5.5 Downlink transmit diversity

25.2243GPPPhysical layer procedures (TDD)TS

Downlink Transmit diversity for PDSCH, DPCH, P-CCPCH, S-CCPCH, PICH, MICH, HS-SCCH, HS-PDSCH, E-AGCH, E-HICH and DwPCH is optional in UTRAN. Its support is mandatory at the UE.

5.5.1 Transmit diversity for PDSCH, DPCH, HS-SCCH, HS-PDSCH and E-AGCH

Time Switched Transmit Diversity (TSTD) may be employed as transmit diversity scheme for downlink DPCH and PDSCH. Closed loop Transmit Diversity may be employed as transmit diversity scheme for downlink DPCH, HS-SCCH, HS-PDSCH and E-AGCH.

5.5.1.1 TSTD for PDSCH and DPCH

TSTD can be employed as transmit diversity scheme for PDSCH and downlink DPCH. An example for the transmitter structure of the TSTD transmitter is shown in figure 6. Channel coding, rate matching, interleaving, bit-to-symbol mapping, spreading, and scrambling are performed as in the non-diversity mode. Then the data is time multiplexed with the midamble sequence. Then, after pulse shaping, modulation and amplification, DPCH and/or PDSCH is transmitted from antenna 1 and antenna 2 alternately every sub-frame. Not all DPCHs and/or PDSCHs in the sub-frame need to be transmitted on the same antenna and not all DPCHs and/or PDSCHs within a sub-frame have to use TSTD. Figure 7 shows an example for the antenna switching pattern for the transmission of DPCH/PDSCH for the case that all physical channels are transmitted with TSTD and are using the same antenna in the sub-frame.

Figure 6: Example for TSTD Transmitter structure for DPCH/PDSCH and P-CCPCH.

Figure 7: Example for the antenna swithing pattern for TSTD transmission of DPCH/PDSCH and P-CCPCH: all physical channels are transmitted with TSTD and are using the same antenna in the sub-frame.

5.5.1.2 Closed loop Tx diversity for PDSCH, DPCH, HS-SCCH, HS-PDSCH and E-AGCH

The transmitter structure to support transmit diversity for DPCH, PDSCH, HS-SCCH, HS-PDSCH and E-AGCH transmission is shown in figure 8. Channel coding, interleaving and spreading are done as in non-diversity mode. The spread complex valued signal is fed to both TX antenna branches, and weighted with antenna specific weight factors w₁ and w₂. The weight factors are complex valued signals (i.e., w_i = a_i + jb_i ), in general. These weight factors are calculated on a per slot and per user basis.

The weight factors are determined by the UTRAN.

Figure 8: Downlink transmitter structure to support Transmit Diversity
for DPCH, PDSCH, HS-SCCH, HS-PDSCH and E-AGCH transmission (UTRAN Access Point) in 1.28 Mcps TDD

5.5.2 Transmit diversity for DwPCH

The transmitter structure to support transmit diversity for DwPCH transmission is shown in figure 9. DwPCH is transmitted from antenna 1 and antenna 2 alternatively.

Figure 9: Downlink transmitter structure to support Transmit Diversity
for DwPCH transmission (UTRAN Access Point) in 1.28 Mcps TDD

5.5.3 Transmit diversity for P-CCPCH

TSTD or Space Code Transmit Diversity (SCTD) can be employed as transmit diversity scheme for the Primary Common Control Physical Channel (P-CCPCH)

5.5.3.1 TSTD transmission scheme for P-CCPCH

A block diagram of an example of a TSTD transmitter is shown in figure 6. Channel coding, rate matching, interleaving, bit-to-symbol mapping, spreading, and scrambling are performed as in the non-diversity mode. Then the data is time multiplexed with the midamble sequence. Then, after pulse shaping and modulation and amplification, P-CCPCH is transmitted from antenna 1 and antenna 2 alternately every sub-frame. If there is a DPCH that uses TSTD, TSTD is also applied to P-CCPCH. An example of the antenna-switching pattern is shown in figure 7. If TSTD is applied to P-CCPCH, it shall also be applied to other beacon channels.

5.5.4 SCTD transmission scheme for beacon channels

The use of SCTD will be indicated by higher layers. If SCTD is active within a cell, SCTD shall be applied to any beacon channel. When beacon channel is used on dedicated MBSFN frequency, SCTD shall not be applied.

The SCTD open loop downlink transmit diversity scheme for beacon channels is shown in figure 10, exemplary for the P-CCPCH. Channel coding, rate matching, interleaving and bit-to-symbol mapping are performed as in the non-diversity mode. In TxDiversity mode the beacon channel that is allocated to code is spread with the channelisation codes and and scrambled with the cell specific scrambling code. The beacon channel that is allocated to code is spread with the channelisation codes and and scrambled with the cell specific scrambling code. The spread sequences on code and code are then transmitted on the diversity antenna. The power applied to each antenna shall be equal.

The use of SCTD will be indicated by higher layers.

Figure 10: Block diagram of the transmitter (SCTD) in 1.28 Mcps TDD, exemplary for the P-CCPCH