Main Work of Primary Common Pilot Channel (PCPICH) in WCDMA is as below.
- Carrying pre-defined sequence
- Fixed channel code: Cch, 256, 0, Fixed rate 30Kbps
- Scrambled by the primary scrambling code
- Broadcast over the entire cell
- A phase reference for SCH, Primary CCPCH, AICH, PICH and
- downlink DPCH, Only one PCPICH per cell
The Common Pilot Channel (CPICH) is a pure physical control channel broadcasted over the entire cell. It is not linked to any transport channel. It consists of a sequence of known bits that are transmitted in parallel with the primary and secondary CCPCH.
The PCPICH is used by the mobile to determine which of the 8 possible primary scrambling codes is used by the cell, and to provide the phase reference for common channels.
Finding the primary scrambling code is done during the cell search procedure through a symbol-by-symbol correlation with all the codes within the code group. After the primary scrambling code has been identified, the UE can decode system information on the P-CCPCH.
The P-CPICH is the phase reference for the SCH, P-CCPCH, AICH and PICH. It is broadcasted over the entire cell. The channelization code used to spread the PCPICH is always Cch, 256, 0 (all ones). Thus, the P-CPICH is a fixed rate channel. Also, it is always scrambled with the primary scrambling code of the cell.