Overall Physical Channel Timing Relationship. In Fig. 7.54, we present various timing diagrams
for the physical channels discussed above. A few points should be mentioned, prior to our discussion.
First, the P-CCPCH is used as a timing reference for all physical channels for the downlink, and since
the uplink has a fixed relationship to the downlink, the P-CCPCH indirectly acts as a timing reference
for the uplink. Second, the P-CCPCH, P-CPICH, S-CPICH, P-SCH, S-SCH, and HS-SCCH have
identical frame timing. In Fig. 7.54, we present the frame timing relationship for some of the downlink
physical channels taken from 3GPP [18].
The S-CCPCH frame timing may be different for different S-CCPCHs transmitted. The offset
from the P-CCPCH frame timing is measured in multiples of 256 chips:
with . The PICH frame timing is prior to the corresponding tPICH 7680 chips, Tk 50, 1,c, 1496 tSCCPCH,k Tk # 256 chips,
S-CCPCH frame timing. Figure 7.54 can be somewhat misleading; let??™s try to clear it up. The paging
indicator is sent in a PICH frame that corresponds to the PCH on the S-CCPCH which has a
frame timing starting chips after the transmitted PICH frame. This discussion on timing is also
applicable to the MBMS indication channel (MICH) and S-CCPCH relationship, which will be
addressed later.
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