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Content for  TS 38.300  Word version:  16.3.0

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15  Self-Configuration and Self-Optimisation

15.1  Definitions

Void.

15.2Void

15.3  Self-configuration

15.3.1  Dynamic configuration of the NG-C interface

15.3.1.1  Prerequisites

The following prerequisites are assumed:
  • An initial remote IP end point to be used for SCTP initialisation is provided to the NG-RAN node for each AMF the NG-RAN node is supposed to connect to.

15.3.1.2  SCTP initialization

NG-RAN establishes the first SCTP (IETF RFC 4960) using a configured IP address.

15.3.1.3  Application layer initialization

Once SCTP connectivity has been established, the NG-RAN node and the AMF shall exchange application level configuration data over NGAP with the NG Setup procedure, which is needed for these two nodes to interwork correctly on the NG interface:
  • The NG-RAN node provides the relevant configuration information to the AMF, which includes list of supported TA(s), etc.;
  • The AMF provides the relevant configuration information to the NG-RAN node, which includes PLMN ID, etc.;
  • When the application layer initialization is successfully concluded, the dynamic configuration procedure is completed and the NG-C interface is operational.
After the application layer initialization is successfully completed, the AMF may add or update or remove SCTP endpoints to be used for NG-C signalling between the AMF and the NG-RAN node pair as specified in TS 23.501.
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15.3.2  Dynamic Configuration of the Xn interfaceWord‑p. 105

15.3.2.1  Prerequisites

The following prerequisites are necessary:
  • An initial remote IP end point to be used for SCTP initialisation is provided to the NG-RAN node.

15.3.2.2  SCTP initialization

NG-RAN establishes the first SCTP (IETF RFC 4960) using a configured IP address.

15.3.2.3  Application layer initialization

Once SCTP connectivity has been established, the NG-RAN node and its candidate peer NG-RAN node are in a position to exchange application level configuration data over XnAP needed for the two nodes to interwork correctly on the Xn interface:
  • The NG-RAN node provides the relevant configuration information to the candidate NG-RAN node, which includes served cell information;
  • The candidate NG-RAN node provides the relevant configuration information to the initiating NG-RAN node, which includes served cell information;
  • When the application layer initialization is successfully concluded, the dynamic configuration procedure is completed and the Xn interface is operational;
  • The NG-RAN node shall keep neighbouring NG-RAN nodes updated with the complete list of served cells, or, if requested by the peer NG-RAN node, by a limited list of served cells, while the Xn interface is operational.
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15.3.3  Automatic Neighbour Cell Relation Function

15.3.3.1  General

The purpose of ANR function is to relieve the operator from the burden of manually managing NCRs. Figure 15.3.3.1-1 shows ANR and its environment:
Reproduction of 3GPP TS 38.300, Figure 15.3.3.1-1: Interaction between gNB and OAM due to ANR
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The ANR function resides in the gNB and manages the Neighbour Cell Relation Table (NCRT). Located within ANR, the Neighbour Detection Function finds new neighbours and adds them to the NCRT. ANR also contains the Neighbour Removal Function which removes outdated NCRs. The Neighbour Detection Function and the Neighbour Removal Function are implementation specific.
An existing NCR from a source cell to a target cell means that gNB controlling the source cell:
  1. Knows the global and physical IDs (e.g. NR CGI/NR PCI, ECGI/PCI) of the target cell; and
  2. Has an entry in the NCRT for the source cell identifying the target cell; and
  3. Has the attributes in this NCRT entry defined, either by OAM or set to default values.
NCRs are cell-to-cell relations, while an Xn link is set up between two gNBs. Neighbour Cell Relations are unidirectional, while an Xn link is bidirectional.
The ANR function also allows OAM to manage the NCRT. OAM can add and delete NCRs. It can also change the attributes of the NCRT. The OAM system is informed about changes in the NCRT.
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15.3.3.2  Intra-system Automatic Neighbour Cell Relation FunctionWord‑p. 106
ANR relies on NCGI (see clause 8.2) and ANR reporting of E-UTRA cells as specified in TS 36.300.
Reproduction of 3GPP TS 38.300, Figure 15.3.3.2-1: Automatic Neighbour Relation Function
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Figure 15.3.3.2-1 depicts an example where the NG-RAN node serving cell A has an ANR function. In RRC_CONNECTED, the NG-RAN node instructs each UE to perform measurements on neighbour cells. The NG-RAN node may use different policies for instructing the UE to do measurements, and when to report them to the NG-RAN node. This measurement procedure is as specified in TS 38.331 and TS 36.331.
Step 1.
The UE sends a measurement report regarding cell B. This report contains Cell B's PCI, but not its NCGI/ECGI.
When the NG-RAN node receives a UE measurement report containing the PCI, the following sequence may be used.
Step 2.
The NG-RAN node instructs the UE, using the newly discovered PCI as parameter, to read all the broadcast NCGI(s) /ECGI(s), TAC(s), RANAC(s), PLMN ID(s) and, for neighbour NR cells, NR frequency band(s). To do so, the NG-RAN node may need to schedule appropriate idle periods to allow the UE to read the NCGI/ECGI from the broadcast channel of the detected neighbour cell. How the UE reads the NCGI/ECGI is specified in TS 38.331 and TS 36.331.
Step 3.
When the UE has found out the new cell's NCGI(s) /ECGI(s), the UE reports all the broadcast NCGI(s)/ECGI(s) to the serving cell NG-RAN node. In addition, the UE reports all the tracking area code(s), RANAC(s), PLMN IDs and, for neighbour NR cells, NR frequency band(s), that have been read by the UE. In case the detected NR cell does not broadcast SIB1, the UE may report noSIB1 indication as specified in TS 38.331.
Step 4.
The NG-RAN node decides to add this neighbour relation, and can use PCI and NCGI(s)/ECGI(s) to:
  1. Lookup a transport layer address to the new NG-RAN node;
  2. Update the Neighbour Cell Relation List;
  3. If needed, setup a new Xn interface towards this NG-RAN node.
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15.3.3.3Void

