Handover Process in LTE

Handover Process in LTE

In LTE, the handover process involves transferring a mobile device’s connection from one cell to another seamlessly. It includes the following key steps:

  1. Measurement: The mobile device continuously measures signal strength and quality from neighboring cells.
  2. Triggering: When certain threshold values are met, a handover is triggered. This can be due to deteriorating signal quality or a stronger signal from another cell.
  3. Preparation: The target cell is identified and preparations are made for the handover. This includes resource allocation and synchronization.
  4. Execution: The actual handover takes place, and the mobile device switches its connection from the source to the target cell.
  5. Handover Decision: The decision to handover is made based on network policies and optimization algorithms.
  6. Post-Handover Optimization: After the handover, the network optimizes parameters to ensure the best possible connection quality.

LTE handovers aim to maintain a continuous and high-quality connection as the mobile device moves through the network.

The source eNB issues a HANDOVER REQUEST message to the target eNB passing the necessary information to prepare the HO on target side (UE X2 signaling context reference at source eNB, UE S1 EPC signaling context reference, target cell ID, KeNB*, RRC context including the C-RNTI of the UE in the source eNB, ASconfiguration, E-RAB context and physical layer ID of the source cell + MAC for possible RLF recovery).

UE X2 / UE S1 signaling references enable the target eNB to address the source eNB and the EPC. The E-RAB context includes necessary RNL and TNL addressing information, and QoS profiles of the E-RABs.

Admission Control may be performed by the target eNB dependent on the received E-RAB QoS information to increase the likelihood of a successful HO, if the resources can be granted by the target eNB. The target eNB configures the required resources according to the received E-RAB QoS information and reserves a C-RNTI and optionally an RACH preamble.

The target eNB prepares HO with L1/L2 and sends the HANDOVER REQUEST ACKNOWLEDGE to the source eNB.

The HANDOVER REQUEST ACKNOWLEDGE message includes a transparent container to be sent to the UE as an RRC message to perform the handover.

The container: includes a new C-RNTI, target eNB security algorithm identifiers for the selected security algorithms,
may include a dedicated RACH preamble, and possibly some other parameters i.e. access parameters, SIBs, etc.

Types of Handover in LTE network

Intra-LTE Handover: In this case source and target cells are part of the same LTE network. means handover in same LTE cell.
Inter-LTE Handover: Handover happens towards other LTE nodes. means other Enb. (Inter-MME and Inter-SGW)
Inter-RAT: Handover between different radio technologies. For example handover from LTE to WCDMA. As similar to inter Vendor Handover.

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