Nokia DRRC and HSPA Layering [PDF]

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RAN2.0079: Directed RRC connection setup (with HSDPA layer) Directed RRC connection setup Directed RRC connection setup is a general feature in the RAN. Directed RRC connection setup provides an efficient way to balance load between two (or more) carrier frequencies within one base station. The RNC balances the load by establishing the RRC connection on the carrier frequency (cell) which has less load. The prerequisite for the directed RRC connection setup procedure is that the cells involved belong to the same sector of the base station. The parameter Sector Identifier (SectorID)uniquely identifies the sector of the base station a cell belongs to. Two (or more) cells can belong to the same sector if they have equal coverage areas. The coverage areas can be considered as equal if the cells have identical values for the following parameters (the RNC is not able to check whether the antenna beams of the cells are directed equally):

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Transmission power of the primary CPICH channel (PtxPrimaryCPICH )

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Offset of the P-CPICH and reference service powers (CPICHtoRefRABoffset)

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PLMN code (MCC + MNC)

For a description of the parameters, see WCDMA RAS05 Parameter Dictionary. The UE initiates the RRC connection setup procedure in the cell on which it camped in idle mode (that is, source cell). The RNC can direct the RRC connection setup request to another (target) cell within the same sector if the target cell has less load than the source cell. The decision procedure is controlled with the following parameters:

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Prx Offset for DRRC (DRRCprxOffset) determines the threshold level which the total received wideband interference power (uplink load) in the source cell must exceed before the RNC may direct the RRC connection setup to another cell within the sector.

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Ptx Offset for DRRC (DRRCptxOffset) determines the threshold level which the total transmitted power (downlink load) in the source cell must exceed before the RNC may direct the RRC connection setup to another cell within the sector.

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Prx Margin for DRRC (DRRCprxMargin) determines the margin by which the uplink load of the source cell must exceed the uplink load of the target cell before the RNC may direct the RRC connection setup to the target cell.

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Ptx Margin for DRRC (DRRCptxMargin) determines the margin by which the downlink load of the source cell must exceed the downlink load of the target cell before the RNC may direct the RRC connection setup to the target cell.

When either the uplink load or the downlink load in the source cell exceeds the relevant threshold level, as defined by the following equations, the RNC examines the difference in loading between the source cell and the target cell (or cells): SourceCellPrxTotal > PrxTarget + DRRCprxOffset

SourceCellPtxTotal > PtxTarget + DRRCptxOffset If both the uplink load and the downlink load in a target cell are lower than the corresponding load in the source cell, the RNC directs the RRC connection setup request to the target cell. The RNC examines the difference in loading between the source cell and the target cell (n) by means of the following equations: SourceCellPrxTotal > TargetCellPrxTotal (n) - DRRCprxMargin(n) SourceCellPtxTotal > TargetCellPtxTotal (n) - DRRCptxMargin(n) The measurement results in the equations are defined as follows:

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SourceCellPrxTotal is the total received wideband interference power in the source cell.

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SourceCellPtxTotal is the total transmitted power in the source cell.

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TargetCellPrxTotal is the total received wideband interference power in the target cell.

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TargetCellPtxTotal is the total transmitted power in the target cell.

Note that in the case of HSDPA, if there is at least one MAC-d flow allocated in the cell, non-HSDPA transmitted power (Transmitted carrier power of all codes not used for HS-PDSCH or HS-SCCH transmission) is used instead of total transmitted power. PtxTargetHSDPA and PtxOffsetHSDPA target levels are also used instead of PtxTarget and PtxOffset. If loading in the source cell do not exceed the relevant thresholds, or the difference in loading between the source cell and the target cell (or cells) is not sufficient, the RNC continues the RRC connection setup procedure in the source cell.

Figure:

Principle of directed RRC connection setup

For more information, see Call setup and release and Radio resource management functions in WCDMA RNC Product Documentation. Directed RRC connection setup for HSDPA layer This feature is based on the feature Directed RRC Connection Setup. The Directed RRC connection setup for HSDPA layer feature enables HSDPA in its own layer without impact to Rel '99 and Rel 4 users. When a 3GPP Release 5 or a newer UE initiates the RRC connection set-up in a nonHSDPA capable cell, the UE is directed to the HSDPA layer if a HSDPA-capable cell exists in the same sector. When a Rel- 99 or Rel-4 UE initiates the RRC connection set-up in a HSDPA-capable cell, it is also directed to the non-HSDPA layer if a non-HSDPA-capable cell exists in the same sector. The load of the serving or target cell is not checked. Different sectors are identified by the SectorID parameter.

