Measurement procedures allow the UE to provide the network with different measurement reports that will be used by the radio resource management strategies.
The network configures
1. what objects to measure (e.g., the cells, transport channels, physical channels)
2. criteria to be used (e.g., periodic reporting or event-trigger)
3. RLC mode to be used (e.g., AM or UM)
This configuration is done by means of Measurement Control Message.
Measurements are required only by UEs in Cell_DCH and Cell_FACH states.
In some cases such as traffic volume monitoring, UEs in Cell_PCH may also send measurement reports. –> I think this is why power consumption during Cell_PCH is higher (around 5mA) than idle mode (around 1mA).
I found out later that even in idle, URA_PCH, measurements may be done.