What is the Handover Process in LTE?
Today, let’s dive into the handover process in LTE, a critical operation that ensures users maintain a stable and uninterrupted connection as they move between different cells in a mobile network. If you’re familiar with the previous discussions about LTE’s architecture and network operations, you’ll appreciate that handover is key to providing seamless mobility and high-quality service in modern mobile networks.
In LTE, the handover process refers to the seamless transfer of an ongoing call, data session, or any active service from one cell or base station (eNodeB) to another, without interrupting the service. This operation is necessary as users move within the coverage area of the LTE network or when the device moves between different network technologies, such as LTE and 3G.
Let’s break down the handover process in LTE step-by-step:
1. Handover Initiation
When a user moves from one cell to another, the User Equipment (UE), which is the mobile device, continuously measures the signal strength of neighboring cells. This process is known as measurement reporting. If the signal strength of a neighboring eNodeB is stronger than the current one, the UE reports this information to the current serving eNodeB (the one currently connected to the device).
The serving eNodeB then evaluates the measurement reports and decides if a handover is required. If the handover is necessary, the serving eNodeB initiates the handover process by notifying the Mobility Management Entity (MME), which is responsible for managing the mobility of the UE.
2. Handover Preparation
Once the MME receives the handover request, it communicates with the target eNodeB (the eNodeB that the UE is moving to) to prepare for the handover. The target eNodeB sets up the necessary resources to accept the incoming UE. During this phase, the MME also informs the Serving Gateway (SGW) about the handover to ensure that the user’s data path is properly configured.
Meanwhile, the UE is kept in a suspended state, meaning it is still connected to the current eNodeB but is not actively communicating during the preparation phase.
3. Handover Execution
Once the target eNodeB is ready, the MME sends a message to the serving eNodeB, instructing it to proceed with the handover. The serving eNodeB then sends the handover command to the UE, which switches its connection to the target eNodeB. At this point, the UE begins communication with the new eNodeB, and the data session is transferred over to the target cell.
To ensure that there is no disruption in service, the data traffic is buffered temporarily during this phase and sent to the target eNodeB after the handover completes. This makes the transition seamless to the user.
4. Handover Completion
After the UE successfully connects to the target eNodeB, the new eNodeB sends a handover complete message to the serving eNodeB, and the eNodeB acknowledges the message. The target eNodeB now takes full control of the communication session, and the serving eNodeB is no longer involved in the ongoing communication.
The MME is also informed that the handover has been successfully completed, and the UE can resume its normal communication with the new eNodeB.
Types of Handover in LTE
In LTE, there are two main types of handovers:
- Intra-eNodeB Handover: This occurs when the UE moves between different cells that are controlled by the same eNodeB. Since the cells are managed by the same base station, the handover process is relatively simpler.
- Inter-eNodeB Handover: This occurs when the UE moves between cells controlled by different eNodeBs. This type of handover involves more complex coordination between the eNodeBs and the core network elements (like the MME and SGW).
Why is Handover Important?
The handover process ensures that you, as a mobile user, experience continuous service as you move through the coverage areas of the LTE network. Whether you’re making a call, browsing the web, or streaming content, handover allows you to maintain connectivity without interruption, even when crossing from one cell’s coverage to another.
As we discussed in our previous article, LTE is designed to handle high-speed data and voice services. The handover process plays an essential role in delivering this promise by maintaining a stable connection across various network elements and ensuring you stay connected as you move across different cells or network technologies.