Understanding Handover Latency and Success Rate in GSM Networks

In GSM networks, handover latency and handover success rate are two critical parameters that impact the performance and reliability of mobile calls, especially when users move across different cell boundaries.

Handover Latency in GSM

Handover Latency refers to the time it takes to transfer an ongoing call or data session from one cell (or base station) to another as the user moves. Minimizing this latency is essential to ensure that users experience seamless connectivity without any noticeable disruption in their calls.

• Definition: Handover latency is the delay, measured in milliseconds (ms), that occurs between the initiation and completion of the handover process.

• Process:

  • When a mobile user moves towards the boundary of a cell, the signal strength from the current cell begins to weaken.
  • The network identifies this change and prepares for a handover to a neighboring cell with a stronger signal.
  • During handover, resources are allocated in the new cell, and the call or data session is transferred to this new base station.

• Typical Latency in GSM: In GSM networks, handover latency is generally in the range of 200 ms to 500 ms, depending on network conditions, the speed of the user’s movement, and network optimization.

• Factors Affecting Handover Latency:

  • Network Congestion: Congested cells may delay the handover process.
  • Signal Quality: Low or fluctuating signal quality can slow down the handover.
  • Interference: Interference from neighboring cells can increase latency.

• Impact of High Handover Latency: High handover latency can cause call interruptions or dropped calls, negatively impacting the user experience. Low latency is therefore critical for providing uninterrupted service, especially in high-mobility scenarios.

Handover Success Rate (HSR) in GSM

Handover Success Rate (HSR) measures the percentage of handovers that are successfully completed without dropping the call or data session. It is a key performance indicator (KPI) for network reliability and is critical to ensuring high call continuity as users move across cells.

• Definition: HSR is the ratio of successful handovers to the total number of attempted handovers, usually expressed as a percentage.

  $HSR = \frac{\text{Number of Successful Handovers}}{\text{Total number of handover attempts}} \times 100$

• Typical Success Rate in GSM: Ideally, GSM networks aim for a HSR of 98% or higher. High success rates indicate stable and well-optimized networks with effective handover processes.

• Factors Affecting HSR:

  • Signal Strength and Quality: Weak or fluctuating signals can lead to handover failures.
  • Congestion in Target Cell: If the target cell is congested, it may not have enough resources to complete the handover, leading to failure.
  • Interference: High levels of interference can disrupt the handover signal and result in a dropped call.
  • Faulty Hardware: Equipment issues, such as malfunctions in base stations, can also cause handover failures.

• Impact of Low Handover Success Rate: A low HSR means that a higher percentage of calls are likely to be dropped during movement between cells, leading to poor user experience and dissatisfaction. Networks with a low HSR need optimization to reduce dropped calls and improve user experience.

Importance of Handover Latency and Handover Success Rate in GSM

• User Experience: Both low handover latency and a high handover success rate are essential to ensure that users can move freely without call interruptions, which is especially important for users traveling in vehicles.

• Network Quality Assessment: HSR is a critical KPI that network operators monitor to assess network stability and reliability. A high HSR indicates an efficient and well-optimized network.

• Network Optimization: Monitoring and improving these metrics helps network engineers identify areas for improvement, such as adding capacity, minimizing interference, and enhancing handover algorithms.

Conclusion

In summary, handover latency and handover success rate are fundamental parameters in GSM networks that ensure seamless call continuity. Low latency and a high success rate contribute to a stable network with fewer dropped calls, directly enhancing user satisfaction.