ANR (Automatic Neighbour Relation)
Each cell broadcast the list of neighbour cells via various SIBs. How a cell knows about the existence of its neighbours ? A conventional way is that network operator manually configure these neighbour cell list for each cell. As you may guess, there would be a couple of big issues with these convetional method.
Then everybody would ask "Would there be any easier way to do this ?" or "Wouldn't it be possible to come out with any method to do this automatically ?"
Yes, there is an automatic way to do this and it is ANR. The idea is to let each cell to detect its neighbour and update its neighbour cell list automatically.
But there is an issue. Cell does not have any measurement functionality for detecting the existence it's neighbour cell. Then how we solve the problem ? This automatica neighbour detection can be possible if UE helps. Since UE can detect all the cells around it, network can order UE to check the existence of cells around it and extract the neighbour cell information from UE report.
Overall procedure is as follows.
I will put the details on protocol sequence and decoded RRC messages later when I have it.