Handover latency in LTE refers to the time delay on the control plane during the handover process. Specifically, it is the period starting from when the User Equipment (UE) receives the RRC (Radio Resource Control) Connection Reconfiguration message, and ending when the UE reports the MSG3 message. This latency is critical as it impacts the seamlessness of the handover, affecting the user’s experience and the network’s performance.
How to Identify Handover Latency?
Handover latency is considered significant when it exceeds the threshold set by the network operator. Monitoring and managing this latency is important for maintaining optimal network performance and user satisfaction. The control plane signaling during handover involves two key stages:
- Latency from the reception of the RRC Connection Reconfiguration message to the sending of the MSG1 message.
- Latency from the sending of the MSG1 message to the reception of the MSG2 message.
How to Solve Handover Latency Issues?
To solve and optimize handover latency issues, the following workflow and methods can be used:
Data Collection and Analysis:
Use appropriate test devices and test terminals to gather signaling data. Analyze the signaling to identify the points of delay.
PRACH Config Index:
If MSG1 is not frequently retransmitted but there is a significant delay between MSG1 retransmission and the RRC Connection Reconfiguration message, check the PRACH (Physical Random Access Channel) Config Index. This index determines the interval of PRACH transmission as specified in protocol 36.211 section 5.7.
If the PRACH Config Index value is high, reduce it to shorten the interval between PRACH transmissions.
Interference and PRACH Reception:
Frequent MSG1 transmissions could indicate uplink interference. Collect statistics of packets received on PRACH and monitor uplink interference levels. If the interference level exceeds -110dBm, address the interference problem or adjust the expected PRACH reception power and the detection threshold of the absolute PRACH preamble.
Uplink and MSG2 Reception:
If the UE has received MSG1 but there is an issue with receiving MSG2, it may indicate a problem with the uplink.
Adjust engineering parameters such as RS (Reference Signal) power, PCI (Physical Cell Identity), and the initial CCE (Control Channel Element) aggregation level.
Practical Steps for Reducing Handover Latency.
Conclusion
Handover latency in LTE is a critical performance metric that affects user experience and network efficiency. By understanding the factors contributing to handover latency and implementing targeted strategies, network operators can significantly reduce delays and enhance the overall performance of the LTE network. Regular monitoring, proactive optimization, and leveraging advanced technologies are key to managing handover latency effectively.