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#LTE_Intra_Frequency_Handover (HO)
In LTE networks, HO procedures are critical for maintaining seamless connectivity as UE moves between cells. The process involves several key steps and parameters. Here’s a detailed look at the intra-frequency
handover:
When a UE starts a PS session with a cell, the eNodeB sends an important message called RRC Connection Reconfiguration. This message includes:
1. Measurement Control Information: Guidelines for the UE to perform measurements.
2. Event Triggering Conditions: Specific conditions that trigger the UE to send measurement reports back to the eNodeB.
📴 The first thing that UE do is :
-Measurement and Reporting
The UE continuously measures signal strengths from its serving cell and neighboring cells. A critical event for intra-frequency HO is Event A3.
-Event A3 Condition
Event A3 is triggered when the following condition is met:
RSRPn + CIOn - HysteresisA3 > RSRPs + A3 Offset ]
Where:
- RSRP(n): Reference Signal Received Power of the neighboring cell.
- CIO(n): Cell Individual Offset of the neighboring cell.
- Hysteresis(A3): A parameter to prevent frequent handovers due to minor signal fluctuations.
- RSRP(s): Reference Signal Received Power of the serving cell.
- A3 Offset: Offset value to adjust the sensitivity of the handover condition.
- Example:
Consider the following example with specific values:
- RSRP(n): -90 dBm (Signal strength from the neighboring cell)
- RSRP(s): -85 dBm (Signal strength from the serving cell)
- CIO(n): 5 dB (Cell Individual Offset to speed up HO)
- Hysteresis(A3): 0 dB (To prevent delay due to minor fluctuations)
- A3 Offset: 0 dB (No additional offset to keep condition straightforward)
Applying these values to the Event A3 condition:
[ -90 + 5 - 0 > -85 + 0 ]
This simplifies to:
[ -85 > -85 ]
Since the condition (-85 > -85) is not met, let’s adjust the example to better illustrate the triggering of Event A3.
Let's modify RSRP(n) to -80 dBm:
[ -80 + 5 - 0 > -85 + 0 ]
This simplifies to:
[ -75 > -85 ]
Now, the condition (-75 > -85) is met, triggering Event A3. The positive CIO(n) = 5 dB makes the neighboring cell more attractive, facilitating a quicker handover.
-Handover Execution
Once Event A3 is triggered, the UE sends a measurement report to the serving eNodeB. The eNodeB then:
2. Prepares for HO: Evaluates the report and prepares resources in the target cell.
3. Executes the HO: Commands the UE to switch to the target cell.
For I-RAT and Inter FreQ HO, there are events inter you to Measurement Gap before triggering, and then comparing between threshold and results.
1- I-RAT trigger with B1 Event
2-Inter FreQ HO trigger with A4 Event
Special Thanks to
Alali Khalaf