24 Uplink MIMO Operation (FDD only)

25.3193GPPEnhanced uplinkOverall descriptionStage 2TS

For FDD and in CELL_DCH state, certain categories of UEs may be configured into uplink MIMO (UL MIMO) operation. UL MIMO builds on top of UL CLTD by adding in parallel the second transport block, transmitted on an orthogonal pre-coding vector with a set of S-E-DPDCHs physical channels. For a UE configured in UL MIMO mode, either single or dual-stream transmissions can take place. In case of single stream (rank1) transmission, the transport block is carried over E-DPDCH(s) as in UL CLTD. In case of dual stream (rank2) transmission, the primary transport block is carried over four E-DPDCHs and the secondary transport block is carried over four S-E-DPDCHs. UL MIMO is not supported for CELL_DCH state when more than one uplink frequencies are configured.

UL MIMO is characterized by the following properties:

– Support of transport channels:

– UL MIMO is applicable for E-DCH only in Cell_DCH state;

– UL MIMO is applicable only when E-DCH and HS-DSCH serving cells are configured;

– Physical channel structure:

– UL MIMO is based on the UL CLTD functionality, where there are two UL pilot channels, the DPCCH and the secondary DPCCH (S-DPCCH), and a single inner and outer power control loop. The precoding weights are determined by the serving cells and the PCI feedback is carried on an F-DPCH-like channel, F-TPICH. Additionally, the serving Node B can use the same HS-SCCH orders as in CLTD, where rank2 transmission is possible if CLTD activation state is 1;

– When performing rank2 transmissions, there are two additional UL channels: secondary E-DPCCH (S-E-DPCCH) and secondary E-DPDCH (S-E-DPDCHs). The primary and the secondary streams are transmitted using 2xSF2+2xSF4 channelization codes;

– The DPCCH, HS-DPCCH, E-DPDCH, E-DPCCH and S-E-DPCCH are pre-coded with the primary pre-coding vector. The S-DPCCH and S-E-DPDCH are pre-coded with the secondary pre-coding vector, which is orthogonal to the primary one;

– The power offsets between the DPCCH and the S-DPCCH and between the DPCCH and the S-E-DPCCH are configurable by RRC;

– The rank indication and offset controlling the presence and the data rate of the second stream are sent to the UE from the serving E-DCH cell by using E-DCH Rank and Offset Channel (E-ROCH) channel;

– The E-AGCH and E-ROCH channels can be independently configured with a channelization code and E-RNTI with a possibility to code multiplex them or time multiplex on one code with different E-RNTIs;

– The two transport blocks are acknowledged independently using the E-HICH channel, where two different signatures are configured on the same E-HICH code channel;

– Rank2 transmission is allowed in soft and softer handover. The serving E-DCH cell and non-serving cells send independently ACK/NACK for each transmitted transport block;

– Scheduling procedures:

– For E-DCH transmission, the DPCCH power is used as the reference for the definition of Serving Grant and UPH the same way as when the UE is not configured in MIMO mode;

– Both primary and the secondary stream use the E-TFC selection procedure defined in [4], where the primary stream E-TFC selection uses the network signalled Serving Grant, and the secondary stream uses the virtual Serving Grant;

– The virtual Serving Grant for the second stream E-TFC selection is calculated based on the transmit power (gain factors) chosen for the primary stream and the offset value, where the offset is provided by the Node B over the E-ROCH channel. The same gain factor tables as with the first stream are used in the second stream E-TFC selection when calculating the secondary stream E-TFC based on the virtual Serving Grant;

– The UE MAC layer is responsible for selecting transmission rank according to the maximum rank signalled by the serving Node B and the rules defined in [4]. A UE falls back from rank2 to rank1 transmission if the TB sizes chosen as a result of the E-TFC selection procedure for the rank2 transmission are less than the network configurable minimum TB size for rank2 transmission;

– Secondary stream interference compensation:

– The inter-stream interference compensation is applied during rank2 transmission in the form of an offset used for the primary stream E-TFC selection;

– The offset is signalled to a UE by means of the RRC signalling;

– MAC architecture:

– Only MAC-i/is is supported;

– There is single E-DCH transport channel per uplink frequency, one HARQ entity per E-DCH transport channel and the total number of HARQ processes is doubled per HARQ entity;

– There is one active HARQ process per TTI for rank1 transmission, and two HARQ processes per TTI for rank2 transmission, and HARQ process activation/deactivation applies to both the first and the second stream;

– TSN field extension must be configured;

– For uplink MIMO there is a primary and secondary E-RNTI configured for the primary stream grant control, and a E-ROCH E-RNTI that can be configured for the secondary stream rank and offset control;

– Discontinuous transmission:

– The UL DTX status and configuration is common for both streams in rank2 transmission.