In LTE (Long-Term Evolution) networks, the decision-making process for handovers involves various entities working together to ensure seamless connectivity as a User Equipment (UE) moves within the network. The handover decision is a critical aspect of maintaining a reliable and efficient connection. The entities involved in making handover decisions in LTE include the UE, the source eNodeB (eNB), the target eNB, and the Mobility Management Entity (MME) within the Evolved Packet Core (EPC).
1. UE (User Equipment):
Measurement Reporting:
- The UE continuously monitors the radio environment and reports measurements related to the signal strength, quality, and other parameters to the serving eNB. These measurements help in assessing the suitability of neighboring cells for potential handovers.
Event Triggers:
- The UE uses event triggers, such as a significant change in signal strength or quality, to indicate to the serving eNB that a handover may be necessary for maintaining a reliable connection.
2. Source eNB (Serving eNodeB):
Measurement Analysis:
- The serving eNB receives measurement reports from the UE and analyzes them to assess the quality of the current connection and the availability of other cells.
Handover Trigger:
- Based on the measurement analysis and predefined handover policies, the serving eNB determines if a handover is required. If the conditions meet the handover criteria, the serving eNB triggers the handover preparation process.
Neighboring Cell Information:
- The serving eNB has information about neighboring cells and their capabilities, including their radio characteristics and the load on those cells. This information is considered during the handover decision-making process.
3. Target eNB (Target eNodeB):
Handover Preparation:
- The target eNB is involved in preparing for the handover by allocating resources and confirming its ability to serve the UE. The target eNB communicates with the source eNB to exchange necessary information for a smooth handover.
Handover Execution:
- Once the handover preparations are complete, the target eNB takes over the communication with the UE, and the handover execution occurs. The user plane and control plane are redirected to the target eNB.
4. MME (Mobility Management Entity):
Coordination and Authorization:
- The MME is responsible for coordinating the handover procedure between the source and target eNBs. It authorizes the handover and facilitates the exchange of key information between the eNBs.
Tracking Area Update:
- The MME updates the tracking area information for the UE, ensuring that the network is aware of the UE’s new location after the handover.
Handover Decision Refinement:
- The MME may contribute to the handover decision by considering higher-level network policies and conditions, providing additional context for optimizing handover decisions.
Conclusion:
The handover decision in LTE is a collaborative effort involving the UE, the serving eNB, the target eNB, and the MME. The decision is based on continuous measurement reports from the UE, analysis by the serving eNB, coordination with the target eNB, and overall management by the MME. This collaborative approach ensures that handovers are performed efficiently and transparently to maintain a seamless user experience during mobility within the LTE network.