Sign in Subscribe

How does LTE manage mobility and handovers between different eNodeBs?

Last updated on 


LTE (Long-Term Evolution) employs various mechanisms and protocols to efficiently manage mobility and seamless handovers between different eNodeBs (Evolved NodeBs). The mobility management procedures in LTE ensure that mobile devices can maintain a continuous connection and experience uninterrupted communication while moving across different cells or eNodeBs. Let's explore the technical aspects of how LTE manages mobility and handovers:

Idle Mode Mobility Management:

  • In the idle mode, the UE (User Equipment) periodically monitors neighboring cells' signals to determine when to perform a cell reselection based on predefined measurement criteria.

Cell Reselection:

  • The UE continuously measures the signal strength and quality of neighboring cells. If a neighboring cell's signal quality exceeds a certain threshold and provides better conditions, the UE may trigger a cell reselection to move to that cell.

Measurement Reports:

  • The UE periodically reports the measured signal strength and quality of neighboring cells to the current serving eNodeB. These reports aid the network in making informed decisions for handovers.

Connected Mode Mobility Management:

  • In the connected mode, when the UE is actively communicating, the eNodeB manages mobility to ensure seamless handovers as the UE moves across cells.

Handover Decision Making:

  • The serving eNodeB continuously monitors the UE's signal conditions, quality, and other parameters. Based on this information and network policies, it decides when a handover should be initiated.

Event Triggers for Handover:

  • Event triggers, such as measurement reports indicating a significant change in signal quality or exceeding predefined thresholds, may initiate handover procedures.

Measurement Control and Configuration:

  • The serving eNodeB configures the UE with measurement parameters, such as the frequency and periodicity of measurements, to enable effective measurement reporting.

X2 Interface for Inter-eNodeB Communication:

  • LTE uses the X2 interface to facilitate direct communication and coordination between neighboring eNodeBs. This allows for efficient handovers without the need to involve the core network (EPC - Evolved Packet Core).

Handover Preparation and Execution:

  • The serving eNodeB, in coordination with the target eNodeB, prepares for the handover. Resources are allocated, and necessary configurations are made.
  • The UE is instructed to switch to the target eNodeB, and data forwarding is coordinated to ensure a seamless transition.

Intra-eNodeB Handover (Soft Handover):

  • In some cases, handovers may occur within the same eNodeB (intra-eNodeB). This is known as soft handover, where the UE is handed over between different sectors of the same eNodeB.

Inter-eNodeB Handover (Hard Handover):

  • When the UE moves from the coverage area of one eNodeB to another, a hard handover occurs. The UE releases its connection with the serving eNodeB and establishes a new connection with the target eNodeB.

Handover Completion and Cleanup:

  • Once the handover is completed, the target eNodeB takes over communication with the UE. The serving eNodeB releases resources and updates the UE's context.

By employing these procedures and mechanisms, LTE effectively manages mobility and facilitates seamless handovers, ensuring continuous and reliable communication for mobile devices as they move within the LTE network.