9 MIMO operation of HS-DSCH

25.2143GPPPhysical layer procedures (FDD)Release 17TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

There are two possibilities for operating MIMO: MIMO mode when single-stream restriction is not configured, in which both single and dual stream transmission can be applied, and MIMO mode when single-stream restriction is configured, which is restricted only to single stream transmission. This section applies only when a UE is configured in MIMO mode.

The general transmitter structure to support MIMO operation of HS-PDSCH transmission is shown in figure 7. Channel coding, interleaving and spreading are done as in non-MIMO mode. When single-stream restriction is not configured the Node B scheduler can decide to transmit one or two transport blocks to a UE in one TTI in the serving HS-DSCH cell, and one or two transport blocks in a secondary serving HS-DSCH cell if the UE is configured with a secondary serving HS-DSCH cell in which MIMO is configured, whereas when single-stream restriction is configured only transmission of single transport block is allowed in any of the cells. The spread complex valued signals are fed to both TX antenna branches, and weighted with precoding weights w₁, w₂, w₃ and w₄. The precoding weights w₁ and w₃ are constant real valued scalars and the precoding weights w₂ and w₄are variable complex valued scalars. The precoding weights w₁, w₂, w₃ and w₄ are defined as follows:

If single-stream restriction is configured, or single-stream restriction is not configured and the Node B schedules a single transport block in a cell to a UE in one TTI, it uses the precoding vector (w_1,w₂) for transmission of that transport block on the HS-PDSCH sub-frame. If single-stream restriction is not configured and the UTRAN schedules two transport blocks in a cell to a UE in one TTI, it uses two orthogonal precoding vectors to transmit the two transport blocks. The precoding vector (w_1,w₂) is called the primary precoding vector which is used for transmitting the primary transport block and the precoding vector (w_3,w₄) is called secondary precoding vector which is used for transmitting the secondary transport block, respectively.

If single-stream restriction is configured (Figure 7a) the secondary transport block is never present. If single-stream restriction is not configured (figure 7) the Node B can dynamically schedule the UE with one or two transport blocks.

Figure 7: The generic downlink transmitter structure to support MIMO operation for HS-PDSCH transmission when single-stream restriction is not configured.

Figure 7a: The generic downlink transmitter structure to support MIMO operation for HS-PDSCH transmission when single-stream restriction is configured.

9.1 General procedure

The UE uses the CPICH to separately estimate the channels seen from each antenna. One of the antennas will transmit the Antenna 1 modulation pattern of the P-CPICH as defined in subclause 5.3.3.1 of [1]. The other antenna will transmit either the Antenna 2 modulation pattern of the P-CPICH or the Antenna 1 modulation pattern of a S-CPICH. The Pilot configuration in support of MIMO operation of HS-DSCH in the cell is signalled by higher layers.

The UE determines a preferred primary precoding vector and signals it to the Node B. The signalled information about the preferred primary precoding vector is termed precoding control indication (PCI) and is defined in subclause 6A.4. The PCI is signalled to the Node B together with channel quality indication (CQI) as a composite PCI/CQI report according to the procedure defined in subclause 6A.1.2.2. The UE transmits the composite PCI/CQI report to the Node B using the CQI field on the HS-DPCCH as defined in [1]. Based on the composite PCI/CQI reports, the Node B scheduler decides when single-stream restriction is not configured whether to schedule one or two transport blocks in a cell to a UE in one TTI and what transport block size(s) and modulation scheme(s) to use for each of them.

The Node B signals to the UE the precoding weight w₂ applied on the HS-PDSCH sub-frame using the precoding weight indication bits of part 1 of the corresponding HS-SCCH sub-frame. The precoding weight adjustment of each HS-PDSCH is done at the HS-PDSCH sub-frame border.