6.1 HS-DSCH MAC architecture – UE side

25.3083GPPHigh Speed Downlink Packet Access (HSDPA)Overall descriptionRelease 17Stage 2TS

This subclause describes the architecture of the MAC and functional split required to support HS-DSCH on the UE side. Both MAC-hs and MAC-ehs handle the HS-DSCH specific functions. Upper layers configure which of the two entities, MAC-hs or MAC-ehs, is to be applied to handle HS-DSCH functionality.

6.1.1 Overall architecture

Figure 6.1.1-1 shows the overall MAC architecture. The data received on HS-DSCH is mapped to the MAC-hs or MAC-ehs. The MAC-hs or MAC-ehs is configured via the MAC Control SAP by RRC similar to the MAC-c/sh and MAC-d, to set the parameters in the MAC-hs or MAC-ehs such as allowed transport format combinations for the HS-DSCH.

The associated Downlink Signalling carries information for support of HS-DSCH while the associated Uplink Signalling carries feedback information.

In FDD, when operating in CELL_FACH CELL_PCH and URA_PCH state HS-DSCH reception is defined in clause 14 and the transmission of HS-DPCCH for HS-DSCH related ACK/NACK and CQI signalling is only supported when the UE is using a common E-DCH resource, is transmitting DTCH/DCCH data, has successfully resolved collision, and has been so configured by the network. Otherwise the transmission of HS-DPCCH is not supported.

In 1.28Mcps TDD, when operating in CELL_FACH HS-DSCH reception is defined in clause 16 and UE with dedicated H-RNTI sends ACK/NACK and CQI signalling on the related HS-SICH.

Figure 6.1.1-1: UE side MAC architecture with HS-DSCH (MAC-hs)

Figure 6.1.1-2: UE side MAC architecture with HS-DSCH (MAC-ehs)

6.1.2 Details of MAC-d

The MAC-d entity is modified with the addition of a link to the MAC-hs or MAC-ehs entity. The links to MAC-hs, MAC-ehs and MAC-c/sh cannot be configured simultaneously in one UE.

The mapping between C/T MUX entity in MAC-d and the reordering buffer in MAC-hs is configured by higher layers. One reordering buffer maps to one C/T MUX entity and many reordering buffers can map to the same C/T MUX entity. If MAC-ehs is configured, C/T MUX toward MAC-ehs is not used.

Figure 6.1.2-1: MAC-d architecture for MAC-hs

Figure 6.1.2-1b: MAC-d architecture for MAC-ehs

Figure 6.1.2-2: Simplified architecture showing MAC-hs inter-working in UE

Figure 6.1.2-3: Simplified architecture showing MAC-ehs inter-working in UE

6.1.3 Details of MAC-c/sh

The MAC-c/sh/m on the UE side is not modified for HS-DSCH operation in CELL_DCH state.

In FDD and 1.28Mcps TDD, when operating in CELL_FACH, CELL_PCH and URA_PCH state, HS-DSCH reception is as defined in clauses 14 and 15 for FDD, 16 and 17 for 1.28Mcps TDD, and the MAC-c/sh is depicted in figure 6.1.3-1.

Figure 6.1.3-1: UE side MAC architecture / MAC-c/sh/m details

6.1.4 Details of MAC-hs

In the model below the MAC-hs comprises the following entity:

– HARQ:
The HARQ entity is responsible for handling the HARQ protocol. For FDD and 3.84 Mcps/7.68 Mcps TDD,there shall be one HARQ process per HS-DSCH per TTI, for 1.28 Mcps TDD, there shall be one HARQ process per HS-DSCH on each carrier per TTI. The HARQ functional entity handles all the tasks that are required for hybrid ARQ. It is for example responsible for generating ACKs or NACKs. The detailed configuration of the hybrid ARQ protocol is provided by RRC over the MAC-Control SAP.

– – Reordering:
The reordering entity organises received data blocks according to the received TSN. Data blocks with consecutive TSNs are delivered to higher layers upon reception. A timer mechanism determines delivery of non-consecutive data blocks to higher layers. There is one reordering entity for each priority class.

– – The following is allowed:

– One MAC-hs PDU contains only MAC-d PDUs with the same priority, and from the same MAC-d flow;

– Different MAC-d PDU sizes can be supported in a given MAC-hs PDU.

Figure 6.1.4-1: UE side MAC architecture/MAC-hs details

Figure 6.1.4-2: UE side MAC architecture / MAC-hs details (1.28Mcps TDD multi-frequency HS-DSCH operation mode only)

6.1.5 Details of MAC-ehs

The model for MAC-ehs comprises the following entities:

– HARQ:
The HARQ entity is responsible for handling the HARQ protocol. There shall be one HARQ process per HS-DSCH per TTI for single stream transmission and two HARQ processes per HS-DSCH per TTI for dual stream transmission. For 1.28 Mcps TDD multi-frequency HS-DSCH cell, there shall be one HARQ process per HS-DSCH on each carrier per TTI. The HARQ functional entity handles all the tasks that are required for hybrid ARQ. It is for example responsible for generating ACKs or NACKs. The detailed configuration of the hybrid ARQ protocol is provided by RRC over the MAC-Control SAP. There can be 1 to 8 HARQ entities, depending on the configuration. For 1.28 Mcps TDD multi-frequency HS-DSCH cell, there can be 1 to 6 HARQ entities, depending on the configurations.

– Disassembly

– The disassembly entity disassembles the MAC-ehs PDUs.

– Reordering queue distribution

– The reordering queue distribution function routes the received MAC-ehs SDUs or segments of MAC-ehs SDUs to correct reordering queues based on the received logical channel identifier.

– Reordering:
The reordering entity organises received MAC-ehs SDUs or segments of MAC-ehs SDUs according to the received TSN. Data blocks with consecutive TSNs are delivered to higher layers upon reception. A timer mechanism determines delivery of non-consecutive data blocks to higher layers. There is one reordering entity for each priority class.

– Reassembly:

– The reassembly entity reassembles segmented MAC-ehs SDUs (corresponding to either MAC-c or MAC-d PDUs) and forwards the MAC PDUs to LCH-ID demultiplexing entity.

– LCH-ID demultiplexing:
The demultiplexing entity routes the MAC-ehs SDUs to correct logical channel based on the received logical channel identifier.

– The following is allowed:

– The MAC-ehs SDUs included in a MAC-ehs PDU can have a different size and a different priority and can be mapped to different MAC-d flows.

Figure 6.1.5-1: UE side MAC architecture/MAC-ehs details

Figure 6.1.5-2: UE side MAC architecture/MAC-ehs details (1.28Mcps TDD multi-frequency HS-DSCH operation mode only)