4G/LTE - ANR  




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.

  • It is tedius and labour intensive to investigate and configure all the neighbour list for each cell
  • The neighbour cell list would change very frequently for various reasons especially when they are putting a lot of new cells here and there.

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) Network send Measurement Command (Measurement Control) to UE to perform the detection/measurement of cells around it.
  • ii) UE detect/performs measurement on the cells and report it to the cells which sent the measurement command
  • iii) Opon the reception of the measurement report, the cell extract the cell information from the measurement report message and update its neigbhour cell list.

I will put the details on protocol sequence and decoded RRC messages later when I have it.