Automatic Neighbor Relation (ANR) in LTE

Manually adding neighbor cells in network is indeed a very hectic process and prone to errors as well. While  networks are becoming more and more complex, it is required to find an automatic and a more optimized way of adding neighbor cells.

ANR comes under the umbrella of Self Organizing Networks ( SON) features. ANR relies on UE to detect unknown cells and report them to eNB. There are two major types:

i) UE based ANR
ii) ANR with OAM Support

UE based ANR

• No OAM support is required.
• UE detects PCI of unknown cell when it needs to do measurement (as configured by network)
• In case of inter-frequency or inter-RAT measurements, eNB needs to configure measurement gaps/or DRX so UE can detect PCI to different frequencies as well.
• UE reports the unknown PCI to eNB via RRC-Reconfiguration message.
• eNB request UE to report Eutran Cell Global ID (ECGI).
• UE reports ECGI by reading BCCH channel.
• eNB retrieves the IP address from MME to further setup the x2 interface. 

ANR with OAM Support

• OAM support is required
• Every new eNB registers to OAM and download the table with information of PCI/ECGI/IP related to neighbors
•  Neighbors also update their own table with new eNB information
• Now like "UE based ANR", UE will detect unknown PCI and report it to the eNB
• eNB doesn't request for ECGI and does not need support from MME
• eNB setups x2 interface with the help of mapping table created in second step above