Mobile Telecom Networks

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.

Mobility is one of the key aspects in the mobile telecom networks. We would like to travel with our phones and has a continuous access to the used service. Moving around the city while still talking to your friend is what we need, want and expect from the mobile network. The phone measures the strength and quality of the radio signal received from the base station. Information about what exactly shall be measured is sent from the gNB to the UE using RRC protocol.  Sometimes it may happen that the phone will find the cell that it was not supposed to find. In such case the phone will report this new "unknown" cell to the gNB. When several phones do the same the gNB may decide to add this "unknown" cell as a known neighbor cell and next time the gNB will tell other devices to actually measure radio signal for this particular cell. This is part of SON functionality called ANR. Measurements There is couple defined Measurement Events. Definitions for those are ...