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Autonomous removal of LTE neighbors
Single RAN Features, Rel. SRAN 23R3, Operating Documentation, Issue 03 (HTML) > Operability Features > Selforganizing Network (SON) and Automatic Neighbor Relation (ANR) > Automatic Neighbor Relation for LTE
Autonomous removal of LTE neighbors
The LTE1685: Neighbor Relation Robustness feature enhances the maintenance of the LTE neighbor relations
(NRs) with a mechanism for autonomous removal of unused LTE neighbors.
Autonomous removal of unused LTE NRs
When the feature is disabled, the ANR Activate autonomous removal of LTE neighbours
( actAutoLteNeighRemoval ) activation parameter is set to false and the operator has to manually
delete the neighbor objects ( LNREL , LNADJ , LNADJL ).
When the feature is enabled, the actAutoLteNeighRemoval activation parameter is set to true and
the BTS decides at the end of every hour if any objects need to be removed.
Note:
You can also delete the NRs manually through NetAct or Network Element Manager.
The are following methods to remove the unused LTE neighbor relations:
The removal of NRs
The BTS can autonomously remove the NR related to the LNREL object if all of the following conditions
are met:
There is no handover preparation (X2, S1, or intra-BTS) to the neighbor cell observed for longer than the
configurable time (the ANR Idle Time Threshold for LTE Neighbour Relations
( idleTimeThresLteNR parameter).
The LNREL Remove allowed ( removeAllowed ) parameter is set to true .
Closing the X2 links
The BTS autonomously closes an available X2 link if:
There is no incoming X2 handover for longer than the configurable time (the ANR Idle Time
Threshold for X2 links ( idleTimeThresX2 ) parameter).
There are no NRs ( LNREL objects) associated with the X2 link.
The X2 link has an enbControlled C-plane IP Address.
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Autonomous removal of LTE neighbors
If the X2 link is closed, the LNADJ X2 link status ( x2LinkStatus ) parameter becomes
unavailable.
The removal of the neighbor BTS ( LNADJ object) and the neighbor cell ( LNADJL object) information
If the BTS (BTS1) stores the configuration information for the neighbor BTS and its served cells, the BTS1
observes the configuration information of the neighbor BTS and its cells. The BTS1 checks if this
configuration information is used for a handover. The BTS1 also checks if the incoming X2 handover
requests are received on a related link. If neither the neighbor BTS, nor any of the neighbor cells is used for
longer than the configurable waiting time, the BTS1 removes the configuration information of the neighbor
BTSs and their cells.
If no associated NRs or an X2 link is available for longer than the configurable time, the LNADJ and the
LNADJL objects are removed from the BTS database. Only the LNADJ objects with the C-Plane IP
address control ( cPlaneIpAddrCtrl ) parameter set to enbControlled are considered.
Note:
To delete the LNADJ and LNADJL objects of the remote BTS, the LTE1685 feature must be
enabled in the remote BTS as well, with the same idle time parameters ( Idle Time Threshold
for LTE Neighbor Relations ( idleTimeThresLteNR ) and Idle Time Threshold
for X2 links ( idleTimeThresX2 )). Thus, the conditions of the removal are fulfilled.
Autonomous neighbor exchange
For the UE-based ANR, if the maximum number of neighbor BTSs (that is, the maximum number of
LNADJ objects) that can be stored in the BTS database is reached, the BTS can still learn new NRs. If the
maximum number of LNADJ objects is reached (128 for FSMr2 and 256 for FSMr3) and the Cell Global
Identity (CGI) measurement provides a new neighbor BTS ( LNADJ ), then the BTS selects the already
existing LNADJ object which hasn't been used for the longest time. This selection is based on the
outgoing X2 and S1 traffic from the BTS. After that, the BTS deletes it and its associated
LNADJL / LNREL object, and creates a new LNADJ object which holds the newly detected neighbor BTS
and neighbor cell in its database.
In this way, the old LTE neighbor is replaced with a new one. The BTS database includes the newly detected
neighbor BTS and the neighbor cell connected to this neighbor BTS.
Warning of PCI confusion
A re-validation of the NR for the physical cell ID (PCI) and frequency leads to a toggling of the NR assigned to
this PCI and frequency. The BTS concludes if these NRs can be subject to a PCI confusion. If a PCI is suspected
of confusion, as shown in the figure below, the BTS raises a PCI warning to the operator.
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Figure: PCI confusion
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