15.3.3.4Void

15.3.3.5  Inter-system Automatic Neighbour Cell Relation FunctionWord‑p. 107
For Inter-system ANR, each cell contains an Inter Frequency Search list. This list contains all frequencies that shall be searched. Figure 15.3.3.5-1 depicts an example where the NG-RAN node serving cell A has an ANR function.
Reproduction of 3GPP TS 38.300, Figure 15.3.3.5-1: Automatic Neighbour Relation Function in case of E-UTRAN detected cell
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In RRC_CONNECTED, the NG-RAN node instructs a UE to perform measurements and detect E-UTRA cells connected to EPC.:
Step 1.
The NG-RAN node instructs a UE to look for neighbour cells in the target system. To do so the NG-RAN node may need to schedule appropriate idle periods to allow the UE to scan all cells in the target system.
Step 2.
The UE reports the PCI and carrier frequency of the detected cells in the target system.
When the NG-RAN node receives the UE reports containing PCIs of cell(s), the following sequence may be used:
Step 3.
The NG-RAN node instructs the UE, using the newly discovered PCI as parameter, to read the ECGI, the TAC and all available PLMN ID(s) of the newly detected cell in case of E-UTRA detected cells. The UE ignores transmissions from the serving cell while finding the requested information transmitted in the broadcast channel of the detected inter-system/inter-frequency neighbour cell. To do so, the NG-RAN node may need to schedule appropriate idle periods to allow the UE to read the requested information from the broadcast channel of the detected inter-system neighbour cell.
Step 4.
After the UE has read the requested information in the new cell, it reports the detected ECGI, TAC, and available PLMN ID(s) to the serving cell NG-RAN node.
Step 5.
The NG-RAN node updates its inter-system NCRT.
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15.3.4  Xn-C TNL address discoveryWord‑p. 108
If the NG-RAN node is aware of the RAN node ID of the candidate NG-RAN node (e.g. via the ANR function) but not of a TNL address suitable for SCTP connectivity, then the NG-RAN node can utilize the 5GC (an AMF it is connected to) to determine the TNL address as follows:
  • The NG-RAN node sends the UPLINK RAN CONFIGURATION TRANSFER message to the AMF to request the TNL address of the candidate NG-RAN node, and includes relevant information such as the source and target RAN node ID;
  • The AMF relays the request by sending the DOWNLINK RAN CONFIGURATION TRANSFER message to the candidate NG-RAN node identified by the target RAN node ID;
  • The candidate NG-RAN node responds by sending the UPLINK RAN CONFIGURATION TRANSFER message containing one or more TNL addresses to be used for SCTP connectivity with the initiating NG-RAN node, and includes other relevant information such as the source and target RAN node ID;
  • The AMF relays the response by sending the DOWNLINK CONFIGURATION TRANSFER message to the initiating NG-RAN node identified by the target RAN node ID.
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15.4  Support for Energy SavingWord‑p. 109

15.4.1  General

The aim of this function is to reduce operational expenses through energy savings.
The function allows, for example in a deployment where capacity boosters can be distinguished from cells providing basic coverage, to optimize energy consumption enabling the possibility for an E-UTRA or NR cell providing additional capacity via single or dual connectivity, to be switched off when its capacity is no longer needed and to be re-activated on a need basis.

15.4.2  Solution description

The solution builds upon the possibility for the NG-RAN node owning a capacity booster cell to autonomously decide to switch-off such cell to lower energy consumption (inactive state). The decision is typically based on cell load information, consistently with configured information. The switch-off decision may also be taken by O&M.
The NG-RAN node may initiate handover actions in order to off-load the cell being switched off and may indicate the reason for handover with an appropriate cause value to support the target node in taking subsequent actions, e.g. when selecting the target cell for subsequent handovers.
All neighbour NG-RAN nodes are informed by the NG-RAN node owning the concerned cell about the switch-off actions over the Xn interface, by means of the NG-RAN node Configuration Update procedure.
All informed nodes maintain the cell configuration data, e.g., neighbour relationship configuration, also when a certain cell is inactive. If basic coverage is ensured by NG-RAN node cells, NG-RAN node owning non-capacity boosting cells may request a re-activation over the Xn interface if capacity needs in such cells demand to do so. This is achieved via the Cell Activation procedure. During switch off time period of the boost cell, the NG-RAN node may prevent idle mode UEs from camping on this cell and may prevent incoming handovers to the same cell.
The NG-RAN node receiving a request should act accordingly. The switch-on decision may also be taken by O&M. All peer NG-RAN nodes are informed by the NG-RAN node owning the concerned cell about the re-activation by an indication on the Xn interface.
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15.4.3  O&M requirements

Operators should be able to configure the energy saving function.
The configured information should include:
  • The ability of an NG-RAN node to perform autonomous cell switch-off;
  • The ability of an NG-RAN node to request the re-activation of a configured list of inactive cells owned by a peer NG-RAN node.
O&;M may also configure
  • policies used by the NG-RAN node for cell switch-off decision;
  • policies used by peer NG-RAN nodes for requesting the re-activation of an inactive cell.


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