Definition of Ping-Pong Handover
Ping-pong handover refers to the frequent and rapid switching of the primary serving cell between two or more cells as the UE (User Equipment) moves within a specific area, known as the handover belt. In these situations:
- Primary Serving Cell Changes Rapidly: Two or more cells alternately become the primary serving cell, with each cell showing good RSRP (Reference Signal Received Power) and SINR (Signal-to-Interference-plus-Noise Ratio) for a short time.
- No Best Cell: Multiple cells have similar RSRP levels, with little difference between them, but the SINR remains low for each cell.
During a ping-pong handover, the UE may immediately initiate another handover after completing one, causing several reconfiguration messages (e.g., CQI reporting mode) to be sent. These frequent changes can result in timeouts, leading to call drops.
How to Find Ping-Pong Handover?
You can detect ping-pong handover by checking the following indicators through GIS/Assistant etc:
- Low Downloading Rate: A significant drop in the downloading speed.
- Low SINR: Poor signal quality.
- Frequent Handovers: The UE conducts handovers more than three times within the handover belt.
How to Eliminate Ping-Pong Handover?
To resolve ping-pong handover issues, follow this workflow:
- Adjust Antenna Positions: Modify the physical positioning of the antennas to improve RF performance.
- Modify Handover Parameters: Fine-tune parameters to ensure that handovers occur more efficiently and with fewer delays.
- Configure CIOs (Cell Individual Offsets): Set CIOs so that handovers can be triggered in advance, reducing the chances of ping-pong effects.
In inter-frequency or inter-RAT (Radio Access Technology) handovers, ensure that gap-assisted measurement starts on time by properly configuring A2 parameters. This helps prevent service drops due to delayed signal quality measurement in the target cell. Also, set the threshold for the target cell appropriately.
Study Cases
Problem Description:
In a specific area, the UE experiences frequent handovers, and traffic levels are quite low.
Problem Analysis:
The UE undergoes more than 15 ping-pong handovers while moving between cell PCI161 and cell PCI150. This results in low SINR and reduced traffic.
Solution:
Lower the antenna tilt by 3 degrees in both cell PCI161 and cell PCI150.
Verification Test Results:
After adjusting the antenna downtilt, traffic and SINR improved in these two cells, and the ping-pong handover issue was resolved.