Event A1 to A6 — Explained Like a Workflowr

[Rajesh_kulhar]

Note: These are mostly used for Intra-frequency and Inter-frequecy HO Event

Event A1: “Serving Cell Becomes Good”

1. Condition:
   Triggered when the quality of the serving cell improves above a predefined threshold.

2. Event Used: A1

3. Why This Event?
   Used to stop measurement reporting of neighboring cells, because the serving cell itself is good enough.

4. Example:
   UE moved out briefly but returned to center of the cell – no handover needed.

5. Fail Condition:
   If wrongly configured threshold, UE may stay stuck in poor coverage.

6. Handover Triggered? No
   Just to suppress neighbor measurement.

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Event A2: “Serving Cell Becomes Worse”

1. Condition:
   Serving cell’s RSRP or RSRQ drops below threshold.

2. Event Used: A2

3. Why This Event?

To initiate neighbor cell measurements – preparing for handover.

4. Example:
   UE enters the building basement – the serving cell becomes weak.

5. Fail Condition:
   Delay in triggering A2 can cause RLF (Radio Link Failure).

6. Handover Triggered? No
   Only measurement is triggered, not actual HO.

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Event A3: “Neighbor Better Than Serving by Offset”

1. Condition:
   Any neighbor becomes better than the serving by a configured offset (e.g., 3 dB).

2. Event Used: A3

3. Why This Event?
   Main trigger for Intra-frequency handovers.

4. Example:
   UE moving towards cell edge – neighbor becomes stronger.

5. Fail Condition:
   Ping-pong handover if offset/hysteresis is poorly tuned.

6. Handover Triggered? Yes
   Most common handover trigger in LTE.

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Event A4: “Neighbor Cell Quality Better Than Threshold”

1. Condition:
   Any neighbor becomes better than a fixed RSRP/RSRQ threshold.

2. Event Used: A4

3. Why This Event?
   Used for Inter-frequency HO – before comparing with serving.

4. Example:
   UE moves into area with better second-carrier coverage.

5. Fail Condition:
   If offset is too high, UE may miss opportunity to move.

6. Handover Triggered? Maybe
   Depends on how good neighbor is and serving condition.

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Event A5: “Serving Becomes Bad AND Neighbor Becomes Good”

1. Condition:
   Dual condition:
   → Serving < Threshold1
   → Neighbor > Threshold2

2. Event Used: A5

3. Why This Event?
   Used for Inter-frequency handovers or cell reselection where cross-check needed.

4. Example:
   UE moving into weak zone of current frequency but another carrier is stronger.

5. Fail Condition:
   If only one of the two conditions satisfied, HO not triggered.

6. Handover Triggered? Yes
   Once both thresholds are crossed.

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Event A6: “Neighbor Secondary Cell Better than Threshold”

1. Condition:
   Secondary cell RSRP/RSRQ goes above threshold.

2. Event Used: A6

3. Why This Event?
   For Carrier Aggregation (CA) — adding/removing Secondary Cells (SCell).

4. Example:
   UE enters a zone where SCell is usable for higher data rate.

5. Fail Condition:
   If SCell becomes weak again, addition fails.

6. Handover Triggered? No
   Not a handover — SCell addition/removal only.

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🔁 Event A1 to A6 — Explained Like a Workflow | Rajesh kulhar