In LTE networks, the call drop rate is a critical performance indicator that directly impacts user experience. It reflects the system’s ability to sustain ongoing services without interruption. While call drops can occur due to various factors across the network, this article focuses on radio-related call drops, which are primarily caused by coverage issues, handover problems, and interference. Understanding and addressing these factors are essential for optimizing LTE network performance and ensuring reliable connectivity.
Call Drop Analysis.
1. Call Drops Caused by Coverage Problems
Coverage issues are a significant cause of call drops in LTE networks. The following are common scenarios where coverage problems lead to call drops:
Isolated Island Effect:
When a UE is located in an isolated cell, it may be unable to make outgoing handovers, leading to call drops.
Coverage Holes:
Gaps in coverage, especially in areas where adjacent cells intersect, can result in the UE losing signal during a call.
Shadow Fading:
High buildings and other large structures can cause shadow fading, creating areas with weak or rapidly fluctuating signals.
Solutions to Coverage Problems:
- Identify and Optimize Weak Coverage Areas:
- Use RF adjustments to enhance coverage in weak areas. For locations like shopping malls, tunnels, underground parking lots, subway entrances, and high-rise buildings, consider installing indoor coverage systems.
- Check Hardware Issues:
- Inspect the hardware, particularly the power output of the serving cell and neighboring cells, to ensure there are no issues causing cell shrinkage, such as power amplifier (PA) problems.
2. Call Drops Caused by Handover Problems.
Handover issues are another major contributor to call drops. The following handover-related problems can lead to call drops:
Hardware Problems:
Faulty hardware can cause abnormal handover processes, resulting in call drops.
Isolated Island Problem:
This issue can also affect handovers, leading to handover failures and call drops.
Interference:
Significant downlink or uplink interference in the source cell can result in handover failures.
Improper Handover Parameters:
Incorrectly set handover parameters can cause handover failures.
Ping Pong Handover:
Frequent handovers between two cells (ping pong effect) can result in call drops.
Sudden Signal Drops:
Rapid signal drops in corners or shadow areas can lead to handover failures and subsequent call drops.
Solutions to Handover Problems:
- Check Hardware Faults:
- Ensure there are no hardware alarms and that all equipment is functioning correctly.
- Manage Interference:
- Make RF adjustments to control network interference and stabilize cell load.
- Optimize Handover Parameters:
- Adjust handover-related radio parameters to match the radio environment.
- Eliminate Interference:
- Control and mitigate both internal and external interference within the network.
3. Call Drops Caused by Interference.
Interference is another important issue that can significantly impact call stability. The following types of interference commonly cause call drops:
Intra-Frequency Interference:
Interference from other UEs operating on the same frequency can lead to call drops.
Inter-RAT System Interference:
Interference from other Radio Access Technologies (RATs) can disrupt LTE signals.
External Interference:
Sources such as microwaves, satellite receivers, radars, and TV receivers can cause significant interference.
Solutions to Interference Problems:
- Control Cell Load:
- Manage and distribute cell load to minimize interference.
- RF Adjustments:
- Make adjustments to control overshooting and reduce interference from neighboring cells.
- Isolation and Filtering:
- Add spatial isolation or Tx/Rx filters to mitigate interference from other systems.
Conclusion:
To solve call drops problem in LTE networks requires a thorough understanding of the causes and implementing targeted solutions. By optimizing coverage, managing handovers effectively, and preventing interference, network operators can significantly reduce call drops and enhance the overall user experience. Regular monitoring, data analysis, and proactive optimization of drop KPIs are key to maintaining a robust and reliable LTE network.