Carrier aggregation — Several carriers, one device
RF and system
Where it sits
What it is
What it is. Using several carriers at once for one device. TS 38.211 clause 4.5, which opens with the whole idea in a sentence: "Transmissions in multiple cells can be aggregated. Unless otherwise noted, the description in this specification applies to each of the serving cells."
That sentence is the design. Aggregation is not a new physical layer; it is the same physical layer, run several times in parallel, with MAC combining the results. Every clause in the PDSCH note applies per carrier. A separate HARQ entity per serving cell (ref-stack §2), a separate transport block, a separate DCI.
It is where the peak rates come from. Table 12 reaches the 20 Gbit/s target only by aggregating eight carriers — the factor $J$ in the sum of PDSCH §11.1.
The hard part is not the physical layer at all. It is which combinations a device may use. Two carriers running at once in one handset generate intermodulation products that can land on the device's own receiver — maximum sensitivity degradation. TS 38.101-1 enumerates the permitted band combinations and the degradation allowed for each, and that enumeration is why the specification is 1 242 pages.
This is the folder's hand-off to nr-carrier-aggregation.md, which is where the band-combination
tables belong.
Read on
This concept was first written up in ref-system, which reads the whole group as one argument.
Before this concept, the hierarchy says to learn the following — the full chain, in order: