10 Uplink Closed Loop Transmit Diversity operation

25.2143GPPPhysical layer procedures (FDD)Release 17TS

The use of uplink CLTD is controlled by higher layer signalling. If the UE is configured with UL CLTD, then UL_CLTD_Enabled is set to TRUE, otherwise UL_CLTD_Enabled is set to FALSE and UL_CLTD_Active is 0. UL_CLTD_Active shall be set to 1, 2 or 3 while UL_CLTD_Enabled is TRUE and CLTD activation state 1, 2 or 3 is activated through HS-SCCH orders respectively.

At the time when UL_CLTD_Enabled is set to TRUE, UL_CLTD_Active shall be set to 1 or 2 as indicated by higher layer signaling. If activation state 1 is configured, or a transition from a different activation state to activation state 1 occurs through an HS-SCCH order, the TPI is initially set to the fixed precoder weight corresponding to the bit pattern "1100" in Table 10. The parameter UL_CLTD_Active may be further switched to other CLTD activation states through HS-SCCH orders, as described in [2].

Upon higher layer signaling that does not result in a serving cell change, the UE shall remember its current UL CLTD activation state and use the last received pre-coding vector after the RRC reconfiguration. Upon higher layer signaling that results in serving cell change, CLTD activation state is either reset or maintained in the RRC reconfiguration message. If activation state 1 is configured, the TPI is initially set to the fixed precoder weight corresponding to the bit pattern "1100" in Table 10.

The secondary dedicated pilot channel, S-DPCCH, is transmitted as long as UL DPCCH is transmitted when UL_CLTD_Enabled is TRUE and UL_CLTD_Active is set to 1.

10.1 General procedure

The general transmitter structure to support uplink CLTD activation state 1 is shown in Figure 8. Channel coding, interleaving and spreading are done as in the case where uplink CLTD is not configured. If UL_CLTD_Active is 1, the complex-valued signal after spreading is fed to both TX antenna branches and weighted with precoding weights w1, w2, w3 and w4. The same precoding weights, w1 and w2, are always applied to DPCCH, DPCCH2 and DPDCH if present, E-DPCCH, E-DPDCH and the HS-DPCCH. The S-DPCCH is pre-coded with precoding weights w3 and w4.

The beamforming weight matrix is given by

=

where normalized amplitude and is the phase to be applied in the current TPI update period, which is determined as follows.

Let be the currently received TPI phase calculated by the NodeB and signalled to the UE via the F-TPICH bit pattern, and the phase applied in the previous TPI update period.

Then the final beamforming phase applied for the current TPI update period is calculated as:

where

and

The mapping between the F-TPICH bit pattern and the TPI phase is given by Table 10.

Table 10: Mapping of precoding weight information

Bit pattern

i

i +1

0

00

00

/2

00

11

11

11

3/2

11

00

Figure 8: The generic uplink transmitter structure to support UL CLTD activation state 1

The channel combining for UL CLTD when UL_CLTD_Enabled is set to TRUE is described in [3] subclause 4.2.4. When UL_CLTD_Active is not equal to 1, no UL closed loop beamforming is performed for uplink transmission.

In the case that UL_CLTD_Active is 2, the DPCCH/DPCCH2/DPDCH/E-DPCCH/E-DPDCH/HS-DPCCH are transmitted on antenna 1, and S-DPCCH is switched off.

In the case that UL_CLTD_Active is 3, the DPCCH/DPCCH2/DPDCH/E-DPCCH/E-DPDCH/HS-DPCCH are transmitted on antenna 2, and S-DPCCH is switched off.

10.2 Downlink TPI transmission and control timing

If UL_CLTD_Enabled is TRUE and UL_CLTD_Active is 1, the Node B determines a precoding phase which is signalled to the UE using the allocated TPI field on the F-TPICH as defined in [1]; see also Table 10. The following applies:

– if the UE is configured with an HS-DPCCH, higher layers indicate to the UE which cells in the active set transmit the F-TPICH, with the restriction that either only the HS-DSCH serving cell transmits the F-TPICH or all cells from the serving radio link set transmit the F-TPICH.

– if the UE is not configured with an HS-DPCCH, higher layers indicate to the UE which cells in the active set transmit the F-TPICH, with the restriction that either only one cell transmits the F-TPICH or all cells from one radio link set transmit the F-TPICH.

– When E-DCH_decoupling is configured, higher layers indicate to the UE which cells in the active set transmit the F-TPICH, with the restriction that either only the E-DCH serving cell transmits the F-TPICH, or only HS-DSCH serving cell transmits the F-TPICH or all cells from the serving radio link set transmit the F-TPICH.

The TPI information update rate is 3 slots. However, the uplink channel measurement periods are not specified for Node B. The UE shall apply the precoding weight indicated by the TPI on the first DPCCH slot boundary, after 512 chips after

– the end of the TPI field carrying the second of the two bits in the TPI bit pattern, if the F-TPICH is configured to be transmitted from one radio link only.

– the end of the last TPI field carrying the second of the two bits in a TPI bit pattern received during a TPI combining period, if the F-TPICH is configured to be transmitted from multiple radio links.

The UE shall measure the reliability of the received TPI bits over the 3 slot period in which the TPI bit pattern corresponding to a precoding weight is received. The received TPI bits are mapped to precoding weights and applied by the UE only if the estimated quality of the TPI bits is determined to be better than a threshold Qtpi. Otherwise, the UE shall apply the precoding weights corresponding to the last reliably received TPI bit pattern. Qtpi is defined implicitly by the relevant tests in [7].

10.3 Combining TPI bits from multiple radio links

When a UE is in softer handover and if F-TPICH is configured to be transmitted from multiple radio links as defined in subclause 10.2, the UE may assume that the transmitted TPI bits from those radio links in a TPI combining period are the same. The TPI combining period has the length of one slot, beginning at the downlink slot boundary of the F-TPICH. Upon reception of one or more TPI bits in a TPI combining period, the UE combines all the TPI bits received in that TPI combining period into a single TPI bit.

10.4 Operation during discontinuous uplink DPCCH operation

When UL_DTX_Active is TRUE (see clause 6C), the UE shall not transmit the uplink S-DPCCH in a slot where UE does not transmit uplink DPCCH according to subclause 6C.2.

The UE shall ignore any TPI commands received in an F-TPICH subframe starting during an uplink DPCCH slot which is in an uplink DPCCH transmission gap as defined in subclause 6C.2. When uplink transmission resumes after a transmission gap, the UE shall apply the precoding weights corresponding to the last applied TPI before the uplink DPCCH transmission gap until a new reliable TPI is received.

10.5 Operation during compressed mode

10.5.1 Uplink compressed mode

In the case that UL_CLTD_Active is 1, the UE shall keep the last applied TPI before an uplink transmission gap until a new reliable TPI is received.

10.5.2 Downlink compressed mode

The following applies for the UE for reception of F-TPICH, during compressed mode on the DPCH or F-DPCH:

The UE shall decode F-TPICH transmissions in all slots that do not overlap with a downlink transmission gap. The UE shall ignore the other TPI bit if one of the two slots carrying the TPI bits overlaps a downlink transmission gap.

10.6 HS-SCCH orders

The Node B may switch uplink CLTD activation state to one of three CLTD activation states through HS-SCCH orders as described in [2]. HS-SCCH ordered transitions between any CLTD activation states are applied at the first E-DCH slot boundary after the end of the HS-DPCCH subframe in which the ACK is sent. The maximum allowed interruption time is 2 slots, ending at the end of the HS-DPCCH subframe in which the ACK is sent. If the UE receives an HS-SCCH order for transitioning to an activation state that is already being applied, then the UE shall not change its activation state, but shall transmit the HARQ-ACK acknowledging the HS-SCCH order.

When E-DCH_decoupling is configured, CLTD activation state cannot be changed through HS-SCCH orders.