Dual Cell HSDPA Concepts

Dual Cell HSDPA Concepts

Last updated: January 7, 2012

This section is only applicable to the lab application or feature-licensed test application.

Dual carrier HSDPA, also referred as dual cell HSDPA or DC-HSDPA in the test standard, is a WCDMA release 8 feature that allows the network to transmit HSDPA data from two cells simultaneously. The peak rate is doubled from 21Mbps to 42Mbps without the use of MIMO.

Dual cell operation require UE categories to be from 21 to 24 (See 3GPP TS 25.306).

See How Does the Test Set Supports DC-HSDPA for what functionalities are supported by the test set.

DC-HSDPA Architecture

Signal Transmission and Reception

While operating in DC-HSDPA mode, the UE receives HSDPA transmissions from two cells. The two cells transmit on separate but adjacent carriers while potentially having different cell powers. DC-HSDPA assumes that the two cells are served by the same Node-B. While the serving cell has a full set of common channels (SCH, P-CCPCH, CPICH, PICH, etc.), the UE must assume that the secondary serving cell only transmit CPICH (i.e., the UE cannot rely on the presence of an SCH/P-CCPCH).

Both cells can transmit HS-PDSCH and HS-SCCH to the UE simultaneously. Each cell's HS-PDSCH carries independent data. The UE determines the configuration of each cell's HS-PDSCH by reading each cell's HS-SCCH with independently assigned H-RNTI. As with single carrier HSDPA (SC-HSDPA), the UE monitors up to 4 HS-SCCHs from each cell, however the standard specifies that the UE can only monitor a total of 6 HS-SCCHs across both cells (see 3GPP TS 25.214 s6A.1.1).

On the uplink the UE transmits a single HS-DPCCH to the serving cell. This HS-DPCCH carries 1 or 2 Ack/Nack bits depending on how many HS-PDSCH transmissions the UE attempts to decode. The HS-DPCCH also carries 2 CQI reports, one for each cell (see 3GPP TS 25.212 s4.7). Despite more information on the HS-DPCCH in DC-HSDPA than SC-HSDPA, the underlying physical channel remains unchanged. Instead more code points are added to the Ack/Nack and CQI fields. While the secondary serving cell is active the UE uses deltaAck+1, deltaNack+1 or deltaCQI+1 (3GPP TS 25.214 s5.1.2.5A) to determine the HSDPA gain factor (Ahs). Ahs=38/15 with index 9 has been added to the table in 3GPP TS 25.213 s4.2.1.2.

MAC Layer

To the MAC-ehs layer (DC-HSDPA requires MAC-ehs), the two cells essentially look like two HS-DSCH transport channels. Each of these HS-DSCH channels are controlled by their own independent HARQ process entity, with each entity containing a unique set of HARQ processes. Each of the two HARQ process entities are fed by a common priority queue which means that the rest of the stack from MAC-d upwards is unaware that two carriers are being used to transmit data to the UE.

To restrict the amount of soft memory that can be allocated to single HARQ process (and thus limit the amount of data that has to be transferred across the UE's internal data buses), the standard specifies that when setting up a DC-HSDPA call with the implicit HARQ memory partitioning the network must configure 6, 7, or 8 HARQ processes per cell (3GPP TS 25.331 s10.3.5.7a). For the explicit HARQ memory partitioning case, the number of HARQ processes can be 1 through 8, but the memory size for each HARQ process can not be greater than the number of soft channel bits for an implicit memory partitioning with 6 processes per HS-DSCH channel (3GPP TS 25.331 s8.6.5.6b).

Layer 1 Timing

For a secondary serving HS-DSCH cell, the nominal radio frame timing for CPICH and the timing reference are the same as the radio frame timing for CPICH and timing reference for the serving HS-DSCH cell (3GPP TS 25.211 s7.1).

Signaling

With signaling, the UE indicates whether it supports DC-HSDPA in the RRC Connection Setup Request message and then signals its DC-HSDPA category in the RRC Connection Setup Complete message.

The network enables and activates DC-HSDPA at call setup in the RRC Connection Setup or RB Setup message. Once on a connection, DC-HSDPA can be enabled or disabled by all the reconfiguration messages (Radio Bearer Reconfiguration (RBR), Transport Channel Reconfiguration (TCR) and Physical Channel Reconfiguration (PCR)), or by using the RB Release or Active Set Update message.

When DC-HSDPA is enabled, the secondary serving cell can also be activated or deactivated using HS-SCCH orders that can be sent on either the serving or secondary serving cell (the UE.s behavior is undefined if it receives conflicting orders).

The DRX status and activation and deactivation of the DRX with HS-SCCH is common to both serving and secondary serving cells, and the related HS-SCCH signaling can be sent on either the serving or the secondary serving HS-DSCH cell.

3GPP TS 34.121 Conformance Test

3GPP TS 34.121-1 added new test cases in both chapter 6 (Receiver Characteristics) and chapter 9 (Performance Requirements for HSDPA) for DC-HSDPA devices testing. New FRC channel configurations are also defined, namely H-Set 3A, H-Set 6A, H-Set 8A, H-Set 10A, and H-Set 12. For each of the H-sets, the same parameters are used for each of the cells, for example: H-Set 3A is formed by applying H-Set 3 parameters to each of the cells.

Reference sensitivity levels have been raised by 4 dB for DC-HSDPA tests. BLER must be measured independently for each cell. Two new Reporting of CQI tests verify the UE.s ability to accurately report CQI for both cells. 3GPP TS 34.108 s7.3.13 defines a call setup procedure for DC-HSDPA RF conformance testing that is almost identical to the regular HSDPA call setup procedure with the exception that the loop is not closed on the 12.2 kbps reference measurement channel (RMC). Instead, each test is required to specify loopback conditions.

3GPP References

Refer to the following 3GPP documents if you want to know more about DC-HSDPA:

How Does the Test Set Supports DC-HSDPA

The test set supports DC-HSDPA with the following functionalities:

Related Topics

W-CDMA Concepts

HSDPA Concepts

HSUPA Concepts