Compressed mode (CM)

CM was introduced to WCDMA to allow inter-frequency (system) handovers.

CM is used to create idle periods (gaps) in the transmission during which cell

measurements on another frequency can be made.

Compressed mode is a radio path feature that enables the UE to maintain the current

connection on a certain frequency while performing measurements on another frequency.

This allows the UE to monitor neighbouring cells on another frequency (FDD) or radio access

technology (RAT), typically GSM. Compressed mode means that transmission and reception are

halted for a short time - a few milliseconds - in order to perform a measurement on another

frequency or RAT. The required reception / transmission gap is produced without any loss of

DCH user data by compressing the data transmission in the time domain.