One of the more labour-intense areas in existing radio technologies is the handling of neighbour relations for handover. A neighbour relation is information that a neighbour cell is a neighbour to an eNB. Each eNB holds a table of detected neighbour cells which are used in connection with handovers. It is a continuous activity that may be more intense during network expansion but is still a time-consuming task in mature networks. The task is multiplied with several layers of cells when having several networks to manage. With LTE, one more layer of cells is added and the development of small cells further increases the number of neighbor relations; thus optimization of neighbor relations may be more complex. Even with the best methods at hand, due to the sheer size of large radio networks – with several hundred thousands of neighbor relations for a single operator – it is a huge undertaking to maintain the neighbor relations manually.
Neighbor cell relations are therefore an obvious area for automation, and Automatic Neighbor Relation (ANR) configuration is one of the most important features for SON. To explore its full potential, ANR must be supported between network equipment from different vendors. ANR is, therefore, one of the first SON functions to be standardized in 3GPP.
Furthermore, the anticipated massive deployment of smallcells, such as femtocells or picocells, as part of moving towards a heterogeneous network (HetNet) deployment strategy will push the ANR functionality, because the manual management of neighbor relations between cells will become even more challenging if not impossible.
Neighbor cell relations are therefore an obvious area for automation, and Automatic Neighbor Relation (ANR) configuration is one of the most important features for SON. To explore its full potential, ANR must be supported between network equipment from different vendors. ANR is, therefore, one of the first SON functions to be standardized in 3GPP.
Furthermore, the anticipated massive deployment of smallcells, such as femtocells or picocells, as part of moving towards a heterogeneous network (HetNet) deployment strategy will push the ANR functionality, because the manual management of neighbor relations between cells will become even more challenging if not impossible.
BENEFITS
ANR will 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.
DescriptionThe ANR in LTE allows automatic discovery and setup of neighbor relations when a user (UE) moves from a serving eNB to another (target) eNB. ANR also automatically sets up of the LTE unique X2 interface between eNBs, primarily used for handover. There are two LTE distinctive functions that make ANR possible:
2. The possibility for the eNB to request the UE to make a full identification of a cell. It allows eNB to determine an unambiguous identity of a neighboring cell.
NEIGHBOR RELATION DISCOVERY
The UE is ordered to report measurements to the serving eNB directly after the RRC connection is set up (i.e. is attached to the cell) and continues to do so while staying in RRC connected mode. The UE reports all detected PCIs (Physical Cell Identities) – the short identity of the LTE cell – that fulfill the measurement criteria set by the eNB at RRC connection. The UE may also measure on legacy radio technologies if it supports multi-mode operation. If there is an unknown cell included in the measurement report then ANR may begin actions to make the cell known and potentially enable handover to the cell.
ANR ACTIONS
If a PCI is reported by a UE that does not correspond to any of the serving eNBs’ defined neighbor cells (i.e. it is not a neighbor cell), the ANR function in the serving eNB may request the UE to retrieve the Global Cell Identity (GCI) of the cell with the unknown PCI in order to identify the cell. This cell is from now called target cell (see figure 4 above). The UE reads the GCI, which is broadcast by the target cell and reports it to the serving eNB. When the serving eNB receives the GCI, it can – with help from MME, one part of SAE – retrieve the target eNB’s IP address, which makes it possible for the serving eNB to contact the target eNB. The serving and target eNBs are now in contact with each other and X2 can be setup. The serving eNB requests X2 setup to the target eNB and includes all necessary cell data to create a neighbor relation (i.e. PCI, GCI, TAC, PLMN-id and frequency) from the target cell to the serving cell. The target cell adds the serving cell to its neighbor list and the target eNB sends the corresponding data for the target cell (PCI, GCI, TAC, PLMN-id and frequency) to the serving cell which in turn adds the target cell to its neighbor list.
With the X2 interface in place, it is possible to use X2 for all future handovers between the cells. For handover from LTE to legacy systems (i.e. GSM and WCDMA), ANR works in the same way with the exception that it only needs to setup a neighbor relation to the target cell and not the X2 since the handover to non-LTE systems is always performed over S1. ANR can automatically remove unused neighbor relations based on the relation usage, handover performance or a combination thereof. When adding and removing neighbors, ANR is under control of policies set by the operator. The black listing allows the operator to decide neighbor relations that ANR may never add as neighbors. The white listing allows the operator to decide permanent neighbor relations that ANR may never remove. These policies are controlled from an Element Management System (EMS) such as OSS.
