WCDMA CD/CA-ICH Explained

In WCDMA/UMTS systems, the Collision Detection/Channel Assignment Indicator Channel (CD/CA-ICH) is a specialized downlink physical channel. It is used during Common Packet Channel (CPCH) access procedure. It plays a pivotal role in managing uplink access attempts from multiple UEs to ensure efficient and collision free communication.

Functions

The CD/CA-ICH serves to inform UEs about the status of their uplink access attempts:

• Collision Detection Indicator (CDI): Indicates whether collision already occurred during access attempt by UE.​
• Channel Assignment Indicator (CAI): Informs UE about assignment of dedicated channel for data transmission.

Procedure

1. When UE attempts to access CPCH, it sends preamble to network.
2. Consecutively, the network responds via AICH to acknowledge preamble.
3. Subsequently, the UE transmits its data on CPCH.
4. The network then uses the CD/CA-ICH to inform the UE whether :
   • The transmission was successful (no collision detected).​
   • A collision occurred (when multiple UEs transmitted simultaneously).​
   • A dedicated channel has been assigned for continued communication.

Summary

The CD/CA-ICH manages uplink access attempts in WCDMA/UMTS networks.