Automatic Neighbour Relation in LTE

Manually provisioning and managing neighbor cells in traditional mobile network is challenging task and it becomes more difficult as new mobile technologies are being rolled out while 2G/3G cells already exist. For LTE, task becomes challenging for operators, as in addition of defining intra LTE neighbour relations for eNBs operator has to provision neighboring 2G, 3G, CDMA2000 cells as well.

According to 3GPP specifications, the purpose of the Automatic Neighbour Relation (ANR) functionality is to relieve the operator from the burden of manually managing Neighbor Relations (NRs). This feature would operators effort to provision 

Figure below shows ANR and its environment as per 3GPP. It shows interaction between eNB and O&M due to ANR.

 

The ANR function resides in the eNB and manages the conceptual Neighbour Relation Table (NRT). Located within ANR, the Neighbour Detection Function finds new neighbours and adds them to the NRT. ANR also contains the Neighbour Removal Function which removes outdated NRs. The Neighbour Detection Function and the Neighbour Removal Function are implementation specific.

An existing Neighbour cell Relation (NR) from a source cell to a target cell means that eNB controlling the source cell  knows the ECGI/CGI and Physical Cell Identifier (PCI) of the target cell and has an entry in the NRT for the source cell identifying the target cell.

For each cell that the eNB has, the eNB keeps a NRT. For each NR, the NRT contains the Target Cell Identifier (TCI), which identifies the target cell. For E-UTRAN, the TCI corresponds to the E-UTAN Cell Global Identifier (ECGI) and Physical Cell Identifier (PCI) of the target cell. 

The ANR function relies on cells broadcasting their identity on global level, E-UTRAN Cell Global Identifier (ECGI) and allows O&M to manage the NRT. O&M can add and delete NRs. It can also change the attributes of the NRT. The O&M system is informed about changes in the NRT.

Intra-LTE/frequency ANR:  

The eNB serving cell with ANR function, instructs each UE to perform measurements on neighbor cells, as a part of the normal call procedure. The eNB may use different policies for instructing the UE to do measurements, and when to report them to the eNB. 

When UE discovers new cell’s ECGI, the UE reports the detected ECGI to the serving cell eNB. In addition the UE reports the tracking area code and all PLMN IDs that have been detected. The eNB adds this neighbour relation to NRT.

Inter-RAT/Inter-frequency ANR:

The eNB serving cell with ANR function can instruct a UE to perform measurements and detect cells on other RATs/frequencies .during connected mode. The eNB may use different policies for instructing the UE to do measurements, and when to report them to the eNB.

The UE reports the PCI of the detected cells in the target RATs/frequencies. When the eNB receives UE reports containing PCIs of cell(s), eNB may instruct the UE to read the CGI and the RAC of the detected neighbour cell in case of GERAN detected cells and CGI, LAC and, RAC in case of UTRAN detected cells. For the Interfrequency case, the eNB may instruct the UE to read the ECGI, TAC and all available PLMN ID(s) of the inter-frequency detected cell.

The eNB updates its inter-RAT/inter-frequency Neighbour Relation Table after receiving relevant info from UE.

 

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Anonymous's picture

question about ANR

Have you more of detaile what conserne the functioning of the ANRi and its avantege by report(relationship) has reporting tools

Pankaj's picture

ANR's purpose

Not sure if I understood question fully, if you are looking for benefits of ANRi. Then ANR's purpose is to remove or at least minimize the manual handling of neighbor relations when establishing new eNBs and when optimizing neighbor lists. This will increase the number of successful handovers and lead to less dropped connections due to missing neighbor relations.

Anonymous's picture

Have you more of detaile what

Have you more of detaile what conserne the functioning of the ANRi and its avantege by report(relationship) has reporting tools

Anonymous's picture

Difference between PCI and ECGI

Hi, thanks for your nice post.

I'm confused about PCIi and ECGIi, could you please explain the differences between PCI and ECGI.
Thank you again.

Anonymous's picture

Each LTEi cell broadcasts a

Each LTEi cell broadcasts a specific Physical Cell Identity (PCIi) that is normally used to identify a cell for radio purposes. Note that there are 504 PCIs values in the LTE system, compared with the 512 primary scrambling codes in WCDMA. The PCI of a cell does not need to be unique across the entire network; however, it must be unique on a local scale to avoid confusion with neighboring cells.

E-UTRANi Cell Global Identifier (ECGIi) used to identify cells globally. The ECGI is constructed from the MCC (Mobile Country Code), MNC (Mobile Network Code) and the ECIi (E-UTRAN Cell Identifier).

Anonymous's picture

Question about 36.331

In MeasObjectEUTRA object in 36.331, there are attributes related to blacklist as below. It is essentially a list of PCIs which you do not want the UEi to perform measurements on.

-- Black list
blackCellsToAddModList BlackCellsToAddModList OPTIONAL, -- Need ON

Can you please help me with the following:
1) Why is it a list of PCI and not CGI?
2) What happens when PCI changes for a cell? The PCI in the blacklist will now be pointing to a wrong cell
3) As indicated in the article, is the information requested from UE different in intra LTEi and inter LTE? i.e why does UE report CGI in intra LTE and PCI in inter LTE?

Thanks very much

Pankaj's picture

Physical Cell ID (PCIi) is

Physical Cell ID (PCIi) is uniquely chosen and a eNB can choose either it's own PCI randomly after excluding neighboring cells or it could be obtained from O&M.

Initially UEi sends a measurement report with neighboring Cell’s PCI, but not its ECGIi. The eNB instructs the UE, using the newly discovered PCI as parameter, to read the ECGI, the TAC and all available PLMNi ID(s) of the related neighbor cell. This is applicable for both Intra and Inter LTEi frequency cases.

In E-UTRANi, Neighbor cell Relation (NR) Table has Target Cell Identifier (TCI) mapping where TCI corresponds to the E-UTAN Cell Global Identifier (ECGI) and PCI of the target cell. As PCI is unique and first known id of a cell, it seems logical to pick it for the fields you mentioned. Note that PCI is defined by the carrier frequency and the Primary Scrambling Code (PSC) in case of UTRAN FDD cell, by the carrier frequency and the cell parameter ID in case of UTRAN TDD cell, by the Band Indicator + BSIC + BCCHi ARFCNi in case of GERANi cell and by the PN Offset in case of CDMA2000 cell.

As PCI can change, I expect that eNB will update its table after it receives fresh data corresponding to the existing PCI.

Anonymous's picture

Very Good Information

Hey , You capture good information in nice way ...very useful info on ANRi.

Thanks !!

Anonymous's picture

RE: Automatic Neighbour Relation in LTE

Very good introduction on ANRi. Well done LteWorld!

One thing not clear to me from this article is who is ultimately responsible for updating the NRT. Is it O&M, or is it eNB? I think it might have implication on implementation.

By QXW

LteWorld's picture

Based on UE reports, eNodeB

Based on UEi reports, eNodeBi can decide to add a cell in its neighbor relation list. The eNB updates its inter-RATi/inter-frequency Neighbour Relation Table after receiving relevant info from UE.

O&M can manage the NRT and can add and delete NRs. It can also change the attributes of the NRT. The O&M system is informed about changes in the NRT

omar_yousri's picture

what is the maximum number of

what is the maximum number of NRT entries in LTEi ?


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