4G Americas Carrier Aggregation_FINALv1 0 (2)

5.2 CELL MANAGEMENT AND CELL ACTIVATION-DEACTIVATIONTo efficiently utilize the multiple component carriers for data transmission, additional procedures,including cell management and cell activation/deactivation, are designed for CA.Figure 7. Overview of the DL User Plane Architecture (left side) and the Corresponding Radio ResourceManagement (RRM) Algorithms (right side) [1].In LTE-Advanced CA, a CC used for data transmission is also referred to as a serving cell and is alsotreated as such by the higher layer procedures.For FDD, a serving cell comprises a pair of different carrier frequencies for DL and UL transmissions. ForTDD, a serving cell is defined for a single carrier frequency where DL and UL transmissions occur indifferent transmission time intervals. In LTE-A, where number of DL and UL CCs could be asymmetric,the relation between DL and UL CCs may be signalled in the system information block (SIB) type 2 and iscommon for all UEs.Also, for each UE there is a single serving cell that provides all necessary control information andfunctions, such as Non-Access Stratum (NAS) mobility information, Radio Resource Control (RRC) andconnection maintenance. This serving cell is referred to as the primary cell (PCell). In the DL, the carriercorresponding to the PCell is the Downlink Primary Component Carrier (DL PCC), while in the UL it is theUplink Primary Component Carrier (UL PCC).Other serving cells are referred to as secondary cells (SCells) and are used for bandwidth expansion forthe particular UE. It is to be noted that there are additional differences in the functionality.The cell where an initial access is performed by the UE is the cell which is related by the network as thePCell. Changing of a PCell can be performed only via a handover procedure. The network can configureadditional CCs as SCells only for a CA-capable device with an RRC connection on a PCell. Theconfiguration of SCells is done via dedicated RRC signalling to the UE, as well as any addition,reconfiguration or removal of SCells.4G Americas LTE Carrier Aggregation October 2014 22