How does GSM handle call handovers between cells?

GSM architecture in mobile communication handles call handovers between cells to ensure that an ongoing call or data session remains

uninterrupted as a mobile station (MS) moves from the coverage area of one cell to another. Handovers are a crucial aspect of providing seamless mobile communication.

Here’s a detailed description of how GSM handles call handovers between cells:

Neighbor Cell Monitoring:

The GSM network continuously monitors the signal strength and quality of neighboring cells surrounding the MS’s current cell. This information is obtained through periodic measurement reports from the MS.

Threshold-Based Decision:

Based on the monitored signal parameters, such as signal strength, quality, and distance from the neighboring cells, the network calculates a handover decision.

If the signal quality in the current cell drops below a certain threshold or if a neighboring cell’s signal becomes stronger and exceeds a predefined threshold, the network initiates the handover process.

Handover Request:

When a handover is deemed necessary, the network sends a handover request to the Mobile Station (MS) via the Base Transceiver Station (BTS) currently serving the MS.

Immediate Assignment:

The MS receives the handover request and prepares to switch to the new cell. The network sends an “Immediate Assignment” message, instructing the MS to tune to the new frequency and timeslot in the target cell.

Handover Execution:

The MS tunes to the new frequency and timeslot in the target cell, effectively transitioning to the new cell’s coverage area.

The handover execution ensures that the MS and the network switch their communication resources to the target cell. This step aims to minimize any interruption in the call.

Data and Voice Transfer:

Once the MS is successfully handed over to the new cell, data, and voice traffic are transferred from the old cell to the new cell. This transfer is designed to be seamless and transparent to the user.

Handover Confirmation:

After the handover is completed, the MS sends a handover confirmation message to the network to signal that it has successfully transitioned to the new cell.

Resource Release:

The resources allocated in the old cell for the call are released once the handover is confirmed. This ensures that network resources are efficiently used.

Re-Establishment of Connections:

If the handover process results in a change in the Base Station Controller (BSC) or Mobile Switching Center (MSC), new connections are established with the new controllers.

The old BSC and MSC release resources associated with the call and update their databases with the MS’s new location information.

Quality Monitoring:

The network continues to monitor the quality of the call after the handover. If signal quality deteriorates again or if a better cell becomes available, additional handovers may be initiated as needed.

Types of Handovers:

GSM supports several types of handovers, including intracell handovers (between different time slots or frequencies within the same cell) and intercell handovers (between cells served by different BTSs).

Handover Priority:

The network may prioritize handovers based on factors such as the MS’s signal strength, call priority (e.g., emergency calls), and network congestion.

In summary, GSM handles call handovers between cells through a series of steps that involve continuous monitoring of signal parameters, threshold-based decision-making, and seamless transfer of communication resources from the old cell to the new partition.

This process ensures that subscribers experience uninterrupted call and data services as they move within the network’s coverage area.

Handovers are essential for maintaining call quality, reducing call drops, and optimizing network resources in a mobile communication system.