LTE (Long-Term Evolution) primarily employs soft handover as the standard handover mechanism. Soft handover is a process where a mobile device is simultaneously connected to multiple base stations (eNodeBs) during a handover. This allows for a seamless transition and continuous communication, enhancing network reliability and coverage. However, in certain scenarios, LTE may use hard handover, also known as “make-before-break” handover, for specific reasons. Let’s explore why LTE may have hard handover in certain situations.
1. Network Mode and Legacy Support:
Interoperability with Legacy Networks:
- LTE networks often coexist with legacy 2G and 3G networks. In scenarios where a mobile device is moving between LTE and non-LTE coverage areas, a hard handover might be initiated to facilitate a switch between different radio access technologies (RATs). This is particularly relevant for voice calls, as LTE may use Circuit-Switched FallBack (CSFB) to hand over calls to 2G or 3G networks.
Hard Handover Between LTE and Legacy Networks:
- When a device moves from LTE to a non-LTE area or vice versa, a hard handover ensures a swift and reliable transition. This is crucial for maintaining voice call continuity and providing a seamless experience for users moving across different network technologies.
2. Handover to Non-LTE Technologies:
Limited Support for Soft Handover:
- While LTE predominantly uses soft handover for intra-LTE handovers, the same mechanism might not be as effective or supported when transitioning to non-LTE technologies. Hard handover becomes necessary in such cases to ensure a more reliable handover process between different radio technologies.
Minimizing Service Disruption:
- Hard handover is chosen when transitioning to non-LTE technologies to minimize service disruption, especially for real-time services like voice calls. It involves completing the connection to the target network before disconnecting from the source network, reducing the likelihood of dropped calls.
3. Inter-System Handover Scenarios:
Inter-System Handovers:
- In scenarios where handovers occur between different systems, such as LTE to Wi-Fi or LTE to other wireless technologies, a hard handover might be preferred. This is because seamless soft handovers may face challenges when transitioning between fundamentally different network architectures.
Ensuring Connection Stability:
- Hard handover helps ensure connection stability and reliability during transitions between diverse wireless systems, providing a more controlled and predictable handover process.
4. Limited Soft Handover Support:
Device and Network Constraints:
- Some devices or network configurations may have limitations in supporting the complexities of soft handover. In such cases, hard handover may be chosen as a more straightforward and reliable alternative, especially if the device or network is not optimized for the soft handover process.
Conclusion:
While soft handover is the preferred mechanism in LTE for its seamless and efficient nature, hard handover is employed in specific scenarios involving transitions between LTE and legacy networks or different wireless technologies. Hard handover ensures continuity of services, particularly for voice calls, in situations where soft handover might face challenges or is less practical. The choice between soft and hard handover depends on the network architecture, device capabilities, and the need for uninterrupted services during transitions between different radio access technologies.