What are the types of handover in LTE?

What Are the Types of Handover in LTE?

In LTE networks, handover refers to the process of transferring an active call or data session from one cell or eNodeB to another. This ensures seamless connectivity and uninterrupted service as users move around the network. There are several types of handover used in LTE, each serving different purposes and conditions. Let me explain the main types of handovers that are employed in LTE systems.

1. Intra-eNodeB Handover

Intra-eNodeB handover occurs when the UE (User Equipment) moves between different cells within the same eNodeB (evolved Node B). In this case, the control plane and user plane remain within the same eNodeB, and the handover process is simpler. The key goal of intra-eNodeB handover is to ensure minimal disruption when the UE moves from one cell to another within the same cell coverage area.

Here’s how intra-eNodeB handover works:

• The UE moves from one cell to another within the same eNodeB.
• The eNodeB handles the handover process without involving other network elements.
• No data or control plane transfers are needed beyond the eNodeB, so the process is fast and efficient.

This type of handover is typically faster and simpler because it stays within the same eNodeB, minimizing complexity and reducing latency.

2. Inter-eNodeB Handover

Inter-eNodeB handover happens when the UE moves between different eNodeBs, meaning it transitions from one eNodeB’s coverage area to another’s. Unlike intra-eNodeB handover, inter-eNodeB handover involves coordination between multiple eNodeBs, as the user session needs to be transferred between different network elements.

Here’s how inter-eNodeB handover works:

• The UE moves from the coverage of one eNodeB to another.
• The source eNodeB sends the necessary information to the target eNodeB.
• Both eNodeBs collaborate to ensure the UE’s connection is maintained during the handover process.

Inter-eNodeB handovers tend to be more complex because they involve multiple eNodeBs and require a more elaborate signaling process, but they still ensure that the connection remains active as the UE moves across network boundaries.

3. X2-Based Handover

X2-based handover is a type of inter-eNodeB handover where two eNodeBs communicate directly with each other via the X2 interface to transfer the user’s data session. This type of handover is commonly used in LTE networks because it reduces the load on the core network by enabling direct communication between eNodeBs.

Here’s how X2-based handover works:

• The source eNodeB and the target eNodeB are directly connected via the X2 interface.
• The eNodeBs exchange signaling messages to handover the UE from one cell to another.
• Data transfer between the eNodeBs is direct, which reduces core network traffic.

X2-based handover improves efficiency and reduces the need for core network involvement, making the process faster and more reliable.

4. S1-Based Handover

S1-based handover occurs when a UE moves between eNodeBs that are not directly connected via the X2 interface. In this case, the signaling and data transfer are routed through the core network, specifically through the S1 interface. This type of handover is less efficient compared to X2-based handover, as it introduces additional latency due to reliance on the core network for coordination.

Here’s how S1-based handover works:

• The source eNodeB and the target eNodeB do not have a direct X2 connection.
• The S1 interface is used to communicate with the EPC (Evolved Packet Core) to transfer user data.
• The core network manages the handover process, directing the user’s session to the appropriate eNodeB.

S1-based handover is used when X2-based handover is not available, typically in situations where the two eNodeBs are not directly connected. It involves more signaling between the eNodeBs and the core network, which can increase handover time and delay.

5. Hard Handover

Hard handover, also known as break-before-make handover, is a process where the UE loses connection to the source eNodeB before establishing a connection with the target eNodeB. This type of handover causes a brief interruption in the connection, but it is generally fast and efficient.

Here’s how hard handover works:

• The UE disconnects from the source eNodeB.
• The UE then connects to the target eNodeB.
• There is a short gap between disconnection and reconnection, causing a momentary loss of service.

Hard handover is typically used in scenarios where network efficiency is prioritized, even if it leads to a short interruption in the connection.

6. Soft Handover

Soft handover, also known as make-before-break handover, allows the UE to maintain connections with both the source and target eNodeBs during the handover process. This reduces the chances of service interruption and provides a more seamless handover, but it is more resource-intensive due to the simultaneous connections to both eNodeBs.

Here’s how soft handover works:

• The UE is connected to both the source and target eNodeBs simultaneously.
• The connection to the target eNodeB is established before the source eNodeB is disconnected.
• Once the connection to the target eNodeB is established, the UE can safely disconnect from the source eNodeB.

Soft handover provides a more reliable handover process with minimal disruption, but it requires more network resources to maintain multiple connections simultaneously.

Summary of Handover Types in LTE

In conclusion, handovers in LTE ensure continuous and seamless service as users move through the network. The type of handover chosen depends on various factors, including network architecture, eNodeB connectivity, and the trade-off between service interruption and resource efficiency.