Home > Technical Articles > Carrier Aggregation and its Challenges in 5G NR
Since it was first introduced in 3GPP Release 10, Carrier aggregation (CA) has become an essential capability in the next-generation wireless system. Rel-16, it has already supported up to 16 carriers of any different bandwidth in both FR1 and FR2 frequency bands, no matter it is in FDD or in TDD. Many enhancements in 5G NR systems have permitted 5G NR to achieve the goals mandated by IMT-2020 to reach a DL peak data rate up to 20Gbps, and a UL peak data rate up to 10Gbps. However, to achieve such a high peak data rate, it requires overcoming many challenges rising from RF design to physical layer signaling design, from resource scheduler algorithm to software deployment. This article is to give a brief technical review of the carrier aggregation and its challenges in the productization of the 5G NR system.
Two types of carrier aggregation are defined in 5G NR: inter-band, and intra-band with its two sub-modes, intra-band contiguous and intra-band non-contiguous (see to Fig-[1, 2, 3]). Intra-band means that the aggregated component carriers reside in the same frequency band. In the case of non-contiguous, however, the carriers are not co-located. Inter-band means the aggregated carriers are in different frequency bands. In the Rel-16, up to four bands can be supported in FR1, and in FR2 it is up to two bands. Note that in FR1 each NR band can have up to 12 different channel bandwidths ranging from 5MHz up to 100MHz depending on the subcarrier spacing (SCS) in 15KHz, 30KHz, or 60KHz. Up to 16 component carriers (both contiguous and non-contiguous) can be aggregated, using different numerologies. In TR 38.101, more than 11 CA bandwidth classes are defined and are labeled from A to L. Each CA bandwidth class indicates a combination of the total aggregated bandwidth and the maximum number of component carriers.