Each SSC is chosen from a set of 16 different codes of length 256. This se- quence on the secondary SCH indicates which of the code groups the cell's downlink scrambling code belongs to. The UTRA Physical Layer Design Slot #0 Slot #1 Slot #14 Primary Secondary 256 chips 2560 chips One 10 ms SCH radio frame Figure 4.24 Structure of synchronization channel (SCH). Symbol a modulates the primary and secondary synchronization codes as illustrated in Figure 4.24. Table 4.25 shows the presence/absence of STTD encoding on the P- CCPCH. Table 4.25 STTD Encoding on the P-CCPCH P-CCPCH STTD encoded P-CCPCH not STTD encoded 4.3.9.4.1 SCH transmitted by TSTD Figure 4.25 shows the SCH's structure transmitted by the TSTD scheme, where we transmit on antenna 1 both PSC and SSC in even numbered slots, and on antenna 2 both PSC and SSC in odd numbered slots. Slot #0 Slot #1 Slot #2 Slot #14 Antenna 1 Antenna 2 Figure 4.25 Structure of SCH transmitted by TSTD scheme. The UMTS Network and Radio Access Technology 4.3.9.5 Physical Downlink Shared Channel (PDSCH) Users share the PDSCH (carrying the transport Downlink Shared Channel (DSCH)), based on code multiplexing. Since the DSCH associates itself always with one or sev- eral DCHs, we also associate the PDSCH with one or several downlink DPCHs. More precisely, we associate each PDSCH radio frame with one downlink DPCH. Figure 4.26 illustrates the PDSCH frame and slot structure. Ndata bits Tslot = 2560 chips, 20*2k bits (k=0..6) Slot #0 Slot #1 Slot #i Slot #14 1 radio frame: Tf=10 ms Figure 4.26 Frame structure for the PDSCH. Two signalling methods indicate if the UE has data to decode on the DSCH, i.e. through the TFCI field or higher layer signalling. For example, when the spreading factor and other physical layer parameters vary on a frame-by-frame basis, the TFCI informs the UE of PDSCH instantaneous parameters including the channelization code from the PDSCH OVSF code tree. Although the PDSCH and DPCH do not necessarily have the same spreading factors, and the PDSCH spreading f