WCDMA CPICH: Common Pilot Channel Explained

This page describes the CPICH, or common pilot channel, with respect to the WCDMA/UMTS system. The pilot channel is used by the base station to provide a reference to all mobile stations and to aid channel estimation at the terminals.

It has a predefined bit sequence (all 1s) which is scrambled with the cell specific primary scrambling code.

WCDMA CPICH functions

• Predefined bit sequence used by CPICH enables UEs to perform channel estimation. Hence it helps UEs in coherent demodulation of channels and to synchronize with timing of base station.
• During cell search procedure, UEs use CPICH for identification of PSC (Primary Scrambling Code) of cell. It helps in distinguishing different cells and to establish the connection.
• With its help, UEs measure RSCP and Ec/No. These parameters are very useful for handover and performance optimization.

Types

There are two types of CPICH: primary and secondary.

• Primary CPICH : Every WCDMA cell transmits P-CPICH using fixed channelization code. It serves as main reference for UEs within cell.

• Secondary CPICH : Optionally used to provide additional reference signals and to support specific services including beamforming (if used).

Summary

CPICH in WCDMA systems is used so that UEs can accurately estimate channel conditions. This helps them to synchronize with network, to identify cells and to maintain reliable communication.