CA-Group-based SCell Configuration

This section describes the procedures of CA-group-based SCell configuration for uplink/ downlink 2CC aggregation, downlink 3CC aggregation, and downlink 4CC aggregation.

NOTE

Uplink and Downlink 2CC Aggregation

Uplink 2CC aggregation and downlink 2CC aggregation use the same SCell configuration procedure. With both uplink and downlink 2CC aggregation enabled, in a single procedure, an eNodeB configures an SCell for a CA UE for both uplink and downlink transmission.

Figure 3-24 CA-group-based SCell configuration for uplink/downlink 2CC aggregation

The eNodeB treats a cell that meets all the following conditions as a candidate SCell for a CA UE:

l The cell is in the same CA group as the PCell of the UE. l The cell has not been configured as an SCell for the UE.

l The cell belongs to the public land mobile network (PLMN) that serves the UE or belongs to an equivalent PLMN.

The eNodeB arranges all candidate SCells in descending order of SCell priority (specified by the CaGroupSCellCfg.SCellPriority parameter) and attempts to select a candidate SCell as an SCell for the UE. Cells with the priority value of 0 cannot be configured as SCells. The SCell configuration procedure varies depending on the settings of the

CaGroupSCellCfg.SCellBlindCfgFlag parameter and SccBlindCfgSwitch under the ENodeBAlgoSwitch.CaAlgoSwitch parameter.

l If SccBlindCfgSwitch is on and CaGroupSCellCfg.SCellBlindCfgFlag is set to TRUE(TRUE) for a top-priority candidate SCell, the eNodeB does not send the A4 measurement configuration. Instead, the eNodeB directly delivers an RRC Connection Reconfiguration message to configure this candidate cell as an SCell for the UE. If multiple candidate SCells have the same top SCell priority and have their

CaGroupSCellCfg.SCellBlindCfgFlag set to TRUE(TRUE), the eNodeB randomly selects one cell from these candidate SCells and attempts to configure this cell as an SCell for the UE in a blind manner (that is, without measurements).

If the SCell is configured successfully, the procedure ends. If the SCell fails to be configured, the eNodeB evaluates next-priority candidate SCells in the same way. l If SccBlindCfgSwitch is off or if SccBlindCfgSwitch is on but

CaGroupSCellCfg.SCellBlindCfgFlag is set to FALSE(FALSE) for a top-priority candidate SCell, the eNodeB does not support blind SCell configuration. In this situation, the eNodeB delivers the A4 measurement configuration related to the candidate SCell. After receiving an A4 measurement report from the UE, the eNodeB determines whether to configure the candidate cell as an SCell for the UE. The configuration procedure is as follows:

The eNodeB delivers the A4 measurement configuration, instructing the UE to measure all of the top-priority candidate SCells. In the measurement configuration, the eNodeB may set up measurement gaps for the UE, depending on the inter-frequency

measurement capability reported by the UE.

– If the UE requires measurement gaps, the eNodeB considers the bearers of the UE. If a bearer with a QCI of 1 has been established for the UE, the SCell configuration procedure ends. If no such bearer has been established, the eNodeB sets up

measurement gaps in the measurement configuration. The configuration includes the E-UTRA absolute radio frequency channel number (EARFCN), frequency- specific offset, measurement bandwidth, and other measurement-related parameters. For details about the measurement parameters, see the descriptions related to inter- frequency measurement in Intra-RAT Mobility Management in Connected Mode. – If the UE does not require measurement gaps, the eNodeB delivers the A4

measurement configuration in which measurement gaps are not set up. NOTE

AutoGapSwitch under the ENodeBAlgoSwitch.HoModeSwitch parameter affects the decision process of the inter-frequency measurement gap setup. If this switch is on, the eNodeB determines whether to set up the gaps based on the reported UE capabilities. If this switch is off, the eNodeB sets up the gaps, without considering UE capabilities. It is recommended that this switch be off to ensure that only cells with satisfactory signal quality can be configured as SCells.

