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Showing posts from May, 2022

Xn Handover

Initialy transmission in both UL and DL directions is done via source gNB. The UE sends measurement report to inform the gNB that signal from other cell is better than the one in the current cell. After report reception the source gNB takes a decision to trigger handover procedure towards target gNB. The target gNB starts to prepare resources to serve this UE and when ready acknowledges this to source gNB. The source gNB sends handover command message with information about target cell. At the same time the source gNB suspends the data transmission and starts forwarding data to target gNB. The UE needs to perform random access procedure towards the target cell. After successful random access procedure the UE confirms the handover towards target gNB. Target gNB starts the DL data transmission and informs the CN about completed handover. Data tunnels from Core Network are switched to target gNB. The target gNB informs source one that it may release UE resources.

NG Interface Protocol Stack


Xn Interface Protocol Stack

  Figure 1 Xn interface protocol stack for control plane (left side) and user plane (right side).