11 Uplink MIMO

25.2143GPPPhysical layer procedures (FDD)Release 17TS

If the UE is configured with UL MIMO, then UL_MIMO_Enabled is set to TRUE, otherwise UL_MIMO_Enabled is set to FALSE. When UL_MIMO_Enabled is set to TRUE, UL_CLTD_Enabled is also set to TRUE. UL_CLTD_Active can be set to 1, 2 or 3 while UL_MIMO_Enabled is TRUE and CLTD activation state can be changed through HS-SCCH orders. The initial state of the UL_CLTD_Active follows the definition in clause 10.

Two separate transport blocks are transmitted via two independent spatial streams when rank-2 transmission is used. The data rates on each stream can be independently adapted. The number of HARQ processes in dual stream operation is double of that in single stream operation, and two E-HICH signature sequences are allocated, providing HARQ-ACK feedback for each stream independently.

Rank-2 transmissions are only possible when the UL_CLTD_Active = 1.

The pre-coded physical channels structure for UL MIMO rank-2 transmission is depicted in Figure 9. When UL_MIMO_Enabled is TRUE either single or dual-stream transmissions can take place. In case of single stream (rank-1) transmission, the transport block is carried over E-DPDCH(s) as in UL CLTD. In case of dual stream (rank-2) transmission, the primary transport block is carried over 4 E-DPDCHs and the secondary transport block is carried over 4 S-E-DPDCHs. S-E-DPCCH is used to indicate the transport block size and retransmission sequence number of the secondary transport block on S-E-DPDCH. S-E-DPCCH is I/Q multiplexed with E-DPCCH and transmitted on primary pre-coding vector. S-E-DPCCH is only sent with rank-2 transmissions. Both the E-DPDCHs and the S-E-DPDCHs are always sent with 2xSF2 + 2xSF4 code combination for rank-2 transmission. The UE can be configured with uplink MIMO only with 2 ms TTI on E-DCH.

For dual stream transmissions the following applies on setting the relative transmit powers of the uplink physical channels:

– For the calculation of the E-DPCCH gain factors, E-DPCCH boosting is always applied regardless of the selected E-TFC to be transmitted,

– The S-DPCCH gain factor equals the E-DPCCH gain factor,

– The S-E-DPCCH gain factor is configured by higher layers.

UL MIMO rank-1 transmission and the setting of the channel transmit powers function as defined for UL CLTD. The pre-coded physical channels structure for UL MIMO rank-1 transmission is depicted in Figure 10.

Figure 9: Pre-coded physical channel structure of UL MIMO with rank-2 transmission

Figure 10: Pre-coded physical channel structure of UL MIMO with rank-1 transmission

11.1 General procedure

The UE transmits two orthogonal pilot signals on DPCCH and S-DPCCH. Node B estimates the preferred rank, precoding vector and S-ETFC Offset of the two streams from the received pilot signals. The Node B transmits the preferred precoding vector to the UE in the form of TPI bits using the F-TPICH as in UL CLTD. The UE applies TPI as with UL CLTD. The preferred rank and S-ETFC Offset to be applied by the UE E-TFC selection are signalled to the UE using the E-ROCH channel.

Rank-1 transmissions occur if the maximum rank signalled over the E-ROCH is 1, or if the UE does not have sufficient data or power headroom to transmit at least the Minimum E-TFCI for Rank 2 transmission sized transport blocks on both streams. Minimum E-TFCI for Rank 2 transmission is configured by higher layers.

The signal after spreading is fed to both TX antenna branches and weighted with pre-coding weights w₁, w₂, w₃ and w₄. The same pre-coding weights, w₁ and w₂ are always applied to DPCCH, DPCCH2, E-DPCCH, E-DPDCH, HS-DPCCH and S-E-DPCCH. The S-DPCCH and S-E-DPDCH are pre-coded with pre-coding weights w₃ and w₄.

11.2 Downlink TPI transmission and control timing

When uplink MIMO is configured, downlink TPI transmission and control timing follows that defined for UL CLTD as defined in subclause 10.2.

11.3 Combining TPI bits from radio links of the serving radio link set

When uplink MIMO is configured, combining TPI bits follows that defined for UL CLTD as defined in subclause 10.3.

11.4 Operation during discontinuous uplink DPCCH operation

When uplink MIMO is configured, operation during discontinuous uplink DPCCH operation follows that defined for UL CLTD as defined in subclause 10.4.

11.5 Operation during compressed mode

When uplink MIMO is configured, operation during compressed mode follows that defined for UL CLTD as defined in subclause 10.5.

11.6 HS-SCCH orders

When uplink MIMO is configured, the HS-SCCH orders as defined for UL CLTD operation in subclause 10.6 apply.

11.7 Uplink power control

When uplink MIMO is configured, the inner loop power control operates without modifications as defined for non-MIMO operation.