After receiving an A4 measurement report from the UE, the eNodeB checks the cells contained in the report. If the report contains a candidate SCell, the eNodeB sends an

RRC Connection Reconfiguration message to configure the cell as an SCell for the UE. If the SCell is configured successfully, the procedure ends. If the eNodeB does not receive a report that contains a candidate SCell or the SCell fails to be configured, the eNodeB continues to evaluate next-priority candidate SCells.

NOTE

l In CA-group-based configuration mode, it is recommended that blind configuration be enabled to facilitate SCell configuration.

l After delivering the A4 measurement configuration related to a candidate SCell to the UE, the eNodeB may receive an A2 measurement report, indicating unsatisfactory signal quality of the PCell, for an inter-frequency or inter-RAT handover. In such a case, the eNodeB will not configure the candidate cell as an SCell for the UE, even if the eNodeB later receives an A4 measurement report that contains the candidate cell.

l The threshold for event A4 used in the preceding procedure is equal to CaMgtCfg.CarrAggrA4ThdRsrp plus CaGroupSCellCfg.SCellA4Offset.

l When a bearer for an emergency call or with a QCI of 1 is set up for a CA UE whose SCell has been configured, the eNodeB does not automatically remove the SCell. The eNodeB removes the SCell only when the conditions described in 3.2.7 SCell Removal are met.

Downlink 3CC Aggregation

The SCell configuration procedure for downlink 3CC aggregation is similar to that for uplink/ downlink 2CC aggregation. The difference lies in the number of SCells to be configured and the consequences that follow. For downlink 3CC aggregation, the eNodeB selects two candidate SCells and attempts to configure them. The consequences are as follows: l Both cells are configured as SCells, and the procedure ends.

l One cell is configured as an SCell. The CA UE stays in the 2CC aggregation state. When the traffic volume of the CA UE meets the triggering condition again, the eNodeB performs an SCell configuration procedure, in which the eNodeB selects only one candidate SCell at a time. The procedure ends when a total of two SCells are configured for the UE.

l Neither cell is configured as an SCell. The CA UE stays in the single carrier state. When the traffic volume of the CA UE meets the triggering condition again, the eNodeB performs an SCell configuration procedure, in which the eNodeB selects two candidate SCells. The procedure ends when a total of two SCells are configured for the UE. Figure 3-25 shows the SCell configuration procedure for downlink 3CC aggregation.

Downlink 4CC Aggregation

The SCell configuration procedure for downlink 4CC aggregation is similar to that for uplink/ downlink 2CC aggregation. The difference lies in the number of SCells to be configured and the consequences that follow. For downlink 4CC aggregation, the eNodeB selects three candidate SCells and attempts to configure them. The consequences are as follows: l All the three cells are configured as SCells, and the procedure ends.

l Two of the cells are configured as SCells. The CA UE stays in the 3CC aggregation state. When the traffic volume of the CA UE meets the triggering condition again, the eNodeB performs an SCell configuration procedure, in which the eNodeB selects only one candidate SCell at a time. The procedure ends when a total of three SCells are configured for the UE.

l Only one cell is configured as an SCell. The CA UE stays in the 2CC aggregation state. When the traffic volume of the CA UE meets the triggering condition again, the eNodeB performs an SCell configuration procedure, in which the eNodeB selects two candidate SCells. The procedure ends when a total of three SCells are configured for the UE. l None of the cells is configured as an SCell. The CA UE stays in the single carrier state.

When the traffic volume of the CA UE meets the triggering condition again, the eNodeB performs an SCell configuration procedure, in which the eNodeB selects three candidate SCells. The procedure ends when a total of three SCells are configured for the UE. Figure 3-26 shows the SCell configuration procedure for downlink 4CC aggregation.

Figure 3-26 CA-group-based SCell configuration for downlink 4CC aggregation