In LTE Rel-1o, the concept of Primary Cell (PCell) and Secondary Cell (SCell) was introduced to support Carrier Aggregation. The PCell is more or less like the serving cell in the non-CA case. The functions provided by the PCell are summarized below (see Section 7.5 of 3GPP TS36.300 for more details).
– Provides Security inputs
– Provides NAS mobility functions
– Have always Uplink and Downlink resources: Carrier frequency (FDD) or UL/DL subframes (TDD)
– Used for PUCCH transmission
– Used for RRC connection re-establishment
– Used for Radio Link Monitoring
– Can be changed only by Handover
– Cannot be deactivated
– Cannot be cross scheduled
– Semi-persistent resources can only be configured for the PCell
– UE acquires system information of PCell from the Physical Broadcast Channel (PBCH)
Carrier Aggregation (CA) is one of the key technologies in LTE-Advanced (Rel. 10 and beyond). In simple terms, CA allows multiple radio channels to be bonded together to create bigger bandwidth pipes. The channels may belong to the same or different spectrum bands. Release 10 supports both intra-band contiguous and inter-band CA in the FDD downlink but only intra-band CA for TDD downlink. Only intra-band CA is supported in both FDD & TDD uplink. More details regarding CA are available in the following Agilent presentation.