5G Handover

5G Systems

The new elements in 5G are gNB, AMF, UPF, which are using new interfaces as the XN and N2 interface to link the AMF with gNB and vice versa, replacing X2 and S1 AP interfaces.

There are also several other components as follows:

• gNB : Refers to the Base Station, like in the old LTE, the eNodeB
• NR: Refers to the “New Radio” technology
• NG-RAN: NG-RAN is Next Generation Radio Access Network. This consists of gNB and ng-ENB.
• AMF Access and Mobility Management Function AF Application Function
• UPF User Plane Function
• NGC: Next Generation Core

There in 5G the handover is called Xn Handover and N2 Handover

• As the UE sends the measurement reports and the Source gNB detects that a handover is required, then it connects with the Target gNB to start a switch
• The UE does a handover and connects to theTarget gNB That has already switched the tunnels to the target
• The UE forwards as part of the handover process, This is called RRC

The NG-RAN sends the UE Notification message to report the current RRC state for the UE (i.e. RRC Inactive state or RRC Connected state). The current UE location information (i.e. TAI + Cell Identity) is always included when RRC state information is reported.

• Thru this, the UE can then handoff fast and all the data is available for you.

How is the difference from the X2 Handover

The differences are subtle, and the main difference is that the X2 handover. We server that Location Information is mandatory, but it was after LTE
Rel-13 as well. The changes are minimum and this facilitates the understanding of all functions including AMF / UPF in 5G. In TS 38.423 V.15, the Xn-AP commands are shown, which is a similar document to the X2-AP specification.

If the Location Reporting InformationIE is included in the HANDOVER REQUEST message, then the target NG-RAN node should initiate the requested location reporting functionality as defined in TS 38.413 [5].

Similarly this is shown in TS 123.502 with

1. Target NG-RAN to AMF: N2 Path Switch Request (List of PDU Sessions To Be Switched with N2 SM Information, List of PDU Sessions Rejected with a rejection Cause per PDU Session, UE Location Information)