The goal of ANR is to manage neighbour relation. Since OAM also has some restrictions on neighbour relation due to the requirements of operators, ANR also needs to consider the restrictions from OAM. So how to describe the neighbour relation based on the restrictions and how to manage the neighbour relation is a question of implementation. Below figure gives an example of possible ANR solutions. Here the neighbour relation is described by Neighbour Relation Table. The table composes of two parts. The left part is the list of Neighbour Relation according to the measurement report. The right part is the Neighbour Relation Attributes controlled by OAM. The attributes include: No Remove, No Handover and No X2. The left part will be updated according to measurement report and the right part will be updated according to OAM commands.
Within ANR, it is divided into three functions: Neighbour Removal Function, Neighbour Detection Function and Neighbour Relation Table Management Function. The first two functions decide whether to remove an existing Neighbour Relation or to add a new Neighbour Relation. The third one is responsible for updating the Neighbour Relation Table according to the input of the previous two functions and OAM.
The Neighbour Relation Detection procedure - instructs RRC to measure the cells on some certain frequency or in another RAT.
1. RRC forwards the measurement reports to Neighbour Detection Function.
2. Neighbour Detection Function decides to add a new Neighbour Relation.
3. Neighbour Relation Table Management Function updates the Neighbour Relation Table.
4. Neighbour Relation Table Management Function sends the updated Neighbour Relation through some standard interface to OAM.
5. OAM will ask Neighbour Relation Table Management Function to update the Neighbour Relation Attributes if necessary.
The Neighbour Relation Removal procedure is similar - neighbour Removal Function receives internal information, such as many times of handover failure to a certain cell.
1. Neighbour Removal Function decides to remove the cell from the neighbour list.
2. The following steps are the same as the detection procedure. The Neighbour Relation Table will be used by eNB for other functions, such as handover and X2 setup.
With the X2 interface in place, it is possible to use X2 for all future handovers between the cells. For handover from LTE to legacy systems (i.e. GSM and WCDMA), ANR works in the same way with the exception that it only needs to setup a neighbor relation to the target cell and not the X2 since the handover to non-LTE systems is always performed over S1. ANR can automatically remove unused neighbor relations based on the relation usage, handover performance or a combination thereof. When adding and removing neighbors, ANR is under control of policies set by the operator. The black listing allows the operator to decide neighbor relations that ANR may never add as neighbors. The white listing allows the operator to decide permanent neighbor relations that ANR may never remove. These policies are controlled from an Element Management System (EMS) such as OSS.
The goal of ANR is to manage neighbour relation. Since OAM also has some restrictions on neighbour relation due to the requirements of operators, ANR also needs to consider the restrictions from OAM. So how to describe the neighbour relation based on the restrictions and how to manage the neighbour relation is a question of implementation. Below figure gives an example of possible ANR solutions. Here the neighbour relation is described by Neighbour Relation Table. The table composes of two parts. The left part is the list of Neighbour Relation according to the measurement report. The right part is the Neighbour Relation Attributes controlled by OAM. The attributes include: No Remove, No Handover and No X2. The left part will be updated according to measurement report and the right part will be updated according to OAM commands.
Within ANR, it is divided into three functions: Neighbour Removal Function, Neighbour Detection Function and Neighbour Relation Table Management Function. The first two functions decide whether to remove an existing Neighbour Relation or to add a new Neighbour Relation. The third one is responsible for updating the Neighbour Relation Table according to the input of the previous two functions and OAM.
The Neighbour Relation Detection procedure - instructs RRC to measure the cells on some certain frequency or in another RAT.
1. RRC forwards the measurement reports to Neighbour Detection Function.
2. Neighbour Detection Function decides to add a new Neighbour Relation.
3. Neighbour Relation Table Management Function updates the Neighbour Relation Table.
4. Neighbour Relation Table Management Function sends the updated Neighbour Relation through some standard interface to OAM.
5. OAM will ask Neighbour Relation Table Management Function to update the Neighbour Relation Attributes if necessary.
The Neighbour Relation Removal procedure is similar - neighbour Removal Function receives internal information, such as many times of handover failure to a certain cell.
1. Neighbour Removal Function decides to remove the cell from the neighbour list.
2. The following steps are the same as the detection procedure. The Neighbour Relation Table will be used by eNB for other functions, such as handover and X2 setup.
