires a software enhancement. On the mobile device side,
implementing carrier aggregation is more challenging. This is due to the limited space
available in small handheld devices that have to accommodate additional hardware per
aggregated band such as additional antennas and analog hardware such as filters, digital
processing capacity, etc. To accommodate different device capabilities and hardware
evolution, a device can announce which band combinations it supports when it con-
nects to the network. Each carrier in a band combination is referred to as a component
carrier (CC). Furthermore, 3GPP TS 36.101 table 5.6A‐1 specifies how many compo-
nent carriers a device can aggregate contiguously in a single band. This is referred to as
the carrier aggregation bandwidth class and is shown in Table 4.8 below.
At the time of publication only bandwidth classes A to C are used in practice. Higher
bandwidth classes are especially of interest for License Assisted Access (LAA) to aggre-
gate licensed spectrum with unlicensed spectrum in the 5 GHz band. The following
examples show a number of typical carrier aggregation configurations used in practice
today and their nomenclature as found in the standards:
CA_3A‐7A: Aggregates up to 20 MHz in band 3 (1800 MHz, 3A) and up to 20 MHz
in band 7 (2600 MHz, 7A) for a combined 40 MHz channel. If a network operator has
less spectrum available, e.g. only 10 MHz in band 3, the combined channel bandwidth
is 30 MHz.
CA_3C‐7A: Aggregates up to 40 MHz in band 3 and up to 20 MHz in band 7 for a
combined 60 MHz channel.
CA_3A‐3A‐7A: Aggregates up to 40 MHz in band 3 and up to 20 MHz in band 7 for
a combined channel of up to 60 MHz. In contrast to the previous example, a device
implementing this combination supports two non‐contiguous channels in band 3, i.e.
two carriers in the same band that are not adjacent to each other.
CA_8A‐3A‐7A: Aggregates up to 20 MHz in band 8 (900 MHz), up to 20 MHz in band
3 (1800 MHz) and up 20 MHz in band 7 (2600 MHz). In practice, it is unlikely that a net-
work operator has 20 MHz of spectrum in the 900 MHz band as it is still used for GSM
and hence a 10 + 20 + 20 MHz for a total of 50 MHz is a more likely practical scenario.

Table 4.8 CA bandwidth classes.

Maximum aggregated Number of contiguous
CA bandwidth class bandwidth component carriers

A 20 MHz 1
B 20 MHz 2
C 20–40 MHz 2
D 40–60 MHz 3
E 60–80 MHz 4
F 80–100 MHz 5
I 140–160 MHz 8