Femtocell Handover Techniques, Challenges and Solutions in 3G UMTS Cellular Network
Femtocell handover is a critical aspect of cellular network management, ensuring that users maintain a stable connection when moving between different femtocell zones or from a femtocell to a macrocell. Understanding how handover works in femtocell networks, the types of handovers, and the challenges involved can help improve the quality of service (QoS) and reduce dropped calls. This page describes various techniques, considerations, and solutions related to femtocell handover to provide a comprehensive overview for network engineers and enthusiasts.
In femtocell based system handover type falls as follows:
1. Between femtocell to femtocell
2. between macrocell and femtocell
Femtocell Handover Techniques
1. Intra-Femtocell Handover : Occurs between different cells within the same femtocell network.
Used when a user moves from one femtocell to another within the same local network
(e.g., different rooms in a large building).
2. Inter-Femtocell Handover : Takes place between two femtocells belonging to different networks
but operated by the same service provider.
Used when a user moves between different femtocell coverage areas (e.g., between two adjacent
houses with femtocells).
3. Macro-to-Femtocell Handover : Happens when a user moves from a macro cell to a femtocell.
Typically used when entering a building or home with a femtocell after being connected to an
outdoor macro cell.
4. Femtocell-to-Macro Handover : Occurs when a user moves out of femtocell coverage and switches
back to the macro network.
Used when leaving the premises covered by a femtocell.
5. Inter-Technology Handover : Involves handovers between femtocell and non-cellular technologies
like Wi-Fi. Useful in scenarios where Wi-Fi and femtocell are used together for seamless connectivity.
Challenges in Femtocell Handover
➨Interference Management :
• Handover between femtocells and macro cells can lead to interference, especially when femtocells
use the same frequency as the macro network.
• Solution: Implement power control mechanisms, interference avoidance techniques,
or spectrum segmentation.
➨Mobility Management :
• Due to the small coverage area of femtocells, frequent handovers may occur,
leading to increased signaling overhead and dropped connections.
• Solution: Use advanced mobility management algorithms that predict user movement and optimize handover decisions.
➨Security and Authentication :
• Ensuring secure and authenticated handovers is critical, especially between femtocells and macro cells.
• Solution: Implement robust encryption, authentication protocols, and closed subscriber group (CSG) management.
➨Synchronization Issues :
• Maintaining time and frequency synchronization between femtocells and the macro network is crucial for a seamless handover.
• Solution: Use GPS or network-based synchronization techniques to ensure alignment.
➨Quality of Service (QoS) Maintenance :
• Maintaining consistent QoS during handovers can be challenging due to variable bandwidth and signal strength.
• Solution: Utilize QoS-aware handover algorithms that prioritize critical data flows during transitions.
Solutions for Femtocell Handover
• Implement advanced decision algorithms that consider parameters
such as signal strength, user speed, and network load to optimize handover timing.
• Use SON features like self-optimization and self-configuration to dynamically manage handovers and minimize interference.
• Set adaptive thresholds based on network conditions to trigger handovers only when necessary, reducing unnecessary handovers and improving performance.
• Utilize carrier aggregation to manage handovers by splitting traffic across multiple bands or technologies, reducing handover frequency and maintaining throughput.
• Implement buffering techniques that temporarily store data during handover to prevent data loss and maintain session continuity.
Macrocell to femtocell handover in 3G UMTS network
The figure depicts femtocell handover between femtocell and macrocell (cellular tower). The handover procedure from macrocell to femtocell in UMTS network is shown in the figure.
Following messages are exchanged between various UMTS system elements (mobile user, NodeB, femtocell Access Point, RNC) to perform handover:
- Measurement report (From Mobile user to Node B)
- Handover request (From RNC to Femtocell Access Point)
- Authorization request (From Femtocell AP to RNC)
- Authorization ACK (From RNC to Femtocell AP)
- Handover response (From Femtocell AP to RNC)
- Radio link setup request (From RNC to Femtocell AP)
- Radio link setup response (From Femtocell to RNC)
- Physical channel re-configuration (Form RNC to Mobile user)
- Physical channel response (From Mobile user to RNC)
- Handover complete (From RNC to Mobile User)
Conclusion
Successful femtocell handover is essential for maintaining seamless connectivity and enhancing user experience in cellular networks. While several challenges such as handover delays and signaling overhead exist, employing the right techniques and optimization strategies can significantly improve handover performance. As femtocell technology continues to evolve, efficient handover management will remain a key focus area for both researchers and network operators.