Note: The directed RRC connection setup for HSDPA layer cannot be used simultaneously in the cell with the Directed RRC Connection Setup feature. For instructions on activating the feature, see Activating HSDPA in RNC product documentation. The basic requirement for the feature to function is that the two layers (HSDPA and non-HSDPA) have the same SectorID within the same base station. The following parameters must be the same for both cells:

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Transmission power of primary CPICH (PtxPrimaryCPIC)

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Offset of the P-CPICH and reference service powers (CPICHtoRefRABoffset)

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PLMN code (MSS+MNC)

The Directed RRC connection setup for HSDPA layer feature is meant for two-layer networks where HSDPA is supported in one layer (carrier frequency). The primary target of this feature is to direct the UEs supporting HSDPA to the cell that supports HSDPA. On the other hand, non-HSDPA UEs are removed from the HSDPA layer. Because of that, the load of the source or target cell is not taken into account in the decision-making. The signalling flow is identical to the Directed RRC connection setup feature. Likewise, the prerequisite for the Directed RRC connection setup for HSDPA layer feature is that the cells involved belong to the same sector of the base station. The parameter Sector Identifier (SectorID) uniquely identifies the sector of the base station a cell belongs to. Two cells can belong to the same sector if they have equal coverage areas. The RNC is not able to check whether the antenna beams of the cells are directed equally. The UE initiates the RRC connection setup procedure in the cell on which it was located in idle mode, that is, the source cell. When the UE initiates the RRC connection setup, it indicates the 3GPP release it supports. According to that information, the RNC directs the UE to the other (layer) cell within the same sector if needed. If the UE is already on the right layer, the RRC connection is established in the current cell.

A 3GPP release 5 or newer UE is directed from a non-HSDPA supporting cell to the cell which supports HSDPA (controlled by the management parameter HSDPA enabled). A 3GPP release 99 or release 4 UE is directed from a HSDPA supporting cell to the cell which does not support HSDPA. The usage of Directed RRC connection setup for HSDPA layer feature is controlled with the Directed RRC

connection setup enabled (DirectedRRCEnabled)management parameter . The parameter can have the following values:

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0: Directed RRC connection setup is not enabled in the cell

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1: Directed RRC connection setup is enabled in the cell

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2: Directed RRC connection setup for HSDPA layer is enabled in the cell

When the Directed RRC connection setup for HSDPA layer feature is used, the maximum number of cells (layers) in one sector of the base station that can be configured is two. If a three-layer network is used, one of the DCH layers (not supporting HSDPA) must have a different sector identifier in the base station than in the layers (DCH layer and HSDPA layer) where the Directed RRC connection setup for HSDPA layer feature is supported. Operational aspects The operator can switch the Directed RRC connection setup for HSDPA layer feature on and off by a management parameter (DirectedRRCEnabled) on a cell basis. It is also possible to use the feature unidirectionally (that is, only to one direction), for example from a non-HSDPA layer to HSDPA only. If this feature is enabled, the Directed RRC connection setup feature is disabled in that cell.

RAN1011: HSPA Layering for UEs in Common Channels

This feature transfers UEs to the correct layer based on their HSDPA and HSUPA capability. The transfer occurs in connection with the state transition from Cell_FACH to Cell_DCH. Non-HSDPA UEs are transferred to the non-HSDPA layer. The HSDPA capable UEs are transferred to the layer that supports HSDPA. The HSUPA capable UEs are transferred to the layer that supports HSUPA. If there are several HSDPA or HSDPA and HSUPA layers, load sharing is utilised. On HSPA layers, the selection criterion is the highest DL throughput (most power per user available for HSDPA). In addition, this feature covers some enhancements to the Directed RRC Connection Setup for HSDPA Layer feature. The requested service in the radio resource control (RRC) Connection Setup Request is taken into account in decision making so that only HSDPA UEs requesting interactive and background services are transferred to the HSDPA layer. Also, HSUPA capability is taken into account when selecting the layer. The interworking with the directed RRC connection setup feature enables the non-HSDPA load sharing between all the layers. The UE that cannot

manage with frequency change in the RRC connection setup phase or in the state transition phase is detected and the feature is not used for that specific connection